Performance Evaluation of the uEXPLORER Total-Body PET/CT Scanner Based on NEMA NU 2-2018 with Additional Tests to Characterize PET Scanners with a Long Axial Field of View

Molecular imaging of psoriatic arthritis

PURPOSE OF REVIEW

Psoriatic arthritis (PsA) is a chronic inflammatory disease associated with psoriasis. Conventional imaging techniques are used to diagnose the disease and detect long-term structural changes. This review will assess molecular imaging in PsA, to evaluate its potential additive value over conventional and advanced anatomical imaging methods (e.g. ultrasound and MRI).

RECENT FINDINGS

Current research is primarily focused on the molecular imaging technique PET/computed tomography (PET/CT) imaging, in which different tracers have been investigated. Fluorodeoxyglucose (FDG) can visualize disease activity and subclinical inflammation. New tracers targeting inflammatory sites have also been studied, such as FAPI (fibroblast activation protein inhibitor). Moreover, NaF (sodium fluoride) shows promise for imaging of new bone formation. Next to PET/CT, also fluorescence imaging and multispectral optoacoustic tomography have been investigated in the context of PsA.

SUMMARY

Molecular imaging techniques hold promise for early diagnosis, monitoring and management of PsA. Future research is needed to define the role of molecular imaging relative to conventional and anatomical imaging techniques in patient care.

Total-body positron emission tomography: a tool for systemic, quantitative evaluation of the inflammatory burden of psoriatic arthritis

OBJECTIVES

To test the hypothesis that recently-developed total body-positron emission tomography (TB-PET) imaging with integrated computed tomography (CT) will enable low-dose, quantitative, domain-specific evaluation of the total inflammatory burden of psoriatic arthritis (PsA) and associate with established outcome measures of the clinical domains of PsA.

METHODS

Seventy-one adult participants (40 with PsA, 16 with rheumatoid arthritis (RA), and 15 with osteoarthritis (OA)) underwent 20-min TB-PET/CT scans using [18F]FDG, a glucose analogue radiotracer. [18F]FDG uptake was assessed qualitatively and quantitatively. Rheumatological examinations were performed prior to the scan. For both evaluations, domain-specific assessments included 68 joints, 6 entheses, 20 nails, axial disease and dactylitis.

RESULTS

[18F]FDG PET uptake consistent with joint involvement and enthesitis was noted in 100% of participants with PsA. Other features included nail matrix pathology (53%), spinal involvement (60%), active sacroiliitis (13%) and dactylitis (10%). Patterns of [18F]FDG uptake in PsA differed from those in participants with RA or OA. There was a high concordance between TB-PET measures and the domain-specific assessments of the joint (75%), entheseal (79%) and nail (65%) pathology. TB-PET was positive for an additional 15% of joints, 20% of entheses and 13% of nails that were negative on clinical assessments.

CONCLUSION

TB-PET/CT identified inflammatory pathologies characteristic to all clinical domains of PsA and thus provided an in vivo evaluation of systemic PsA inflammatory burden. This promising tool may further contribute to identifying pathologies that may be occult, provide biomarkers to diagnose and differentiate PsA at an early stage, and to monitor early treatment response.

Dual-ended readout TOF-DOI PET detectors based on 3.2 mm and 1.6 mm pitch LYSO arrays

BACKGROUND

The image quality of positron emission tomography (PET) can be significantly enhanced by using time-of-flight (TOF) and depth-of-interaction (DOI) information. PET detectors are pivotal in determining the TOF and DOI capabilities of PET scanners.

METHODS

This study developed and evaluated TOF-DOI PET detectors based on the dual-ended readout method and lutetium-yttrium oxyorthosilicate (LYSO) arrays with two different pitches and reflector configurations. Specifically, the performance of detectors based on three types of LYSO arrays with 20 mm thickness, 8 × 8 arrays with a 3.2 mm pitch, 16 × 16 arrays with a 1.6 mm pitch and normal reflectors, and 16 × 16 arrays with a 1.6 mm pitch and partial short reflectors, were assessed. Hamamatsu S14161-3050-08 silicon photomultiplier arrays were used as the photodetectors, and PETsys TOFPET2 was used as the readout electronics.

RESULTS

The flood histograms showed that all crystals in the three types of LYSO arrays were clearly resolved. The detectors based on the 8 × 8 LYSO arrays provided a coincidence timing resolution (CTR) of 207 ± 5 ps and a DOI resolution of 3.9 ± 0.6 mm. The detectors based on the 16 × 16 LYSO arrays with normal reflectors provided a CTR of 218 ± 7 ps and a DOI resolution of 2.6 ± 0.2 mm. In comparison, the detector based on the 16 × 16 LYSO arrays with partial short reflectors provided a CTR of 228 ± 11 ps and a DOI resolution of 2.9 ± 0.3 mm, and superior crystal resolvability compared to the detectors based on the 16 × 16 LYSO arrays with normal reflectors.

CONCLUSION

These detectors are promising candidates for developing whole-body and brain PET scanners, offering effective sensitivity and uniform spatial resolution improvements across the field-of-view.

Performance evaluation of a medium axial field-of-view sparse PET system based on flat panels of monolithic LYSO detectors: a simulation study

BACKGROUND

The combination of longer axial field-of-view (AFOV) and time-of-flight positron emission tomography (PET) has significantly improved system sensitivity and, as a result, image quality. This study investigates a cost-effective extended AFOV PET system design using monolithic LYSO detectors with depth-of-interaction capabilities. These detectors, arranged in a vertical flat-panel geometry and positioned closer to the patient, enable superior spatial resolution while maintaining a compact and affordable system design. We simulate the performance of two flat-panel PET configurations: one with a fully populated 106 cm AFOV and another cost-efficient design featuring a reduced AFOV with axial gaps and vertical panel motion optimized for head and torso imaging.

METHODS

Both configurations consist of two monolithic LYSO-based flat panels placed 50 cm apart. The panels are 71 cm wide, with the Long Flat Panel (L-FP) design extending to a length of 106 cm while the Sparse Medium Flat Panel (SpM-FP) design measures 60 cm in length. Monte Carlo simulations evaluated the two designs using the NEMA protocol and additional tests for a more thorough assessment. Sensitivity, spatial resolution, axial noise variability, and image quality were analyzed, and an XCAT phantom at standard dose was used to demonstrate the achievable clinical image quality.

RESULTS

The SpM-FP showed 4-5 times lower sensitivity than the L-FP, requiring an acquisition time of 2-3 min to match the image quality achieved by the L-FP in 30 s. This finding is supported by the contrast-to-noise ratio of the image quality phantom and the standard deviation values obtained from the liver and lung regions of the XCAT phantom. Both configurations achieved uniform spatial resolution below 2 mm in the two directions parallel to the panels and an average of 3-3.5 mm in the direction towards the panels, with slight degradation observed away from the center of the AFOV. Additionally, the axial noise profile of the SpM-FP revealed minimal variability.

CONCLUSIONS

The SpM-FP design shows potential as a cost-effective system, combining the benefits of extended AFOV, superior spatial resolution and high patient throughput.

Managing incidental findings in total body PET/CT studies: balancing ethical considerations and resource constraints

Total body positron emission tomography (TB-PET) represents a major advancement in molecular imaging. While this technology expands the capabilities of PET imaging for both research and clinical applications, it also introduces significant ethical and operational challenges, particularly in the management of incidental findings. Current ethical and regulatory guidance acknowledge the need to address incidental findings that arise during research studies, but often provides ambiguous or insufficient direction. This leaves institutions to independently balance participant safety, ethical responsibilities, and resource constraints. Using the Australian National Total Body PET Facility as a case study, this article explores strategies for managing incidental findings in PET/CT research. By comparing research workflows with clinical practices, we highlight critical differences and propose a practical framework to help institutions establish ethically sound and feasible protocols. This framework aims to balance the duty of care to the participant with the logistical demands of PET research, contributing to the ongoing discourse on ethical imaging practices and offering guidance for managers of TB-PET research facilities.

First clinical investigation to predict lymphovascular and/or perineural invasion in gastric cancer using 18F-FAPI-42 PET/CT parameters

OBJECTIVE

This study was conducted to explore the predictive value of PET parameters derived from 18F-FAPI-42 PET/CT in assessing lymphovascular and/or perineural invasion (LVI/PNI) in gastric cancer (GC) patients.

METHODS

72 GC patients who underwent 18F-FAPI-42 PET/CT prior to surgical resection were included. Clinicopathological factors and PET parameters were collected and analyzed in LVI/PNI-negative and LVI/PNI-positive groups. The predictive value of PET parameters for LVI/PNI status was evaluated using the receiver operating characteristic (ROC) curve. A nomogram was developed using significant predictors from multivariate stepwise regression analysis and its performance was assessed by decision curve analysis (DCA).

RESULTS

Univariate analysis indicated a significant association between LVI/PNI status and PET parameters (SUVmax, SUVmean, and TBR) (all p < 0.001). The area under the ROC curve (AUC) values for predicting LVI/PNI were 0.932 [95% CI (0.877-0.987)] for SUVmax, 0.923 [95% CI (0.861-0.984)] for SUVmean, and 0.925 [95% CI (0.865-0.985)] for TBR. The optimal cutoff values for prediction, along with their corresponding sensitivity and specificity, were 3.86 (93.3% and 81.5%) for SUVmax, 2.04 (93.3% and 81.5%) for SUVmean, and 9.75 (91.1% and 81.5%) for TBR. Multivariate analysis identified histological grade and SUVmax as independent risk factors for LVI/PNI prediction. Our nomogram had good discriminatory ability (AUC = 0.934) and offered net benefits in predicting LVI/PNI status by DCA.

CONCLUSION

This study demonstrates that FAPI uptake parameters exhibit an exceptionally high capacity and serve as a noninvasive preoperative tool for predicting LVI/PNI status in GC, with SUVmax emerging as the most suitable predictive indicator.

Reproducibility of 18F-Sodium Fluoride Positron Emission Tomography for Assessing Microcalcification in Coronary Arterial and Thoracic Aortic Atherosclerosis: Is the Signal below the Resolution of PET?

PURPOSE OF REVIEW

The rising prevalence of atherosclerosis has prompted the development of novel diagnostic methods capable of identifying early-stage disease when therapeutic interventions may be most effective. 18F-sodium fluoride (NaF) positron emission tomography/computed tomography (PET/CT) is a molecular imaging technique that can quantify subclinical microcalcification in arterial plaque. The focus of this review article is to discuss the utility of 18F-NaF PET/CT in assessing atherosclerotic disease of major susceptible blood vessels, particularly the coronary arteries and thoracic aorta.

RECENT FINDINGS

18F-NaF uptake observed on PET imaging demonstrates promising potential as a marker of atherosclerotic burden in individual coronary arteries, whole heart segmentations, and the thoracic aorta. Global versus focal assessment of 18F-NaF uptake in small arteries is a significant source of methodological heterogeneity among studies. The accuracy and reproducibility of 18F-NaF PET/CT may be improved by standardized quantification methods in light of the limited spatial resolution of PET, particularly through the use of techniques to evaluate global atherosclerotic burden.

