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Introduction We aimed to assess the feasibility of SPECT and PET Y-90 imaging, and to compare these modalities by visualizing hot and cold foci in phantoms for varying isotope concentrations. Materials and methods The data was acquired from the Jaszczak and NEMA phantoms. In the Jaszczak phantom Y-90 concentrations of 0.1 MBq/ml and 0.2 MBq/ml were used, while higher concentrations, up to 1.0 MBq/ml, were simulated by acquisition time extension with respect to the standard clinical protocol of 30 sec/projection for SPECT and 30 min/bed position for PET imaging. For NEMA phantom, the hot foci had concentrations of about 4 MB/ml and the background 0.1 or 0.0 MBq/ml. All of the acquired data was analysed both qualitatively and quantitatively. Qualitative assessment was conducted by six observers asked to identify the number of visible cold or hot foci. Inter-observer agreement was assessed. Quantitative analysis included calculations of contrast and contrast-to-noise ratio (CNR), and comparisons with the qualitative results. Results For SPECT data up to two cold foci were discernible, while for PET four foci were visible. We have shown that CNR (with Rose criterion) is a good measure of foci visibility for both modalities. We also found good concordance of qualitative results for the Jaszczak phantom studies between the observers (corresponding Krippendorf’s alpha coefficients of 0.76 to 0.84). In the NEMA phantom without background activity all foci were visible in SPECT/CT images. With isotope in the background, 5 of 6 spheres were discernible (CNR of 3.0 for the smallest foci). For PET studies all hot spheres were visible, regardless of the background activity. Conclusions PET Y-90 imaging provided better results than Bremsstrahlung based SPECT imaging. This indicates that PET/CT might become the method of choice in Y-90 post radioembolization imaging for visualisation of both necrotic and hot lesions in the liver.

Purpose of the Report The aim of the study was to prospectively compare performance of 18F-fluorocholine (FCH) and 18F-prostate-specific membrane antigen (PSMA)-1007 PET/CT in patients with biochemical relapse (BCR) of prostate cancer and low prostate-specific antigen levels. Methods We prospectively enrolled 40 BCR patients after radical treatment and prostate-specific antigen levels 2.0 ng/mL or less. 18F-FCH and 18F-PSMA-1007 PET/CT imaging was performed within a mean interval of 54 ± 21 days. Scans were done 87 ± 10 and 95 ± 12 minutes after injecting 248 ± 35 and 295 ± 14 MBq of 18F-FCH and 18F-PSMA-1007, respectively. Rates of negative, equivocal, and positive scan results were compared per patient. Per lesion, findings were grouped as equivocal or highly suggestive of malignancy and then compared for their number, localization (local relapse, lymph nodes, bones), and SUVmax values. Results Positive, equivocal, and negative results were reported in 60%, 27.5%, and 12.5% of 18F-PSMA-1007 and in 5%, 37.5%, and 57.5% of 18F-FCH scans, respectively. In 70% of scans, 18F-PSMA-1007 PET/CT upgraded 18F-FCH PET/CT results. 18F-PSMA-1007 scans also showed significantly more lesions (184 vs 63, P = 0.0006). Local relapse, lymph node, and bone lesions accounted, respectively, for 9%, 58%, and 33% of 18F-PSMA-1007 and 5%, 89%, and 6% 18F-FCH of PET/CT findings. Highly suspicious lesions accounted for 74% of 18F-PSMA-1007 and 11% of 18F-FCH PET/CT findings. In 18F-PSMA-1007 PET/CT SUVmax values of highly suggestive lesions were significantly higher than in equivocal lesions (median, 3.6 vs 2.5; P < 0.00001). Conclusions In early BCR patients 18F-PSMA-1007 showed a higher detection rate than 18F-FCH PET/CT. The former also showed more lesions in total, more highly suggestive lesions and less equivocal lesions.

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Background The aim of the study was to compare widely used ordered subset expectation maximisation (OSEM) algorithm with a new Bayesian penalised likelihood (BPL) Q.Clear algorithm in 18F-PSMA-1007 PET/CT. Methods We retrospectively assessed 25 18F-PSMA-1007 PET/CT scans with both OSEM and Q.Clear reconstructions available. Each scan was independently reported by two physicians both in OSEM and Q.Clear. SUVmax, SUVmean and tumour-to-background ratio (TBR) of each lesion were measured. Reports were also compared for their final conclusions and the number and localisation of lesions. Results In both reconstructions the same 87 lesions were reported. Mean SUVmax, SUVmean and TBR were higher for Q.Clear than OSEM (7.01 vs 6.53 [p = 0.052], 4.16 vs 3.84 [p = 0.036] and 20.2 vs 16.8 [p < 0.00001], respectively). Small lesions (< 10 mm) had statistically significant higher SUVmax, SUVmean and TBR in Q.Clear than OSEM (5.37 vs 4.79 [p = 0.032], 3.08 vs 2.70 [p = 0.04] and 15.5 vs 12.5 [p = 0.00214], respectively). For lesions ≥ 10 mm, no significant differences were observed. Findings with higher tracer avidity (SUVmax ≥ 5) tended to have higher SUVmax, SUVmean and TBR values in Q.Clear (11.