Quantitative and visual analyses of the effect of activity reduction on image metrics and quality in 18F-FDG PET/MRI in pediatric oncology.

BACKGROUND: : The aim of our study was to evaluate the effect of reduced injected tracer activities on the quantitative image metrics and the visual image quality in whole-body 18F-FDG PET/MRI with TOF capability in pediatric oncology. METHODS: Seventy-seven PET/MRI examinations of 54 patients were analyzed (standard injected activity: 1.9 MBq/kg, standard PET scan duration: 5 min per bed position). Lower activity PET images (1.2 MBq/kg and 0.9 MBq/kg) were retrospectively simulated from the originally acquired list-mode data sets. Quantitative parameters were assessed by measuring the SUV metrics, signal-to-noise ratio (SNR), contrast-to-noise ratios (CNR), and textural features in each PET data set. PET images were also evaluated visually for image quality by using a scoring system. RESULTS: SNRs were found as significantly different among PET data sets (p < 0.001) and showed increasing image noise with decreasing activities. CNR values did not show significant differences among PET data sets. The mean relative percentage changes in SUV metrics were found to be lower in 1.2 MBq/kg data set compared to 0.9 MBq/kg data set. Lesion SUVmax, SUVmean, SULpeak, and textural features were significantly different in 0.9 MBq/kg data set compared to the original data set (p < 0.05 for all). However, SUV metrics and textural features did not show a significant difference between the original and 1.2 MBq/kg data sets. While, the mean visual scores in 0.9 MBq/kg data set were significantly different compared to the original data set (p < 0.001), there was no significant difference between the original and 1.2 MBq/kg data sets in terms of general image quality and image sharpness. DISCUSSION: Our analyses showed that the reduction of injected activity to 1.2 MBq/kg may be feasible in pediatric oncological PET/ MRI, with a smaller relative percentage change in quantitative parameters and with similar image quality to the original data set.

The role of histopathological and biochemical parameters for predicting metastatic disease on 68 Ga-PSMA-11 PET in prostate cancer.

BACKGROUND: The aim of this study was to evaluate the role of histopathological and biochemical parameters in the prediction of the presence and number of PSMA positive lesions consistent with the metastatic spread of prostate cancer on 68 Ga-PSMA PET images. METHODS: Biochemical, histopathological and imaging data of 302 prostate cancer patients who underwent 68 Ga-PSMA-11 PET/CT or PET/MR imaging for primary staging were retrospectively analyzed. Patients were divided into two groups as "PET positive" and "PET negative" according to the presence of pathologic extraprostatic PSMA involvement. "PET positive" patients were additionally divided into two groups: oligometastatic (1-3 metastatic lesion) and multimetastatic (>3 metastatic lesions). RESULTS: The mean age of patients was 66.8 ± 7.6 years. Imaging modality was PET/MR in 223 (73.8%) and PET/CT in 79 (26.2%) of patients. Total PSA, PSA density (PSAD), ALP, and tumor ratio in biopsy specimens were found to be significantly higher in "PET positive" group compared to "PET negative" group and in multimetastatic group compared to oligometastatic group. PET positivity was observed in 3.8% of the low-intermediate risk groups (ISUP 1-3 and total PSA ≤ 20 ng/ml and PSAD < 0.15 ng/ml/cc). This ratio was 46% in the high-risk group (ISUP 4-5 or total PSA > 20 ng/ml or PSAD ≥ 0.15 ng/ml/cc) with a relative risk of 12 (p < .001). The prediction models to predict the PET positivity and the presence of distant metastasis had AUCs of 0.901 and 0.925, respectively; with ALP, total PSA, and tumor ratio in needle biopsy specimen as significant independent predictors (p < .05). CONCLUSIONS: In this study, 68 Ga-PSMA-11 PET positivity was significantly higher in the high-risk patient group than in the low-intermediate risk groups. The prediction models used for predicting the PET positivity and the presence of distant metastasis on PET imaging were successful with high discriminatory powers. In addition to total PSA and ISUP GG, ALP and tumor ratio in biopsy specimens can be used to identify high-risk patients.

