Total-Body PET/Computed Tomography Highlights in Clinical Practice: Experiences from Zhongshan Hospital, Fudan University

Extracting value from total-body PET/CT image data - the emerging role of artificial intelligence

The evolution of Positron Emission Tomography (PET), culminating in the Total-Body PET (TB-PET) system, represents a paradigm shift in medical imaging. This paper explores the transformative role of Artificial Intelligence (AI) in enhancing clinical and research applications of TB-PET imaging. Clinically, TB-PET's superior sensitivity facilitates rapid imaging, low-dose imaging protocols, improved diagnostic capabilities and higher patient comfort. In research, TB-PET shows promise in studying systemic interactions and enhancing our understanding of human physiology and pathophysiology. In parallel, AI's integration into PET imaging workflows-spanning from image acquisition to data analysis-marks a significant development in nuclear medicine. This review delves into the current and potential roles of AI in augmenting TB-PET/CT's functionality and utility. We explore how AI can streamline current PET imaging processes and pioneer new applications, thereby maximising the technology's capabilities. The discussion also addresses necessary steps and considerations for effectively integrating AI into TB-PET/CT research and clinical practice. The paper highlights AI's role in enhancing TB-PET's efficiency and addresses the challenges posed by TB-PET's increased complexity. In conclusion, this exploration emphasises the need for a collaborative approach in the field of medical imaging. We advocate for shared resources and open-source initiatives as crucial steps towards harnessing the full potential of the AI/TB-PET synergy. This collaborative effort is essential for revolutionising medical imaging, ultimately leading to significant advancements in patient care and medical research.

Current Role and Future Prospects of Positron Emission Tomography (PET)/Computed Tomography (CT) in the Management of Breast Cancer

Breast cancer has become the most diagnosed cancer in women globally, with 2.3 million new diagnoses each year. Accurate early staging is essential for improving survival rates with metastatic spread from loco regional to distant metastasis, decreasing mortality rates by 50%. Current guidelines do not advice the routine use of positron emission tomography (PET)-computed tomography (CT) in the staging of early breast cancer in the absence of symptoms. However, there is a growing body of evidence to suggest that the use of PET-CT in this early stage can benefit the patient by improving staging and as a result treatment and outcomes, as well as psychological burden, without increasing costs to the health service. Ongoing research in PET radiomics and artificial intelligence is showing promising future prospects in its use in diagnosis, staging, prognostication, and assessment of responses to the treatment of breast cancer. Furthermore, ongoing research to address current limitations of PET-CT by improving techniques and tracers is encouraging. In this narrative review, we aim to evaluate the current evidence of the usefulness of PET-CT in the management of breast cancer in different settings along with its future prospects, including the use of artificial intelligence (AI), radiomics, and novel tracers.

Practical Considerations for Total-Body PET Acquisition and Imaging

The world's first total-body PET/CT system has been in routine clinical and research use at UC Davis since 2019. The uEXPLORER total-body PET scanner has been designed with an axial field-of-view long enough to completely encompass most human subjects (194 cm or 76 inches long), allowing for a 15-68-fold gain in the PET signal collection efficiency over conventional PET scanners. A high-sensitivity PET scanner that can image the entire subject with a single bed position comes with new benefits and challenges to consider for efficient and practical use. In this chapter, we discuss the common clinical and research imaging protocols implemented at our institution, along with the appropriate technical and practical considerations of total-body PET imaging.

Quantitative Perfusion Imaging with Total-Body PET

Recently, PET systems with a long axial field of view have become the current state of the art. Total-body PET scanners enable unique possibilities for scientific research and clinical diagnostics, but this new technology also raises numerous challenges. A key advantage of total-body imaging is that having all the organs in the field of view allows studying biologic interaction of all organs simultaneously. One of the new, promising imaging techniques is total-body quantitative perfusion imaging. Currently, 15O-labeled water provides a feasible option for quantitation of tissue perfusion at the total-body level. This review summarizes the status of the methodology and the analysis and provides examples of preliminary findings on applications of quantitative parametric perfusion images for research and clinical work. We also describe the opportunities and challenges arising from moving from single-organ studies to modeling of a multisystem approach with total-body PET, and we discuss future directions for total-body imaging.

