The interobserver agreement for Ga-PSMA-11 PET/CT study interpretations in patients with prostate cancer is unknown.Ga-PSMA-11 PET/CT was performed in 50 patients with prostate cancer for biochemical recurrence ( = 25), primary diagnosis ( = 10), biochemical persistence after primary therapy ( = 5), or staging of known metastatic disease ( = 10). Images were reviewed by 16 observers who used a standardized approach for interpretation of local (T), nodal (N), bone (Mb), or visceral (Mc) involvement. Observers were classified as having a low (<30 prior Ga-PSMA-11 PET/CT studies; = 5), intermediate (30-300 studies; = 5), or high level of experience (>300 studies; = 6). Histopathology ( = 25, 50%), post-external-beam radiation therapy prostate-specific antigen response ( = 15, 30%), or follow-up PET/CT ( = 10, 20%) served as a standard of reference. Observer groups were compared by overall agreement (% patients matching the standard of reference) and Fleiss' κ with mean and corresponding 95% confidence interval (CI). Agreement among all observers was substantial for T (κ = 0.62; 95% CI, 0.59-0.64) and N (κ = 0.74; 95% CI, 0.71-0.76) staging and almost perfect for Mb (κ = 0.88; 95% CI, 0.86-0.91) staging. Level of experience positively correlated with agreement for T (κ = 0.73/0.66/0.50 for high/intermediate/low experience, respectively), N (κ = 0.80/0.76/0.64, respectively), and Mc staging (κ = 0.61/0.46/0.36, respectively). Interobserver agreement for Mb was almost perfect irrespective of prior experience (κ = 0.87/0.91/0.88, respectively). Observers with low experience, when compared with intermediate and high experience, demonstrated significantly lower median overall agreement (54% vs. 66% and 76%, = 0.041) and specificity for T staging (73% vs. 88% and 93%, = 0.032). The interpretation of Ga-PSMA-11 PET/CT for prostate cancer staging is highly consistent among observers with high levels of experience, especially for nodal and bone assessments. Initial training on at least 30 patient cases is recommended to ensure acceptable performance.
BackgroundIn patients with differentiated thyroid cancer (DTC), serial 124I PET/CT imaging is, for instance, used to assess the absorbed (radiation) dose to lesions. Frequently, the lesions are located in the neck and they are close to or surrounded by different tissue types. In contrast to PET/CT, MR-based attenuation correction in PET/MR may be therefore challenging in the neck region. The aim of this retrospective study was to assess the quantitative performance of 124I PET/MRI of neck lesions by comparing the MR-based and CT-based 124I activity concentrations (ACs). Sixteen DTC patients underwent PET/CT scans at 24 and 120 h after administration of about 25 MBq 124I. Approximately 1 h before or after PET/CT examination, each patient additionally received a 24-h PET/MR scan and sometimes a 120-h PET/MR scan. PET images were reconstructed using the respective attenuation correction approach. Appropriate reconstruction parameters and corrections were used to harmonize the reconstructed PET images to provide, for instance, similar spatial resolution. For each lesion, two types of ACs were ascertained: the maximum AC (max-AC) and an average AC (avg-AC). The avg-AC is the average activity concentration obtained within a spherical volume of interest with a diameter of 7 mm, equaling the PET scanner resolution. For each type of AC, the percentage AC difference between MR-based and CT-based ACs was determined and Lin’s concordance correlation analysis was applied. Quantitative performance was considered acceptable if the standard deviation was ± 25% (precision), and the mean value was within ± 10% (accuracy).ResultsThe avg-ACs (max-ACs within parentheses) of 74 lesions ranged from 0.20 (0.33) to 657 (733) kBq/mL. Excluding two lesions with ACs of approximately 1 kBq/mL, the mean (median) ± standard deviation (range) was − 4% (− 5%) ± 14% (− 28 to 29%) for the avg-AC and − 9% (− 11%) ± 14% (− 33 to 33%) for the max-AC. Lin’s concordance correlation coefficients were ≥ 0.97, indicating substantial AC agreement.ConclusionsQuantification of lesions in the neck region using 124I PET/MR showed acceptable quantitation performance to 124I PET/CT for AC above 1 kBq/mL. The PET/MRI-based 124I ACs in the neck region can be therefore reliably used in pre-therapy dosimetry planning.
PurposeThe trend towards faster acquisition protocols in whole-body positron emission tomography/magnetic resonance (PET/MR) arises the question of whether short PET data acquisition protocols in a whole-body multi-station context allow for reduced PET acquisition times while providing adequate PET image quality and accurate quantification parameters. The study goal is to investigate how reducing PET acquisition times affects PET image quality and quantification in whole-body PET/MR in patients with oncologic findings.MethodsFifty-one patients with different oncologic findings underwent a clinical whole-body 18F-Fluorodeoxyglucose PET/MR examination. PET data was reconstructed with 4, 3, 2, and 1 min/bed time intervals for each patient to simulate the effect of reduced PET acquisition times. The 4-minute PET reconstructions served as reference standard. All whole-body PET data sets were analyzed regarding image quality, lesion detectability, PET quantification and standardized uptake values.ResultsA total of 91 lesions were detected in the 4-minute PET reconstructions. The same number of congruent lesions was also noticed in the 3 and 2 minutes-per-bed (mpb) reconstructed images. A total of 2 lesions in 2 patients was not detected in the 1 minute PET data reconstructions due to poor image quality. Image noise in the blood pool increased from 22.2% (4 mpb) to 42.1% (1 mpb). Signal-to-noise ratio declined with shorter timeframes from 13.1 (4 mpb) to 9.3 (1 mpb). SUVmean and SUVmax showed no significant changes between 4 and 1 mpb reconstructed timeframes.ConclusionsReconstruction of PET data with different time intervals has shown that 2 minutes acquisition time per bed position instead of 4 minutes is sufficient to provide accurate lesion detection and adequate image quality in a clinical setting, despite the trends to lower image quality with shorter PET acquisition times. This provides latitude for potential reduction of PET acquisition times in fast PET/MR whole-body examinations.
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