Early 10-Minute Postinjection [18F]F-FAPI-42 uEXPLORER Total-Body PET/CT Scanning Protocol for Staging Lung Cancer Using HYPER Iterative Reconstruction

Sensitive detection of small metastatic lesions, which is highly dependent on lesion visualization, is crucial for staging lung cancer. We investigated the potential benefit of HYPER Iterative for improving the visualization of small metastatic lesions of lung cancer on early 18F-labeled fibroblast activation protein inhibitor (FAPI) PET/CT. Methods: A total of 19 patients with lung cancer underwent a 60-min [18F]F-FAPI-42 dynamic total-body uEXPLORER PET/CT scan. PET images with a 5-min acquisition time were extracted at 10, 30 min, and 60 min after tracer injection. Ordered-subset expectation maximization (OSEM) and HYPER Iterative were used for image reconstruction. SUVmax, tumor-to-liver ratio, tumor-to-blood ratio, and tumor-to-adjacent-nontumor ratio were calculated and compared between the 2 reconstruction methods and at 10, 30, and 60 min after injection. Results: All HYPER and OSEM PET images were of high quality, with HYPER PET images showing superior clarity. Small positive lesions (maximum diameter, ≤1 cm) were depicted clearer on HYPER PET than on OSEM PET images at all time points, particularly at 10 min after injection, where 16.4% of lesions were poorly visualized on OSEM PET but clearly depicted on HYPER PET images. The tumor-to-liver ratio, tumor-to-blood ratio, and tumor-to-nontumor ratio at 10, 30, and 60 min after injection scan on HYPER PET images were significantly higher than those on OSEM images at corresponding time points (P ≥ 0.05 for all comparisons). SUVmax was more than 2-fold greater in large positive lesions (maximum diameter, >1.0 cm) than in small positive lesions (maximum diameter, ≤1 cm) on both OSEM and HYPER PET images at 10, 30, and 60 min after injection (P < 0.05 for all comparisons). The visualization of large positive lesions was not significantly affected by reconstruction methods or scan times. Conclusion: HYPER Iterative reconstruction enhanced the visualization of small metastatic lesions in lung cancer when compared with conventional OSEM, enabling effective early imaging using [18F]F-FAPI-42 uEXPLORER total-body PET/CT at 10 min after tracer injection.

Quantitative Total-Body Imaging of Blood Flow with High-Temporal-Resolution Early Dynamic 18F-FDG PET Kinetic Modeling

Past efforts to measure blood flow with the widely available radiotracer 18F-FDG were limited to tissues with high 18F-FDG extraction fraction. In this study, we developed an early dynamic 18F-FDG PET method with high-temporal-resolution (HTR) kinetic modeling to assess total-body blood flow based on deriving the vascular phase of 18F-FDG transit and conducted a pilot comparison study against a 11C-butanol flow-tracer reference. Methods: The first 2 min of dynamic PET scans were reconstructed at HTR (60 × 1 s/frame, 30 × 2 s/frame) to resolve the rapid passage of the radiotracer through blood vessels. In contrast to existing methods that use blood-to-tissue transport rate as a surrogate of blood flow, our method directly estimated blood flow using a distributed kinetic model (adiabatic approximation to tissue homogeneity [AATH] model). To validate our 18F-FDG measurements of blood flow against a reference flow-specific radiotracer, we analyzed total-body dynamic PET images of 6 human participants scanned with both 18F-FDG and 11C-butanol. An additional 34 total-body dynamic 18F-FDG PET images of healthy participants were analyzed for comparison against published blood-flow ranges. Regional blood flow was estimated across the body, and total-body parametric imaging of blood flow was conducted for visual assessment. AATH and standard compartment model fitting was compared using the Akaike information criterion at different temporal resolutions. Results: 18F-FDG blood flow was in quantitative agreement with flow measured from 11C-butanol across same-subject regional measurements (Pearson correlation coefficient, 0.955; P < 0.001; linear regression slope and intercept, 0.973 and -0.012, respectively), which was visually corroborated by total-body blood-flow parametric imaging. Our method resolved a wide range of blood-flow values across the body in broad agreement with published ranges (e.g., healthy cohort values of 0.51 ± 0.12 mL/min/cm3 in the cerebral cortex and 2.03 ± 0.64 mL/min/cm3 in the lungs). HTR (1-2 s/frame) was required for AATH modeling. Conclusion: Total-body blood-flow imaging was feasible using early dynamic 18F-FDG PET with HTR kinetic modeling. This method may be combined with standard 18F-FDG PET methods to enable efficient single-tracer multiparametric flow-metabolism imaging, with numerous research and clinical applications in oncology, cardiovascular disease, pain medicine, and neuroscience.

PSMA PET/CT for prostate cancer diagnosis: current applications and future directions

Prostate cancer (PCa) requires improved diagnostic strategies beyond conventional imaging. This review aimed to evaluate the role of prostate-specific membrane antigen positron emission tomography/computed tomography (PSMA PET/CT) in diagnosing advanced PCa. The review analyzed the diagnostic performance of PSMA PET/CT in various clinical contexts, including locoregional staging, extracapsular extension (ECE), seminal vesicle invasion (SVI), pelvic lymph node metastases, distant metastases, and biochemical recurrence (BCR). Further, challenges such as PSMA-negative tumors, need for standardized protocols, and potential of emerging imaging targets (neurotensin receptor 1 and fibroblast activation proteins) were reviewed. The role of artificial intelligence (AI) and advancements in tracer development were explored. PSMA PET/CT demonstrated exceptional specificity for locoregional staging, ECE, and SVI while reducing unnecessary biopsies and optimizing biopsy strategies. The diagnostic accuracy for pelvic lymph node metastases was higher with PSMA PET/CT than with traditional methods, although sensitivity for micrometastasis detection remained challenging. For distant metastases, PSMA PET/CT outperformed bone scintigraphy (BS) and conventional imaging, particularly in identifying bone and atypical lesions. In BCR cases, PSMA PET/CT reliably detected recurrent lesions at low prostate-specific antigen levels, significantly influencing treatment strategies. The review findings indicate that PSMA PET/CT is a superior diagnostic tool for PCa due to its high specificity and accuracy. Despite limitations such as PSMA-negative tumors and sensitivity challenges, advancements in AI, novel imaging targets, and affordable tracer development hold promise for broader clinical adoption. This review underscores the transformative potential of PSMA PET/CT in PCa diagnosis and management, advocating for ongoing research and protocol standardization.

Nonmaximal entanglement of photons from positron-electron annihilation demonstrated using a plastic PET scanner

In state-of-the-art positron emission tomography (PET), information about annihilation photon polarization is unavailable. Here, we present a PET scanner built from plastic scintillators, where annihilation photons primarily interact via the Compton effect, providing information about both photon polarization and propagation direction. Using this plastic-based PET, we determined the distribution of the relative angle between polarization planes of photons from positron-electron annihilation in a porous polymer. The amplitude of the observed distribution is smaller than predicted for maximally quantum entangled two-photon states but larger than expected for separable photons. This result can be well explained by assuming that photons from pick-off annihilation are not entangled, while photons from direct and parapositronium annihilations are maximally entangled. Our result indicates that the degree of entanglement depends on the annihilation mechanism in matter, opening avenues for exploring polarization correlations in PET as a diagnostic indicator.

Flexible and modular PET: Evaluating the potential of TOF-DOI panel detectors

BACKGROUND

Panel detectors have the potential to provide a flexible, modular approach to Positron Emission Tomography (PET), enabling customization to meet patient-specific needs and scan objectives. The panel design allows detectors to be positioned close to the patient, aiming to enhance sensitivity and spatial resolution through improved geometric coverage and reduced noncollinearity blurring. Parallax error can be mitigated using depth of interaction (DOI) information.

PURPOSE

One of the key questions the article addresses is: Do panel detectors offer viable clinical imaging capabilities, or does limited angular sampling restrict their utility by causing image distortions and artifacts? Additionally, this article explores the scalability of panel detectors for constructing scanners with a long axial field of view (LAFOV).

METHODS

Monte Carlo simulations using GATE software were used to assess the performance of panel detectors with various DOI resolutions and Time-of-Flight (TOF) resolutions as fine as 70 ps. The 30 × $\times$ 30 cm panels comprised pixelated 3 × $\times$ 3 × $\times$ 20 mm LSO crystals. Simulations were run on large high-performance computing clusters (122,000 CPU cores). Open-source CASToR software was used for (TOF MLEM) image reconstruction. The image quality of the scanners was assessed using a range of phantoms (NEMA, Derenzo, XCAT, and a high-resolution brain phantom). The Siemens Biograph Vision PET/CT scanner served as the reference model. The performance of larger 120 × $\times$ 60 cm panels was also evaluated.

RESULTS

Sensitivity increases over threefold when panel-panel distance is reduced from 80 to 40 cm. The noise equivalent count rate, unmodified by TOF gain, of the panel detectors matches that of the reference clinical scanner at a distance of approximately 50 cm between the panels. Spatial resolution perpendicular to the panels improves from 8.7 to 1.6 mm when the panel-panel distance is reduced, and 70 ps + DOI detectors are used instead of 200 ps, no-DOI detectors. With enhanced TOF and DOI capabilities, panel detectors achieve image quality that matches or surpasses the reference scanner while using about four times less detector material. These detectors can be extended for LAFOV imaging without distortions or artifacts. Additionally, improving TOF and DOI performance enhances contrast-to-noise ratios, thereby improving lesion detection.

CONCLUSIONS

A compact 2-panel PET scanner can match the performance of conventional scanners, producing high-quality, distortion-free images. Its mobility and flexibility enable novel applications, including bedside imaging and intensive care unitdiagnostics, as well as imaging in positions such as sitting or standing. Furthermore, the modularity of panel detectors offers the potential to construct cost-effective, high-performance total-body imaging systems.

Realistic total-body J-PET geometry optimization: Monte Carlo study

BACKGROUND

Total-body (TB) Positron Emission Tomography (PET) is one of the most promising medical diagnostics modalities, opening new perspectives for personalized medicine, low-dose imaging, multi-organ dynamic imaging or kinetic modeling. The high sensitivity provided by total-body technology can be advantageous for novel tomography methods like positronium imaging, demanding the registration of triple coincidences. Currently, state-of-the-art PET scanners use inorganic scintillators. However, the high acquisition cost reduces the accessibility of TB PET technology. Several efforts are ongoing to mitigate this problem. Among the alternatives, the Jagiellonian PET (J-PET) technology, based on axially arranged plastic scintillator strips, offers a low-cost alternative solution for TB PET.

PURPOSE

The work aimed to compare five total-body J-PET geometries with plastic scintillators suitable for multi-organ and positronium tomography as a possible next-generation J-PET scanner design.

METHODS

We present comparative studies of performance characteristics of the cost-effective total-body PET scanners using J-PET technology. We investigated in silico five TB scanner geometries, varying the number of rings, scanner radii, and other parameters. Monte Carlo simulations of the anthropomorphic XCAT phantom, the extended 2-m sensitivity line source and positronium sensitivity phantoms were used to assess the performance of the geometries. Two hot spheres were placed in the lungs and in the liver of the XCAT phantom to mimic the pathological changes. We compared the sensitivity profiles and performed quantitative analysis of the reconstructed images by using quality metrics such as contrast recovery coefficient, background variability and root mean squared error. The studies are complemented by the determination of sensitivity for the positronium lifetime tomography and the relative cost analysis of the studied setups.

RESULTS

The analysis of the reconstructed XCAT images reveals the superiority of the seven-ring scanners over the three-ring setups. However, the three-ring scanners would be approximately 2-3 times cheaper. The peak sensitivity values for two-gamma vary from 20 to 34 cps/kBq and are dominated by the differences in geometrical acceptance of the scanners. The sensitivity curves for the positronium tomography have a similar shape to the two-gamma sensitivity profiles. The peak values are lower compared to the two-gamma cases, from about 20-28 times, with a maximum value of 1.66 cps/kBq. This can be contrasted with the 50-cm one-layer J-PET modular scanner used to perform the first in-vivo positronium imaging with a sensitivity of 0.06 cps/kBq.

CONCLUSIONS

The results show the feasibility of multi-organ imaging of all the systems to be considered for the next generation of TB J-PET designs. Among the scanner parameters, the most important ones are related to the axial field-of-view coverage. The two-gamma sensitivity and XCAT image reconstruction analyzes show the advantage of seven-ring scanners. However, the cost of the scintillator materials and SiPMs is more than two times higher for the longer modalities compared to the three-ring solutions. Nevertheless, the relative cost for all the scanners is about 10-4 times lower compared to the cost of the uExplorer. These properties coupled together with J-PET cost-effectiveness and triggerless acquisition mode enabling three-gamma positronium imaging, make the J-PET technology an attractive solution for broad application in clinics.

Feasibility of Ultra-Low-Activity 18F-FDG PET/CT Imaging Using a Long-Axial-Field-of-View PET/CT System

18F-FDG PET/CT imaging is widely used in oncology. Long-axial-field-of-view (LAFOV) PET/CT systems exhibit ultrahigh sensitivity and signal-to-noise ratios, enabling significant reductions in tracer activity and shorter acquisition times. This study aimed to evaluate the feasibility of using ultralow activities for semiquantitative measurements in 18F-FDG PET/CT imaging performed on an LAFOV PET/CT system through a high-low activity test-retest study. Methods: Eleven oncology patients underwent 2 18F-FDG PET/CT scans, the first with standard activity (3.0 MBq/kg) and, within 7 d, 1 with ultralow activity (0.3 MBq/kg). List-mode data of both scans were resampled to simulate activities of 0.3 and 0.03 MBq/kg. Semiquantitative measurements (SUVmean, SUVpeak, and SUVmax) and their repeatability in healthy organs and lesions were compared across different activities and reconstruction protocols. Results: SUVmean remained stable across activity reductions and reconstruction protocols, whereas SUVpeak showed stability except when simulating 1% of the standard 18F-FDG activity. SUVmax significantly increased at lower 18F-FDG activities, particularly with clinically preferred scans. Repeatability analysis showed that SUVmean and SUVpeak maintained variability within acceptable limits (<15%) even at 0.03 MBq/kg, whereas SUVmax variability often exceeded these limits. Lesion detection was reliable at 0.3 MBq/kg, but several lesions could not be delineated at 0.03 MBq/kg, indicating compromised image quality. Conclusion: The use of ultralow 18F-FDG activity (0.3 MBq/kg) is feasible for PET/CT imaging on an LAFOV PET/CT system, as shown by semiquantitative measurements, repeatability analyses, lesion detectability, and semiautomated delineation methods. These findings support imaging protocols that keep radiation exposure levels as low as reasonably or practically achievable, which are particularly relevant for radiation-sensitive patients (e.g., children, pregnant women).

Is Long-Axial-Field-of-View PET/CT Cost-Effective? An International Health-Economic Analysis

Our aim is to assess the cost-effectiveness of long-axial-field-of-view (LAFOV) versus short-axial FOV (SAFOV) PET/CT systems using international data. Methods: Our model compares equipment and operational costs for a PET/CT center and investigates the effect of camera choice (SAFOV vs. LAFOV) and operational models. Variables include scanner, personnel, radiopharmaceuticals, and operational costs. Economic performance was measured as cost per scan per patient, the total maximum number of scans possible, and the incremental cost-effectiveness ratio. The willingness-to-pay threshold (WTPT) was taken as the cost of a PET/CT scan using the baseline scenario. Radiopharmaceutical requirements, radiation dose to staff and patients, and patient time were modeled. Results: An LAFOV system can examine as many patients per day (n = 36) as 2 SAFOV systems but requires fewer technologists (4.5 LAFOV vs. 6.8 SAFOV full-time equivalents) and lower activity (12.5 vs. 35.6 GBq/d), resulting in lower personnel doses (0.9 vs. 2.0 mSv/y). For all countries, LAFOV resulted in lowest per-patient scan costs. The most cost-ineffective method was the use of extended hours. Incremental cost-effectiveness ratio analysis strongly favored LAFOV for all countries, including low-income economies, with WTPT met for all jurisdictions. Net monetary benefit was highest for LAFOV. The minimum number of patients needed to meet WTPT for LAFOV was lowest in lower-income countries, suggesting that high throughput or high per-procedure income is not a prerequisite for cost-effective LAFOV usage. Conclusion: LAFOV was shown to facilitate higher patient throughput at lower per-patient and total lifetime operational costs and with lower radiopharmaceutical requirements. These data suggest that LAFOV systems are not just suited to well-resourced academic centers but also are an economically attractive solution for community and resource-limited settings.

Depth-of-interaction encoding techniques for pixelated PET detectors enabled by machine learning methods and fast waveform digitization

Objective. Pixelated detectors with single-ended readout are routinely used by commercial positron emission tomography scanners owing to their good energy and timing resolution and optimized manufacturing, but they typically do not provide depth-of-interaction (DOI) information, which can help improve the performance of systems with higher resolution and smaller ring diameter. This work aims to develop a technique for multi-level DOI classification that does not require modifications to the detector designs.Approach. We leveraged high-speed (5 Gs s-1) waveform sampling electronics with the Domino Ring Sampler (DRS4) and machine learning (ML) methods to extract DOI information from the entire scintillation waveforms of pixelated crystals. We evaluated different grouping schemes for multi-level DOI classification by analyzing the DOI positioning profile and DOI positioning error. We examined trade-offs among crystal configurations, detector timing performance, and DOI classification accuracy. We also investigated the impact of different ML algorithms and input features-extracted from scintillation waveforms-on model accuracy.Main results. The DOI positioning profile and positioning error suggest that 2- or 3-level binning was effective for 20 mm long crystals. 2-level discrete DOI models achieved 95% class-wise accuracy and 83% overall accuracy in positioning events into the correct DOI level and 3-level up to 90% class-wise accuracy for long and narrow crystals (2 × 2 × 20 mm3). Long short-term memory networks trained with time-frequency moments were twice as efficient in training time while maintaining equal or better accuracy compared to those trained with waveforms. Classical ML algorithms exhibit comparable accuracy while consuming one order less training time than deep learning models.Significance. This work demonstrates a proof-of-concept approach for obtaining DOI information from commercially available pixelated detectors without altering the detector design thereby avoiding potential degradation in detector timing performance. It provides an alternative solution for multi-level DOI classification, potentially inspiring future scanner designs.

Feasibility of an Ultra-Low-Dose PET Scan Protocol with CT-Based and LSO-TX-Based Attenuation Correction Using a Long-Axial-Field-of-View PET/CT Scanner

Long-axial-field-of-view (LAFOV) PET scanners enable substantial reduction in injected radiotracer activity while maintaining clinically feasible scan times. Whole-body CT scans performed for PET attenuation correction can significantly add to total radiation exposure. We investigated the feasibility of an ultra-low-dose PET protocol and the application of a CT-less PET attenuation correction method (lutetium oxyorthosilicate background transmission [LSO-TX]) that uses 176Lu background radiation from detector scintillators with low-count PET data. Methods: Each of the 4 study subjects was scanned for 90 min using an ultra-low-dose 18F-FDG protocol (injected activity, 6.7-9.0 MBq) with an LAFOV PET scanner. PET images were reconstructed with different frame durations using low-dose CT-based and LSO-TX-based attenuation maps (μ-maps). The image quality of PET images was assessed by the signal-to-noise ratio (SNR) in the liver and the contrast-to-noise ratio in the brain. Absolute errors in SUVs between PET images reconstructed with LSO-TX-based and CT-based μ-maps were assessed at each scan duration. Results: Visual assessment showed that 20-30 min of PET data obtained using 18F-FDG activities below 10 MBq (i.e., 0.1 MBq/kg) can yield high-quality images. PET images reconstructed with CT-based and LSO-TX-based μ-maps had comparable SNRs and contrast-to-noise ratios at all scan durations. The mean ± SD SNRs of PET images reconstructed with the CT-based and the LSO-TX-based μ-maps were 9.2 ± 1.9 dB and 9.8 ± 2.0 dB at 90-min scan duration, 6.8 ± 1.7 dB and 6.9 ± 1.8 dB at 30-min scan duration, and 5.5 ± 1.2 dB and 5.6 ± 1.2 dB at 20-min scan duration, respectively. The relative absolute SUV errors between PET images reconstructed with LSO-TX-based and CT-based μ-maps ranged from 3.1% to 6.4% across different volumes of interest with a 20-min scan duration. Conclusion: PET scans with an LAFOV scanner maintained good visual image quality with 18F-FDG activities below 10 MBq for scan durations of 20-30 min. The LSO-TX-based attenuation correction method yielded images comparable to those obtained with the CT-based attenuation correction method in such protocols.

Total-Body Parametric Imaging Using Relative Patlak Plot

The standard Patlak plot, a simple yet efficient model, is widely used to describe irreversible tracer kinetics for dynamic PET imaging. Its widespread application to whole-body parametric imaging remains constrained because of the need for a full-time-course input function (e.g., 1 h). In this paper, we demonstrate the relative Patlak (RP) plot, which eliminates the need for the early-time input function, for total-body parametric imaging and its application to 20-min clinical scans acquired in list mode. Methods: We conducted a theoretic analysis to indicate that the RP intercept b' is equivalent to a ratio of the SUV relative to the plasma concentration, whereas the RP slope Ki ' is equal to the standard Patlak Ki (net influx rate) multiplied by a global scaling factor for each subject. One challenge in applying RP to a short scan duration (e.g., 20 min) is the resulting high noise in the parametric images. We applied a self-supervised deep-kernel method for noise reduction. Using the standard Patlak plot as the reference, the RP method was evaluated for lesion quantification, lesion-to-background contrast, and myocardial visualization in total-body parametric imaging in 22 human subjects (12 healthy subjects and 10 cancer patients) who underwent a 1-h dynamic 18F-FDG scan. The RP method was also applied to the dynamic data reconstructed from a clinical standard 20-min list-mode scan either at 1 or 2 h after injection for 2 cancer patients. Results: We demonstrated that it is feasible to obtain high-quality parametric images from 20-min scans using RP parametric imaging with a self-supervised deep-kernel noise-reduction strategy. The RP slope Ki ' was highly correlated with the standard Patlak Ki in lesions and major organs, demonstrating its quantitative potential across subjects. Compared with conventional SUVs, the Ki ' images significantly improved lesion contrast and enabled visualization of the myocardium for potential cardiac assessment. The application of the RP parametric imaging to the 2 clinical scans also showed similar benefits. Conclusion: Using total-body PET with the RP approach, it is feasible to generate parametric images using data from a 20-min clinical list-mode scan.

