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 (Ki) and apparent volume of distribution (VD), 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 methodology 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.

Performance characteristics of the 5-ring GE Discovery MI PET/CT scanner using AAPM TG-126 report.

AIM: To report on the performance characteristics of the 5-ring GE Discovery MI PET/CT systems using the AAPM TG-126 report and compare these results to NEMA NU 2-2012 where applicable. MATERIALS AND METHODS: TG-126 testing was performed on two GE 5-Rings Discovery MI scanners. Tests performed included spatial resolution, PET/CT image-registration accuracy, sensitivity, count rate performance, accuracy of corrections, image contrast, scatter/attenuation correction, and image uniformity. All acquired data were analyzed using scanner console or free software tools as described by TG-126 and the results were then compared to published NEMA NU 2-2012 values. RESULTS: Both scanners gave similar resolution results for TG-126 and NEMA NU 2-2012 and were within manufacturer specifications. Image-registration accuracy between PET and CT using our clinical protocol showed excellent results with values ≤1 mm. Sensitivity using TG-126 was 19.43 cps/kBq while for NEMA the value was 20.73 cps/kBq. The peak noise-equivalent counting rate was 2174 kcps at 63.1 kBq/mL and is not comparable to NEMA NU 2-2012 due to differences in phantoms and methods used to measure and calculate this parameter. The accuracy of corrections for count losses for TG-126 were expressed in SUV values and found to be within 10% of the expected SUV measurement of 1. Image contrast and scatter/attenuation correction using the TG-126 method gave acceptable results. Image uniformity assessment resulted in values within the recommended ± 5% limits. CONCLUSION: These results show that the 5-ring GE Discovery MI PET/CT scanner testing using TG-126 is reproducible and has similar results to NEMA NU 2-2012 tests where applicable. We hope these results start to form the basis to compare PET/CT systems using TG-126.

Impact of low injected activity on data driven respiratory gating for PET/CT imaging with continuous bed motion.

Data driven respiratory gating (DDG) in positron emission tomography (PET) imaging extracts respiratory waveforms from the acquired PET data obviating the need for dedicated external devices. DDG performance, however, degrades with decreasing detected number of coincidence counts. In this paper, we assess the clinical impact of reducing injected activity on a new DDG algorithm designed for PET data acquired with continuous bed motion (CBM_DDG) by evaluating CBM_DDG waveforms, tumor quantification, and physician's perception of motion blur in resultant images. Forty patients were imaged on a Siemens mCT scanner in CBM mode. Reduced injected activity was simulated by generating list mode datasets with 50% and 25% of the original data (100%). CBM_DDG waveforms were compared to that of the original data over the range between the aortic arch and the center of the right kidney using the Pearson correlation coefficient (PCC). Tumor quantification was assessed by comparing the maximum standardized uptake value (SUVmax) and peak SUV (SUVpeak) of reconstructed images from the various list mode datasets using elastic motion deblurring (EMDB) reconstruction. Perceived motion blur was assessed by three radiologists of one lesion per patient on a continuous scale from no motion blur (0) to significant motion blur (3). The mean PCC of the 50% and 25% dataset waveforms was 0.74 ± 0.18 and 0.59 ± 0.25, respectively. In comparison to the 100% datasets, the mean SUVmax increased by 2.25% (p = 0.11) for the 50% datasets and by 3.91% (p = 0.16) for the 25% datasets, while SUVpeak changes were within ±0.25%. Radiologist evaluations of motion blur showed negligible changes with average values of 0.21, 0.3, and 0.28 for the 100%, 50%, and 25% datasets. Decreased injected activities degrades the resultant CBM_DDG respiratory waveforms; however this decrease has minimal impact on quantification and perceived image motion blur.

Reclassifying patients with early-stage Hodgkin lymphoma based on functional radiographic markers at presentation.

