Ultrafast 30-s total-body PET/CT scan: a preliminary study

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.

Leveraging small voxel with optimal acquisition time for [18F]mFBG total-body PET/CT imaging in pediatric patients with neuroblastoma: a preliminary study

PURPOSE

The advent of total-body PET/CT presents an opportunity for significant advancements in imaging of neuroblastoma with [18F]meta-fluorobenzylguanidine ([18F]mFBG). Small voxel imaging has proven to have better lesion detectability but need enough radioactivity counts. This study aims to balance shortened acquisition times and small voxel reconstruction to keep sufficient image quality and diagnostic confidence on [18F]mFBG total-body PET for neuroblastoma.

METHODS

We retrospectively enrolled 33 pediatric patients with neuroblastoma who underwent 37 [18F]mFBG total-body uEXPLORER PET/CT scans of 10-min duration. PET images were reconstructed with varying acquisition times (0.5-10 min) and three matrix sizes (192 × 192, 512 × 512 and 1024 × 1024). The subjective (scored on a 5-point scale) and objective image quality (signal-to-noise ratio, SNR) of all the sets of reconstructed images were analyzed by nuclear medicine physicians. For indeterminate lesions identified in the group of 192 × 192 matrix with the 10-min scan (G192-10), diagnostic confidence was further evaluated in images reconstructed with the 512 × 512 and 1024 × 1024 matrices (G512 and G1024).

RESULTS

Of the 33 patients with 37 [18F]mFBG PET/CT scans, 17 patients with 20 scans had positive [18F]mFBG PET/CT findings. Sufficient subjective image quality was achieved with at least 2-min acquisition of 192 × 192 matrix and 4-min acquisition of 512 × 512 matrix (with all scores ≥ 3). SNR increased with longer acquisition times for the same voxel size, while decreased as voxel size shrunk. Although the Curie and SIOPEN scores remained consistent across G192, G512, and G1024-10 groups, the G512 groups with at least 2-min acquisition and G1024-10 showed significantly higher confidence scores for characterizing indeterminate lesions on the G192-10 images, with almost all indeterminate lesions being rated as very confident.

CONCLUSIONS

A matrix of 512 × 512 with a minimum of 4-min acquisition on [18F]mFBG total-body PET/CT is recommended for sufficient image quality and improved diagnostic confidence, particularly in detecting indeterminate lesions.

The SwiftScan step-and-shoot continuous mode improves SPECT scanning efficiency: a preliminary phantom and clinical test

PURPOSE

The aim of the study was to investigate the value of SwiftScan Step-and-Shoot Continuous (SSC) scanning mode in enhancing image quality and to explore appropriate scanning parameters for reducing scan time.

METHODS

This study was composed of a phantom study and two clinical tests. The differences in visual image quality scores, coefficient of variance (COV) of the background, image signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and recovery coefficient (RC) of the sphere were compared between SSC mode and traditional Step-and-Shoot (SS) mode in the phantom study. Various "shoot" acquisition times (5s, 10s, 15s) and "step" angles (3-degree, 6-degree, 9-degree) were evaluated and verified. In the clinical tests, bone tomography and parathyroid tomography were performed on 30 patients each. Differences in visual image quality scores, background COV, image SNR, CNR, and standardized uptake value (SUV) of lesions were compared between the two modes.

RESULTS

In the phantom study, SSC mode demonstrated higher visual scores and significantly reduced background COV (P < 0.05), and significantly increased SNR and CNR (P < 0.05) compared to SS mode. No significant alteration in RC was observed (P > 0.05). In the clinical tests, no significant differences were found between the optimal SSC scan combination (10s "shoot" and 6-degree "step")/ (10s "shoot" and 3-degree "step") and the traditional SS scan combination (15s "shoot" and 6-degree "step")/ (15s "shoot" and 3-degree "step") in visual image quality scores, background COV, image SNR, CNR, and SUV of bone and parathyroid high uptake lesions (P > 0.05).

CONCLUSION

The SwiftScan SSC mode can reduce acquisition time by 33% while maintaining similar image quality and quantification accuracy compared to SS mode. An SSC scanning protocol with a 10s "shoot" acquisition and 6-degree "step" or with a 10s "shoot" acquisition and 3-degree "step" over a 360-degree rotation, is recommended for clinical use.

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.

Sedation-free pediatric [18F]FDG imaging on totalbody PET/CT with the assistance of artificial intelligence

PURPOSE

While sedation is routinely used in pediatric PET examinations to preserve diagnostic quality, it may result in side effects and may affect the radiotracer's biodistribution. This study aims to investigate the feasibility of sedation-free pediatric PET imaging using ultra-fast total-body (TB) PET scanners and deep learning (DL)-based attenuation and scatter correction (ASC).

METHODS

This retrospective study included TB PET (uExplorer) imaging of 35 sedated pediatric patients under four years old to determine the minimum effective scanning time. A DL-based ASC method was applied to enhance PET quantification. Both quantitative and qualitative assessments were conducted to evaluate the image quality of ultra-fast DL-ASC PET. Five non-sedated pediatric patients were subsequently used to validate the proposed approach.

RESULTS

Comparisons between standard 300-second and ultra-fast 15-second imaging, CT-ASC and DL-ASC ultra-fast 15-second images, as well as DL-ASC ultra-fast 15-second images in non-sedated and sedated patients, showed no significant differences in qualitative scoring, lesion detectability, and quantitative Standard Uptake Value (SUV) (P = ns).

CONCLUSIONS

This study demonstrates that pediatric PET imaging can be effectively performed without sedation by combining ultra-fast imaging techniques with a DL-based ASC. This advancement in sedation-free ultra-fast PET imaging holds potential for broader clinical adoption.

Ultrashort Oncologic Whole-Body [18F]FDG Patlak Imaging Using LAFOV PET

Methods to shorten [18F]FDG Patlak PET imaging procedures ranging from 65-90 to 20-30 min after injection, using a population-averaged input function (PIF) scaled to patient-specific image-derived input function (IDIF) values, were recently evaluated. The aim of the present study was to explore the feasibility of ultrashort 10-min [18F]FDG Patlak imaging at 55-65 min after injection using a PIF combined with direct Patlak reconstructions to provide reliable quantitative accuracy of lung tumor uptake, compared with a full-duration 65-min acquisition using an IDIF. Methods: Patients underwent a 65-min dynamic PET acquisition on a long-axial-field-of-view (LAFOV) Biograph Vision Quadra PET/CT scanner. Subsequently, direct Patlak reconstructions and image-based (with reconstructed dynamic images) Patlak analyses were performed using both the IDIF (time to relative kinetic equilibrium between blood and tissue concentration (t*) = 30 min) and a scaled PIF at 30-60 min after injection. Next, direct Patlak reconstructions were performed on the system console using only the last 10 min of the acquisition, that is, from 55 to 65 min after injection, and a scaled PIF using maximum crystal ring difference settings of both 85 and 322. Tumor lesion and healthy-tissue uptake was quantified and compared between the differently obtained parametric images to assess quantitative accuracy. Results: Good agreement was obtained between direct- and image-based Patlak analyses using the IDIF (t* = 30 min) and scaled PIF at 30-60 min after injection, performed using the different approaches, with no more than 8.8% deviation in tumor influx rate value (Ki ) (mean difference ranging from -0.0022 to 0.0018 mL/[min × g]). When direct Patlak reconstruction was performed on the system console, excellent agreement was found between the use of a scaled PIF at 30-60 min after injection versus 55-65 min after injection, with 2.4% deviation in tumor Ki (median difference, -0.0018 mL/[min × g]; range, -0.0047 to 0.0036 mL/[min × g]). For different maximum crystal ring difference settings using the scan time interval of 55-65 min after injection, only a 0.5% difference (median difference, 0.0000 mL/[min × g]; range, -0.0004 to 0.0013 mL/[min × g]) in tumor Ki was found. Conclusion: Ultrashort whole-body [18F]FDG Patlak imaging is feasible on an LAFOV Biograph Vision Quadra PET/CT system without loss of quantitative accuracy to assess lung tumor uptake compared with a full-duration 65-min acquisition. The ultrashort 10-min direct Patlak reconstruction with PIF allows for its implementation in clinical practice.

The impact of deep-inspiration breath-hold total-body PET/CT imaging on thoracic 18F-FDG avid lesions compared with free-breathing

OBJECTIVES

To investigate PET/CT registration and quantification accuracy of thoracic lesions of a single 30-second deep-inspiration breath-hold (DIBH) technique with a total-body PET (TB-PET) scanner, and compared with free-breathing (FB) PET/CT.

METHODS

137 of the 145 prospectively enrolled patients finished a routine FB-300 s PET/CT exam and a 30-second DIBH TB-PET with chest to pelvis low dose CT. The total-body FB-300 s, FB-30 s, and DIBH-30 s PET images were reconstructed. Quantitative assessment (SUVmax and SUVmean of lung and other organs), PET/CT registration assessment and lesion analysis (SUVmax, SUVpeak, SUVmean and tumor-background ratio) were compared with Wilcoxon signed-rank tests.

RESULTS

The SUVmax and SUVmean of the lung with DIBH-30 s were significantly lower than those with FB. The distances of the liver dome between PET and CT were significantly smaller with DIBH-30 s than with FB. 195 assessable lesions in 106 patients were included, and the detection sensitivity was 97.9 % and 99.0 % in FB-300 s, and DIBH-30 s, respectively. For both small co-identified lesions (n = 86) and larger co-identified lesions with a diameter ≥ 1 cm (n = 91), the lesion SUVs were significantly greater with DIBH-30 s than with FB-300 s. Regarding lesion location, the differences of the SUVs for the lesions in the lower thorax area (n = 97, p < 0.001) were significant between DIBH-30 s and FB-300 s, while these differences were not statistically significant in the upper thorax (n = 80, p > 0.05). The lesion tumor-to-surrounding-background ratio (TsBR) was significantly increased, both in the upper and lower thorax.

CONCLUSION

The TB DIBH PET/CT technique is feasible in clinical practice. It reduces the background lung uptake and achieves better registration and lesion quantification, especially in the lower thorax.

Intelligent ultrafast total-body PET for sedation-free pediatric [18F]FDG imaging

PURPOSE

This study aims to develop deep learning techniques on total-body PET to bolster the feasibility of sedation-free pediatric PET imaging.

METHODS

A deformable 3D U-Net was developed based on 245 adult subjects with standard total-body PET imaging for the quality enhancement of simulated rapid imaging. The developed method was first tested on 16 children receiving total-body [18F]FDG PET scans with standard 300-s acquisition time with sedation. Sixteen rapid scans (acquisition time about 3 s, 6 s, 15 s, 30 s, and 75 s) were retrospectively simulated by selecting the reconstruction time window. In the end, the developed methodology was prospectively tested on five children without sedation to prove the routine feasibility.

RESULTS

The approach significantly improved the subjective image quality and lesion conspicuity in abdominal and pelvic regions of the generated 6-s data. In the first test set, the proposed method enhanced the objective image quality metrics of 6-s data, such as PSNR (from 29.13 to 37.09, p < 0.01) and SSIM (from 0.906 to 0.921, p < 0.01). Furthermore, the errors of mean standardized uptake values (SUVmean) for lesions between 300-s data and 6-s data were reduced from 12.9 to 4.1% (p < 0.01), and the errors of max SUV (SUVmax) were reduced from 17.4 to 6.2% (p < 0.01). In the prospective test, radiologists reached a high degree of consistency on the clinical feasibility of the enhanced PET images.

CONCLUSION

The proposed method can effectively enhance the image quality of total-body PET scanning with ultrafast acquisition time, leading to meeting clinical diagnostic requirements of lesion detectability and quantification in abdominal and pelvic regions. It has much potential to solve the dilemma of the use of sedation and long acquisition time that influence the health of pediatric patients.

Advantages and Challenges of Total-Body PET/CT at a Tertiary Cancer Center: Insights from Sun Yat-sen University Cancer Center

In recent decades, researchers worldwide have directed their efforts toward enhancing the quality of PET imaging. The detection sensitivity and image resolution of conventional PET scanners with a short axial field of view have been constrained, leading to a suboptimal signal-to-noise ratio. The advent of long-axial-field-of-view PET scanners, exemplified by the uEXPLORER system, marked a significant advancement. Total-body PET imaging possesses an extensive scan range of 194 cm and an ultrahigh detection sensitivity, and it has emerged as a promising avenue for improving image quality while reducing the administered radioactivity dose and shortening acquisition times. In this review, we elucidate the application of the uEXPLORER system at the Sun Yat-sen University Cancer Center, including the disease distribution, patient selection workflow, scanning protocol, and several enhanced clinical applications, along with encountered challenges. We anticipate that this review will provide insights into routine clinical practice and ultimately improve patient care.

Clinical Implementation of Total-Body PET in China

Total-body (TB) PET/CT is a groundbreaking tool that has brought about a revolution in both clinical application and scientific research. The transformative impact of TB PET/CT in the realms of clinical practice and scientific exploration has been steadily unfolding since its introduction in 2018, with implications for its implementation within the health care landscape of China. TB PET/CT's exceptional sensitivity enables the acquisition of high-quality images in significantly reduced time frames. Clinical applications have underscored its effectiveness across various scenarios, emphasizing the capacity to personalize dosage, scan duration, and image quality to optimize patient outcomes. TB PET/CT's ability to perform dynamic scans with high temporal and spatial resolution and to perform parametric imaging facilitates the exploration of radiotracer biodistribution and kinetic parameters throughout the body. The comprehensive TB coverage offers opportunities to study interconnections among organs, enhancing our understanding of human physiology and pathology. These insights have the potential to benefit applications requiring holistic TB assessments. The standard topics outlined in The Journal of Nuclear Medicine were used to categorized the reviewed articles into 3 sections: current clinical applications, scan protocol design, and advanced topics. This article delves into the bottleneck that impedes the full use of TB PET in China, accompanied by suggested solutions.

Fully automated computational measurement of noise in positron emission tomography

OBJECTIVES

To introduce an automated computational algorithm that estimates the global noise level across the whole imaging volume of PET datasets.

METHODS

[18F]FDG PET images of 38 patients were reconstructed with simulated decreasing acquisition times (15-120 s) resulting in increasing noise levels, and with block sequential regularized expectation maximization with beta values of 450 and 600 (Q.Clear 450 and 600). One reader performed manual volume-of-interest (VOI) based noise measurements in liver and lung parenchyma and two readers graded subjective image quality as sufficient or insufficient. An automated computational noise measurement algorithm was developed and deployed on the whole imaging volume of each reconstruction, delivering a single value representing the global image noise (Global Noise Index, GNI). Manual noise measurement values and subjective image quality gradings were compared with the GNI.

RESULTS

Irrespective of the absolute noise values, there was no significant difference between the GNI and manual liver measurements in terms of the distribution of noise values (p = 0.84 for Q.Clear 450, and p = 0.51 for Q.Clear 600). The GNI showed a fair to moderately strong correlation with manual noise measurements in liver parenchyma (r = 0.6 in Q.Clear 450, r = 0.54 in Q.Clear 600, all p < 0.001), and a fair correlation with manual noise measurements in lung parenchyma (r = 0.52 in Q.Clear 450, r = 0.33 in Q.Clear 600, all p < 0.001). Classification performance of the GNI for subjective image quality was AUC 0.898 for Q.Clear 450 and 0.919 for Q.Clear 600.

CONCLUSION

An algorithm provides an accurate and meaningful estimation of the global noise level encountered in clinical PET imaging datasets.

CLINICAL RELEVANCE STATEMENT

An automated computational approach that measures the global noise level of PET imaging datasets may facilitate quality standardization and benchmarking of clinical PET imaging within and across institutions.

KEY POINTS

• Noise is an important quantitative marker that strongly impacts image quality of PET images. • An automated computational noise measurement algorithm provides an accurate and meaningful estimation of the global noise level encountered in clinical PET imaging datasets. • An automated computational approach that measures the global noise level of PET imaging datasets may facilitate quality standardization and benchmarking as well as protocol harmonization.

Current and Future Use of Long Axial Field-of-View Positron Emission Tomography/Computed Tomography Scanners in Clinical Oncology

The latest technical development in the field of positron emission tomography/computed tomography (PET/CT) imaging has been the extension of the PET axial field-of-view. As a result of the increased number of detectors, the long axial field-of-view (LAFOV) PET systems are not only characterized by a larger anatomical coverage but also by a substantially improved sensitivity, compared with conventional short axial field-of-view PET systems. In clinical practice, this innovation has led to the following optimization: (1) improved overall image quality, (2) decreased duration of PET examinations, (3) decreased amount of radioactivity administered to the patient, or (4) a combination of any of the above. In this review, novel applications of LAFOV PET in oncology are highlighted and future directions are discussed.

