Patient Preparation for CT Colonography

JUDY YEE

CONTENTS

3.1 Colonic Preparation 24

3.1.1 Polyethylene Glycol 25

3.1.2 Sodium Phosphate 26

3.1.3 Magnesium Citrate 27

3.2 Colonic Distension 27

3.2.1 Room Air 29

3.2.2 Carbon Dioxide 29

3.3 Anti-Spasmodic Agents 30

3.3.1 Glucagon 30

3.3.2 Hyoscine n-Butylbromide 31 References 32

CT colonography or virtual colonoscopy has increasing support as a screening tool for colorectal polyps and carcinoma. This radiologic examination uses the patient data acquired from a helical CT scanner and combines it with computer software that post-processes the data to generate both two- and three-dimensional images of the colon for analysis. However, before the patient undergoes the CT scan, there are initial steps that must be taken to help obtain images of the colon that are of high diagnostic quality. The key element for a high-quality CT colonography examination is a well-cleansed and well-distended colon (Figs. 3.1, 3.2). When the colon contains residual fluid and/or stool, this can cause false negative and false positive results. If the colon is poorly distended, this too can lead to lesions being missed, and an area of collapse may simulate the apple-core appearance of a carcinoma. Patients are typically scanned in two opposing positions (supine and prone) so that portions of the colon that have residual material or poor distension in one position may be re-evaluated in the opposing view.

Fig. 3.1. a Coronal multiplanar reformat demonstrates a well-cleansed transverse colon with no layering fluid or residual solid stool. b Three-dimensional endoluminal view from the same patient showing normal haustral folds which are easily evaluated because of the absence of residual material

Associate Professor and Vice Chair of Radiology, University of California, San Francisco; Chief of Radiology, San Francisco VA Medical Center, 4150 Clement Street, San Francisco, CA 94121, USA

Fig. 3.1. a Coronal multiplanar reformat demonstrates a well-cleansed transverse colon with no layering fluid or residual solid stool. b Three-dimensional endoluminal view from the same patient showing normal haustral folds which are easily evaluated because of the absence of residual material a b a

Fig. 3.2. a Excellent distension of the ascending colon and cecum on a sagittal multiplanar reformat optimizes diagnostic ability. b A well-distended segment in the same patient on the endoluminal view allows easy navigation

Fig. 3.2. a Excellent distension of the ascending colon and cecum on a sagittal multiplanar reformat optimizes diagnostic ability. b A well-distended segment in the same patient on the endoluminal view allows easy navigation a

Scopolamine Butylbromide Synthesis

Fig. 3.3. a Suboptimal bowel preparation due to a large amount of residual fluid layering along the dependent wall of the colon as seen on this sagittal multiplanar reformatted view. b Poor cleansing with a large amount of layering fluid that obscures the colonic wall beneath it on this endoluminal view in the same patient

Fig. 3.3. a Suboptimal bowel preparation due to a large amount of residual fluid layering along the dependent wall of the colon as seen on this sagittal multiplanar reformatted view. b Poor cleansing with a large amount of layering fluid that obscures the colonic wall beneath it on this endoluminal view in the same patient

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