Use of maximum intensity projections in CT angiography: a basic review

Maximum intensity projection (MIP) is a simple three-dimensional visualization tool that can be used to display computed tomographic angiography data sets. MIP images are not threshold dependent and preserve attenuation information. Thus, they often yield acceptable results even in cases in which shaded surface display images fail because of threshold problems. MIP is particularly useful for depicting small vessels. Because MIP does not allow for differentiation between foreground and background, MIP images are best suited for displaying relatively simple anatomic situations in which superimposition of structures does not occur (eg, the abdominal aorta). If anatomic structures are superimposed over the vessel of interest, the MIP technique can provide images of diagnostic quality as long as the contrast of the vessel of interest is sufficiently high compared with that of surrounding structures. Editing procedures for MIP are usually used to exclude unwanted structures from the volume of interest and include cutting functions and region-growing algorithms. Artifacts from vessel pulsation and respiratory motion may occur and simulate abnormalities, but, with careful attention, they can be distinguished from real disease. MIP images should always be interpreted together with the original transaxial data set. Knowledge of display properties and artifacts is necessary for correct interpretation of MIP images and helps one create images of optimal quality, choose appropriate examination parameters, and distinguish artifacts from disease.