Head-to-head intra-individual comparison of total-body 2-[18F]FDG PET/CT and digital PET/CT in patients with malignant tumor: how sensitive could it be?

OBJECTIVES

To comparatively evaluate the lesion-detecting ability of 2-[18F]FDG total-body PET/CT (TB PET/CT) and conventional digital PET/CT.

METHODS

This study enrolled 67 patients (median age, 65 years; 24 female and 43 male patients) who underwent a TB PET/CT scan and a conventional digital PET/CT scan after a single 2-[18F]FDG injection (3.7 MBq/kg). Raw PET data for TB PET/CT were acquired over the course of 5 min, and images were reconstructed using data from the first 1, 2, 3, and 4 min and the entire 5 min (G1, G2, G3, G4, and G5, respectively). The conventional digital PET/CT scan acquired in 2-3 min per bed (G0). Two nuclear medicine physicians independently assessed subjective image quality using a 5-point Likert scale and recorded the number of 2-[18F]FDG-avid lesions.

RESULTS

A total of 241 lesions (69 primary lesions; 32 liver, lung, and peritoneum metastases; and 140 regional lymph nodes) among 67 patients with various types of cancer were analyzed. The subjective image quality score and SNR (signal-to-noise ratio) increased gradually from G1 to G5, and these values were significantly higher than the values at G0 (all p < 0.05). Compared to conventional PET/CT, G4 and G5 of TB PET/CT detected an additional 15 lesions (2 primary lesions; 5 liver, lung, and peritoneum lesions; and 8 lymph node metastases).

CONCLUSION

TB PET/CT was more sensitive than conventional whole-body PET/CT in detecting small (4.3 mm, maximum standardized uptake value (SUVmax) of 1.0) or low-uptake (tumor-to-liver ratio of 1.6, SUVmax of 4.1) lesions.

CLINICAL RELEVANCE STATEMENT

This study explored the gain of the image quality and lesion detectability of TB PET/CT, compared to conventional PET/CT, and recommended the appropriate acquisition time for TB PET/CT in clinical practice with an ordinary 2-[18F] FDG dose.

KEY POINTS

• TB PET/CT increases the effective sensitivity to approximately 40 times that of conventional PET scanners. • The subjective image quality score and signal-to-noise ratio of TB PET/CT from G1 to G5 were better than those of conventional PET/CT. • 2-[18F]FDG TB PET/CT with a 4-min acquisition time at a regular tracer dose detected an additional 15 lesions compared to conventional PET/CT.

Total-Body Positron Emission Tomography: Adding New Perspectives to Cardiovascular Research

The recent advent of positron emission tomography (PET) scanners that can image the entire human body opens up intriguing possibilities for cardiovascular research and future clinical applications. These new systems permit radiotracer kinetics to be measured in all organs simultaneously. They are particularly well suited to study cardiovascular disease and its effects on the entire body. They could also play a role in quantitatively measuring physiologic, metabolic, and immunologic responses in healthy individuals to a variety of stressors and lifestyle interventions, and may ultimately be instrumental for evaluating novel therapeutic agents and their molecular effects across different tissues. In this review, we summarize recent progress in PET technology and methodology, discuss several emerging cardiovascular applications for total-body PET, and place this in the context of multiorgan and systems medicine. Finally, we discuss opportunities that will be enabled by the technology, while also pointing to some of the challenges that still need to be addressed.

An exploration of the feasibility and clinical value of half-dose 5-h total-body 18F-FDG PET/CT scan in patients with Takayasu arteritis

PURPOSE

To explore the feasibility and clinical value of 5-h delayed 18F-fluorodeoxyglucose (18F-FDG) total-body (TB) positron emission tomography/computed tomography (PET/CT) in patients with Takayasu arteritis (TA).

METHODS

This study included nine healthy volunteers who underwent 1-, 2.5-, and 5-h triple-time TB PET/CT scans and 55 patients with TA who underwent 2- and 5-h dual-time TB PET/CT scans with 1.85 MBq/kg 18F-FDG. The liver, blood pool, and gluteus maximus muscle signal-to-noise ratios (SNRs) were calculated by dividing the SUVmean by its standard deviation to evaluate imaging quality. TA lesions' 18F-FDG uptake was graded on a three-point scale (I, II, III), with grades II and III considered positive lesions. Lesion-to-blood maximum standardised uptake value (SUVmax) ratio (LBR) was calculated by dividing the lesion SUVmax by the blood pool SUVmax.

