TY - JOUR T1 - Improving <sup>68</sup>Ga-PSMA PET/MRI of the Prostate with Unrenormalized Absolute Scatter Correction JF - Journal of Nuclear Medicine JO - J Nucl Med SP - 1642 LP - 1648 DO - 10.2967/jnumed.118.224139 VL - 60 IS - 11 AU - Maike E. Lindemann AU - Nika Guberina AU - Axel Wetter AU - Wolfgang P. Fendler AU - Bjoern Jakoby AU - Harald H. Quick Y1 - 2019/11/01 UR - http://jnm.snmjournals.org/content/60/11/1642.abstract N2 - A limitation of using 68Ga-labeled prostate-specific membrane antigen (68Ga-PSMA) for detection and staging of prostate cancer is a frequently observed halo artifact around the urinary bladder caused by inaccurate scatter correction (SC) of PET data. The aim of this study was to investigate the impact of unrenormalized absolute SC on 68Ga-PSMA PET quantification in PET/MRI of the prostate in 100 patients. Methods: The PET data of 100 patients were reconstructed twice using standard SC and improved unrenormalized SC. The visual presence of the halo artifact was rated in each PET data reconstruction using 5 grades (0, no halo artifact; 4, severe halo artifact). The number of visible lesions in the pelvis was recorded. SUVmean and SUVmax were measured in the lesions, in the bladder, in the gluteus maximus, and within the halo margin. Furthermore, the signal-to-noise-ratio and image noise were measured in all PET data. Relative differences between standard and unrenormalized SC were calculated. Results: With standard SC, the average grade in the presence of the halo artifact was 2 (moderate halo artifact), whereas for unrenormalized SC, the average grade was 0.9 (slight halo artifact). The same number of congruent lesions (n = 74) was detected for both PET data reconstructions. Relative changes in PET signal-to-noise-ratio and image noise were not statistically significant (P &gt; 0.05). The mean (±SD) increase in SUVmean using unrenormalized SC was 23.0% ± 9.2% in the gluteus maximus, 7.1% ± 4.5% in the bladder, 325.4% ± 748.5% in the halo margin, and 12.4% ± 16.8% in all 74 detected lesions. The mean increase using unrenormalized SC in SUVmean was 17.5% for lesions inside the halo margin (38 lesions) and 6.9% for lesions outside the halo margin (36 lesions). Conclusion: For PET/MRI of prostate cancer using 68Ga-PSMA, a proper SC is important to ensure the best possible diagnostic quality and PET quantification. Unrenormalized absolute SC significantly reduces the halo artifact around the bladder and improves PET/MRI of the prostate. ER -