Feasibility of PET-enabled dual-energy CT imaging: First physical phantom and initial patient study results

PURPOSE

Dual-energy (DE) CT enables material decomposition by using two different x-ray energies and may be combined with PET for improved multimodality imaging. However, this increases radiation dose and may require a hardware upgrade due to the added second x-ray CT scan. The recently proposed PET-enabled DECT method allows dual-energy imaging using a conventional PET/CT scanner without the need to change scanner hardware or increase radiation exposure. Here we demonstrate the first-time physical phantom and patient data evaluation of this method.

METHODS

The PET-enabled DECT method reconstructs a gamma-ray CT (gCT) image at 511 keV from the time-of-flight PET data with the maximum-likelihood attenuation and activity (MLAA) approach and then combines this image with the low-energy x-ray CT images to form a dual-energy image pair for material decomposition. To improve the image quality of gCT, a kernel MLAA method was developed using the x-ray CT as a priori information. Here we developed a general open-source implementation for gCT reconstruction and used this implementation for the first real data validation using both physical phantom study and human-subject study. Results from PET-enabled DECT were compared using x-ray DECT as the reference. Further, we applied the PET-enabled DECT method in another patient study to evaluate bone lesions.

RESULTS

Compared to the standard MLAA, results from the kernel MLAA showed significantly improved image quality. PET-enabled DECT with the kernel MLAA was able to generate fractional images that were comparable to the x-ray DECT, with high correlation coefficients for both the phantom study and human subject study (R > 0.99). The application study also indicates that PET-enabled DECT has potential to characterize bone lesions.

CONCLUSION

Results from this study have demonstrated the feasibility of this PET-enabled method for CT imaging and material decomposition. PET-enabled DECT shows promise to provide comparable results to x-ray DECT.

Low dose optimization for total-body 2-[18F]FDG PET/CT imaging: a single-center study on feasibility based on body mass index stratification

OBJECTIVES

Implementing personalization protocol in clinical routine necessitates diverse low-dose PET/CT scan protocols. This study explores the clinical feasibility of one-third (1/3) dose regimen and evaluates the diagnostic image quality and lesion detectability of BMI-based 1/3-injection doses for 2-[18F]FDG PET/CT imaging.

METHODS

Seventy-four cancer patients underwent total-body 2-[18F]FDG PET/CT examination, with 37 retrospectively enrolled as full-dose group (3.7 MBq/kg) and 37 prospectively enrolled as the 1/3-dose group (1.23 MBq/kg). The 1/3-dose group was stratified by BMI, with an acquisition time of 5 min (G5), 6 min (G6), and 8 min (G8) for BMI < 25, 25 ≤ BMI ≤ 29, and BMI > 29, respectively. Image quality was subjectively and objectively assessed, and lesion detectability was quantitatively analyzed.

RESULTS

Subjective assessments of 1/3-dose and full-dose PET images showed strong agreement among readers (κ > 0.88). In the 1/3-dose group, the Likert scores were above 4. G5, G6, and G8 showed comparable image quality, with G5 demonstrating higher lesion conspicuity than G6 and G8 (p = 0.045). Objective evaluation showed no significant differences in SUVmax, liver SUVmean and TBR between 1/3- and full-dose groups (p > 0.05). No statistical differences were observed in the SUVmax of primary tumor, SUVmean of liver and TBR across all BMI categories between the 1/3-dose and full-dose groups. Lesion detection rates showed no significant difference between the 1/3-dose (93.24%, 193/207) and full-dose groups (94.73%, 198/209) (p = 0.520).

CONCLUSION

A BMI-stratified 1/3-dose regimen is a feasible low-dose alternative with clinically acceptable lesion detectability equivalent to full-dose protocol, potentially expanding the applicability of personalized protocols.

CLINICAL RELEVANCE STATEMENT

This study demonstrated that BMI-stratified 1/3-dose regimens for [18F]FDG total-body PET/CT yielded equivalent outputs compared to the full-dose regimen, which aligns with clinical needs for personalization in dose and BMI.

KEY POINTS

Currently, limited personalized low-dose total-body PET/CT protocols are available, particularly for patients with varied BMI. Reducing the radiotracer dose to 1/3 the standard demonstrated comparable image quality and lesion detectability equivalent to full dose. BMI-stratified 1/3-dose regimen is a clinically feasible low-dose alternative.

Quantitative PET imaging and modeling of molecular blood-brain barrier permeability

Neuroimaging of blood-brain barrier permeability has been instrumental in identifying its broad involvement in neurological and systemic diseases. However, current methods evaluate the blood-brain barrier mainly as a structural barrier. Here we developed a non-invasive positron emission tomography method in humans to measure the blood-brain barrier permeability of molecular radiotracers that cross the blood-brain barrier through its molecule-specific transport mechanism. Our method uses high-temporal resolution dynamic imaging and kinetic modeling for multiparametric imaging and quantification of the blood-brain barrier permeability-surface area product of molecular radiotracers. We show, in humans, our method can resolve blood-brain barrier permeability across three radiotracers and demonstrate its utility in studying brain aging and brain-body interactions in metabolic dysfunction-associated steatotic liver inflammation. Our method opens new directions to effectively study the molecular permeability of the human blood-brain barrier in vivo using the large catalogue of available molecular positron emission tomography tracers.

Diagnostic accuracy in NSCLC lymph node staging with Total-Body and conventional PET/CT

INTRODUCTION

Our aim was to characterize the diagnostic accuracy indices for nodal (N)-staging with [18F]FDG Total-Body (TB) and short-axial field-of-view (SAFOV) PET/CT in non-small cell lung cancer (NSCLC) patients referred for staging or restaging.

METHODS

In this prospective single center cross-over head-to-head comparative study 48 patients underwent [18F]FDG TB and SAFOV PET/CT on the same day. In total 700 lymph node levels (1R/L, 2R/L, 3a/p, 4R/L, 5, 6, 7, 8R/L, 9R/L, 10-14R/L) of 28 patients could be correlated to a composite reference standard (histopathological correlation, imaging after localized or systemic treatment), which allowed determination of true positive (TP), false positive (FP), true negative (TN) and false negative (FN) lesions. Lymph nodes were characterized semi-quantitatively by maximum standardized uptake value (SUVmax), tumor-to-background ratio (TBR), metabolic tumor volume (MTV) and total lesion glycolysis (TLG) leading to threshold for each scanner.

RESULTS

TB and SAFOV PET/CT showed high diagnostic accuracy indices for patient-based N-staging. Sensitivity and specificity were 86.0% (CI: 77.0-95.0%) and 98.3% (CI: 97.3-99.3%) for TB; 77.2% (CI: 66.3-88.1%) and 97.4% (CI: 96.1-98.6%) for SAFOV PET. Positive predictive value was higher for TB (81.7%, CI: 71.9-91.5%) compared to SAFOV PET (72.1%, CI: 60.9-83.4%). However, this finding was not statistically significant (p = 0.08). Negative predictive values for TB (98.6%, CI: 97.9-99.6%) and SAFOV PET/CT (98.0%, CI: 96.9-99.1%) were comparable. Overall, NSCLC N-staging was affected in six cases on SAFOV and only in one case on TB PET/CT. Semi-quantitative analysis revealed a threshold of SUVmax 3.0 to detect TP lesions on both scanners. However, TBR, MTV and TLG thresholds were lower on TB compared to SAFOV PET (TBR: 1.2 vs. 1.7, MTV: 0.5 ml vs. 1.0 ml and TLG: 1.0 ml vs. 3.0 ml).

CONCLUSION

TB and SAFOV PET/CT showed high diagnostic accuracy indices for N-staging in NSCLC patients. Sensitivity and PPV on TB PET/CT were slightly higher, compared to SAFOV PET/CT without statistical significance. However, TB PET/CT showed lower rate of incorrect N-staging and lower semi-quantitative thresholds for the detection positive mediastinal lymph nodes. Therefore, TB PET/CT might be advantageous in detecting small and low [18F]FDG-avidity mediastinal lymph node metastases in NSCLC patients.

3Dπ: three-dimensional positron imaging, a novel total-body PET scanner using xenon-doped liquid argon scintillator

Objective.This paper introduces a novel PET imaging methodology called 3-dimensional positron imaging (3Dπ), which integrates total-body coverage, time-of-flight (TOF) technology, ultra-low dose imaging capabilities, and ultra-fast readout electronics inspired by emerging technology from the DarkSide collaboration.Approach.The study evaluates the performance of 3Dπusing Monte Carlo simulations based on NEMA NU 2-2018 protocols. The methodology employs a homogenous, monolithic scintillator composed of liquid argon (LAr) doped with xenon (Xe) with silicon photomultipliers (SiPMs) operating at cryogenic temperatures.Main results.Substantial improvements in system performance are observed, with the 3Dπsystem achieving a noise equivalent count rate of 3.2 Mcps at 17.3 kBq ml-1, continuing to increase up to 4.3 Mcps at 40 kBq ml-1. Spatial resolution measurements show an average FWHM of 2.7 mm across both axial positions. The system exhibits superior sensitivity, with values reaching 373 kcps MBq-1with a line source at the center of the field of view. Additionally, 3Dπachieves a TOF resolution of 151 ps at 5.3 kBq ml-1, highlighting its potential to produce high-quality images with reduced noise levels.Significance.The study underscores the potential of 3Dπin improving PET imaging performance, offering the potential for shorter scan times and reduced radiation exposure for patients. The Xe-doped LAr offers advantages such as fast scintillation, enhanced light yield, and cost-effectiveness. Future research will focus on optimizing system geometry and further refining reconstruction algorithms to exploit the strengths of 3Dπfor clinical applications.

13N-NH3 myocardial perfusion imaging with reduced scan duration: a feasibility study in the era of total-body PET/CT

PURPOSE

To explore the feasibility of reducing scan duration of 13N-NH3 myocardial perfusion imaging (MPI) using a total-body PET/CT scanner.

METHODS

Forty-five patients with known or suspected coronary artery disease (CAD) performing rest 13N-NH3 MPI with total-body PET/CT were retrospectively included. PET data were acquired in list mode for 10 min, and reconstructed into sequence images of different scan duration: 10-min, 7-min, 5-min, 3-min, and 2-min (G10 to G2). Subjective visual evaluation including overall impression, image noise and lesion visibility was evaluated using 5-point Likert scale. Quantitative parameters including perfusion defect extent (Extent), total perfusion defect (TPD), summed rest score (SRS), end-diastolic volume (EDV), end-systolic volume (ESV), ejection fraction (EF), and myocardial blood flow (MBF) were analyzed. The full-time images (G10) were served as the reference.

RESULTS

There were no significant differences in subjective visual scores between G7-G5 and G10 groups (p > 0.05). A significant decrease in overall impression and image noise of G3-G2 was observed when compared to G10 (p < 0.05). However, no significant difference in lesion visibility was noted between G3 and G10 (p > 0.05). All G3 image quality was clinically acceptable (≥ 3 points). Except for EDV and ESV, other quantitative parameters showed no significant difference between G7-G3 and G10 (p > 0.05) and agreements were good (ICC = 0.974-0.998). For G2, only TPD exhibited no significant difference when compared to G10 (p > 0.05).