RESULTS

The liver, blood pool, and muscle SNR of the healthy volunteers at 2.5- and 5-h were similar (0.117 and 0.115, respectively, p = 0.095). We detected 415 TA lesions in 39 patients with active TA. The average 2- and 5-h scan LBRs were 3.67 and 7.59, respectively (p < 0.001). Similar TA lesion detection rates were noted in the 2-h (92.0%; 382/415) and 5-h (94.2%; 391/415) scans (p = 0.140). We detected 143 TA lesions in 19 patients with inactive TA. The 2- and 5-h scan LBRs were 2.99 and 5.71, respectively (p < 0.001). Similar positive detection rates in inactive TA were noted in the 2-h (97.9%; 140/143) and 5-h (98.6%; 141/143) scans (p = 0.500).

CONCLUSION

The 2- and 5-h 18F-FDG TB PET/CT scans had similar positive detection rates, but both combined could better detect inflammatory lesions in patients with TA.

One-stop [18F]FDG and [68Ga]Ga-DOTA-FAPI-04 total-body PET/CT examination with dual-low activity: a feasibility study

PURPOSE

Positron emission tomography/computed tomography (PET/CT) based on fibroblast activation protein inhibitors (FAPI) has shown complementary values to 2-[18F]-fluoro-2-deoxy-D-glucose ([18F]FDG) in cancer imaging. This study aimed to investigate the feasibility of a one-stop FDG-FAPI dual-tracer imaging protocol with dual-low activity for oncological imaging.

METHODS

Nineteen patients with malignancies underwent one-stop [18F]FDG (0.37 MBq/kg) PET (PETFDG) and dual-tracer PET 30-40 and 50-60 min (hereafter, PETD30-40 and PETD50-60, respectively) after additional injection of [68Ga]Ga-DOTA-FAPI-04 (0.925 MBq/kg), with a single diagnostic CT to generate the PET/CT. The lesion detection rate and tumor-to-normal ratios (TNRs) of tracer uptake were compared between PETFDG/CT and PETD50-60/CT and between PETD50-60/CT and PETD30-40/CT. In addition, a visual scoring system was established to compare the lesion detectability.

RESULTS

The dual-tracer PETD50-60 and PETD30-40/CT showed similar performance in detecting primary tumors but presented significantly higher lesion TNRs than PETFDG. Significantly, more metastases with higher TNRs were identified on PETD50-60 than PETFDG (491 vs. 261, P < 0.001). The dual-tracer PETD50-60 received significantly higher visual scores than single PETFDG (111 vs. 10) in demonstrating both primary tumors (12 vs. 2) and metastases (99 vs. 8). However, these differences were not significant between PETD50-60 and PETD30-40. These resulted in tumor upstaging in 44.4% patients taking PET/CT for initial assessment, and more recurrences (68 vs. 7) were identified in patients taking PET/CT for restaging, both on PETD50-60 and PETD30-40, compared to PETFDG. The reduced effective dosimetry per patient (26.2 ± 2.57 mSv) was equal to that of a single standard whole-body PET/CT.

CONCLUSION

The one-stop dual-tracer dual-low-activity PET imaging protocol combines the strengths of [18F]FDG and [68Ga]Ga-DOTA-FAPI-04 with shorter duration and lesser radiation and is thus clinically applicable.

Neuroendocrine Neoplasms: Total-body PET/Computed Tomography

Total-body PET/computed tomography (CT) (uExplorer) static and dynamic scan using low-dose (48.1 to 73.6 MBq) gallium-68 (⁶⁸Ga) DOTATATE combined with low-dose (1.55 MBq/kg) or ultra-low-dose (0.37 MBq/kg) 18F-fluorodeoxyglucose (18F-FDG) were used as a routine in patients with neuroendocrine neoplasms (NENs). ⁶⁸Ga DOTATATE and 18F-FDG PET/CT static imaging play complementary roles in diagnosis, staging, and therapy-response evaluation in a patient with NENs. Kinetic parameters and time activity curve derived from the dynamic scan is helpful for understanding tumors biological characteristics and differential diagnosis of NENs.

