Faecal residues

Adequate bowel preparation is essential for an accurate CTC examination. Individuals undergoing CTC should consume a low residue diet, avoiding high-fibre food such as fruit and vegetables that produce faecal residues. Residual fluid and solid residues may reduce sensitivity and specificity of CTC. Endo-luminal fluid can obscure polyps solid stool can mimic a true polyp and, if present in large quantities, obscure polyps. 

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). 

In these three studies primary 2D read was performed. Adequately reading and interpreting the data sets is an arduous task and needs a lot of experience as with laxative-free CT colonography more residue is present in the colon. For the same reason primary 3D read is impossible. To do so the faecal residue has to be removed or subtracted using dedicated software. 

The procedure of sample preparation for faecal BA analysis and derivatisation is an adaptation of the method of Czubayko et al. [17]. The internal standard (125 pg HDCA) is added to the aqueous phase of extraction. The sample is saponified with 200 pi 10 mol/1 sodium hydroxide at 120°C for 120 min and then acidified to pH 1 with hydrochloric acid. After extraction of BAs with diethyl ether (4 x 1 ml), the solvent phases are pooled and evaporated under a stream of nitrogen. The residue is... 

The metabolism of six different PCB congeners, administered orally in food, have been studied in N. virens by two groups of workers. Metabolism was dependent on both the degree of chlorination and the chemical structure of the compounds. Metabolism of MCBP was observed but not of TCBP and HCBP (McElroy and Means 1988). After 6 weeks of exposure to MCBP, worms contained only 2% unmetabolized compound, 22% polar metabolites and 76% unextractable (macromolecular) residues (McElroy and Means unpubl. data). Only a minor presence of metabolites was observe(l in faecal pellets. However, in the case of all three congeners, a large percentage of the radiolabelled compounds (> 60%) fed to the worms was not subsequently recovered in worm tissue or faecal pellets. 

The patients receive a dedicated low residue diet (Nutra Prep , E-Z-EM, Lake Success, NY, USA). This diet is provided in a box and supplies the patient with all the meals and drinks for the entire day before CT colonography (Fig. 4.2). This box contains powdered drinks with vanilla flavour, fruit drinks, soups, chips and nutrition bars. The diet reduces the fat intake and the faecal output. Patients are allowed to have breakfast (8 a.m.), lunch (noon) and dinner (5 p.m.). Breakfast consists of a tropical fruit juice, one vanilla drink and tea or coffee. At lunch patients drink another tropical fruit juice and vanilla drink and/or apple sauce, a soup and tea or coffee. At dinner they can have another soup and/or vanilla drink. Between the meals they can eat the chips and nutrition bars. The patients are allowed to drink as much additional water as they want to. 

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). 

A multivariate analysis was conducted that included N intake and ME intake as covariates in predicting N output in faeces, urine and milk. Metabolizable intake had a significant effect on predicting urinary N excretion and milk N secretion but not faecal N excretion. It should be noted that ME intake already includes faecal and urinary energy as part of the calculation, therefore, correlations are expected. The residual standard deviations from the multivariate arralysis including ME intake as a covariate were 13.8, 27.9 and 15.0 g/d. The prediction equations for urinary N excretion and milk N secretion (which had significant effect of ME intake) were ... 

Several studies have highlighted the wide variation in N excretion, particularly urine N. Weiss et al. (2009) reported that the variation in urinary N was 3.5 times greater than for faecal N excretion and Mills et al (2009) also found that there was greater variation in N excretion relative to milk yield. The residual standard deviations for N losses in faeces, urine and milk in the present study were estimated to be 14.6, 32.5 and 17.5 g/d, respectively from the univariate analysis. The higher residual standard deviation for urine N compared to faeces or milk output presents an opportunity to manipulate diets to reduce urine N excretion and may be, in part, explained by metabolizability of the diet. 

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