Sub-minute acquisition with deep learning-based image filter in the diagnosis of colorectal cancers using total-body 18F-FDG PET/CT

BACKGROUND

This study aimed to retrospectively evaluate the feasibility of total-body ¹⁸F-FDG PET/CT ultrafast acquisition combined with a deep learning (DL) image filter in the diagnosis of colorectal cancers (CRCs).

METHODS

The clinical and preoperative imaging data of patients with CRCs were collected. All patients underwent a 300-s list-mode total-body ¹⁸F-FDG PET/CT scan. The dataset was divided into groups with acquisition durations of 10, 20, 30, 60, and 120 s. PET images were reconstructed using ordered subset expectation maximisation, and post-processing filters, including a Gaussian smoothing filter with 3 mm full width at half maximum (3 mm FWHM) and a DL image filter. The effects of the Gaussian and DL image filters on image quality, detection rate, and uptake value of primary and liver metastases of CRCs at different acquisition durations were compared using a 5-point Likert scale and semi-quantitative analysis, with the 300-s image with a Gaussian filter as the standard.

RESULTS

All 34 recruited patients with CRCs had single colorectal lesions, and the diagnosis was verified pathologically. Of the total patients, 11 had liver metastases, and 113 liver metastases were detected. The 10-s dataset could not be evaluated due to high noise, regardless of whether it was filtered by Gaussian or DL image filters. The signal-to-noise ratio (SNR) of the liver and mediastinal blood pool in the images acquired for 10, 20, 30, and 60 s with a Gaussian filter was lower than that of the 300-s images (P < 0.01). The DL filter significantly improved the SNR and visual image quality score compared to the Gaussian filter (P < 0.01). There was no statistical difference in the SNR of the liver and mediastinal blood pool, SUVmax and TBR of CRCs and liver metastases, and the number of detectable liver metastases between the 20- and 30-s DL image filter and 300-s images with the Gaussian filter (P > 0.05).

CONCLUSIONS

The DL filter can significantly improve the image quality of total-body ¹⁸F-FDG PET/CT ultrafast acquisition. Deep learning-based image filtering methods can significantly reduce the noise of ultrafast acquisition, making them suitable for clinical diagnosis possible.

Impact of Reduced Image Noise on Deauville Scores in Patients with Lymphoma Scanned on a Long-Axial Field-of-View PET/CT-Scanner

BACKGROUND

Total body and long-axial field-of-view (LAFOV) PET/CT represent visionary innovations in imaging enabling either improved image quality, reduction in injected activity-dose or decreased acquisition time. An improved image quality may affect visual scoring systems, including the Deauville score (DS), which is used for clinical assessment of patients with lymphoma. The DS compares SUVmax in residual lymphomas with liver parenchyma, and here we investigate the impact of reduced image noise on the DS in patients with lymphomas scanned on a LAFOV PET/CT.

METHODS

Sixty-eight patients with lymphoma underwent a whole-body scan on a Biograph Vision Quadra PET/CT-scanner, and images were evaluated visually with regard to DS for three different timeframes of 90, 300, and 600 s. SUVmax and SUVmean were calculated from liver and mediastinal blood pool, in addition to SUVmax from residual lymphomas and measures of noise.

RESULTS

SUVmax in liver and in mediastinal blood pool decreased significantly with increasing acquisition time, whereas SUVmean remained stable. In residual tumor, SUVmax was stable during different acquisition times. As a result, the DS was subject to change in three patients.

CONCLUSIONS

Attention should be drawn towards the eventual impact of improvements in image quality on visual scoring systems such as the DS.

Extending the clinical capabilities of short- and long-lived positron-emitting radionuclides through high sensitivity PET/CT

This review describes the main benefits of using long axial field of view (LAFOV) PET in clinical applications. As LAFOV PET is the latest development in PET instrumentation, many studies are ongoing that explore the potentials of these systems, which are characterized by ultra-high sensitivity. This review not only provides an overview of the published clinical applications using LAFOV PET so far, but also provides insight in clinical applications that are currently under investigation. Apart from the straightforward reduction in acquisition times or administered amount of radiotracer, LAFOV PET also allows for other clinical applications that to date were mostly limited to research, e.g., dual tracer imaging, whole body dynamic PET imaging, omission of CT in serial PET acquisition for repeat imaging, and studying molecular interactions between organ systems. It is expected that this generation of PET systems will significantly advance the field of nuclear medicine and molecular imaging.