The presence of bulky disease in Hodgkin lymphoma (HL), traditionally defined with a 1-dimensional measurement, can change a patient's risk grouping and thus the treatment approach. We hypothesized that 3-dimensional measurements of disease burden obtained from baseline 18F-fluorodeoxyglucose positron emission tomography-computed tomography (PET-CT) scans, such as metabolic tumor volume (MTV) and total lesion glycolysis (TLG), would more accurately risk-stratify patients. To test this hypothesis, we reviewed pretreatment PET-CT scans of patients with stage I-II HL treated at our institution between 2003 and 2013. Disease was delineated on prechemotherapy PET-CT scans by 2 methods: (1) manual contouring and (2) subthresholding of these contours to give the tumor volume with standardized uptake value ≥2.5. MTV and TLG were extracted from the threshold volumes (MTVt, TLGt) and from the manually contoured soft-tissue volumes. At a median follow-up of 4.96 years for the 267 patients evaluated, 27 patients were diagnosed with relapsed or refractory disease and 12 died. Both MTVt and TLGt were highly correlated with freedom from progression and were dichotomized with 80th percentile cutoff values of 268 and 1703, respectively. Consideration of MTV and TLG enabled restratification of early unfavorable HL patients as having low- and high-risk disease. We conclude that MTV and TLG provide a potential measure of tumor burden to aid in risk stratification of early unfavorable HL patients.

Characterization of continuous bed motion effects on patient breathing and respiratory motion correction in PET/CT imaging.

Continuous bed motion (CBM) was recently introduced as an alternative to step-and-shoot (SS) mode for PET/CT data acquisition. In CBM, the patient is continuously advanced into the scanner at a preset speed, whereas in SS, the patient is imaged in overlapping bed positions. Previous investigations have shown that patients preferred CBM over SS for PET data acquisition. In this study, we investigated the effect of CBM versus SS on patient breathing and respiratory motion correction. One hundred patients referred for PET/CT were scanned using a Siemens mCT scanner. Patient respiratory waveforms were recorded using an Anzai system and analyzed using four methods: Methods 1 and 2 measured the coefficient of variation (COV) of the respiratory cycle duration (RCD) and amplitude (RCA). Method 3 measured the respiratory frequency signal prominence (RSP) and method 4 measured the width of the HDChest optimal gate (OG) window when using a 35% duty cycle. Waveform analysis was performed over the abdominothoracic region which exhibited the greatest respiratory motion and the results were compared between CBM and SS. Respiratory motion correction was assessed by comparing the ratios of SUVmax, SUVpeak, and CNR of focal FDG uptake, as well as Radiologists' visual assessment of corresponding image quality of motion corrected and uncorrected images for both acquisition modes. The respiratory waveforms analysis showed that the RCD and RCA COV were 3.7% and 33.3% lower for CBM compared to SS, respectively, while the RSP and OG were 30.5% and 2.0% higher, respectively. Image analysis on the other hand showed that SUVmax, SUVpeak, and CNR were 8.5%, 4.5%, and 3.4% higher for SS compared to CBM, respectively, while the Radiologists' visual comparison showed similar image quality between acquisition modes. However, none of the results showed statistically significant differences between SS and CBM, suggesting that motion correction is not impacted by acquisition mode.

A measurement of the attenuation of radiation from F-18 by a PET/MR scanner.

The attenuation of 511 keV photons by the structure of a PET/MR scanner was measured prior to energizing the magnet. The exposure rate from a source of fluorine-18 was measured in air and, with the source placed at the isocenter of the instrument, at various points outside of the scanner. In an arc from 45 to 135 degrees relative to the long axis of the scanner and at a distance of 1.5 m from the isocenter, the attenuation by the scanner is at least 5.6 half-value layers from the MR component alone and at least 6.6 half-value layers with the PET insert installed. This information could inform better design of the radiation shielding for PET/MR scanners.

Early-stage Hodgkin lymphoma outcomes after combined modality therapy according to the post-chemotherapy 5-point score: can residual pet-positive disease be cured with radiotherapy alone?

