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Published online before print June 13, 2002, 10.1148/radiol.2241011222
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(Radiology 2002;224:393-403.)
© RSNA, 2002

Gastrointestinal Imaging

Dietary Fecal Tagging as a Cleansing Method before CT Colonography: Initial Results—Polyp Detection and Patient Acceptance1

Philippe A. Lefere, MD, Stefaan S. Gryspeerdt, MD, Jef Dewyspelaere, MD, Marc Baekelandt, MD and Bartel G. Van Holsbeeck, MD

1 From the Departments of Radiology (P.A.L., S.S.G., M.B., B.G.V.H.) and Gastroenterology (J.D.), Stedelijk Ziekenhuis, Bruggesteenweg 90, 8800 Roeselare, Belgium. From the 2000 RSNA scientific assembly. Received July 23, 2001; revision requested August 27; revision received October 22; accepted December 10. Address correspondence to P.A.L. (e-mail: radiologie@skynet.be).


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
 REFERENCES
 
PURPOSE: To compare reduced colonic cleansing based on dietary fecal tagging (FT) with standard (non-FT) colonic cleansing with regard to patient acceptance, sensitivity, and specificity.

MATERIALS AND METHODS: In 50 patients (FT group), FT was performed by means of diet, magnesium citrate, and a barium suspension. In another 50 patients (non-FT group), preparation was based on polyethylene glycol administration. All patients underwent conventional colonoscopy after computed tomographic (CT) colonography. Sensitivity and specificity for polyp detection were calculated by using conventional colonography as the reference standard. At CT colonography, fecal residue was evaluated. Patients were interviewed to determine discomfort, side effects, sleep quality, final opinion on examination comfort, and whether they would be reluctant to undergo the same examination again.

RESULTS: FT left more fecal residue but improved differentiation from polyps (FT specificity, 88% [30 of 34 patients]; non-FT, 77% [23 of 30 patients]). Sensitivities were comparable: FT, 88% (14 of 16 patients); non-FT, 85% (17 of 20 patients). FT significantly reduced discomfort, side effects, and sleep disturbance, and resulted in an improved final opinion of how comfortable the examination was (P < .05). Although FT improved patient willingness to repeat the examination, this improvement was not statistically significant (P > .05).

CONCLUSION: FT offers the patient a well-tolerated preparation and improves specificity, with improved differentiation of polyps from residual stool.

© RSNA, 2002

Index terms: Colon, CT, 75.12115, 75.12117, 75.1283 • Colon neoplasms, 75.311, 75.32 • Colonoscopy, 75.12115, 75.12117, 75.1283


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
 REFERENCES
 
Colorectal cancer is the third most common malignancy in the United States and is the second most important cause of cancer-related mortality. In Europe, population-based data for colorectal cancer show that mortality has declined, while incidence has increased. A positive correlation was also found between the probability of 5-year survival and the proportion of resected cancers. On the other hand, recent advances in surgical techniques and adjuvant therapy have resulted in only moderate effects for patients with advanced disease (1–5). Early-stage diagnosis of colorectal cancer is therefore mandatory to reduce mortality and morbidity. As a result, colorectal cancer screening has been questioned. Various authors (5–9) have demonstrated that screening for colorectal cancer is justified, and it has recently been shown that compliance is the major determining factor in the cost-effectiveness of colorectal cancer screening (10). Existing screening tests, however, are not without risk: They have variable accuracy, and, most important, their compliance rate is poor (11–14). Consequently, the need for a new screening test to evaluate the whole colon safely that has good sensitivity and specificity for polyp detection and results in good patient compliance has been asserted.

Since its development by Vining et al (15) in 1994, computed tomographic (CT) colonography has emerged as a potential screening technique that complies with the preceding requirements. Various authors (16–20) have reported good results in the detection of polypoid or neoplastic lesions larger than 5 mm in diameter. Other authors (21,22), however, have reported conflicting results. Moreover, as a recently developed technique, CT colonography continues to be afflicted by some other drawbacks. First, as with all other total colonic examinations, a fully cleansed colon is necessary. This requires intensive preparation prior to the examination, resulting in low patient compliance (23). This low patient compliance is well known in colorectal cancer screening (7). Second, standard colonic cleansing still leaves fecal residue. This makes differential diagnosis of polypoid lesions difficult and produces false-positive findings that result in unnecessary conventional colonoscopic examinations (24).

The feasibility of electronic cleansing after labeling fecal residues with barium has been reported by Chen et al (25), Zalis and Hahn (26), and Callstrom et al (27). This presents the opportunity to omit colonic cleansing (26,27) or at least reduce it (25) and differentiate fecal residue from polyps, since fecal residue is labeled with barium. The proposed techniques, however, require dedicated electronic cleansing software.

Our efforts have been focused on finding a technique that first reduces the need for colonic cleansing. Second, the technique was required to label residual fecal residue with barium, allowing visual differentiation from polyps without use of dedicated electronic cleansing software. It was anticipated that such a technique could improve specificity and patient compliance.

The purpose of our study was to compare reduced colonic cleansing with fecal tagging (FT) and colonic cleansing without FT with regard to patient acceptance, sensitivity, and specificity.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
 REFERENCES
 
Patient Groups
Patients who were ambulatory and scheduled to undergo conventional colonoscopy between December 1999 and October 2000 were invited to participate in the study. Patient age, sex, and referral reasons were recorded (Tables 1, 2). Referral reasons were colorectal cancer screening (due to personal history of polypectomy or colorectal cancer, family history of colorectal cancer, or age greater than 50 years [28]) or evaluation of symptoms (including stools with positive hemoccult test results, abdominal pain, or change in bowel habit). Pregnant patients and patients with known renal insufficiency or known heart disease were excluded. As a result, two patients were not admitted to the study. One of the patients had renal insufficiency at presentation; the other had known heart disease. The study was approved by the institutional review board.


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  		TABLE 1. Patient Demographic Data

 

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  		TABLE 2. Indications for Screening

 
A total of 100 consecutive patients were registered to take part in the study. After informed consent was obtained, 50 patients were assigned to receive a preparation with polyethylene glycol (PEG) (Colopeg; Roche, Gaillard, France) and bisacodyl (Dulcolax; Boehringer Ingelheim, Paris, France). This group is hereafter referred to as the "non-FT" group. The other 50 patients were assigned to undergo preparation with use of a dedicated kit consisting of magnesium citrate (Loso Prep; E-Z-Em, Westbury, NY), bisacodyl, and FT with barium solution (Nutra-Prep; E-Z-Em). This group is hereafter referred to as the "FT" group. Preparation consisted of a colonic cleansing regimen designed especially for CT colonography. It was used in a trial after acquisition of informed consent and was provided on a per-patient basis. Due to interrupted availability of this preparation kit, assignment of patients was neither structured nor strictly randomized. Patients were consecutively assigned to the FT group if the preparation kit was available. When it was not available, patients were assigned to the non-FT group. For both groups of patients, oral as well as written information was provided, with emphasis on the importance of screening for colorectal cancer, an explanation of why the colon had to be cleansed, further explanation of the colonic cleansing method, and encouragement.

Preparation
Non-FT group.—The first 50 patients underwent optimized, PEG-based, standard colonoscopic cleansing 1 day before the examination (29). This consisted of a combination of a low-residue diet and ingestion of a cleansing medication (described later in paragraph) 1 day before the examination. Breakfast consisted of 1–3 slices of white bread with black coffee or tea. Patients were advised to drink approximately 2 L additional water in the morning. For lunch, patients were allowed three slices of thin meat with two glasses of water or apple juice. At 1:00 PM, colonic cleansing was started by using two tablets of bisacodyl. Bisacodyl was added to reduce the amount of fluid ingested by the patient, since it is well known that this huge amount especially reduces patient compliance (29). Between 3:00 and 5:00 PM, PEG was ingested in a dosage of 59 g dissolved in 1 L of water per 30 kilograms of body weight at a rate of 1 L/h, with a maximum of 3 L.

The day of the examination, no breakfast was allowed, and CT colonography was performed at 8:30 AM.