Optimal clinical protocols for total-body 18F-FDG PET/CT examination under different activity administration plans

BACKGROUND

Highly sensitive digital total-body PET/CT scanners (uEXPLORER) have great potential for clinical applications and fundamental research. Given their increasing sensitivity, low-dose scanning or snapshot imaging is now possible in clinics. However, a standardized total-body ¹⁸F-FDG PET/CT protocol is still lacking. Establishing a standard clinical protocol for total-body 18F-FDG PET/CT examination under different activity administration plans can help provide a theoretical reference for nuclear radiologists.

METHODS

The NEMA image quality (IQ) phantom was used to evaluate the biases of various total-body ¹⁸F-FDG PET/CT protocols related to the administered activity, scan duration, and iterations. Several objective metrics, including contrast recovery (CR), background variability (BV), and contrast-to-noise ratio (CNR), were measured from different protocols. In line with the European Association of Nuclear Medicine Research Ltd. (EARL) guidelines, optimized protocols were suggested and evaluated for total-body ¹⁸F-FDG PET/CT imaging for three different injected activities.

RESULTS

Our NEMA IQ phantom evaluation resulted in total-body PET/CT images with excellent contrast and low noise, suggesting great potential for reducing administered activity or shortening the scan duration. Different to the iteration number, prolonging the scan duration was the first choice for achieving higher image quality regardless of the activity administered. In light of image quality, tolerance of oncological patients, and the risk of ionizing radiation damage, the 3-min acquisition and 2-iteration (CNR = 7.54), 10-min acquisition and 3-iteration (CNR = 7.01), and 10-min acquisition and 2-iteration (CNR = 5.49) protocols were recommended for full-dose (3.70 MBq/kg), half-dose (1.95 MBq/kg), and quarter-dose (0.98 MBq/kg) activity injection schemes, respectively. Those protocols were applied in clinical practices, and no significant differences were observed for the SUV_max of large/small lesions or the SUV_mean of different healthy organs/tissues.

CONCLUSION

These findings support that digital total-body PET/CT scanners can generate PET images with a high CNR and low-noise background, even with a short acquisition time and low administered activity. The proposed protocols for different administered activities were determined to be valid for clinical examination and can maximize the value of this imaging type.

Ultralow-dose [18F]FDG PET/CT imaging: demonstration of feasibility in dynamic and static images

OBJECTIVES

Validation of [¹⁸F]FDG PET/CT at ultralow-dose (0.37 MBq/kg) and compared to imaging at half-dose (1.85 MBq/kg).

METHODS

This prospective head-to-head intraindividual study compared dynamic and static parameters of ultralow-dose with half-dose [¹⁸F]FDG total-body PET/CT. In static imaging, the ultralow-dose groups of PET images were denoted ULD5, 60-65 min; ULD8, 60-68 min; ULD10, 60-70 min; and ULD15, 60-75 min. The half-dose group images were reconstructed to 60-61, 60-62, 60-63, and 60-75 min, defined as LD1, LD2, LD3, and LD15, respectively. A 5-point Likert scale was used to subjectively evaluate the quality of static PET images, with a score greater than 3 considered to meet the requirements for clinical diagnosis.

RESULTS

Thirty participants were included in this study, and in terms of kinetic indicators, no special differences were found between the two groups of normal organs and lesions. In static images, those in groups ULD8 and LD2 achieved scores of [Formula: see text] 3.0, meeting the requirements for clinical diagnosis. In static imaging, four lesions were missed in the LD1 group with a lesion detectability of 89.7% (35/39). In the meantime, lesions were not missed in the whole ultra-low dose group (ULD5, ULD8, ULD10, and ULD15) and half-dose groups (LD2 and LD3).

CONCLUSIONS

Compared with half-dose imaging, ultralow-dose [¹⁸F]FDG total-body PET/CT imaging is clinically feasible, and there was no meaningful difference between the two groups of quantitative and qualitative analysis either dynamic or static images. Total-body PET/CT with ultralow-dose activity, the corresponding acquisition time of 8 min provides acceptable image quality and lesion detection.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: ChiCTR2000036487 KEY POINTS: • A prospective single-center study showed that the total-body PET scanner allows ultralow-dose [¹⁸F]FDG imaging with acceptable image quality and lesion detectability. • For the participant, radiation exposure can be reduced with ultralow-dose [¹⁸F]FDG total-body PET/CT imaging.

Respiratory-gated PET imaging with reduced acquisition time for suspect malignancies: the first experience in application of total-body PET/CT

OBJECTIVES

This study aimed to investigate the performance of respiratory-gating imaging with reduced acquisition time using the total-body positron emission tomography/computed tomography (PET/CT) scanner.

METHODS

Imaging data of 71 patients with suspect malignancies who underwent total-body 2-[¹⁸F]-fluoro-2-deoxy-D-glucose PET/CT for 15 min with respiration recorded were analyzed. For each examination, four reconstructions were performed: Ungated-15, using all coincidences; Ungated-5, using data of the first 5 min; Gated-15 using all coincidences but with respiratory gating; and Gated-6 using data of the first 6 min with respiratory gating. Lesions were quantified and image quality was evaluated; both were compared between the four image sets.

RESULTS

A total of 390 lesions were found in the thorax and upper abdomen. Lesion detectability was significantly higher in gated-15 (97.2%) than in ungated-15 (93.6%, p = 0.001) and ungated-5 (92.3%, p = 0.001), but comparable to Gated-6 (95.9%, p = 0.993). A total of 131 lesions were selected for quantitative analyses. Lesions in Gated-15 presented significantly larger standardized uptake values, tumor-to-liver ratio, and tumor-to-blood ratio, but smaller metabolic tumor volume, compared to those in Ungated-15 and Ungated-5 (all p < 0.001). These differences were more obvious in small lesions and in lesions from sites other than mediastinum/retroperitoneum. However, these indices were not significantly different between Gated-15 and Gated-6. Higher, but acceptable, image noise was identified in gated images than in ungated images.

CONCLUSIONS

Respiratory-gating imaging with reduced scanning time using the total-body PET/CT scanner is superior to ungated imaging and can be used in the clinic.

KEY POINTS

• In PET imaging, respiratory gating can improve lesion presentation and detectability but requires longer imaging time. • This single-center study showed that the total-body PET scanner allows respiratory-gated imaging with reduced and clinically acceptable scanning time.

Total-body PET: a new paradigm for molecular imaging

Total body (TB) positron emission tomography (PET) instruments have dramatically changed the paradigm of PET clinical and research studies due to their very high sensitivity and capability to image dynamic radiopharmaceutical distributions in the major organs of the body simultaneously. In this manuscript, we review the design of these systems and discuss general challenges and trade-offs to maximize the performance gains of current TB-PET systems. We then describe new concepts and technology that may impact future TB-PET systems. The manuscript summarizes what has been learned from the initial sites with TB-PET and explores potential research and clinical applications of TB-PET. The current generation of TB-PET systems range in axial field-of-view (AFOV) from 1 to 2 m and serve to illustrate the benefits and opportunities of a longer AFOV for various applications in PET. In only a few years of use these new TB-PET systems have shown that they will play an important role in expanding the field of molecular imaging and benefiting clinical practice.

Half-dose versus full-dose 18 F-FDG total-body PET/CT in patients with colorectal cancer

PURPOSE

The purpose of this study was to investigate image quality and lesion detectability of half-dose (1.85 MBq/kg) 18 F-fluorodeoxyglucose (FDG) total-body positron emission tomography/computed tomography (PET/CT) for colorectal cancer, full-dose (3.7 MBq/kg) 18 F-FDG serving as a reference.

METHODS

Fifty patients confirmed to have colorectal cancer who underwent total-body PET/CT with half-dose 18 F-FDG were included. Another 50 colorectal cancer patients with 3.70 MBq/kg 18 F-FDG activity were selected for the full-dose group. PET images in the half-dose group were scanned for 15 min and split into 1-, 2-, 3-, 4- and 10-min duration groups, denoted G1, G2, G3, G4 and G10, respectively. In the full-dose group, PET scanning was performed for 5 min, reconstructed with the first 0.5, 1, 2 and 5 min intervals, defined as G0.5', G1', G2' and G5', respectively. Subjective image quality was assessed with 5-point Likert scales. Objective image quality parameters included maximum standardized uptake values (SUV max) , mean standardized uptake values (SUV mean )and signal-to-noise ratio (SNR) of the liver, blood pool and muscle and SUV max and tumor-to-background ratio (TBR) of lesions.

