Fig. 33.

Double line rim in MRI. a In the illustrated case, on T2-weighted image, high signal intensity lines project behind the low signal intensity lines at the anterior aspect of the osteonecrotic areas (arrowhead), but also behind the lines with low signal at the posterior part of the osteonecrotic areas (arrows). This shifted position of the lines in the same direction in front and behind the necrotic areas is consistent with a chemical shift artifact. b On fat-suppressed T2-weighted image, the low signal component of the cellular rim has the same signal as the suppressed fat, and therefore a double rim line cannot be seen