The Impact of TE and TR on Apparent Diffusion Coefficient and Diffusion-derived Vessel Density Quantification: Studies of Healthy Liver and Spleen

Abstract This study investigates the impact of echo time (TE) and repetition time (TR) on apparent diffusion coefficient (ADC) and diffusion-derived vessel density (DDVD) values. Spleen has longer T1 and T2 than the liver, and spleen has a T2 similar to most hepatocellular carcinomas. Liver and spleen diffusion MRI was conducted with six volunteers at 3.0 T with multiple sessions. When TE was changed with steps of TE=46 ms, 52 ms, 60 ms, 70 ms, and 80 ms, TR was fixed at 2000 ms. When TR was changed with steps of TR=200 ms, 300 ms, 500 ms, 1000 ms, and 2000 ms, TE was fixed at 46 ms. The b-values included 0, 1, 2, 10, and 600 s/mm². ADC was calculated with b=0 and b=600 s/mm² images. DDVD was the signal difference between on b=0 image and a very low b-value image (b=1, 2, 10 s/mm2). Thirty-five scans for each ADC data point and 23 scans for each DDVD data point were included. Following the increase in TE from 46ms to 80ms, the ADC value increased by 23.9% (median) for the liver and 18.2% (median) for the spleen, while the ADCspleen/ADCliver ratio was smaller when TE was longer. Following the increase in TR from 200ms to 2000 ms, the ADC value decreased by 4.8% (median) for the liver and 14.6% (median) for the spleen, while the ADCspleen/ADCliver ratio was smaller when TR was longer. Following the increase in TE from 46ms to 80ms, there was a decrease in the DDVD value. DDVDspleen/DDVDliver ratios were greater when TE was long. Following the increase in TR from 200ms to 2000ms, there was a biphasic change in the DDVD value. The DDVD values were highest when TR was 500ms, and DDVDspleen/DDVDliver ratios followed a mono-phasic decrease. TR and TE have very notable impact on the ADC and DDVD values of the liver and spleen.