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Abstract
ObjectiveThe aim of this optimization study was to minimize the acquisition time of 68Ga-HBED-CC-PSMA positron emission tomography/magnetic resonance imaging (PET/MRI) in patients with local and metastatic prostate cancer (PCa) to obtain a sufficient image quality and quantification accuracy without any appreciable loss.MethodsTwenty patients with PCa were administered intravenously with the 68Ga-HBED-CC-PSMA ligand (mean activity 99 MBq/patient, range 76–148 MBq) and subsequently underwent PET/MRI at, on average, 168 min (range 77–320 min) after injection. PET and MR imaging data were acquired simultaneously. PET acquisition was performed in list mode and PET images were reconstructed at different time intervals (1, 2, 4, 6, 8, and 10 min). Data were analyzed regarding radiotracer uptake in tumors and muscle tissue and PET image quality. Tumor uptake was quantified in terms of the maximum and mean standardized uptake value (SUVmax, SUVmean) within a spherical volume of interest (VOI). Reference VOIs were drawn in the gluteus maximus muscle on the right side. PET image quality was evaluated by experienced nuclear physicians/radiologists using a five-point ordinal scale from 5–1 (excellent—insufficient).ResultsLesion detectability linearly increased with increasing acquisition times, reaching its maximum at PET acquisition times of 4 min. At this image acquisition time, tumor lesions in 19/20 (95%) patients were detected. PET image quality showed a positive correlation with increasing acquisition time, reaching a plateau at 4–6 min image acquisition. Both SUVmax and SUVmean correlated inversely with acquisition time and reached a plateau at acquisition times after 4 min.ConclusionIn the applied image acquisition settings, the optimal acquisition time of 68Ga-PSMA-ligand PET/MRI in patients with local and metastatic PCa was identified to be 4 min per bed position. At this acquisition time, PET image quality and lesion detectability reach a maximum while SUVmax and SUVmean do not change significantly beyond this time point.
Highlights
Prostate cancer (PCa) causes significant morbidity and accounts for a tremendous amount of cancer-related deaths in men
Lesion detectability linearly increased with increasing acquisition times, reaching its maximum at PET acquisition times of 4 min
PET image quality showed a positive correlation with increasing acquisition time, reaching a plateau at 4–6 min image acquisition
Summary
Prostate cancer (PCa) causes significant morbidity and accounts for a tremendous amount of cancer-related deaths in men. The use of choline as a tracer for PET/CT is restricted by limited sensitivity for the detection of PCa in patients with serum prostate-specific antigen (PSA) levels of < 2 ng/ml [1,2,3,4]. To address this limitation, new tracers which allow more sensitive and specific detection of PCa with PET have been developed, such as ligands of the prostate-specific membrane antigen (PSMA) [5]. In malignant tissue, increased PSMA expression was found to be expressed in the stroma adjacent to neovasculature of solid tumors, suggesting
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