CONCLUSION

Regarding imaging quality and parametric quantification accuracy of 13N-NH3 MPI, a 3-min scan is clinically acceptable, while a 5-min scan is sufficiently reliable.

Comparison of clinical performance between late and standard total-body [68 Ga]Ga-PSMA-11 in biochemical recurrent prostate cancer

BACKGROUND AND PURPOSE

Enhanced lesion detection in prostate cancer is observed with late [68 Ga]Ga-PSMA-11 PET/CT imaging compared to standard [68 Ga]Ga-PSMA-11 PET/CT imaging (50-100 min p.i.). However, the poor image quality of late imaging using short axial field of view (SAFOV) PET/CT has hindered its sole clinical adoption. Conversely, the image quality of late imaging with a long axial field of view (LAFOV) [68 Ga]Ga-PSMA-11 PET/CT fulfills clinical diagnostic requirements. Nonetheless, the diagnostic efficacy of late LAFOV [68 Ga]Ga-PSMA-11 PET/CT with forced diuresis and its impact on treatment decisions, compared to standard LAFOV [68 Ga]Ga-PSMA-11 PET/CT, remains unclear. This study aims to compare the rate of PET positivity between late and standard LAFOV [68 Ga]Ga-PSMA-11 PET/CT and to evaluate the influence of late LAFOV [68 Ga]Ga-PSMA-11 PET/CT with forced diuresis on treatment decisions relative to standard scans.

METHODS

From January 2021 to April 2024, 127 patients with biochemical recurrence of prostate cancer post-radical prostatectomy were enrolled to undergo both standard and late LAFOV [68 Ga]Ga-PSMA-11 PET/CT scans at Shanghai Renji Hospital. We compared the rate of PET positivity between the two modalities at the patient level and across different anatomical regions. We assessed the added diagnostic value of late LAFOV [68 Ga]Ga-PSMA-11 PET/CT and its impact on modifying patient treatment plans.

RESULTS

The image quality of late LAFOV [68 Ga]Ga-PSMA-11 PET/CT with forced diuresis in all patients met clinical diagnostic requirements. The rate of PET positivity of late LAFOV [68 Ga]Ga-PSMA-11 PET/CT with forced diuresis were significantly higher than those of standard LAFOV [68 Ga]Ga-PSMA-11 PET/CT (80.31% [102/127] vs. 65.35% [83/127]; P < 0.001). Late LAFOV [68 Ga]Ga-PSMA-11 PET/CT demonstrated higher lesion SUVmax (16.69 ± 16.42 vs. 11.91 ± 10.72, P < 0.001) and TBR (6.26 ± 7.21 vs. 3.44 ± 3.57, P < 0.001) compared to standard LAFOV scans. Additionally, 14.17% (18/127) of patients experienced changes in their treatment regimen due to the superior detection capabilities of late LAFOV [68 Ga]Ga-PSMA-11 PET/CT with forced diuresis compared to the standard scan.

CONCLUSIONS

The rate of PET positivity of late LAFOV [68 Ga]Ga-PSMA-11 PET/CT with forced diuresis compared to standard LAFOV [68 Ga]Ga-PSMA-11 PET/CT highlight its potential as a valuable diagnostic tool for biochemically recurrent prostate cancer. This study paves the way for using late LAFOV [68 Ga]Ga-PSMA-11 PET/CT with forced diuresis for prostate cancer imaging in daily clinical practice, facilitating more accurate and timely diagnoses.

Total-Body PET System Designs with Axial and Transverse Gaps: A Study of Lesion Quantification and Detectability

High-sensitivity total-body PET enables faster scans, lower doses, and dynamic multiorgan imaging. However, the higher system cost of a scanner with a long axial field of view (AFOV) hinders its wider application. This paper investigates the impact on the lesion quantification and detectability of cost-effective total-body PET sparse designs. Methods: Using the PennPET Explorer (PPEx) as a model, 3 sparse configurations with the same 142-cm AFOV were considered, including designs with only axial gaps (AGs), only transverse gaps (TGs), and a mixture of AGs and TGs (MG), with retained detector fractions (DFs) ranging from 71% to 40%. Human data from the PPEx were used to emulate sparse designs by discarding lines of response as a proxy for missing detectors. We embedded lesion events in the resultant list data with varying uptakes in the lung and liver before reconstruction. A generalized scan statistics methodology was used to measure lesion detectability and quantification as a function of lesion uptake and scan duration. Results: Relative to a fully populated system, an AG design with 71% performs well but is susceptible to image artifacts as the DF decreases to 58%. A TG design performs well with a DF of 58% but requires twice the scan time to achieve similar lesion detectability and is susceptible to transverse field-of-view truncation below 60 cm as the DF is further decreased. An MG design with a DF of 58% requires 3 times the scan time to achieve similar lesion detectability, and with no evidence of artifacts even as the DF is decreased to 40%. Conclusion: Sparse designs with artifact-free images can provide comparable lesion quantification and detectability to the fully populated PPEx after compensating for the reduced sensitivity with increased scan time. Because an AG design is more susceptible to image artifacts with a lower DF, a system with only AGs is not an optimal choice for dramatic cost reduction. A TG design provides a higher relative sensitivity than AG or MG designs for a given DF, leading to a shorter scan time to achieve comparable lesion detectability. However, the increased truncation of the transverse field of view with decreasing DF limits this design choice. An MG design allows for the greatest cost reduction (lowest DF) if the scan duration is increased to compensate for the higher loss in sensitivity. Sparse designs of PET with a long AFOV provide a technologic solution for introducing such systems at reduced cost into routine clinical use.

Long-axial field-of-view PET/CT improves radiomics feature reliability

PURPOSE

To assess the influence of long-axial field-of-view (LAFOV) PET/CT systems on radiomics feature reliability, to assess the suitability for short-duration or low-activity acquisitions for textural feature analysis and to investigate the influence of acceptance angle.

METHODS

34 patients were analysed: twelve patients underwent oncological 2-[18F]-FDG PET/CT, fourteen [18F]PSMA-1007 and eight [68Ga]Ga-DOTATOC. Data were obtained using a 106 cm LAFOV system for 10 min. Sinograms were generated from list-mode data corresponding to scan durations of 2, 5, 10, 20, 30, 60, 120, 240, 360 and 600s using both standard (minimum ring difference MRD 85 crystals) and maximum acceptance angles (MRD 322). Target lesions were segmented and radiomics features were calculated. To assess feature correlation, Pearson's product-moment correlation coefficient (PPMCC) was calculated with respect to the full duration acquisition for MRD 85 and 322 respectively. The number of features with excellent (r > 0.9), moderate (r > 0.7 and < 0.9) and poor (r ≤ 0.7) correlation was compared as a measure of feature stability. Intra-class heterogeneity was assessed by means of the quartile coefficient of dispersion.

RESULTS

As expected, PPMCC improved with acquisition time for all features. By 240s almost all features showed at least moderate agreement with the full count (C100%) data, and by 360s almost all showed excellent agreement. Compared to standard-axial field of view (SAFOV) equivalent scans, fewer features showed moderate or poor agreement, and this was most pronounced for [68Ga]Ga-DOTATOC. Data obtained at C100% at MRD 322 were better able to capture between-patient heterogeneities.

CONCLUSION

The improved feature reliability at longer acquisition times and higher MRD demonstrate the advantages of high sensitivity LAFOV systems for reproducible and low-noise data. High fidelity between MRD 85 and MRD 322 was seen at all scan durations > 2s. When contrasted with data comparable to a simulated SAFOV acquisition, full-count and full-MRD data were better able to capture underlying feature heterogeneities.

Digital detector PET/CT increases Centiloid measures of amyloid in Alzheimer's disease: A head-to-head comparison of cameras

BACKGROUND

The introduction of therapeutics for Alzheimer's disease has led to increased interest in precisely quantifying amyloid-β (Aβ) burden for diagnosis, treatment monitoring, and further clinical research. Recent positron emission tomography (PET) hardware innovations including digital detectors have led to superior resolution and sensitivity, improving quantitative accuracy. However, the effect of PET scanner on Centiloid remains relatively unexplored and is assumed to be minimized by harmonizing PET resolutions.

OBJECTIVE

To quantify the differences in Centiloid between scanners in a paired cohort.

METHODS

36 participants from the Australian Imaging, Biomarker and Lifestyle study (AIBL) cohort were scanned within a year on two scanners. Each participant underwent 18F-NAV4694 imaging on two of the three scanners investigated, the Siemens Vision, the Siemens mCT and the Philips Gemini. We compared Aβ Centiloid quantification between scanners and assessed the effectiveness of post-reconstruction PET resolution harmonization. We further compared the scanner differences in target sub-regions and with different reference regions to assess spatial variability.

RESULTS

Centiloid from the Vision camera was found to be significantly higher compared to the Gemini and mCT; the difference was greater at high-Centiloid levels. Post-reconstruction resolution harmonization only accounted for and corrected ∼20% of the Centiloid (CL) difference between scanners. We further demonstrated that residual differences have effects that vary spatially between different subregions of the Centiloid mask.

CONCLUSIONS

We have demonstrated that the type of PET scanner that a participant is scanned on affects Centiloid quantification, even when scanner resolution is harmonized. We conclude by highlighting the need for further investigation into harmonization techniques that consider scanner differences.

Expert consensus on workflow of PET/CT with long axial field-of-view

PURPOSE

Positron emission tomography/computed tomography (PET/CT) imaging has been widely used in clinical practice. Long axial field-of-view (LAFOV) systems have enhanced clinical practice by leveraging their technological advantages and have emerged as the new state-of-the-art PET imaging modalities. A consensus was conducted to explore expert views in this emerging field to comprehensively elucidate the proposed workflow in LAFOV PET/CT examinations and highlight the potential challenges inherent in the workflow.

METHODS

A multidisciplinary task group formed by 28 experts from six countries over the world discussed and approved the consensus based on the published guidelines, peer-reviewed articles of LAFOV PET/CT, and the collective experience from clinical practice. This consensus focuses on the workflow that allows for a broader range of imaging protocols of LAFOV PET/CT, catering to diverse patient needs and in line with precision medicine principles.

RESULTS

This consensus describes the workflows and imaging protocols of LAFOV PET/CT for various imaging scenarios including routine static imaging, dynamic imaging, low-activity imaging, fast imaging, prolonged imaging, delayed imaging, and dual-tracer imaging. In addition, imaging reconstruction and reviewing specific to LAFOV PET/CT imaging, as well as the main challenges facing installation and application of LAFOV PET/CT scanner were also summarized.

CONCLUSION

This consensus summarized the various imaging workflow, imaging protocol, and challenges of LAFOV PET/CT imaging, aiming to enhance the clinical and research applications of these scanners.

