Abstract
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Objectives: Respiratory motion during PET/MR acquisition may result in image blurring and error in measurement for quantification and volume of lesion. The aim of this study was to evaluate effectiveness of minimum time gate (MTG) method as a respiratory synchronized MR based respiratory motion compensation (RSMBRMC) using integrated PET/MR scanner.
Methods: Data of 30 patients (aged 62.5 ± 10.2 y) underwent 18F-FDG liver PET/MR (Biograph mMR 3.0T, Siemens) study were collected. PET listmode data for 7 minutes was simultaneously acquired with maximum average gate (MAG), minimum time gate (MTG) and non gate (NG) T1 weighted MR images. Gated PET reconstruction was performed using mu-maps generated from MAG and MTG by setting 35% of efficiency window. Maximum SUV (SUVmax), peak SUV (SUVpeak), tumor size and full width at half maximum (FWHM) of MAG, MTG and NG PET images were evaluated.
Results: Compared to NG, mean SUVmax and SUVpeak were increased in MAG 13.15%(p<0.0001), 8.66%(p<0.0001), MTG 13.27%(p<0.0001), 8.80%(p<0.0001) and mean tumor size and FWHM were decreased in MAG 14.47%(p<0.0001), 15.49%(p=0.0004), MTG 14.89%(p<0.0001), 15.79%(p=0.0003) respectively. Mean SUVmax and SUVpeak of MTG were increased by 0.07%(p=0.8802), 0.13%(p=0.7766). Mean tumor size and FWHM of MTG were decreased by 0.49%(p=0.2786), 0.36%(p=0.2488) compared to MAG. There was no statistically significant difference between MAG and MTG which increase total scan time for 7 and 2 minutes.
Conclusion: Accuracy of quantification, tumor size and spatial resolution were improved by applying RSMBRMC without installing additional hardware in liver PET/MR study. And accurate information can be provided with the increase of 2 minutes scan time if applying MTG method as a RSMBRMC to various abdominal PET/MR studies affected by respiratory motion.