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Background: New digital detectors and block-sequential regularized expectation maximization (BSREM) reconstruction algorithm improve positron emission tomography (PET)/magnetic resonance (MR) image quality. The impact on image quality may differ from analogue PET/computed tomography (CT) protocol. The aim of this study is to determine the potential reduction of injected [ 68 Ga]Ga-DOTA-TATE activity for digital PET/MR with BSREM reconstruction while maintaining at least equal image quality compared to the current analogue PET/CT protocol., Methods: NEMA IQ phantom data and 25 patients scheduled for a diagnostic PET/MR were included. According to our current protocol, 1.5 MBq [ 68 Ga]Ga-DOTA-TATE per kilogram (kg) was injected. After 60 min, scans were acquired with 3 (≤ 70 kg) or 4 (> 70 kg) minutes per bedposition. PET/MR scans were reconstructed using BSREM and factors β 150, 300, 450 and 600. List mode data with reduced counts were reconstructed to simulate scans with 17%, 33%, 50% and 67% activity reduction. Image quality was measured quantitatively for PET/CT and PET/MR phantom and patient data. Experienced nuclear medicine physicians performed visual image quality scoring and lesion counting in the PET/MR patient data., Results: Phantom analysis resulted in a possible injected activity reduction of 50% with factor β = 600. Quantitative analysis of patient images revealed a possible injected activity reduction of 67% with factor β = 600. Both with equal or improved image quality as compared to PET/CT. However, based on visual scoring a maximum activity reduction of 33% with factor β = 450 was acceptable, which was further limited by lesion detectability analysis to an injected activity reduction of 17% with factor β = 450., Conclusion: A digital [ 68 Ga]Ga-DOTA-TATE PET/MR together with BSREM using factor β = 450 result in 17% injected activity reduction with quantitative values at least similar to analogue PET/CT, without compromising on PET/MR visual image quality and lesion detectability., (© 2024. The Author(s).)

CT and bone scintigraphy are not useful for response evaluation of bone metastases to 223 Ra treatment in metastatic castration-resistant prostate cancer (mCRPC). PET using 68 Ga prostate-specific membrane antigen 11 ( 68 Ga-PSMA) is a promising tool for response evaluation of mCRPC. The aim of this study was to determine the utility of 68 Ga-PSMA PET/CT for response evaluation of 223 Ra treatment in patients with mCRPC. Methods: Within this prospective, multicenter, imaging discovery study, 28 patients with mCRPC, eligible for 223 Ra treatment, were included between 2019 and 2022. Patients received 223 Ra according to the standard of care. Study procedures included CT, bone scintigraphy, and 68 Ga-PSMA PET/CT at baseline, after 3 and 6 cycles of 223 Ra treatment, and on treatment failure. Response to 223 Ra treatment was visually assessed on all 3 imaging modalities. Total tumor volume within bone (TTV bone ) was determined on 68 Ga-PSMA PET/CT. Intrapatient heterogeneity in response was studied using a newly developed image-registration tool for sequential images of PET/CT. Results were compared with failure-free survival (good responders vs. poor responders; cutoff, 24 wk) and alkaline phosphatase (ALP) response after 3 cycles. Results: Visual response assessment criteria could not distinguish good responders from poor responders on 68 Ga-PSMA PET/CT and bone scintigraphy. For 68 Ga-PSMA PET/CT, TTV bone at baseline was lower in good responders than in poor responders, whereas TTV bone increased in both groups during treatment. TTV bone was higher in patients with new extraosseous metastases during 223 Ra treatment. Although TTV bone and ALP correlated at baseline, changes in TTV bone and ALP on treatment did not. 68 Ga-PSMA response of TTV bone showed intrapatient heterogeneity in most patients. Conclusion: mCRPC patients with lower TTV bone on 68 Ga-PSMA PET/CT have the best clinical outcome after 223 Ra treatment. Response is highly heterogeneous in most patients. A decrease in ALP, which occurred in most patients, was not correlated with a decrease in TTV bone , which might make one question the value of ALP for disease monitoring during 223 Ra treatment in clinical practice., (© 2023 by the Society of Nuclear Medicine and Molecular Imaging.)

Background: Malignant peripheral nerve sheath tumors (MPNST) carry a dismal prognosis and require early detection and complete resection. However, MPNSTs are prone to sampling errors and biopsies or resections are cumbersome and possibly damaging in benign peripheral nerve sheath tumor (BPNST). This study aimed to systematically review and quantify the diagnostic accuracy of noninvasive tests for distinguishing MPNST from BPNST., Methods: Studies on accuracy of MRI, FDG-PET (fluorodeoxyglucose positron emission tomography), and liquid biopsies were identified in PubMed and Embase from 2000 to 2019. Pooled accuracies were calculated using Bayesian bivariate meta-analyses. Individual level-patient data were analyzed for ideal maximum standardized uptake value (SUVmax) threshold on FDG-PET., Results: Forty-three studies were selected for qualitative synthesis including data on 1875 patients and 2939 lesions. Thirty-five studies were included for meta-analyses. For MRI, the absence of target sign showed highest sensitivity (0.99, 95% CI: 0.94-1.00); ill-defined margins (0.94, 95% CI: 0.88-0.98); and perilesional edema (0.95, 95% CI: 0.83-1.00) showed highest specificity. For FDG-PET, SUVmax and tumor-to-liver ratio show similar accuracy; sensitivity 0.94, 95% CI: 0.91-0.97 and 0.93, 95% CI: 0.87-0.97, respectively, specificity 0.81, 95% CI: 0.76-0.87 and 0.79, 95% CI: 0.70-0.86, respectively. SUVmax ≥3.5 yielded the best accuracy with a sensitivity of 0.99 (95% CI: 0.93-1.00) and specificity of 0.75 (95% CI: 0.56-0.90)., Conclusions: Biopsies may be omitted in the presence of a target sign and the absence of ill-defined margins or perilesional edema. Because of diverse radiological characteristics of MPNST, biopsies may still commonly be required. In neurofibromatosis type 1, FDG-PET scans may further reduce biopsies. Ideal SUVmax threshold is ≥3.5., (© The Author(s) 2020. Published by Oxford University Press on behalf of the Society for Neuro-Oncology.)

