Evaluation of an extra PET focus region of the upper abdomen in alveolar echinococcosis using F-18-FDG-PET/MRI in comparison to standard protocol.

Introduction: F-18-FDG PET/MRI has proven effective in qualitatively assessing the activity of clinically confirmed, macroscopic alveolar echinococcosis (AE) manifestations providing excellent MRI soft tissue contrast and metabolic information from FDG. In addition to a single PET acquisition during the whole body scan a second PET scan during the MRI focus region of the upper abdomen can be acquired. Thus, we systematically evaluated the properties and image quality of this extra, longer PET acquisition in conjunction to the shorter primary whole body PET acquisition.

Methods: 38 patients (53 ± 16 years) with clinically confirmed AE were examined with a PET/MRI (3T Biograph mMR, Siemens) and a dedicated extra PET/MRI focus region protocol. Regions of interest (ROIs) were drawn in the primary and secondary focus region in the upper abdomen (index lesion of the liver, liver parenchyma, blood pool, muscle, lung, air) and their SUVmean as well as the SNR extracted. For intraindividual normalisation ratios for index lesion to blood pool and liver parenchyma were calculated. Wilcoxon signed-rank test corrected for multiple testing was employed for group comparisons.

Results: There was a significant higher SUVmean for the hepatic index lesion in the focus region PET scan (3.9±1.6) in comparison to the 1° scan (3.5±1.6) (p=0.03; Z=-4.6). No significant difference was found for the SUVmean in the physiological liver parenchyma (p=0.35; Z=-0.9). The normalising ratio of index lesion to liver parenchyma showed a significant difference ()in the focus region PET scan (mean=2.0±0.7) compared to the primary scan (mean=2.0±0.7; p=0.03; Z=-4.1) with little variation around the mean (IQR: 1°=1.9, 1.04; 2°=1.6, 0.7).

Conclusions: The extra PET acquisition of the focus region showed significantly higher SUVmean values for the hepatic manifestations in alveolar echinococcosis. Also, the normalising ratio of liver lesion to liver parenchyma exhibited less variation, which may improve overall image contrast and possibly aid detection of residual foci.