FT group.—Two days before the procedure, patients were asked to avoid products containing too much fiber or pulp or producing fecal residue (flavored cheese, condiments, whole-grain bread, crackers, cereal, popcorn, raw fruit, mustard, jam, and garlic).

The day before the examination, patients received a single preparation kit containing food and beverages (eg, nutritional bowel cleansing), the cleansing medication (eg, physical bowel cleansing) and the barium solution (250 mL three times per day, at breakfast, lunch, and dinner). The nutritional bowel cleansing procedure incorporated a structured low-residue diet (vanilla drinks, fruit juice, soup, applesauce, potato nuggets, and nutrition bars) to control fat intake and decrease fecal residue. Physical bowel cleansing included 16.4 g of orally administered magnesium citrate solution (Loso Prep), four orally administered bisacodyl tablets, and a rectally administered bisacodyl suppository (Dulcolax). Magnesium citrate was preferred over PEG, since a much lower volume of fluid is required to cleanse the colon (30). FT was achieved with three doses of 250 mL of barium diluted at 2.1% weight/volume to be consumed at breakfast, lunch, and dinner 1 day before the procedure. The magnesium citrate solution and bisacodyl tablets were to be consumed at 6 PM 1 day before the procedure.

On the day of the examination, patients were asked to insert the bisacodyl suppository into their rectum at 7:00 AM. On the morning of the procedure, no breakfast was allowed. CT colonography was performed at 8:30 AM.

Examination Techniques
CT colonography.—Prior to CT colonography, smooth-muscle relaxation was obtained with 10 mL scopolaminebuthylbromide (Buscopan; Boehringer Ingelheim) diluted in 100 mL of 0.9% sodium chloride and administered intravenously at a rate of 10 mL/min. After this, a rectal tube was inserted, and the colon was inflated with room air to patient tolerance (30–50 bulb compressions). All patients underwent CT colonography (Tomoscan AV-EU; Philips, Best, the Netherlands) with single-section helical scanning. Colonic distention was assessed on the scout view. In the event of insufficient colonic distention, additional insufflation was performed. In the event of good colonic distention, the patient underwent scanning while supine with the tube still in the rectum. The patient was subsequently turned to the prone position. If necessary, additional inflation of the colon was performed. To avoid concealment of rectal polyps by the rectal tube, the tube was removed at this time.

All patients were examined by using a 5-mm section thickness, a 7-mm table feed (pitch, 1.4), and a 3-mm reconstruction index, with a 350-mm field of view and a 512 x 512 matrix. Scans were obtained at 100 mA and 120 kV. Before scanning, patients were asked to hyperventilate. With the patient supine, the entire colon was scanned in a single run. Scanning times were 50–60 seconds. If the patient became short of breath during scanning, he or she was asked to slowly exhale through the nose at the end of the examination. With the patient prone, the entire colon was scanned in two runs.

The obtained images were transferred to a workstation (Ultrasparc 30/60; Sun, Palo Alto, Calif) equipped with Endoview Easy Vision software (Philips). Transverse images were inspected first by using the zoomed technique (31). Subsequently, three-dimensional imaging was performed by using perspective volume rendering, with a depth cuing of 0% and a viewing angle of 90°. The colon was examined in both antegrade and retrograde directions by using 5-mm increments.

On the screen, reformatted two-dimensional images in two planes and three-dimensional images were displayed so that whenever necessary, two- and three-dimensional images could be compared.

Conventional colonoscopy.—Since the preparation used for CT colonography was reduced, as compared with the standard conventional colonoscopic preparation of at least 4 L PEG (as used by the endoscopists at our institution), patients underwent additional colonic cleansing with PEG prior to conventional colonoscopy. This cleansing was performed until stool became watery and completely clear. The time between CT colonography and conventional colonoscopy in the two groups was 2–3 hours.

All conventional colonoscopic examinations were performed by the same experienced staff endoscopist (J.D.), with patients under conscious sedation. First, the cecum was reached; second, the colonoscope was removed from cecum to rectum. The colon was evaluated for lesions in both antegrade and retrograde directions. The endoscopist was informed about the results of CT colonography before removing the colonoscope. This was done to assess eventual false-positive lesions detected at CT colonography and to avoid a false-negative diagnosis at conventional colonoscopy.