The impact of long axial field of view (LAFOV) PET on oncologic imaging

The development of long axial field of view (LAFOV) positron emission tomography coupled with computed tomography (PET/CT) scanners might be considered the biggest step forward in PET imaging since it became a mainstream clinical modality. Despite increased capital and maintenance costs and data storage requirements, the improvement in image quality, significantly faster acquisition times and lower radiopharmaceutical administered activities, allow a high quality and more efficient clinical service. This step change in technology overcomes some of the limitations of standard short axial field of view scanners. It allows simultaneous imaging of all body systems, and with the ability to obtain high temporal resolution data, it increases potential research applications, particularly in multisystem disease or for dosimetry measurements of novel radiopharmaceuticals. The improvements in sensitivity and signal-to-noise facilitates the use of tracers with long half-lives and low administered activity (e.g. [89Zr]-labelled monoclonal antibodies) or very short half-lives (e.g. [82Rb]), opening up applications that hitherto have been challenging. It is early in the evolution of LAFOV PET/CT and the advantages these systems offer have still to be fully realised in providing additional impact in clinical practice. In this article we describe the potential advantages of LAFOV PET technology and some of the clinical and research applications where it has been applied as well as some of the future developments that may enhance the modality further.

Multi-organ kinetic modeling for Na[18F]F pre-clinical total-body PET studies

BACKGROUND

Total-body positron emission tomography (PET), already well-established in the pre-clinical setting, makes it possible to study multi-parameters in biological systems as a whole, rather than focusing on single tissues analysis. Simultaneous kinetic analysis of multiple organs poses some daunting new challenges.

PURPOSE

To explore quantifying the pharmacokinetics of Na[18F]F in multiple dissimilar murine organs simultaneously in vivo with total-body PET imaging using different compartmental models for each organ and a shared cardiovascular system.

METHODS

Six mice underwent a 60-min total-body PET scan following intravenous bolus injection of Na[18F]F. Compartmental models were constructed for each organ (heart, lungs, liver, kidneys, and bone) using an image derived input function. Non-linear least squares fitting of a model that connects the five organs to a shared cardiovascular system was used to analyze both the first 3 min of data and the full hour. Analysis was repeated 5000 times using different initial parameter values for each duration, permitting analysis of correlations between parameters.

RESULTS

The models give a good qualitative account of the activity curves irrespective of the duration of the data; however, the quality of the fits to 3 min of data (averageχ ν 2 $\chi _\nu ^2$ is 2.72) was generally better. Comparison of perfusion values to literature values was possible for the liver and lungs with the former (liver, 0.540 ± 0.177 mL/ml/min) being well-above expectations and the latter (lungs, 0.184 ± 0.413 mL/ml/min) in rough agreement. Correlations between microparameter values (especially affecting k2) caused very noticeable problems for data modeling from both the kidneys and the femur.

CONCLUSION

The present study demonstrates an approach to performing kinetic modeling for multiple organs simultaneously with Na[18F]F. The observed correlations between microparameter values remain a challenge. Nonetheless, many microparameters can be estimated reliably with a quantitative analysis of perfusion being possible for some organs.

Optimisation of low and ultra-low dose scanning protocols for ultra-extended field of view PET in a real-world clinical setting

True total-body and extended axial field-of-view (AFOV) PET/CT with 1m or more of body coverage are now commercially available and dramatically increase system sensitivity over conventional AFOV PET/CT. The Siemens Biograph Vision Quadra (Quadra), with an AFOV of 106cm, potentially allows use of significantly lower administered radiopharmaceuticals as well as reduced scan times. The aim of this study was to optimise acquisition protocols for routine clinical imaging with FDG on the Quadra the prioritisation of reduced activity given physical infrastructure constraints in our facility. Low-dose (1 MBq/kg) and ultra-low dose (0.5 MBq/g) cohorts, each of 20 patients were scanned in a single bed position for 10 and 15 min respectively with list-mode data acquisition. These data were then reconstructed simulating progressively shorter acquisition times down to 30 s and 1 min, respectively and then reviewed by 2 experienced PET readers who selected the shortest optimal and minimal acquisition durations based on personal preferences. Quantitative analysis was also performed of image noise to assess how this correlated with qualitative preferences. At the consensus minimum acquisition durations at both dosing levels, the coefficient of variance in the liver as a measure of image noise was 10% or less and there was minimal reduction in this measure between the optimal and longest acquisition durations. These data support the reduction in both administered activity and scan acquisition times for routine clinical FDG PET/CT on the Quadra providing efficient workflows and low radiation doses to staff and patients, while achieving high quality images.

Quantitative Accuracy Assessment of the NeuroEXPLORER for Diverse Imaging Applications: Moving Beyond Standard Evaluations

Quantitative molecular imaging with PET can offer insights into physiologic and pathologic processes and is widely used for studying brain disorders. The NeuroEXPLORER is a recently developed dedicated brain PET system offering high spatial resolution and high sensitivity with an extended axial length. This study evaluated the quantitative precision and accuracy of the NeuroEXPLORER with phantom and human data for a variety of imaging conditions that are relevant to dynamic neuroimaging studies. Methods: Thirty-minute scans of an image quality (IQ) phantom and a 3-dimensional Hoffman brain phantom filled with [18F]FDG were performed over 13 h, covering phantom activities of 1.3-177 MBq. Furthermore, a uniform cylindric phantom filled with 558 MBq of 11C was scanned for 4 h. Quantitative accuracy was assessed using the contrast recovery coefficient (CRC), background variability, and background bias in the IQ phantom, the recovery coefficients (RCs) in the Hoffman phantom, and the bias in the uniform phantom. Results were compared at delayed time points, with different reconstruction parameters and frame lengths down to 1 s. Moreover, randomly subsampled frames of 2 imaging time points (0-2 min and 60-90 min) from a dynamic scan of a healthy volunteer with a 177-MBq injected dose of (R)-4-(3-fluoro-5-(fluoro-18F)phenyl)-1-((3-methylpyridin-4-yl)methyl)pyrrolidin-2-one ([18F]SynVesT-1) were used to assess quantification of brain uptake and image-derived input function extraction. Results: Negligible effects were observed on CRC and background bias with 3-177 MBq in the IQ phantom, and bias was less than 5% with 1-558 MBq in the uniform phantom. RC variations were within ±1% with 2-169 MBq in the Hoffman phantom, showcasing the system's high spatial resolution and high sensitivity. Short-frame reconstructions of the 60- to 90-min healthy-volunteer scan showed a ±1% mean difference in quantification of brain uptake for frame lengths down to 30 s and demonstrated the feasibility of measuring image-derived input function with mean absolute differences below 10% for frame lengths down to 1 s. Conclusion: The NeuroEXPLORER, with its high detection sensitivity, maintains high precision and accuracy across a wide range of imaging conditions beyond those evaluated in standard performance tests. These results demonstrate its potential for quantitative neuroimaging applications.

High Detection Rates for Prostate-specific Membrane Antigen-avid Prostate Cancer Recurrence at Low Prostate-specific Antigen levels on Extended Axial Field-of-view Positron Emission Tomography/Computed Tomography

Background and objective

Although prostate-specific membrane antigen (PSMA) positron emission tomography/computed tomography (PET/CT) has impacted the investigation and management of biochemical recurrence (BCR) of prostate cancer, negative scans are common at low rising prostate-specific antigen (PSA) levels. PET/CT devices with an extended axial field-of-view, such as the Siemens Biograph Vision Quadra (Quadra) scanner, have substantially higher sensitivity than conventional field-of-view scanners. Our aim was to assess whether the enhanced signal-to-noise ratios achieved on the Quadra scanner improve detection of low-volume disease and thereby increase detection of PC at low PSA levels.

Methods

We analysed data for the first 300 consecutive patients who underwent clinically indicated PSMA PET/CT for BCR using a Quadra scanner. We assessed scan positivity and the location of detected disease by PSA category.

Key findings and limitations

The positivity rate increased with the PSA level from 67% for PSA <0.2 ng/ml to >90% for PSA >1.0 ng/ml (p < 0.05). Disease location also differed by PSA category, with prostate bed recurrence alone identified in 63% of positive cases with PSA <0.2 ng/ml, but <25% of cases with PSA >1.0 ng/ml, and distant metastases present in only 6% of positive cases with PSA <0.2 ng/ml versus >40% of cases with PSA >1.0 ng/ml. In the group with PSA <0.2 ng/ml, pelvic nodal disease without local recurrence was identified in 31% of cases.

Conclusions and clinical implications

In comparison to literature data, the Quadra scanner has substantially higher positivity rates at very low PSA levels. At these levels, disease was largely confined to the pelvis and potentially amenable to salvage radiotherapy. However, more than one-third of these patients had disease exclusively outside the prostate bed, with implications for the efficacy and morbidity of current salvage radiotherapy approaches.

Patient summary

We investigated a new PET/CT scanner (positron emission tomography/computed tomography) for detection of prostate cancer recurrence. This more sensitive scanner had a higher detection rate, particularly for patients with low PSA (prostate-specific antigen) in their blood. Our results suggest that the new scanner can detect disease recurrence earlier and more accurately than standard PET/CT scanners, which can help in planning further treatment.

Total Body Positron Emission Tomography/Computed Tomography: Current Status in Oncology

Positron Emission Tomography (PET) is a crucial imaging modality in oncology, providing functional insights by detecting metabolic activity in tissues. Total-body (TB) PET and large field-of-view PET have emerged as advanced techniques, offering whole-body imaging in a single acquisition. TB PET enables simultaneous imaging from head to toe, providing comprehensive information on tumor distribution, metastasis, and treatment response. This is particularly valuable in oncology, where metastatic spread often requires evaluation of multiple body areas. By covering the entire body, TB PET improves diagnostic accuracy, reduces scan time, and increases patient comfort. Furthermore, these new tomographs offer a marked increase in sensitivity, thanks to their ability to capture a larger volume of data simultaneously. This heightened sensitivity enables the detection of smaller lesions and more subtle metabolic changes, improving diagnostic accuracy in the early stages of cancer or in the evaluation of minimal residual disease. Moreover, the increased sensitivity allows for lower radiotracer doses without compromising image quality, reducing patient exposure to radiation or very quick acquisitions. Another significant advantage is the possibility of dynamic acquisitions, which allow for continuous monitoring of tracer kinetics over time. This provides critical information about tissue perfusion, metabolism, and receptor binding in real time. Dynamic imaging is particularly useful for assessing treatment response in oncology, as it enables the evaluation of tumor behavior over a period rather than a single static snapshot, offering insights into tumor aggressiveness and potential therapeutic targets. This review is focused on the current applications of TB and large field-of-view PET scanners in oncology.

Performance evaluation of a small-animal PET scanner with 213 mm axis using NEMA NU 4-2008

BACKGROUND

Long-axis positron emission tomography (PET) has emerged as one of the recent research directions in PET due to its ability to significantly enhance sensitivity and counting performance for low-dose imaging, rapid imaging, and whole-body dynamic imaging.

PURPOSE

The PET system presented in this study is a long-axis animal PET based on lutetium-yttrium orthosilicate and silicon photomultiplier, designed for whole-body imaging in rats. It features a diameter of 143 mm and an axial length of 213.3 mm. This study evaluated the performance of this PET system in accordance with the National Electrical Manufacturers Association (NEMA) NU 4-2008 standards.

METHODS

The performance evaluation was conducted according to the NEMA NU 4-2008 standards in terms of spatial resolution, sensitivity, counting rate performance, scatter fraction (SF) and image quality. In addition, a rat imaging study was conducted to assess the imaging capability of this PET system.

RESULTS

The average energy resolution of the PET system was 12.87%, the average coincidence timing resolution was 751 ps. The FWHM of spatial resolution reconstructed by filtered back projection and 3D-OSEM-PSF algorithm at 5 mm radial offset from the axial center were 1.65 and 0.88 mm. The peak absolute sensitivity measured by a point source at the center of the field of view was evaluated as 6.71% (361-661 keV) and 10.31% (250-750 keV). For the mouse-like phantom, the SF was 11.0% and the peak noise equivalent counting rate (NECR) was 1193 kcps at 94.2 MBq (2.54 mCi). For the rat-like phantom, the SF was 26.8% and the NECR was 682.5 kcps at 78.6 MBq (2.12 mCi).

CONCLUSIONS

The performance measurement results demonstrate that this PET system exhibits high sensitivity and count rate performance, making it potential for high-quality whole-body dynamic imaging of rats.

Role of Total Body PET/CT in Inflammatory Disorders

Inflammatory disorders historically have been difficult to monitor with conventional PET imaging due to limitations including radiation exposure, lack of validated imaging biomarkers, low spatial resolution, and long acquisition durations. However, the recent development of long-axial field-of-view (LAFOV) PET/CT scanners may allow utilization of novel noninvasive biomarkers to diagnose, predict outcomes, and monitor therapeutic response of inflammatory conditions. LAFOV PET scanners can image most of the human body (if not the entire body) simultaneously in one bed position, with improved signal collection efficiency compared to conventional PET scanners. This allows for imaging with shorter acquisition durations, decreased injected radiotracer dose, prolonged uptake times, or a combination of any of these. In addition, LAFOV PET scanners enable whole-body dynamic imaging. Altogether, these intrinsically superior capabilities in assessing both local and systemic diseases, have allowed these scanners to make increasingly significant contributions to the assessment of inflammatory conditions. This review aims to further explore the role and benefits of LAFOV scanners for imaging various inflammatory conditions while addressing future developments and challenges faced by this technology.

Total Body PET/CT: Future Aspects

Total-body (TB) positron emission tomography (PET) scanners are classified by their axial field of view (FOV). Long axial field of view (LAFOV) PET scanners can capture images from eyes to thighs in a one-bed position, covering all major organs with an axial FOV of about 100 cm. However, they often miss essential areas like distal lower extremities, limiting their use beyond oncology.TB-PET is reserved for scanners with a FOV of 180 cm or longer, allowing coverage of most of the body. LAFOV PET technology emerged about 40 years ago but gained traction recently due to advancements in data acquisition and cost. Early research highlighted its benefits, leading to the first FDA-cleared TB-PET/CT device in 2019 at UC Davis. Since then, various LAFOV scanners with enhanced capabilities have been developed, improving image quality, reducing acquisition times, and allowing for dynamic imaging. The uEXPLORER, the first LAFOV scanner, has a 194 cm active PET AFOV, far exceeding traditional scanners. The Panorama GS and others have followed suit in optimizing FOVs. Despite slow adoption due to the COVID pandemic and costs, over 50 LAFOV scanners are now in use globally. This review explores the future of LAFOV technology based on recent literature and experiences, covering its clinical applications, implications for radiation oncology, challenges in managing PET data, and expectations for technological advancements.

Feasibility of ultra-low-activity 18F-FDG PET/CT imaging in children

OBJECTIVES

To investigate the feasibility of paediatric 18F-FDG total-body PET/CT imaging with an ultra-low activity and explore an optimized acquisition time range.

METHODS

A total of 38 paediatric patients were prospectively enrolled and underwent dynamic total-body PET/CT imaging using ultra-low 18F-FDG activity (0.37 MBq/kg). The 60-minute list-mode raw data were acquired and then reconstructed as static PET images by using 50-51, 50-52, 50-53, 50-54, 50-55, 50-58, 50-60, and 45-60 minutes data, which were noted as G1, G2, G3, G4, G5, G8, G10, and G15, respectively. Image qualities were subjectively evaluated using the Likert scale and were objectively evaluated by the quantitative metrics including standard uptake value (SUV), signal-to-noise ratio (SNR), target-to-background ratio (TBR), and contrast-to-noise ratio (CNR).

RESULTS

The injected activity of FDG was 13.38 ± 5.68 MBq (4.40-28.16 MBq) and produced 0.58 ± 0.19 mSv (0.29-1.04 mSv) of effective dose. The inter-reader agreement of subjective image quality was excellent (kappa = 0.878; 95% CI, 0.845-0.910). The average scores of image quality for G1-G15 were 1.10 ± 0.20, 2.03 ± 0.26, 2.66 ± 0.35, 3.00 ± 0.27, 3.32 ± 0.34, 4.25 ± 0.30, 4.49 ± 0.36, and 4.70 ± 0.37, respectively. All image scores are above 3, and all lesions are detectable starting from G8. SNRs of backgrounds, TBRs, and CNRs were significant differences from the control group before G8 (all P < 0.05).

CONCLUSION

The image quality of the 8 min acquisition for paediatric 18F-FDG total-body PET/CT with an ultra-low activity could meet the diagnostic requirements.

ADVANCES IN KNOWLEDGE

This study confirms the feasibility of ultra-low dose PET imaging in children, and its methods and findings may guide clinical practice. Paediatric patients will benefit from reduced radiation doses.

Assessment of image-derived input functions from small vessels for patlak parametric imaging using total-body PET/CT

PURPOSE

The image-derived input function (IDIF) from the descending aorta has demonstrated performance comparable to arterial blood sampling while avoiding its invasive nature in parametric imaging. However, in conventional PET, large vessels may not always be within the imaging field of view (FOV). This study aims to evaluate the efficacy of dynamic parametric Ki imaging using image-derived input functions (IDIFs) extracted from various arteries, facilitated by total-body PET/CT.

METHOD

Twenty-three participants underwent a 60-minute total-body [18F]FDG PET scan. Data from each subject were used to reconstruct both total-body PET images and short-axis field-of-view PET images at different bed positions, each with a 25 cm axial field-of-view (AFOV). Partial volume correction (PVC) was performed using the blurred Van Cittert iterative deconvolution. IDIFs extracted from the descending aorta, carotid artery, abdominal aorta, and iliac artery were employed for Patlak analysis. The resulting Ki images were compared using quantification indicators and subjective assessment. Linear regression analysis was conducted to examine the correlation of Ki values among IDIFs in normal organ and lesion regions of interest (ROIs).

RESULT

High similarities were observed in Ki images derived from the IDIFs from the descending aorta and other arteries, with a median structural similarity index measure (SSIM) above 0.98 and a median peak signal-to-noise ratio (PSNR) above 37dB. Linear regression analysis revealed strong correlations in Ki values (r² > 0.88) between the descending aorta and the three alternative vessels, with slopes of the linear fits close to 1. No significant difference in lesion detectability among IDIFs was found, as assessed visually and using metrics such as tumor-to-background ratio (TBR) and contrast-to-noise ratio (CNR) (P < 0.05).

CONCLUSION

IDIFs from smaller vessels can reliably reconstruct parametric Ki images without compromising lesion detectability, providing clinically relevant information.

CT-Free Attenuation Correction in Paediatric Long Axial Field-of-View Positron Emission Tomography Using Synthetic CT from Emission Data

Background/Objectives: Paediatric PET/CT imaging is crucial in oncology but poses significant radiation risks due to children's higher radiosensitivity and longer post-exposure life expectancy. This study aims to minimize radiation exposure by generating synthetic CT (sCT) images from emission PET data, eliminating the need for attenuation correction (AC) CT scans in paediatric patients. Methods: We utilized a cohort of 128 paediatric patients, resulting in 195 paired PET and CT images. Data were acquired using Siemens Biograph Vision 600 and Long Axial Field-of-View (LAFOV) Siemens Vision Quadra PET/CT scanners. A 3D parameter transferred conditional GAN (PT-cGAN) architecture, pre-trained on adult data, was adapted and trained on the paediatric cohort. The model's performance was evaluated qualitatively by a nuclear medicine specialist and quantitatively by comparing sCT-derived PET (sPET) with standard PET images. Results: The model demonstrated high qualitative and quantitative performance. Visual inspection showed no significant (19/23) or minor clinically insignificant (4/23) differences in image quality between PET and sPET. Quantitative analysis revealed a mean SUV relative difference of -2.6 ± 5.8% across organs, with a high agreement in lesion overlap (Dice coefficient of 0.92 ± 0.08). The model also performed robustly in low-count settings, maintaining performance with reduced acquisition times. Conclusions: The proposed method effectively reduces radiation exposure in paediatric PET/CT imaging by eliminating the need for AC CT scans. It maintains high diagnostic accuracy and minimises motion-induced artifacts, making it a valuable alternative for clinical application. Further testing in clinical settings is warranted to confirm these findings and enhance patient safety.

Performance Characteristics of a New Generation 148-cm Axial Field-of-View uMI Panorama GS PET/CT System with Extended NEMA NU 2-2018 and EARL Standards

The uMI Panorama GS PET/CT system is a new long-axial-field-of-view scanner featuring high sensitivity, time-of-flight (TOF) resolution, spatial resolution, and count rate performance. The aim of this study is to assess the PET system on the basis of the National Electrical Manufacturers Association (NEMA) NU 2-2018 and European Association of Nuclear Medicine Research Limited (EARL) standards. Methods: Spatial resolution, count rate performance, sensitivity, accuracy, image quality, TOF resolution, and coregistration accuracy were evaluated following the NEMA NU 2-2018 standard. Additional experiments included energy resolution, 200-cm-long line sources for sensitivity, a 175-cm-long scatter phantom for count rate and TOF resolution, as well as the compliance with the EARL guideline. Moreover, an 18F-FDG PET patient study was reconstructed with various frame durations. Results: The PET system achieved sub-3-mm transaxial and axial spatial resolutions at a 1-cm radial offset. The sensitivities with the 70-cm-long and 200-cm-long line sources were observed to be 176.3 and 90.8 kcps/MBq, respectively, at the center of the field of view. The noise-equivalent count rates (NECRs) of the 70-cm-long and 175-cm-long scatter phantoms were measured to be 3.35 Mcps at 57.57 kBq/mL and 2.24 Mcps at 33.27 kBq/mL, respectively. The TOF resolutions for both phantoms were approximately 189 ps at 5.3 kBq/mL and lower than 200 ps below the NECR peaks. The absolute count rate errors of all 34 acquisitions were less than 3% below the NECR peak for the 70-cm-long scatter phantom. With the standard NEMA image quality phantom experiment, the contrast recovery coefficient varied from 68.17% to 94.20% and the background variabilities were all below 2%. The maximum PET/CT coregistration error was 1.33 mm. Regarding EARL compliance, the gaussian filter of 5-mm full width at half maximum could produce acceptable images. The patient data demonstrate visually satisfactory image quality with short frames (less than 1 min). Conclusion: The uMI Panorama GS exhibits spatial resolution and TOF resolution similar to those of the uMI Panorama system (35-cm axial field of view), despite the extended axial field of view. The 148-cm axial coverage, sub-200-ps TOF resolution, high sensitivity, and count rate performances are expected to yield superior image quality and offer new opportunities for various clinical applications.

Modeling PET Data Acquired During Nonsteady Conditions: What If Brain Conditions Change During the Scan?