Early-stage classical Hodgkin lymphoma (HL) patients are evaluated by an end-of-chemotherapy positron emission tomography-computed tomography (eoc-PET-CT) after doxorubicin, bleomycin, vinblastine and dacarbazine (ABVD) and before radiation therapy (RT). We determined freedom from progression (FFP) in patients treated with ABVD and RT according to the eoc-PET-CT 5-point score (5PS). Secondarily, we assessed whether patients with a positive eoc-PET-CT (5PS of 4-5) can be cured with RT alone. The cohort comprised 174 patients treated for stage I-II HL with ABVD and RT alone. ABVD was given with a median of four cycles and RT with a median dose of 30·6 Gy. Five-year FFP was 97%. Five-year FFP was 100% (0 relapses/98 patients) for patients with a 5PS of 1-2, 97% (2/65) for a 5PS of 3, 83% (1/8) for a 5PS of 4, and 67% (1/3) for a 5PS of 5 (P < 0·001). Patients with positive eoc-PET-CT scans who were selected for salvage RT alone had experienced a very good partial response to ABVD. Risk factors for recurrence in this subgroup included a small reduction in tumour size and a 'bounce' in ≥1 PET-CT parameter (reduction then rise from interim to final scan). Thus, a positive eoc-PET-CT is associated with inferior FFP; however, appropriately selected patients can be cured with RT alone.

Stage III Non-Small Cell Lung Cancer: Prognostic Value of FDG PET Quantitative Imaging Features Combined with Clinical Prognostic Factors.

PURPOSE: To determine whether quantitative imaging features from pretreatment positron emission tomography (PET) can enhance patient overall survival risk stratification beyond what can be achieved with conventional prognostic factors in patients with stage III non-small cell lung cancer (NSCLC). MATERIALS AND METHODS: The institutional review board approved this retrospective chart review study and waived the requirement to obtain informed consent. The authors retrospectively identified 195 patients with stage III NSCLC treated definitively with radiation therapy between January 2008 and January 2013. All patients underwent pretreatment PET/computed tomography before treatment. Conventional PET metrics, along with histogram, shape and volume, and co-occurrence matrix features, were extracted. Linear predictors of overall survival were developed from leave-one-out cross-validation. Predictive Kaplan-Meier curves were used to compare the linear predictors with both quantitative imaging features and conventional prognostic factors to those generated with conventional prognostic factors alone. The Harrell concordance index was used to quantify the discriminatory power of the linear predictors for survival differences of at least 0, 6, 12, 18, and 24 months. Models were generated with features present in more than 50% of the cross-validation folds. RESULTS: Linear predictors of overall survival generated with both quantitative imaging features and conventional prognostic factors demonstrated improved risk stratification compared with those generated with conventional prognostic factors alone in terms of log-rank statistic (P = .18 vs P = .0001, respectively) and concordance index (0.62 vs 0.58, respectively). The use of quantitative imaging features selected during cross-validation improved the model using conventional prognostic factors alone (P = .007). Disease solidity and primary tumor energy from the co-occurrence matrix were found to be selected in all folds of cross-validation. CONCLUSION: Pretreatment PET features were associated with overall survival when adjusting for conventional prognostic factors in patients with stage III NSCLC.

AAPM/SNMMI Joint Task Force: report on the current state of nuclear medicine physics training.

The American Association of Physicists in Medicine (AAPM) and the Society of Nuclear Medicine and Molecular Imaging (SNMMI) recognized the need for a review of the current state of nuclear  medicine physics training and the need to explore pathways for improving nuclear medicine physics training opportunities. For these reasons, the two organizations formed a joint AAPM/SNMMI Ad Hoc Task Force on Nuclear Medicine Physics  Training. The mission of this task force was to assemble a representative group of stakeholders to:• Estimate the demand for board-certified nuclear medicine physicists in the next 5-10 years,• Identify the critical issues related to supplying an adequate number of physicists who have received the appropriate level of training in nuclear medicine physics, and• Identify approaches that may be considered to facilitate the training of nuclear medicine physicists.As a result, a task force was appointed and chaired by an active member of both organizations that included representation from the AAPM, SNMMI, the American Board of Radiology (ABR), the American Board of Science in Nuclear Medicine (ABSNM), and the Commission for the Accreditation of Medical Physics Educational Programs (CAMPEP). The Task Force first met at the AAPM Annual Meeting in Charlotte in July 2012 and has met regularly face-to-face, online, and by conference calls. This manuscript reports the findings of the Task Force, as well as recommendations to achieve the stated mission.