Polyp Detection
CT colonographic images were interpreted by two radiologists (P.A.L., S.S.G.). A diagnosis was made after consensus reading. All detected lesions were localized according to their segmental location in the colon (cecum with appendix; ascending, transverse, descending, or sigmoid colon; or rectum [32]).

From conventional colonoscopic images, the following data were collected for each lesion: location (by using the same segmental classification scheme as used for CT colonography) and size (measured by means of comparison with an open-biopsy forceps [18]). Conventional colonoscopic findings were considered the reference standard. Sensitivity for polyp detection was calculated on a per-lesion basis. Sensitivity and specificity together with positive and negative predictive values for polyp detection were also calculated on a per-patient basis. CT colonographic findings were reviewed for causes of false-positive and false-negative results.

Fecal Residue
Evaluation of residual stool was performed by two radiologists (P.A.L., S.S.G.) by means of consensus. To this end, the colon was divided into six segments by using the classification system used for polyp localization at conventional and CT colonography (eg, cecum with appendix; ascending, transverse, descending, and sigmoid colon; and rectum). In doing so, 300 segments per patient group were evaluated. Segmental evaluation of the amount of residual stool, regardless of its size, was performed by assigning a score of 0–5 (33) as follows: 5, residual stool absent; 4, residual stool present in one segment; 3, two segments; 2, three segments; 1, most segments; or 0, all segments.

To evaluate the effectiveness of tagging, fecal residue was considered as either labeled or not labeled. This was done on a visual percentage (0%, 25%, 50%, 75%, 100%) (27) basis for each segment and for three size categories per segment (0–5, 6–10, and >10 mm). Because visual identification of an even partially and/or non–homogeneously labeled lesion is considered proof of fecal residue and because electronic cleansing was not performed, the homogeneity and intensity of barium labeling were not taken into account.

Patient Compliance
To evaluate patient acceptance of the preparation, patients were interviewed the morning after ingesting the preparation material, immediately before CT colonography, by using a standardized evaluation form, which was gleaned from other studies (30,34–37). Patients were queried in terms of global discomfort, sleep and diet disturbance, and side effects (headache, nausea, vomiting, cramps, dizziness, or palpitations). Discomfort and sleep disturbance were rated as follows: 0, none; 1, mild; 2, moderate; or 3, severe. A visual analog scale was used (35). The group of patients who received the preparation kit was also asked whether they had positive memories of the diet (eg, the vanilla drinks, applesauce, fruit juice, soup, potato nuggets, and nutrition bars). To assess patient memory of the whole procedure, a questionnaire was sent to patients 2 weeks later. Patients were asked to assess their level of global discomfort and sleep disturbance, as well as their final opinion and whether they would be reluctant to repeat the examination if necessary. Final opinion was graded as follows: 1, examination was comfortable; 2, moderately comfortable; or 3, uncomfortable. The number of patients who returned the questionnaire (free of charge) was recorded.

Statistical Analysis
Global physical discomfort, sleep disturbance, and final opinion were compared by using the Mann-Whitney U test (30). The prevalence of side effects and willingness to repeat the examination were compared by using the Fisher exact test.

To evaluate within each group whether there was a significant change in perception of discomfort after 2 weeks, answers of patients who responded were compared by using the multilevel McNemar test. For all tests, a P value of .05 or less indicated a statistically significant difference.

To compare polyp detection between the non-FT and FT groups in an exploratory way, exact one-sided 95% CIs were calculated for the differences in diagnostic criteria (sensitivity, specificity, positive predictive value, and negative predictive value).


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
 REFERENCES
 
Patient Compliance
One hundred patients underwent assessment. There were no cancellations. Eighty-eight patients returned the evaluation form after 2 weeks, and 12 patients (seven from the non-FT group and five from the FT group) failed to do so. There were no significant differences in patient demographic data (Table 1). There was a slight predominance of patients with a personal or familial history of polypectomy or colonic carcinoma in the non-FT group (Table 2). This resulted in a slight preponderance of polyp richness in the non-FT group. This is explained by the fact that patients could not be strictly randomized due to the interrupted availability of the preparation kit.