RESULTS

In the two groups, the G3 and G2' images met clinical diagnosis requirements in terms of subjective image quality, with scores ≥3. There were no differences in terms of subjective and objective image quality between the groups (G1 and G0.5', G2 and G1', G4 and G2' and G10 and G5'). In the half-dose group, 56 colorectal lesions in 50 patients confirmed by surgical pathology were clearly visible in all groups. The number of FDG-avid lymph nodes was 37 in G1, 38 in G2 and 39 in the remaining half-dose groups. The number of missed metastatic liver lesions was 1 both in G1 and G2.

CONCLUSIONS

Total-body PET/CT with half-dose was feasible for diagnosing and staging colorectal cancer compared with full-dose 18 F-FDG PET/CT. Moreover, for half-dose total-body PET/CT, a 3-min scan duration could maintain image quality and lesion detectability.

Optimizing acquisition times for total-body positron emission tomography/computed tomography with half-dose 18F-fluorodeoxyglucose in oncology patients

Background

The present study aimed to explore the boundary of acquisition time and propose an optimized acquisition time range for total-body positron emission tomography (PET)/computed tomography (CT) oncological imaging using half-dose (1.85 MBq/kg) ¹⁸F-fluorodeoxyglucose activity based on diagnostic needs.

Methods

In this retrospective study based on a total-body PET system (uEXPLORER), an exploration cohort (October 2019–December 2019) of 46 oncology patients was first studied. The acquisition time for all patients was 15 min, and the acquired images were reconstructed and further split into 15-, 8-, 5-, 3-, 2-, and 1-min duration groups (abbreviated as G15, G8, G5, G3, G2, and G1). The image quality and lesion detectability of reconstructed PET images with different acquisition times were evaluated subjectively (5-point scale, lesion detection rate) and objectively (standardized uptake values, tumor-to-background ratio). In the same way, the initial optimized acquisition times were further validated in a cohort of 147 oncology patients (December 2019–June 2021) by using the Gs images (the images obtained using the 15- and 10-min acquisition times) as controls.

Results

In the exploration cohort, the subjective scores for G1, G2, G3, G5, and G8 images were 2.0 ± 0.2, 2.9 ± 0.3, 3.0 ± 0.0, 3.9 ± 0.2, and 4.2 ± 0.4, respectively. Two cases in G1 were rated as 1 point. No significant difference in scores was observed between G5 and G8 (p > 0.99). In general, groups with a longer acquisition time showed lower background uptake and lesion conspicuity. Compared with G15, lesion detection rate significantly reduced to 85.3% in G1 (p < 0.05). In the validation cohort, the subjective score was 3.0 ± 0.2 for G2, 3.0 ± 0.1 for G3, 3.6 ± 0.5 for G5, 4.0 ± 0.3 for G8, and 4.4 ± 0.5 for Gs. Only the scores between G2 and G3 were not significantly different (p > 0.99). The detection rates (204 lesions) significantly reduced to 94.1–90.2% in G3 and G2 (all p < 0.05).

Conclusion

A 2-min acquisition time provided acceptable performance in certain groups and specific medical situations. And protocols with acquisition times ≥ 5 min could provide comparable lesion detectability as regular protocols, showing better compatibility and feasibility with clinical practice.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40658-022-00474-y.

Expert consensus on oncological [18F]FDG total-body PET/CT imaging (version 1)

BACKGROUND

[¹⁸F]FDG imaging on total-body PET/CT (TB PET/CT) scanners, with improved sensitivity, offers new potentials for cancer diagnosis, staging, and radiation treatment planning. This consensus provides the protocols for clinical practices with a goal of paving the way for future studies with the total-body scanners in oncological [¹⁸F]FDG TB PET/CT imaging.

METHODS

The consensus was summarized based on the published guidelines and peer-reviewed articles of TB PET/CT in the literature, along with the opinions of the experts from major research institutions with a total of 40,000 cases performed on the TB PET/CT scanners.

RESULTS

This consensus describes the protocols for routine and dynamic [¹⁸F]FDG TB PET/CT scanning focusing on the reduction of imaging acquisition time and FDG injected activity, which may serve as a reference for research and clinic oncological PET/CT studies.

CONCLUSION

This expert consensus focuses on the reduction of acquisition time and FDG injected activity with a TB PET/CT scanner, which may improve the patient throughput or reduce the radiation exposure in daily clinical oncologic imaging.

