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2-D, 3-D Images Both Permit Good Evaluation of Colon

August 17, 2009
Written by: , Filed in: Gastrointestinal Imaging
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After a patient has undergone virtual colonoscopy and the images have been processed by the radiologist’s workstation, the radiologist must decide how to display and interpret the images.

The basic two approaches are for the radiologist to be a 2-dimensional (2-D) reader with 3-dimensional (3-D) problem solving or to be a 3-D reader with 2-D problem solving. Both approaches have some advantages.

2-D Reader
2-D display techniques are faster, and these images are easier to interpret when the colon prep is poor (a lot of stool present). Radiologists who are primarily 2-D readers use 3-D for problem solving.

3-D Reader
Radiologists who are primarily 3-D readers track the surface area of the colon that has been examined so that they know what percentage they have seen. Unseen parts can be “painted” so they can later be reviewed manually. 3-D display techniques may be more sensitive for polyps and may be more sensitive for false positives (more false-positive results). Radiologists who are primarily 3-D readers use 2-D for problem solving.

Reviewing the Colon

The 2-D reader looks at the examination using a high-contrast window (high contrast between air and colon wall). The reader then links the supine and prone images and gets an overview of the following:
the colon position and its mobility, the supine and prone positions, the degree of colon distention, the tortuosity of the colon, and the quality of the prep. This overview is also performed by 3-D readers.

Next, the 2-D reader systematically reviews the colon. Each part is magnified as it is reviewed. Frequent realigning is necessary, especially at the flexures. The 2-D reader may select an “ascending mode” and watch the screen change automatically, or the 2-D reader may elect to scroll through the images manually.

As images are reviewed, the reader bookmarks the findings (both true findings and things to be reviewed later) so that they can be found on some sort of a model of the colon.

Some readers like to perform an initial fly-through, bookmark anything that might be of interest, and then later return to work up the things that have been bookmarked.

Other readers prefer to work up each finding as they come to it, determine if the finding is “real” or not, and then move on to the next section of the colon.

Extracolonic Tissues

After reviewing the colon, both 2-D and 3-D readers look at extracolonic findings. Because the images are somewhat grainy and no IV contrast was used, the reader may struggle to determine the significance of the findings, such as a mass in the liver. An ultrasound may be needed to determine if a mass is a cyst or a solid mass.

Take-Home Pearl
When reviewing images from a virtual colonoscopy examination, the reader first links the supine and prone images and gets an overview of the colon position and its mobility, the tortuosity of the colon, and the quality of the prep.

Approaches to Image Interpretation for Virtual Colonoscopy.
Richard S. Breiman, MD

This review is an abstract of an audio presentation from Practical Reviews in Radiology. If you do not have access to this presentation and would like to purchase a copy, please call 1-800-633-4743, email service@oakstonepub.com, or write Oakstone Medical Publishing, 100 Corporate Parkway, Suite 600, Birmingham, Alabama 35242.

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