Scout view

However bowel preparation should be tailored to the indication, with full or reduced cathartic preparation associated to tagging of fluids or stool. Adequate colonic distension (pneumocolon) is cru-dal for identification of colorectal polyps and differentiation between obstructive cancers and a collapsed segment. Distension is achieved by rectal air or carbon-dioxide insufflation, and standard scout view in lateral and anterior-posterior projections are acquired to verify the distension of the entire colon. The intravenous administration of a muscle rdaxant, to reduce large bowel movement and... 

Before proceeding to image acquisition, the degree of colon distension is assessed on frontal and lateral CT scout views the colon can thus be re-inflated if necessary (Fig. 17.3). CT scanning is performed in the prone and supine positions while the patient holds his breath, as dual acquisition has been shown to significantly improve CTC sensitivity (Fig. 17.4) and specificity (Fig. 17.5) (Fletcher et al. 2000 Morrin et al. 2002). 

Fig. 17.3a-d. Scouts in the lateral and AP views show how gas distributes within the large bowel in the supine (a,b) and prone (c,d) positions. All images are from the same patient. In the supine position gas is displaced anteriorly, and images show poor distension of the rectum (a, arrow) and good distension of the transverse colon (b, arrows). Conversely, in the prone position gas prevails in those colon segments that are located posteriorly, and images show a distended rectum (c, arrows) and a sub-optimally distended transverse colon (d, arrows)... 

The view in the main mirror corresponds to the evolutionarily developed foveal purpose, namely targeted scouting into the distance. 

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