Abstract: On diffusion-weighted (DW) imaging, blood vessels show high signal when there is no diffusion gradient (b=0s/mm2), while they show low signal even when very low b-values (such as b=1 or 2s/mm2) are applied. Thus, the signal difference between images when the diffusion gradient is ‘off’ and images when the diffusion gradient is‘on’reflects the extent of tissue vessel density. We measure this via MRI diffusion derived vessel density (DDVD). For spin-echo type echo-planar imaging sequence, the second motion probing gradient after the 180-degree radiofrequency pulse could not fully re-focus the flowing spins in vessel and micro-vessels after being de-phased by the first motion probing gradient before the 180-degree radiofrequency pulse. The analysis of DDVD requires only two b-values (with one being b=0s/mm2 and the other being a non-zero low b-value), with a significantly shorter scanning time than contrast enhanced CT/MRI while without the need of a contrast agent injection and without radiation associated with CT. DDVD measure appears to be useful as a straightforward imaging biomarker in diverse clinical scenarios, including hepatitis B liver fibrosis, hepatocellular carcinoma, rectal carcinoma, liver hemangioma, early preeclampsia placenta, placenta accreta spectrum disorder, ischemic penumbra of brain stroke.

Key words: Magnetic resonance imaging, Diffusion-weighted imaging, Vessel density, Hepatitis B liver fibrosis