KEY POINTS

• [¹⁸F]FDG-imaging protocols for oncological total-body PET/CT with reduced acquisition time or with different FDG activity levels have been summarized from multicenter studies. • Total-body PET/CT provides better image quality and improved diagnostic insights. • Clinical workflow and patient management have been improved.

Exploration of the total-body PET/CT reconstruction protocol with ultra-low 18F-FDG activity over a wide range of patient body mass indices

Purpose

The purpose of this study was to investigate the image quality and diagnostic performance of different reconstructions over a wide range of patient body mass indices (BMIs) obtained by total-body PET/CT with ultra-low ¹⁸F-FDG activity (0.37 MBq/kg).

Methods

A total of 63 patients who underwent total-body PET/CT with ultra-low activity (0.37 MBq/kg) ¹⁸F-FDG were enrolled. Patients were grouped by their BMIs. Images were reconstructed with the following two algorithms: the ordered subset expectation maximization (OSEM) algorithm (2, 3 iterations), both with time of flight (TOF) and point spread function (PSF) corrections (hereinafter referred as OSEM2, OSEM3) and HYPER Iterative algorithm (β-values of 0.3, 0.4, 0.5, 0.6) embedded TOF and PSF technologies (hereinafter referred as HYPER0.3, HYPER0.4, HYPER0.5 and HYPER0.6, respectively). Subjective image quality was assessed by two experienced nuclear medicine physicians according to the Likert quintile, including overall image quality, image noise and lesion conspicuity. The standard deviation (SD) and signal-to-noise ratio (SNR) of the liver, and maximum standard uptake value (SUV_max), peak standard uptake value (SUV_peak), tumour background ratio (T/N) and the largest diameter of lesions were quantitatively analysed by a third reader who did not participate in the subjective image assessment.

Results

Increased noise was associated with increased BMI in all reconstruction groups. Significant differences occurred in the liver SNR among BMI categories of OSEM reconstructions (P < 0.001) but no difference was seen in the HYPER Iterative reconstructions between any of the BMI categories (P > 0.05). With the increase in BMI, overall image quality and image noise scores decreased significantly in all reconstructions, but there was no statistically significant difference of lesion conspicuity. The overall image quality score of the obese group was not qualified (score = 2.7) in OSEM3, while the others were qualified. The lesion conspicuity scores were significantly higher in HYPER Iterative reconstructions and lower in OSEM2 than in OSEM3 (all P < 0.05). The values of SUV_max, SUV_peak and T/N in HYPER0.3, HYPER0.4 and HYPER0.5 were higher than those in OSEM3. In different reconstructions, there was a correlation between lesion size (median, 1.55 cm; range, 0.7–11.0 cm) and SUV_peak variation rate compared to OSEM3 (r = 0.388, − 0.515, − 0.495, − 0.464, and − 0.423, respectively, and all P < 0.001).

Conclusion

Considering the image quality and lesion analysis in ¹⁸F-FDG total-body PET/CT with ultra-low activity injection, OSEM reconstructions with 3 iterations meet the clinical requirements in patients with BMI < 30. In patients with BMI ≥ 30, it is recommended that the HYPER Iterative algorithm (β-value of 0.3–0.5) be used to ensure consistent visual image quality and quantitative assessment.

Advantages and Applications of Total-Body PET Scanning

Recent studies have focused on the development of total-body PET scanning in a variety of fields such as clinical oncology, cardiology, personalized medicine, drug development and toxicology, and inflammatory/infectious disease. Given its ultrahigh detection sensitivity, enhanced temporal resolution, and long scan range (1940 mm), total-body PET scanning can not only image faster than traditional techniques with less administered radioactivity but also perform total-body dynamic acquisition at a longer delayed time point. These unique characteristics create several opportunities to improve image quality and can provide a deeper understanding regarding disease detection, diagnosis, staging/restaging, response to treatment, and prognostication. By reviewing the advantages of total-body PET scanning and discussing the potential clinical applications for this innovative technology, we can address specific issues encountered in routine clinical practice and ultimately improve patient care.

