Reduced Acquisition Time Per Bed Position for PET/MRI Using 68Ga-RM2 or 68Ga-PSMA11 in Patients With Prostate Cancer: A Retrospective Analysis.

Background: Growing clinical adoption of PET/MRI for prostate cancer (PC) evaluation has increased interest in reducing PET/MRI scan times. Reducing acquisition time per bed position below current times of at least 5 minutes would allow shorter examination lengths. Objective: To evaluate the effect of different reduced PET acquisition times in patients with PC who underwent 68Ga-PSMA11 or 68Ga-RM2 PET/MRI using highly sensitive silicon photomultiplier-based PET detectors. Methods: This study involved retrospective review of men with PC who underwent PET/MRI as part of one of two prospective trials. Fifty men (mean age, 69.9±6.8 years) who underwent 68Ga-RM2 PET/MRI and 50 men (66.6±5.7 years) who underwent 68Ga-PSMA11 PET/MRI were included. PET/MRI used a time-of-flight-enabled system with silicon photomultiplier-based detectors. Acquisition time was 4 minutes per bed position. PET data were reconstructed using acquisition times of 30 seconds, 1 minute, 2 minutes, 3 minutes, and 4 minutes. Three readers independently assessed image quality for each reconstruction using 1-5 scale (1=non-diagnostic; 5=excellent quality). One reader measured SUVmax for up to 6 lesions per patient. Two readers independently assessed lesion conspicuity using 1-3 scale (1=not visualized; 3=definitely visualized). Results: Mean image quality across readers at 30 seconds, 1 minutes, 2 minutes, 3 minutes, and 4 minutes was, for 68Ga-RM2 PET/MRI, 1.0±0.2 to 1.7±0.7, 2.0±0.3 to 2.6±0.8, 3.1±0.5 to 3.9±0.8, 4.6±0.6 to 4.7±0.6, and 4.8±0.4 to 4.8±0.5, respectively, and for 68Ga-PSMA11 PET/MRI was 1.2±0.4 to 1.8±0.6, 2.2±0.4 to 2.8±0.7, 3.6±0.6 to 4.1±0.8, 4.8±0.4 to 4.9±0.4, and 4.9±0.3 to 5.0±0.2, respectively. Mean lesion SUVmax for 68Ga-RM2 PET/MRI was 11.1±12.4, 10.2±11.7, 9.6±11.3, 9.5±11.6, and 9.4±11.6, respectively, and for 68Ga-PSMA11 PET/MRI was 14.7±8.2, 12.9±7.4, 12.1±7.8, 11.7±7.9, and 11.6±7.9, respectively. Mean lesion conspicuity (reader 1/reader 2) was, for 68Ga-RM2 PET/MRI, 2.4±0.5/2.7±0.5, 2.9±0.3/2.9±0.3, 3.0±0.0/3.0±0.0, 3.0±0.0/3.0±0.0, and 3.0±0.0/3.0±0.0, respectively, and for 68Ga-PSMA11 PET/MRI was 2.6±0.5/2.8±0.4, 3.0±0.2/2.9±0.3, 3.0±0.1/3.0±0.2, 3.0±0.0/3.0±0.0, and 3.0±0.0/3.0±0.0, respectively. Conclusion: Our data support routine 3 minute acquisitions, which provided very similar results as 4 minute acquisitions. Two minute acquisition, though somewhat lowering quality, provided acceptable performance and warrants consideration. Clinical Impact: When evaluating PC using modern PET/MRI equipment, time per bed position may be reduced compared with historically used times.

AJR. American journal of roentgenology. 2021 Aug 18 [Epub ahead of print]

Heying Duan, Lucia Baratto, Negin Hatami, Tie Liang, Craig S Levin, Mohammad Mehdi Khalighi, Andrei Iagaru

Department of Radiology, Division of Nuclear Medicine and Molecular Imaging, Stanford University, Stanford, CA, USA., Department of Radiology, Molecular Imaging Program, Stanford University, Stanford, CA, USA.

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