Faecal tagging

Specific CT colonography protocols should be established at a local level and should be based on the currently available published evidence. Protocols should address the method of bowel preparation (clean colon vs fluid or faecal tagging), use or not of intravenous contrast, use or not of spasmolytics, method of colon distension, scanning parameters, and methods of interpretation. The specifics of many of these options are discussed in subsequent chapters. 

The purpose of this chapter is 1) to explain what faecal tagging is 2) to demonstrate why this particular type of preparation is important 3) to explain how faecal tagging is performed at our institution 4) to show imaging findings. 

The rationale of developing a preparation with faecal tagging was twofold 1) improving diagnosis 2) improving patient compliance. 

Faecal tagging is performed with a 40% weight/ volume barium suspension (Tagitol V , E-Z-EM). The patients only have to drink a total of 60 ml 20 ml at breakfast, lunch and dinner respectively. The patients are instructed to drink the barium at once after the meal. 

In case of an obstructing tumour, faecal tagging is not hampered. In these cases patients present with efficient tagging and the colon is relatively clean (Fig. 4.3). In our experience none of these patients suffered from post-procedural colonic impaction with baroliths. 

Faecal residue with a foamy appearance is mostly detected in the cecum or ascending colon. It appears as an amorphous inhomogeneous mixture mostly of air bubbles and stool. They occur in both preparations without and with faecal tagging. In the latter case the foam is tagged or non-tagged. This foam may distract the reader s attention or cover a lesion making detection difficult (Fig 4.19). 

Several studies using a preparation based on faecal tagging have been performed. The results of polyp detection of these studies are listed in Table 4.1. 

Last but not least, Pickhardt et al. (2003) obtained tbe best results of polyp detection to date with virtual colonoscopy in a large cohort of 1233 asymptomatic patients. The day before CT colonography they combined a clear liquid diet with a double dose of oral sodium phosphate and two bisacodyl tablets. Faecal tagging was performed with 2x250 ml of a 2.1% w/v barium suspension and 60 ml of Gas-trografin. Excellent results of polyp detection were obtained. 

Iannaccone et al. (2004) examined successfully 203 patients with laxative-free CT colonography. They performed faecal tagging over two days with a total of 200 ml of diatrizoate meglumine and diatrizoate sodium. The patients were also on a low residue diet for two days. They obtained very good results of polyp detection 86% for lesions >6 mm (79 lesions), 95.5% for lesions >8 mm (45 lesions), 100% for lesions >1 cm (24 lesions). 

Callstrom et al. (2001) performed laxative-free CT colonography without dietary restrictions in 58 patients. Faecal tagging was obtained with a combination of iodine and barium administered over one or two days. The best results of tagging were obtained by combining 6x225 ml of a 2.1% w/v barium suspension and 1x225 ml dilute diatrizoate meglumine and diatrizoate sodium. All residue with a density >150 H.U. was electronically labelled. In that way a 100% sensitivity for lesions >1 cm was obtained (5/5 lesions). 

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