PET-CT: current applications and new developments in the thorax.

Positron emission tomography computed tomography(PET-CT) imaging has emerged as an essential clinical diagnostic tool in the evaluation of thoracic abnormalities. Currently, its primary role is for tumor imaging; it helps to differentiate benign from malignant nodules, stage tumors, determine response, and follow patients after therapy is complete. It has also been used for nononcologic diseases, but the indications are less well defined. PET is a fundamental component of the molecular imaging initiative, and as new more specific imaging probes and better instrumentation are developed, PET-CT is certain to improve diagnostic accuracy and become even more integrated into the imaging armamentarium.

Correlation of PUV and SUV in the extremities while using PEM as a high-resolution positron emission scanner.

OBJECTIVE: Owing to its unique configuration of two adjustable plate detectors positron emission mammography, or PEM, could theoretically also function as a high-resolution positron emission scanner for the extremities or neck. PEM quantitates its activity via a "PEM uptake value," or PUV, and although its relationship to the standardized uptake value, or SUV, has been demonstrated in the breasts, to our knowledge there are no studies validating PUV in other sites such as the extremities. MATERIALS AND METHODS: This was a retrospective chart review of two separate protocols of a total of 15 patients. The patients all had hypermetabolic lesions in the extremities or neck on imaging with PET/CT and were sent after their PET/CT to PEM for further imaging. Owing to the sequential nature of these examinations no additional radiotracer was administered. RESULTS: Spearman's rank order correlation was calculated between the PUVmax obtained from PEM images, and the SUVmax for all. Spearman's rank order correlation for all sites was 0.42, which is not significantly different from 0 (p = 0.13). When neck lesions were excluded from the group, there was a strong and statistically significant correlation between PUVmax and SUVmax, with Spearman's rank correlation of 0.73, and significantly different from 0 (p = 0.0068). DISCUSSION: The correlation of PUV and SUV in the extremities indicates the potential use of PEM as a semiquantitative, high-resolution positron emission scanner and warrants further investigation, especially in the realms of disease processes that often present in the extremities, such as melanoma, osteomyelitis, and arthritis, as well as playing a role in the imaging of patients with metallic hardware post-limb salvage surgery.

Defining internal target volume using positron emission tomography for radiation therapy planning of moving lung tumors.

Substantial disagreement exists over appropriate PET segmentation techniques for non-small cell lung cancer. Currently, no segmentation algorithm explicitly considers tumor motion in determining tumor borders. We developed an automatic PET segmentation model as a function of target volume, motion extent, and source-to-background ratio (the VMSBR model). The purpose of this work was to apply the VMSBR model and six other segmentation algorithms to a sample of lung tumors. PET and 4D CT were performed in the same imaging session for 23 patients (24 tumors) for radiation therapy planning. Internal target volumes (ITVs) were autosegmented on maximum intensity projection (MIP) of cine CT. ITVs were delineated on PET using the following methods: 15%, 35%, and 42% of maximum activity concentration, standardized uptake value (SUV) of 2.5 g/mL, 15% of mean activity concentration plus background, a linear function of mean SUV, and the VMSBR model. Predicted threshold values from each method were compared to measured optimal threshold values, and resulting volume magnitudes were compared to cine-CT-derived ITV. Correlation between predicted and measured threshold values ranged from slopes of 0.29 for the simplest single-threshold techniques to 0.90 for the VMSBR technique. R2 values ranged from 0.07 for the simplest single-threshold techniques to 0.86 for the VMSBR technique. The VMSBR segmentation technique that included volume, motion, and source-to-background ratio, produced accurate ITVs in patients when compared with cine-CT-derived ITV.

Assessing Radiology and Radiation Therapy Needs for Cancer Care in Low-and-Middle-Income Countries: Insight From a Global Survey of Departmental and Institutional Leaders.

Purpose: The global cancer burden and mortality rates are increasing, with significant disparities in access to care in low- and middle-income countries (LMICs). This study aimed to identify radiology and radiation therapy needs in LMICs from the perspective of departmental and institutional leaders. Methods and Materials: A survey was developed and conducted by the American Association of Physicists in Medicine Global Needs Assessment Committee and the American Association of Physicists in Medicine International Council. The survey, organized into 5 sections (Introduction, Infrastructure Needs, Education Needs, Research Needs, and General Information), was open to respondents from March 1, to August 16, 2022. Results: A total of 175 responses were received from 6 global regions: Africa (31.4%), the Americas (17.7%), the Eastern Mediterranean (14.3%), Europe (9.1%), Southeast Asia (23.4%), and the Western Pacific (4.0%). The greatest reported need was for new or updated equipment, particularly positron emission tomography/computed tomography imaging technology. There was also a high demand for clinical and equipment training. Approximately 25% of institutions reported a lack of radiology-based cancer screening programs because of high health care costs and a shortage of specialized equipment. Many institutions that expressed interest in research face funding and grant challenges. Conclusions: The findings highlight critical areas where organizations can support LMICs in enhancing radiology and radiation therapy services to mitigate the growing cancer burden.

(18)F-FDG PET/CT predicts survival in patients with inflammatory breast cancer undergoing neoadjuvant chemotherapy.

PURPOSE: The objective of this study was to evaluate the role of (18)F-FDG PET/CT in predicting overall survival in inflammatory breast cancer patients undergoing neoadjuvant chemotherapy. METHODS: Included in this retrospective study were 53 patients with inflammatory breast cancer who had at least two PET/CT studies including a baseline study before the start of neoadjuvant chemotherapy. Univariate and multivariate analyses were performed to assess the effects on survival of the following factors: tumor maximum standardized uptake value (SUVmax) at baseline, preoperatively and at follow-up, decrease in tumor SUVmax, histological tumor type, grade, estrogen, progesterone, HER2/neu receptor status, and extent of disease at presentation including axillary nodal and distant metastases. RESULTS: By univariate analysis, survival was significantly associated with decrease in tumor SUVmax and tumor receptor status. Patients with decrease in tumor SUVmax had better survival (P = 0.02). Patients with a triple-negative tumor (P = 0.0006), a Her2/neu-negative tumor (P = 0.038) or an ER-negative tumor (P = 0.039) had worse survival. Multivariate analysis confirmed decrease in tumor SUVmax and triple-negative receptor status as significant predictors of survival. Every 10% decrease in tumor SUVmax from baseline translated to a 15% lower probability of death, and complete resolution of tumor FDG uptake translated to 80% lower probability of death (P = 0.014). Patients with a triple-negative tumor had 4.11 times higher probability of death (P = 0.004). CONCLUSION: Decrease in tumor SUVmax is an independent predictor of survival in patients with inflammatory breast cancer undergoing neoadjuvant chemotherapy. Further investigation with prospective studies is warranted to clarify its role in assessing response and altering therapy.

Primary salivary gland-type lung cancer: imaging and clinical predictors of outcome.

OBJECTIVE: The objective of our study was to assess whether CT features and FDG up-take of primary salivary gland-type tumors of the lung are associated with tumor type, disease stage, or survival. MATERIALS AND METHODS: CT (n = 30) and PET (n = 15) data of 30 consecutive patients with primary salivary gland-type tumors of the lung were retrospectively evaluated for tumor size, location, and homogeneity and the presence of lymphadenopathy, pleural effusions, and metastases. Maximum FDG uptake and volumetric FDG uptake of the tumors were recorded. The Wilcoxon rank sum and Fisher exact tests and univariate Cox regression were used for statistical calculations. RESULTS: Compared with mucoepidermoid carcinomas, adenoid cystic carcinomas (57%) were larger (mean, 3.5 vs 2.2 cm, respectively; p = 0.03), more frequently involved the central airways (94% vs 63%; p = 0.002), and had a higher median FDG uptake (p = 0.0264). Higher FDG uptake of the primary tumor was associated with nodal tumor involvement (p = 0.05). The median overall survival times for patients with adenoid cystic carcinoma and mucoepidermoid carcinoma were 7.7 and 4.0 years, respectively. Imaging features that significantly affected overall survival included the presence of mediastinal or hilar lymphadenopathy (hazard ratio [HR], 4.33; 95% CI, 1.15-16.26; p = 0.03), suspected metastatic disease (HR, 5.10; 95% CI, 1.27-20.47; p = 0.02), and primary tumor heterogeneity (HR, 3.46; 95% CI, 1.04-11.55; p = 0.04). CONCLUSION: Higher FDG uptake is associated with nodal disease in patients with primary salivary gland-type tumors of the lung but is not predictive of survival, whereas CT features suggestive of advanced disease correlate with worse outcome.

Dosimetry of a Novel 111Indium-Labeled Anti-P-Cadherin Monoclonal Antibody (FF-21101) in Non-Human Primates.

P-cadherin is associated with a wide range of tumor types, making it an attractive therapeutic target. FF-21101 is a human-mouse chimeric monoclonal antibody (mAb) directed against human P-cadherin, which has been radioconjugated with indium-111 (111In) utilizing a DOTA chelator. We investigated the biodistribution of FF-21101(111In) in cynomolgus macaques and extrapolated the results to estimate internal radiation doses of 111In- and yttrium-90 (90Y)-FF-21101 for targeted radioimmunotherapy in humans. Whole-body planar and SPECT imaging were performed at 0, 2, 24, 48, 72, 96, and 120 h post-injection, using a dual-head gamma camera. Volumes of interest of identifiable source organs of radioactivity were defined on aligned reference CT and serial SPECT images. Organs with the highest estimated dose values (mSv/MBq) for FF-21101(111In) were the lungs (0.840), spleen (0.816), liver (0.751), kidneys (0.629), and heart wall (0.451); and for FF-21101(90Y) dose values were: lungs (10.49), spleen (8.21), kidneys (5.92), liver (5.46), and heart wall (2.61). FF-21101(111In) exhibits favorable biodistribution in cynomolgus macaques and estimated human dosimetric characteristics. Data obtained in this study were used to support the filing of an investigational new drug application with the FDA for a Phase I clinical trial.

Sequential Targeting of Retinoblastoma and DNA Synthesis Pathways Is a Therapeutic Strategy for Sarcomas That Can Be Monitored in Real Time.

Treatment strategies with a strong scientific rationale based on specific biomarkers are needed to improve outcomes in patients with advanced sarcomas. Suppression of cell-cycle progression through reactivation of the tumor suppressor retinoblastoma (Rb) using CDK4/6 inhibitors is a potential avenue for novel targeted therapies in sarcomas that harbor intact Rb signaling. Here, we evaluated combination treatment strategies (sequential and concomitant) with the CDK4/6 inhibitor abemacicib to identify optimal combination strategies. Expression of Rb was examined in 1,043 sarcoma tumor specimens, and 50% were found to be Rb-positive. Using in vitro and in vivo models, an effective two-step sequential combination strategy was developed. Abemaciclib was used first to prime Rb-positive sarcoma cells to reversibly arrest in G1 phase. Upon drug removal, cells synchronously traversed to S phase, where a second treatment with S-phase targeted agents (gemcitabine or Wee1 kinase inhibitor) mediated a synergistic response by inducing DNA damage. The response to treatment could be noninvasively monitored using real-time positron emission tomography imaging and serum thymidine kinase activity. Collectively, these results show that a novel, sequential treatment strategy with a CDK4/6 inhibitor followed by a DNA-damaging agent was effective, resulting in synergistic tumor cell killing. This approach can be readily translated into a clinical trial with noninvasive functional imaging and serum biomarkers as indicators of response and cell cycling. SIGNIFICANCE: An innovative sequential therapeutic strategy targeting Rb, followed by treatment with agents that perturb DNA synthesis pathways, results in synergistic killing of Rb-positive sarcomas that can be noninvasively monitored.