Potential and Most Relevant Applications of Total Body PET/CT Imaging

ABSTRACT

The introduction of total body (TB) PET/CT instruments over the past 2 years has initiated a new and exciting era in medical imaging. These instruments have substantially higher sensitivity (up to 68 times) than conventional modalities and therefore allow imaging the entire body over a short period. However, we need to further refine the imaging protocols of this instrument for different indications. Total body PET will allow accurate assessment of the extent of disease, particularly, including the entire axial and appendicular skeleton. Furthermore, delayed imaging with this instrument may enhance the sensitivity of PET for some types of cancer. Also, this modality may improve the detection of venous thrombosis, a common complication of cancer and chemotherapy, in the extremities and help prevent pulmonary embolism. Total body PET allows assessment of atherosclerotic plaques throughout the body as a systematic disease. Similarly, patients with widespread musculoskeletal disorders including both oncologic and nononcologic entities, such as degenerative joint disease, rheumatoid arthritis, and osteoporosis, may benefit from the use of TB-PET. Finally, quantitative global disease assessment provided by this approach will be superior to conventional measurements, which do not reflect overall disease activity. In conclusion, TB-PET imaging may have a revolutionary impact on day-to-day practice of medicine and may become the leading imaging modality in the future.

Monte Carlo evaluation of hypothetical long axial field-of-view PET scanner using GE discovery MI PET front-end architecture

PURPOSE

The development of total-body PET scanners is of growing interest in the PET community. Investigation into the imaging properties of a hypothetical extended axial field-of-view (AFOV) GE Healthcare SiPM-based Discovery MI (DMI) system architecture has not yet been performed. In this work, we assessed its potential as a whole-body scanner using Monte Carlo simulations. The aim of this work was to (1) develop and validate a Monte Carlo model of a 4-ring scanner and (2) extend its AFOV up to 2 m to evaluate performance gain through NEMA-based evaluation.

METHODS

The DMI 4-ring geometry and its pulse digitization scheme were modeled within the GATE Monte Carlo platform using published literature. The GATE scanner model was validated by comparing results against published NEMA performance measurements. Following the validation of the 4-ring model, the model was extended to simulate 8, 20, 30, and 40-ring systems. Spatial resolution, sensitivity, NECR, and scatter fraction were characterized with modified NEMA NU-2 2018 standards; however, the image quality measurements were not acquired due to computational limitations. Spatial resolutions were simulated for all scanner ring configurations using point sources to examine the effects of parallax errors. NEMA count rates were estimated using a standard 70 cm scatter phantom and an extended version of scatter phantom of length 200 cm with (1-800) MBq of ¹⁸ F for all scanners. Sensitivity was evaluated using NEMA methods with a 70 cm standard and a 200 cm long line source.

RESULTS

The average FWHM of the radial/tangential/axial spatial resolution reconstructed with filtered back-projection at 1 and 10 cm from the scanner center were 3.94/4.10/4.41 mm and 5.29/4.89/5.90 mm for the 4-ring scanner. Sensitivity was determined to be 14.86 cps/kBq at the center of the FOV for the 4-ring scanner using a 70 cm line source. Sensitivity enhancement up to 21-fold and 60-fold were observed for 1 m and 2 m AFOV scanners compared to 4-ring scanner using a 200 cm long line source. Spatial resolution simulations in a 2 m AFOV scanner suggest a maximum degradation of ∼23.8% in the axial resolution compared to the 4-ring scanner. However, the transverse resolution was found to be relatively constant when increasing the axial acceptance angle up to ±70°. The peak NECR was 212.92 kcps at 22.70 kBq/mL with a scatter fraction of 38.9% for a 4-ring scanner with a 70 cm scatter phantom. Comparison of peak NECR using the 200 cm long scatter phantom relative to the 4-ring scanner resulted in a NECR gain of 15 for the 20-ring and 28 for the 40-ring geometry. Spatial resolution, sensitivity, and scatter fraction showed an agreement within ∼7% compared with published measured values.

CONCLUSIONS

The 4-ring DMI scanner simulation was successfully validated against published NEMA measurements. Sensitivity and NECR performance of extended 1 and 2 meters AFOV scanners based upon the DMI architecture were subsequently simulated. Increases in sensitivity and count-rate performance are consistent with prior simulation studies utilizing extensions of the Siemens mCT architecture and published NEMA measurements with the uEXPLORER system. This article is protected by copyright. All rights reserved.