Researchers use dynamic PET imaging with target-selective tracer molecules to probe molecular processes. Kinetic models have been developed to describe these processes. The models are typically fitted to the measured PET data with the assumption that the brain is in a steady-state condition for the duration of the scan. The end results are quantitative parameters that characterize the molecular processes. The most common kinetic modeling endpoints are estimates of volume of distribution or the binding potential of a tracer. If the steady state is violated during the scanning period, the standard kinetic models may not apply. To address this issue, time-variant kinetic models have been developed for the characterization of dynamic PET data acquired while significant changes (e.g., short-lived neurotransmitter changes) are occurring in brain processes. These models are intended to extract a transient signal from data. This work in the PET field dates back at least to the 1990s. As interest has grown in imaging nonsteady events, development and refinement of time-variant models has accelerated. These new models, which we classify as belonging to the first, second, or third generation according to their innovation, have used the latest progress in mathematics, image processing, artificial intelligence, and statistics to improve the sensitivity and performance of the earliest practical time-variant models to detect and describe nonsteady phenomena. This review provides a detailed overview of the history of time-variant models in PET. It puts key advancements in the field into historical and scientific context. The sum total of the methods is an ongoing attempt to better understand the nature and implications of neurotransmitter fluctuations and other brief neurochemical phenomena.

Glove Phenomenon Detected by Total-Body PET/CT With 68 GA-DOTATATE

ABSTRACT

Accidental intra-arterial injections of radiotracers are rare events resulting in a specific imaging pattern, described as "hot-forearm," "hot-hand," "glove-phenomenon," or "glove-like pattern." We present a case 68 Ga-DOTATATE total-body PET/CT for restaging of a neuroendocrine tumor, where intra-arterial misinjection resulted in a glove phenomenon. Since patients may present with minimal symptoms, like in this case, and PET findings may only be seen at the distal upper extremity (placed above the head), these accidental injections may be more frequently detected with total-body PET/CT due to the longer field-of-view. Radiologists and technologists should be aware of this possibility to avoid accidental misinjections.

Deep learning-aided respiratory motion compensation in PET/CT: addressing motion induced resolution loss, attenuation correction artifacts and PET-CT misalignment

PURPOSE

Respiratory motion (RM) significantly impacts image quality in thoracoabdominal PET/CT imaging. This study introduces a unified data-driven respiratory motion correction (uRMC) method, utilizing deep learning neural networks, to solve all the major issues caused by RM, i.e., PET resolution loss, attenuation correction artifacts, and PET-CT misalignment.

METHODS

In a retrospective study, 737 patients underwent [18F]FDG PET/CT scans using the uMI Panorama PET/CT scanner. Ninety-nine patients, who also had respiration monitoring device (VSM), formed the validation set. The remaining data of the 638 patients were used to train neural networks used in the uRMC. The uRMC primarily consists of three key components: (1) data-driven respiratory signal extraction, (2) attenuation map generation, and (3) PET-CT alignment. SUV metrics were calculated within 906 lesions for three approaches, i.e., data-driven uRMC (proposed), VSM-based uRMC, and OSEM without motion correction (NMC). RM magnitude of major organs were estimated.

RESULTS

uRMC enhanced diagnostic capabilities by revealing previously undetected lesions, sharpening lesion contours, increasing SUV values, and improving PET-CT alignment. Compared to NMC, uRMC showed increases of 10% and 17% in SUVmax and SUVmean across 906 lesions. Sub-group analysis showed significant SUV increases in small and medium-sized lesions with uRMC. Minor differences were found between VSM-based and data-driven uRMC methods, with the SUVmax was found statistically marginal significant or insignificant between the two methods. The study observed varied motion amplitudes in major organs, typically ranging from 10 to 20 mm.

CONCLUSION

A data-driven solution for respiratory motion in PET/CT has been developed, validated and evaluated. To the best of our knowledge, this is the first unified solution that compensates for the motion blur within PET, the attenuation mismatch artifacts caused by PET-CT misalignment, and the misalignment between PET and CT.

Whole-Body Multiparametric PET in Clinical Oncology: Current Status, Challenges, and Opportunities

The interpretation of clinical oncologic PET studies has historically used static reconstructions based on SUVs. SUVs and SUV-based images have important limitations, including dependence on uptake times and reduced conspicuity of tracer-avid lesions in organs with high background uptake. The acquisition of dynamic PET images enables additional PET reconstructions via Patlak modeling, which assumes that a tracer is irreversibly trapped by tissues of interest. The resulting multiparametric PET images capture a tracer's net trapping rate and apparent volume of distribution, separating the contributions of bound and free tracer fractions to the PET signal captured in the SUV. Potential benefits of multiparametric PET include higher quantitative stability, superior lesion conspicuity, and greater accuracy for differentiating malignant and benign lesions. However, the imaging protocols necessary for multiparametric PET are inherently more complex and time intensive, despite the recent introduction of automated or semiautomated scanner-based reconstruction packages. In this Review, we examine the current state of multiparametric PET in whole-body oncologic imaging. We summarize the Patlak method and relevant tracer kinetics, discuss clinical workflows and protocol considerations, and highlight clinical challenges and opportunities. We aim to help oncologic imagers make informed decisions about whether to implement multiparametric PET in their clinical practices.

Trends in cancer imaging

Molecular imaging of cancer is a collaborative endeavor, uniting scientists and physicians from diverse fields. Such collaboration is actively developing and translating cutting-edge molecular imaging approaches to enhance the diagnostic landscape of human malignancies. The advent of positron emission tomography (PET) and PET imaging tracers has realized non-invasive target annotation and tumor characterization at the molecular level. In surgical procedures, novel imaging techniques, such as fluorescence or Cherenkov luminescence, help identify tumors and enhance surgical precision. Simultaneously, progress in imaging equipment, innovative algorithms, and artificial intelligence has opened avenues for next-generation cancer screening and imaging, augmenting the efficiency and accuracy of cancer diagnosis. In this review, we provide a panorama of molecular cancer imaging and ongoing developments in the field.

Total-body dynamic PET/CT imaging reveals kinetic distribution of [13N]NH3 in normal organs

PURPOSE

To systematically investigate kinetic metrics and metabolic trapping of [13N]NH3 in organs.

METHODS

Eleven participants performed total-body [13N]NH3 dynamic positron emission tomography (PET). Regions of interest were drawn in organs to obtain time-to-activity curves (TACs), which were fitted with an irreversible two-tissue compartment model (2TC) to investigate constant rates K1, k2 and k3, and to calculate Ki. Additionally, one-tissue compartment model using full data (1TCfull) and the first four minutes of data (1TC4min) were fitted to TAC data. K1 and k2 were compared among different models to assess [13N]NH3 trapping in organs.

RESULTS

Kinetic rates of [13N]NH3 varied significantly among organs. The mean K1 ranged from 0.049 mL/cm3/min in the muscle to 2.936 mL/cm3/min in the kidney. The k2 and k3 were lowest in the liver (0.001 min- 1) and in the pituitary (0.009 min- 1), while highest in the kidney (0.587 min- 1) and in the liver (0.800 min- 1), respectively. The Ki was largest in the myocardium (0.601 ± 0.259 mL/cm3/min) while smallest in the bone marrow (0.028 ± 0.022 mL/cm3/min). Three groups of organs with similar kinetic characteristics were revealed: (1) the thyroid, the lung, the spleen, the pancreas, and the kidney; (2) the liver and the muscle; and (3) the cortex, the white matter, the cerebellum, the pituitary, the parotid, the submandibular gland, the myocardium, the bone, and the bone marrow. Obvious k3 was identified in multiple organs, and significant changes of K1 in multiple organs and k2 in most organs were found between 2TC and 1TCfull, but both K1 and k2 were comparable between 2TC and 1TC4min.

CONCLUSION

The kinetic rates of [13N]NH3 differed among organs with some have obvious 13N-anmmonia trapping. The normal distribution of kinetic metrics of 13N-anmmonia in organs can serve as a reference for its potential use in tumor imaging.

PICASSO: a universal brain phantom for positron emission tomography based on the activity painting technique

Objective. This study presents a universal phantom for positron emission tomography (PET) that allows arbitrary static and dynamic activity distributions of various complexities to be generated using a single PET acquisition.Approach. We collected a high-statistics dataset (with a total of 22.4 × 109prompt coincidences and an event density of 2.75 × 106events mm-3) by raster-scanning a single plane with a22Na point source mounted on a robotic arm in the field-of-view of the uEXPLORER PET/CT scanner. The source position was determined from the reconstructed dynamic frames. Uniquely, true coincidences were separated from scattered and random events based on the distance between their line-of-response and the known source location. Finally, we randomly sampled the dataset to generate the desired activity distributions modeling several different phantoms.Main results. Overall, the target and the reconstructed phantom images had good agreement. The analysis of a simple geometric distribution showed high quantitative accuracy of the phantom, with mean error of <-3.0% relative to the ground truth for activity concentrations ranging from 5.3 to 47.7 kBq ml-1. The model of a high-resolution18F-fluorodeoxyglucose distribution in the brain illustrates the usefulness of the technique in simulating realistic static neuroimaging studies. A dynamic18F-florbetaben study was modeled based on the time-activity curves of a human study and a segmented brain phantom with no coincidences repeating between frames. For all time points, the mean voxel-wise errors ranged from -4.4% to -0.7% in grey matter and from -3.9% to +2.8% in white matter.Significance. The proposed phantom technique is highly flexible and allows modeling of static and dynamic brain PET studies with high quantitative accuracy. It overcomes several key limitations of the existing phantoms and has many promising applications for the purposes of image reconstruction, data correction methods, and system performance evaluation, particularly for new high-performance dedicated brain PET scanners.

Assessing the deep learning based image quality enhancements for the BGO based GE omni legend PET/CT

BACKGROUND

This study investigates the integration of Artificial Intelligence (AI) in compensating the lack of time-of-flight (TOF) of the GE Omni Legend PET/CT, which utilizes BGO scintillation crystals.

METHODS

The current study evaluates the image quality of the GE Omni Legend PET/CT using a NEMA IQ phantom. It investigates the impact on imaging performance of various deep learning precision levels (low, medium, high) across different data acquisition durations. Quantitative analysis was performed using metrics such as contrast recovery coefficient (CRC), background variability (BV), and contrast to noise Ratio (CNR). Additionally, patient images reconstructed with various deep learning precision levels are presented to illustrate the impact on image quality.

RESULTS

The deep learning approach significantly reduced background variability, particularly for the smallest region of interest. We observed improvements in background variability of 11.8 % , 17.2 % , and 14.3 % for low, medium, and high precision deep learning, respectively. The results also indicate a significant improvement in larger spheres when considering both background variability and contrast recovery coefficient. The high precision deep learning approach proved advantageous for short scans and exhibited potential in improving detectability of small lesions. The exemplary patient study shows that the noise was suppressed for all deep learning cases, but low precision deep learning also reduced the lesion contrast (about -30 % ), while high precision deep learning increased the contrast (about 10 % ).

CONCLUSION

This study conducted a thorough evaluation of deep learning algorithms in the GE Omni Legend PET/CT scanner, demonstrating that these methods enhance image quality, with notable improvements in CRC and CNR, thereby optimizing lesion detectability and offering opportunities to reduce image acquisition time.