Reliability of predicting image signal-to-noise ratio using noise equivalent count rate in PET imaging.

PURPOSE: Several investigators have shown that noise equivalent count rate (NECR) is linearly proportional to the square of image signal-to-noise ratio (SNR) when PET images are reconstructed using filtered back-projection. However, to our knowledge, none have shown a similar relationship in fully 3D ordered-subset expectation maximization (OSEM) reconstruction. This paper has two aims. The first is to investigate the NECR-SNR relationship for 3D-OSEM reconstruction using phantom studies while the second aim is to evaluate the NECR-SNR relationship using patient data. METHODS: An anthropomorphic phantom was scanned on a GE Discovery-STE (DSTE) PET∕CT scanner in 3D mode with an initial activity concentration of 66.34 kBq∕cc. PET data were acquired over the lower chest∕upper abdomen region in dynamic mode. The experiment was repeated with the same activity concentration on a GE Discovery-RX (DRX) scanner. Care was taken to place the phantom at identical positions in both scanners. PET data were then reconstructed using 3D Reprojection (3D-RP) and 3D-OSEM with different reconstruction parameters and the NECR and SNR for each frame∕image were calculated. SNR(2) was then plotted versus the NECR for each scanner, reconstruction method and parameters. In addition, 40 clinical PET∕CT studies from the two scanners (20 patients∕scanner) were evaluated retrospectively. The patient studies from each scanner were further divided into two subgroups of body mass indices (BMI). Each PET study was acquired in 3D mode and reconstructed using both 3D-OSEM and 3D-RP. The NECR and SNR of the bed position covering the patient liver were calculated for each patient and averaged for each subgroup. Comparisons of the NECR and SNR between scanner types and BMIs were performed using a t-test and a p value less than 0.05 was considered significant. RESULTS: Phantom results showed that SNR(2) versus NECR was linear for 3D-RP reconstruction across all activity concentration on both scanners, as expected. However, when 3D-OSEM was used, this relationship was nonlinear at activity concentrations beyond the peak NECR on both scanners. On the other hand, the plot of SNR(2) versus trues count rate was linear for 3D-OSEM across all activity concentrations on both scanners independent of reconstruction parameters used. In addition, for activity concentrations <30kBq∕cc, phantom results showed a higher SNR (by 12 ± 10%; p < 0.05) and NECR for the DRX scanner compared to DSTE for 3D-RP reconstruction. However, for 3D-OSEM reconstruction, these two scanners had similar SNRs (different by 2% ± 9%; p > 0.05), despite having different NECRs. Patient studies showed a statistically significant difference in NECR as well as the SNR for 3D-RP reconstruction between the two scanners. However, no statistically significant difference was found for 3D-OSEM. A statistically significant difference in both NECR and SNR were found between the different BMI subgroups for both 3D-RP and 3D-OSEM reconstructions. CONCLUSIONS: For the scanners and reconstruction algorithm used in this study, our results suggest that the image SNR cannot be predicted by the NEC when using 3D-OSEM reconstruction particularly for those clinical applications requiring high activity concentration. Instead, our results suggest that image SNR varies with activity concentration and is dominated by the 3D-OSEM reconstruction algorithm and its associated parameters, while not being affected by the scanner type for the range of activity concentrations usually found in the clinic.