Results of the interview performed prior to and 2 weeks after CT colonography are listed in Tables 3–5.


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  		TABLE 3. Interview Results

 

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  		TABLE 4. Evaluation of Diet: Was Food Tasty?

 

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  		TABLE 5. Side Effects

 
When interviewed the morning after the procedure, patients in the non-FT group reported a significantly higher level of sleep disturbance and global discomfort, although in both groups nearly all patients reported at least some sleep disturbance caused by bowel movements. Side effects were more common in the non-FT group. Nausea, vomiting, and cramps were significantly more prevalent in the non-FT group. In the FT group, most components of the kit were well appreciated.

Answers received from the FT group after 2 weeks showed significantly more positive opinions in terms of sleep and global discomfort. This resulted in an improved final opinion in this group. When inquired of their willingness to undergo repeat examination, patients in the FT group were less reluctant than those in the non-FT group, but the distinction was not statistically significant (P > .05).

Although in both groups there was no significant alteration in perception of global discomfort and sleep after 2 weeks versus immediately prior to CT colonography (P > .05 for all questions), there was a discrete tendency toward a negative opinion in the non-FT group after 2 weeks.

Polyp Detection
In all patients, both CT colonographic and conventional colonoscopic examinations were completed. Results on a per-lesion basis are listed in Table 6.


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  		TABLE 6. FT vs. Non-FT Group: Sensitivity and Diagnostic Performance on a Per-Lesion Basis

 
In the non-FT group, conventional colonoscopy enabled detection of 58 lesions, while CT colonography enabled detection of 45 lesions. This resulted in an overall sensitivity of 78%. With regard to lesions larger than 10 mm, there were neither false-negative nor false-positive results. Two 6–9-mm lesions were not detected; this resulted in a sensitivity of 89% (16 of 18 lesions). In one case, the lesion was missed because of severe diverticulosis. In the other case, the lesion was missed at the level of the cecum and was detected retrospectively at CT colonography.

Eleven lesions of 5 mm or smaller were not detected, resulting in a sensitivity of 56% (14 of 25 lesions). There were 18 false-positive results. Eight of these 18 lesions were 6–9 mm. Causes of false-positive diagnoses were fecal residue mimicking a polypoid lesion in four cases, severe diverticulosis in two cases, thickened haustral fold with an irregular margin in one case, and colonic spasm at the rectosigmoid junction in one case. The other 10 lesions were 5 mm or smaller; in one patient, the false-positive finding was related to a fruit pit adhered to the bowel wall. For the other nine false-positive lesions, no clear cause was identified; fecal residue was assumed to be the most likely reason.

In the FT group, 44 lesions were detected with conventional colonoscopy, while 34 lesions were detected with CT colonography. This resulted in an overall sensitivity of 77%. As in the non-FT group, sensitivity was 100% (10 of 10 lesions) for lesions larger than 10 mm (Fig 1). One 8-mm lesion was missed, resulting in a sensitivity of 92% (12 of 13 lesions) in the 6–9-mm range. This lesion was situated in the rectum and was detected retrospectively at CT colonography on two- and three-dimensional images (Fig 2). Nine lesions of 5 mm or smaller were missed (sensitivity, 57% [12 of 21 lesions]). Only four lesions were detected retrospectively. There were five false-positive lesions. One false-positive 6–9-mm lesion was caused by polypoid mucosal prolapse syndrome in a patient with severe diverticulosis. Four false-positive lesions were 5 mm or smaller. None of these false-positive lesions were detected at conventional colonoscopy; they were considered unlabeled fecal residue.



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  		Figure 1a. Images show a polyp larger than 10 mm, which resulted in a true-positive diagnosis. (a) Transverse two-dimensional CT colonographic image obtained with the patient supine shows a polypoid lesion (arrow) near the ileocecal valve (arrowhead). This lesion is not tagged (eg, does not contain barium) and is thus considered a polyp. L = left, P = posterior. (b) Three-dimensional CT colonographic image obtained with the patient supine shows the same lesion as in a, a lobulated elongated polyp (arrow). (c) Conventional colonoscopic image shows the polyp (arrowheads) with the same appearance as in b.