The Added-value of Staging 18F-FDG PET/CT in the Prediction of Overall Survival in the Patients with Bladder Cancer.

Objectives: This retrospective study aimed to evaluate the prognostic importance of 18F-fluorodeoxyglucose (18F-FDG)-positive pelvic lymph nodes (LNs) and extra-pelvic disease on staging 18F-FDG positron emission tomography/computed tomography (PET/CT) in patients with bladder cancer. Methods: Bladder cancer patients who underwent staging 18F-FDG PET/CT were included in the study. Histopathologic features of tumors, therapy histories, presence of distinguishable tumors on CT and PET images, sizes and maximum standardized uptake value (SUVmax) of primary tumors, total numbers, sizes, and SUVmax of 18F-FDG-positive pelvic and extra-pelvic LNs, and total numbers and SUVmax of distant metastases (M1a/1b) were recorded. Patients were followed up until death or the last medical visit. Factors predicting overall survival were determined using Cox regression analysis. Results: Fifty-five patients [median age: 70 (53-84), 48 (87.3%) male, 7 (12.7%) female] with bladder cancer were included in this study. Twenty-nine (52.7%) patients had 18F-FDG positive pelvic LNs, while 24 (43.7%) patients had 18F-FDG positive extra-pelvic disease. Patients with 18F-FDGpositive pelvic LNs had a higher rate of extra-pelvic disease (p=0.003). The median follow-up duration was 13.5 months. The median overall survival was 16.3 months [95% confidence interval (CI) 8.9-23.7]. The primary tumor distinguishability on PET (p=0.011) and CT (p=0.009) images, the presence of 18F-FDG-positive pelvic LNs (p<0.001) and 18F-FDG-positive extra-pelvic disease/distant metastases (M1a/M1b) (p<0.001), and the number of distant metastases (p=0.034) were associated with mortality. The 18F-FDG-positive extra-pelvic disease/distant metastases [p=0.029, odds ratio: 4.15 (95% CI 1.16-14.86)] was found to be an independent predictor of mortality in patients with bladder cancer. Conclusion: The presence of 18F-FDG-positive extra-pelvic disease in pretreatment 18F-FDG PET/CT is an important prognostic factor in bladder cancer patients.

Relationship Between Metabolic Activity, Cellularity, Histopathological Features of Primary Tumors and Distant Metastatic Potential in Breast Cancer.

Objectives: The aim of this study was to evaluate the relationship between the types of distant metastatic spread, histopathological features, and imaging features of primary tumor on positron emission tomography/magnetic resonance imaging (PET/MRI) for primary staging in newly diagnosed breast invasive ductal carcinoma (IDC) patients. Methods: Data from 289 female patients were retrospectively evaluated. Maximum standardized uptake value, metabolic tumor volume (MTV), total lesion glycolysis (TLG), and minimum apparent diffusion coefficient (ADCmin) values of primary tumors were obtained from PET/MRI. The patients were grouped as non-metastatic, oligometastatic (1-5 metastatic lesions) and multimetastatic (>5 metastatic lesions) disease according to the number of distant metastases, and divided into two groups as isolated bone metastasis (IBM) and mixed/soft tissue metastasis (M-SM) groups according to the sites of metastatic spread. Results: Metabolic parameters had higher values and ADCmin had lower values in the multimetastatic and oligometastatic groups than in the non-metastatic group. MTV was the only parameter that showed significant difference between the multimetastatic and oligometastatic groups. MTV and TLG were significantly higher in the M-SM group than in the IBM group. 18F-fluorodeoxyglucose PET parameters had significantly higher values in grade 3, hormone receptor negative, human epidermal growth factor receptor 2 positive, triple negative, and highly proliferative (Ki-67 ≥14%) tumors. The prediction models that included imaging parameters to predict the presence of distant metastasis had higher discriminatory powers than the prediction models that included only histopathological parameters. Conclusion: Primary tumors with higher metabolic-glycolytic activity and higher cellularity were more aggressive and had higher metastatic potential in breast IDC. Compared with histopathological parameters alone, the combination of imaging parameters and histopathological features of primary tumors may help to better understand tumor biology and behavior.