A software tool for stitching two PET/CT body segments into a single whole-body image set.

A whole-body PET/CT scan extending from the vertex of the head to the toes of the patient is not feasible on a number of commercially available PET/CT scanners due to a limitation in the extent of bed travel on these systems. In such cases, the PET scan has to be divided into two parts: one covering the upper body segment, while the other covering the lower body segment. The aim of this paper is to describe and evaluate, using phantom and patient studies, a software tool that was developed to stitch two body segments and output a single whole-body image set, thereby facilitating the interpretation of whole-body PET scans. A mathematical model was first developed to stitch images from two body segments using three landmarks. The model calculates the relative positions of the landmarks on the two segments and then generates a rigid transformation that aligns these landmarks on the two segments. A software tool was written to implement this model while correcting for radioactive decay between the two body segments, and output a single DICOM whole-body image set with all the necessary tags. One phantom, and six patient studies were conducted to evaluate the performance of the software. In these studies, six radio-opaque markers (BBs) were used as landmarks (three on each leg). All studies were acquired in two body segments with BBs placed in the overlap region of the two segments. The PET/CT images of each segment were then stitched using the software tool to create a single DICOM whole-body PET/CT image. Evaluation of the stitching tool was based on visual inspection, consistency of radiotracer uptake in the two segments, and ability to display the resultant DICOM image set on two independent workstations. The software tool successfully stitched the two segments of the phantom image, and generated a single whole-body DICOM PET/CT image set that had the correct alignment and activity concentration throughout the image. The stitched images were viewed by two independent workstations from two different manufacturers, attesting the ability of the software tool to produce a DICOM compliant image set. The study demonstrated that this software tool allows the stitching of two segments of a whole-body PET/CT scan with minimal user interaction, thereby facilitating the interpretation of whole body PET/CT scans from a number of scanners with limited extent of bed travel.

Impact of acquisition time and misregistration with CT on data-driven gated PET.

Objective. Data-driven gating (DDG) can address patient motion issues and enhance PET quantification but suffers from increased image noise from utilization of <100% of PET data. Misregistration between DDG-PET and CT may also occur, altering the potential benefits of gating. Here, the effects of PET acquisition time and CT misregistration were assessed with a combined DDG-PET/DDG-CT technique.Approach. In the primary PET bed with lesions of interest and likely respiratory motion effects, PET acquisition time was extended to 12 min and a low-dose cine CT was acquired to enable DDG-CT. Retrospective reconstructions were created for both non-gated (NG) and DDG-PET using 30 s to 12 min of PET data. Both the standard helical CT and DDG-CT were used for attenuation correction of DDG-PET data. SUVmax, SUVpeak, and CNR were compared for 45 lesions in the liver and lung from 27 cases.Main results. For both NG-PET (p= 0.0041) and DDG-PET (p= 0.0028), only the 30 s acquisition time showed clear SUVmaxbias relative to the 3 min clinical standard. SUVpeakshowed no bias at any change in acquisition time. DDG-PET alone increased SUVmaxby 15 ± 20% (p< 0.0001), then was increased further by an additional 15 ± 29% (p= 0.0007) with DDG-PET/CT. Both 3 min and 6 min DDG-PET had lesion CNR statistically equivalent to 3 min NG-PET, but then increased at 12 min by 28 ± 48% (p= 0.0022). DDG-PET/CT at 6 min had comparable counts to 3 min NG-PET, but significantly increased CNR by 39 ± 46% (p< 0.0001).Significance. 50% counts DDG-PET did not lead to inaccurate or biased SUV-increased SUV resulted from gating. Improved registration from DDG-CT was equally as important as motion correction with DDG-PET for increasing SUV in DDG-PET/CT. Lesion detectability could be significantly improved when DDG-PET used equivalent counts to NG-PET, but only when combined with DDG-CT in DDG-PET/CT.