CT heart scans allow the acqusition of raw volumetric X-ray images which can be displayed in myriad formats, both 2- and 3-dimensional. These different display formats are not equally useful for all diagnostic applications. They have specific strengths as well as specific weaknesses, limitations, and artifacts. A full technical analysis of each display format is beyond the scope of this presentation. Our goal here is to make you familiar with the most common types of image displays and their clinical uses.
The raw data from a typical ECG-gated CT coronary angiogram is reconstructed into a set of standard axial images from a specific point in the cardiac cycle, usually late diastole, which can subsequently be reformatted with a computer workstation into various types of displays.
VRT stands for "volume rendering technology" and is the most visually arresting of all the standard CT displays, frequently appearing in both printed and broadcast media. This technology, which is similar to that used in the film industry, depends on complicated mathematical algorithms for display of volume, density, and surface texture. Because such images are highly dependent on mathematical assumption and operator interaction, they are not very useful for assessing plaque or stenoses. They are extremely useful, however, for assessing the anatomy of anomalous coronary arteries or by-pass grafts.
This display can also be viewed as a movie:
SSD stands for "shaded surface display" and is a simpler form of volume display than VRT. The display algorithms highlight the surface of the contrast volume within the arteries but do not render soft-tissue volume. These displays, although also visually striking, are rarely used for diagnostic purposes. Their main uses are as road-maps in interactive workstation programs for data analysis.
MPR stands for "multi-planar reformatting" and MIP stands for "maximum intensity projection." These two image displays, which are relatively similar in appearance, and their derivatives are the work-horses for diagnosing coronary artery disease and analyzing plaque. They are 2-dimensional images which can manipulated by the operator to display short longitudinal or cross-sectional segments of an artery in high detail. MIP images functionally exhibit very high detail and are useful for detecting coronary stenoses but are compromised by heavy calcification. MRP images are less compromised by calcification and are most useful for plaque characterization.
The following images will illustrate the usefulness of these various displays in a patient with a high-grade stenosis of the right coronary artery followed by an occluded segment, the distal vessel filling from left-sided collaterals.
The SSD image shows both coronary arteries and displays both the stenosis and the occluded segment of the right coronary artery:
The VRT image, of lower quality in this large man, also displays both the stenosis and the occluded segment:
The MIP image shows both the stenosis and the occlusion and better displays the degree of mixed plaque within the artery:
This special MPR view, called curvilinear MPR, follows the centerline of the vessel throughout multiple planes, reconstituting the entire vessel in a single 2-dimensional (but not anatomically correct) image: