MIP

MIP images are created by displaying only the
highest attenuation value from the data encountered
by a ray cast through an object to the viewer’s
eye (5,6). The depth information along the
projection ray is lost; to visualize the spatial relationship
of various structures, the volume has to
be rotated and viewed from different angles. If
bone or calcifications are within the projection
ray, these structures are represented on the MIP
image instead of the contrast-enhanced vessel
because of higher attenuation values. Therefore,
bone elimination techniques are essential for pro-
cessing vascular MIP images. Superimposition of
vessels leads to artificially altered lumen margins,
and pathologic conditions may be hidden. To
cope with this problem, a modification of MIP
called closest vessel projection has been proposed
(7). Thin-slab MIP images viewed interactively
may be an alternative, as the necessity for bone
elimination is limited. MIP is not suitable
for the evaluation of stenosis in cases of dense
calcification or stents, but thin-slab MIP can provide
an excellent “road map” of the vessel course
for further evaluation with MPR.