Background: Positron emission tomography (PET) imaging with 68 Gallium labeled somatostatin analogues ( 68 Ga-DOTA-SSA) plays a key role in neuroendocrine tumor management. The impact of patient size on PET image quality is not well known for PET imaging with 68 Ga-DOTA-SSA. The aim of this study is to propose a dose regimen based on patient size that optimizes image quality and yields sufficient image quality for diagnosis., Methods: Twenty-one patients (12 males, 9 females) were prospectively included for 68 Gallium-DOTA-Tyr3-Octreotate ( 68 Ga-DOTA-TATE) PET/CT, which was acquired in whole body list mode using 6 min per bed position (mbp). The list-mode events were randomly sampled to obtain 1 to 6 mbp PET reconstructions. For semi-quantitative assessment of image quality, the signal-to-noise ratio (SNR) was measured in the liver. The SNR normalized (SNRnorm) for administered activity and mbp was correlated with body mass, length, body mass index, body mass/length, and lean body mass. Three experienced nuclear medicine physicians visually graded image quality using a 4-point scale, and categorically scored the number of somatostatin-receptor positive lesions for each reconstruction. To investigate the impact of image quality on lesion quantification, the mean, maximum, and peak standardized uptake values (SUVs) of one abdominal lesion were measured in the 1 to 6 mbp PET reconstructions., Results: Of all patient-dependent parameters, body mass showed the strongest correlation (R 2 = 0.6) with SNRnorm. Lesion detectability analysis showed no significant difference for 3-5 mbp compared with the complete 6 mbp PET reconstruction. The SUV measurements showed no significant (p > 0.05) differences across the reconstructions. Visual assessment revealed that an SNR of 6.2 results in PET scans with moderate to good image quality. A non-linear expression was derived to calculate the required (dose × acquisition time) product (DTP) for the chosen SNR level of 6.2 that would yield a more constant image quality., Conclusion: Body mass can be used to predict 68 Ga-DOTA-TATE PET image quality. The proposed non-linear dose regimen based on body mass standardizes the image quality while maintaining sufficient image quality for diagnosis.

Our purpose was to prospectively investigate optimal evaluation of qualitative and quantitative 18 F-FDG PET/CT in response evaluations 12-14 wk after neoadjuvant chemoradiotherapy (nCRT) in esophageal cancer patients. Methods: This was a side study of the prospective diagnostic pre-SANO trial. 18 F-FDG PET/CT scans at baseline and at 12-14 wk after nCRT were qualitatively assessed for the presence of tumor. Maximum SUVs normalized for lean body mass (SUL max ) were measured in all scans. The primary endpoint was the proportion of false-negative patients with tumor regression grade (TRG) 3-4 (>10% vital residual tumor) in qualitative and quantitative analyses. Receiver-operating-characteristic curve analysis for TRG1 versus TRG3-4 using SUL max , SUL max tumor-to-esophagus ratio, and Δ%SUL max was performed to define optimal cutoffs. Secondary endpoints were sensitivity, specificity, negative predictive value, and positive predictive value for TRG1 versus TRG2-4. Results: In total, 129 of 219 patients were analyzed. Qualitative 18 F-FDG PET/CT was unable to detect TRG3-4 in 15% of patients. Sensitivity, specificity, negative predictive value, and positive predictive value in qualitative analysis for detecting TRG1 versus TRG2-4 was 80%, 37%, 42%, and 77%, respectively. In 18 of 190 patients (10%) with follow-up scans after nCRT, 18 F-FDG PET/CT identified new interval metastases. Quantitative parameters did not detect TRG3-4 tumor in 27%-61% of patients. The optimal cutoff for detecting TRG1 versus TRG2-4 was a post-nCRT SUL max of 2.93 (area under receiver-operating-characteristic curve, 0.70). Conclusion: Qualitative and quantitative analyses of 18 F-FDG PET/CT are unable to accurately detect TRG3-4 and to discriminate substantial residual disease from benign inflammation-induced 18 F-FDG uptake after nCRT. However, 18 F-FDG PET/CT is useful for the detection of interval metastases and might become useful in an active surveillance strategy with serial 18 F-FDG PET/CT scanning., (© 2019 by the Society of Nuclear Medicine and Molecular Imaging.)