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Effect of Region-Of-Interest Selection On IVIM Analysis in the Liver

J Vasquez*, S Deng, G Clarke, UT Health San Antonio, San Antonio, TX

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: investigate the effect of region-of-interest (ROI) selection, including (Ri) and excluding (Re) vascular or biliary structures, on intravoxel incoherent motion (IVIM) analysis and to determine correlations with ultrasound (US) measurements of liver stiffness in non-alcoholic fatty liver disease (NAFLD).

Methods:
Nineteen patients, 8 with a liver fat fraction (FF) > 5%, were included, with a 3 Tesla abdominal magnetic resonance imaging examination, a diffusion-weighted sequence (EPI factor=121, and SPAIR; 7 b-values: 0, 50, 100, 150, 200, 400, and 1500 s/mm²) and ¹H-MRS (volume=(20 mm)³, TR=2000 ms, TE=20-35 ms, TM=10 ms, BW=1250 kHz, flip-angle=90°) to quantify hepatic steatosis. All subjects were also scanned with Fibroscan to acquire liver stiffness measurements (LSM). Diffusion parameters in the right hepatic lobe were compared. T-tests were performed to determine differences in ROI selection with significance at p<0.05. The fraction of fast-diffusion, fast-diffusion, and slow-diffusion (f, Df, Ds) were calculated from the IVIM images using nonlinear least-squares fitting. The shifted ADC (sADC=ln(SI150/SI1500)) was also calculated. T2 corrected FF were fitted using AMARES in jMRUI. The relationship between diffusion parameters and US LSM were evaluated by Pearson correlation R.

Results:
Pair-wise comparisons between Re and Ri respectively for all subjects yielded the following averages for f, Df, Ds, sADC: 38.6,43.5%; 64.5,72.4x10?³mm²/s; 0.693,0.716x10?³mm²/s; 0.908,0.911. The f showed a significant difference between Re and Ri with p<0.001. Only Ds appeared to be correlated with LSM although not significantly (r=0.372,p=0.127 for Re; r=0.371,p=0.123 for Ri).

Conclusion:
These data indicate that the exclusion of biliary or vascular structures for selecting ROIs may not be necessary for IVIM analysis of the liver parenchyma. A larger sample size with varying degrees of steatosis and stiffness are needed to determine more robust differences and correlations.

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