Masakazu Tsujimoto

Background 18F-fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT) is a pivotal tool for diagnosing cardiac sarcoidosis, but its prognostic value during the phase of stable medical and device therapy after initiation of immunosuppressive therapy remains unclear. We aimed to evaluate the prognostic significance of cardiac FDG uptake in patients with cardiac sarcoidosis after treatment initiation. Methods We retrospectively analyzed 79 patients who underwent FDG-PET/CT ≥ 12 months after initiating immunosuppressive therapy (June 2013–October 2023). Patients were categorized into the cardiac accumulation (+) and (-), and Cardiac metabolic activity (CMA) was also quantitatively measured. Major adverse cardiac events—including cardiac death, ventricular arrhythmias, ICD therapy, and heart failure hospitalization—were evaluated. Results Patients in the cardiac accumulation (+) had a higher 2-year incidence of major adverse cardiac events than those in the cardiac accumulation (-), as determined by Kaplan–Meier analysis (log-rank P = 0.030), but FDG uptake was not identified as a predictor in Cox regression analysis. In long-term outcomes, the incidence of cardiac events tended to be higher in the cardiac accumulation (+) group, although this difference did not reach statistical significance (log-rank P = 0.078). Among patients with preserved left ventricular ejection fraction (LVEF ≥50%, independently associated with fewer events), annual cardiac event rates were similarly low regardless of uptake status (1.3% vs. 0.8%; log-rank P = 0.91). In 41 patients who underwent repeat PET imaging, CMA significantly decreased (median 4.83 to 0.82, P = 0.038). Among 23 patients without intensified immunosuppression despite uptake, it resolved spontaneously in 8 patients. Conclusions Follow-up cardiac FDG uptake may be associated with an increased risk of short-term events but has limited value for predicting long-term prognosis. LVEF and the temporal dynamics of FDG uptake should be considered when managing cardiac sarcoidosis.

Purpose ¹⁷⁷ Lu-DOTATATE-targeted radionuclide therapy (TRT) is effective for patients with somatostatin receptor (SSTR)-positive neuroendocrine tumors; however, radiation safety regulations often necessitate hospitalization, particularly in countries with stringent discharge criteria. This study aimed to identify pretreatment factors predicting outpatient eligibility. Methods We retrospectively analyzed 26 patients who underwent their first cycle of ¹⁷⁷ Lu-DOTATATE TRT with complete data for analysis. The external dose rate at 1 m (EDR-1 m) was measured 6 h after administration. Patients were divided into two groups: EDR-1 m greater than or equal to 18 μSv/h and less than 18 μSv/h. Characteristics, including age, sex, BMI, body surface area, estimated glomerular filtration rate, administered dose, and tumor site, were compared. In addition, the whole-body washout rate from pretreatment SSTR imaging was evaluated as a potential predictor. Logistic regression and receiver operating characteristic (ROC) analyses were conducted. Results Fourteen of the 26 (53.8%) patients met the discharge criterion at 6 h. No significant differences were observed in demographic or clinical characteristics between groups. The median washout rate was significantly higher in those meeting the criterion (57.6 vs. 35.0%; P  < 0.001). The area under the ROC curve for the washout rate was 0.929, indicating excellent predictive ability. An optimal cut-off value of 53.5% predicted same-day discharge with a sensitivity of 92.9% and specificity of 91.7%. Conclusion The whole-body washout rate derived from pretreatment SSTR imaging is a strong, practical predictor for outpatient eligibility following ¹⁷⁷ Lu-DOTATATE TRT. Incorporating this simple, noninvasive marker into clinical workflow could support individualized discharge planning and improve patient access under strict radiation safety regulations.

This study aimed to determine the optimal measurement conditions for accurate standardized uptake value (SUV) analysis of iodine-123 metaiodobenzylguanidine (¹²³I-MIBG) by examining the relationship between image convergence and quantitation. Single-photon emission computed tomography/computed tomography images were acquired using JS-10 and National Electrical Manufacturers Association (NEMA) body phantoms, with acquisition time per view varied (10, 30, 50, and 100 s/view). Image reconstruction was performed using three-dimensional-ordered subset expectation maximization, adjusting the product of subset and iteration (SI product; 60, 120, 180) and Gaussian filter parameters (8, 10, 12 mm). For the JS-10 phantom, we evaluated the dose linearity (DL), the recovery coefficient (RC) of individual rods, the scatter ratio (SR), and the coefficient of variation (CV). For the NEMA body phantom, we assessed the contrast-to-noise ratio (CNR) of the 17-mm-diameter hot sphere. We also evaluated the maximum and mean SUVs for all its hot spheres, and their relative standard error (RSE), using SUVs obtained at 100 s/view as reference. In the JS-10 phantom, the DL remained stable under all conditions. The RC decreased when the Gaussian filter was large and the SI product was small. A trade-off between the CV and the SR emerged, depending on the acquisition time and the SI product; optimal results were observed at 50 − 100 s/view and an SI product of 120 − 180. In the NEMA body phantom, contrast improved with acquisition times of ≥30 s/view, and the CNR increased as noise declined with longer acquisition times. At ≥50 s/view, variation in the maximum and mean SUVs decreased, with the RSE remaining below 5%. In conclusion, accurate SUV measurement with ¹²³I-MIBG requires an acquisition time of ≥50 s/view, an SI product of approximately 120, and a Gaussian filter of 10 − 12 mm. These findings provide a foundation for future studies comparing this method with the heart-to-mediastinum ratio, supporting its clinical application.