  Apparent diffusion coefficient (ADC) is a measure of the magnitude of
diffusion of water molecules within tissues. We argue that ADC value contains
information of both diffusion and T2 relaxation. In this letter, we list
literature evidence to support our argument. Firstly, we list uterine
myometrium tumors as examples. Myometrium has a T2 relaxation time of 79 ms at
3T. Literature shows, when the myometrium tumors are T2 weighted signal
intensity hypertensive (relative to myometrium), these tumors likely show
diffusion restriction. This is similar to that, while the spleen is T2 weighted
signal intensity hypertensive relative to the liver, the spleen demonstrates
diffusion restriction relative to the liver. On the other hand, when the
myometrium tumors are T2 weighted signal intensity hypotensive (relative to
myometrium), these tumors likely do not show diffusion restriction. However,
when the myometrium tumors are very highly hypertensive such as the cases of
leiomyoma cystic degeneration and myxoid degeneration, the relationship between
T2 weighted signal intensity and diffusion is similar to that of a normal
gallbladder, i.e., T2 weighted signal highly hypertensive without diffusion
restriction. For most of the tumors, much longer T2 may suggest a tumor is
waterier. On b=0 images, the signal of tumor (relative to other tissues) can be
dominated by T2 effect. On a high b-value images such as b=1000 images, it is
possible that tumor regions are dominated by noises. In the end, the ADCs,
which are determined by the slope between the signal at b=0 and the signal at
b=1000, are also dominated by the T2 effect, with longer T2 being associated
with higher ADC measure. In fact, since there is no diffusion gradient with b=0
images, and there are only noises on b=1000 (or b=800), ADC map is devoid of
diffusion information.