 


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  		Figure 1b. Images show a polyp larger than 10 mm, which resulted in a true-positive diagnosis. (a) Transverse two-dimensional CT colonographic image obtained with the patient supine shows a polypoid lesion (arrow) near the ileocecal valve (arrowhead). This lesion is not tagged (eg, does not contain barium) and is thus considered a polyp. L = left, P = posterior. (b) Three-dimensional CT colonographic image obtained with the patient supine shows the same lesion as in a, a lobulated elongated polyp (arrow). (c) Conventional colonoscopic image shows the polyp (arrowheads) with the same appearance as in b.

 


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  		Figure 1c. Images show a polyp larger than 10 mm, which resulted in a true-positive diagnosis. (a) Transverse two-dimensional CT colonographic image obtained with the patient supine shows a polypoid lesion (arrow) near the ileocecal valve (arrowhead). This lesion is not tagged (eg, does not contain barium) and is thus considered a polyp. L = left, P = posterior. (b) Three-dimensional CT colonographic image obtained with the patient supine shows the same lesion as in a, a lobulated elongated polyp (arrow). (c) Conventional colonoscopic image shows the polyp (arrowheads) with the same appearance as in b.

 


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  		Figure 2a. An 8-mm polyp, which resulted in false-negative diagnosis at CT colonography, is shown. (a) Transverse two-dimensional CT colonographic image obtained with the patient prone shows the polypoid lesion (arrow) in the rectum. This lesion is not tagged (eg, does not contain barium) and is thus considered a polyp. (b) Three-dimensional CT colonographic image obtained with the patient prone shows the same lesion as in a, a small polyp (arrow). A = anterior, H = head, L = left, P = posterior, R = right. (c) Conventional colonoscopic image shows the same polyp appearance (arrow). This lesion was missed at CT colonography but was detected retrospectively.

 


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  		Figure 2b. An 8-mm polyp, which resulted in false-negative diagnosis at CT colonography, is shown. (a) Transverse two-dimensional CT colonographic image obtained with the patient prone shows the polypoid lesion (arrow) in the rectum. This lesion is not tagged (eg, does not contain barium) and is thus considered a polyp. (b) Three-dimensional CT colonographic image obtained with the patient prone shows the same lesion as in a, a small polyp (arrow). A = anterior, H = head, L = left, P = posterior, R = right. (c) Conventional colonoscopic image shows the same polyp appearance (arrow). This lesion was missed at CT colonography but was detected retrospectively.

 


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  		Figure 2c. An 8-mm polyp, which resulted in false-negative diagnosis at CT colonography, is shown. (a) Transverse two-dimensional CT colonographic image obtained with the patient prone shows the polypoid lesion (arrow) in the rectum. This lesion is not tagged (eg, does not contain barium) and is thus considered a polyp. (b) Three-dimensional CT colonographic image obtained with the patient prone shows the same lesion as in a, a small polyp (arrow). A = anterior, H = head, L = left, P = posterior, R = right. (c) Conventional colonoscopic image shows the same polyp appearance (arrow). This lesion was missed at CT colonography but was detected retrospectively.

 
Comparison between obtained sensitivity ratios in the FT and non-FT group showed that observed differences were minimal and not statistically significant (Table 6).

Results on a per-patient basis are listed in Table 7. In the non-FT group, the overall sensitivity and specificity and positive and negative predictive values were 85% (17 of 20 patients), 77% (23 of 30 patients), 71% (17 of 24 patients), and 88% (23 of 26 patients), respectively. All patients with a lesion larger than 10 mm were correctly identified. For 6–9-mm tumors, sensitivity, specificity, and positive and negative predictive values were 91% (10 of 11 patients), 87% (34 of 39 patients) 67% (10 of 15 patients), and 97% (34 of 35 patients), respectively. With regard to lesions 5 mm or smaller, sensitivity and specificity were 55% (six of 11 patients) and 79% (31 of 39 patients), respectively, with a positive predictive value of 43% (six of 14 patients) and a negative predictive value of 86% (31 of 36 patients).


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  		TABLE 7. FT vs. Non-FT Group: Polyp Detection with CT Colonography on a Per-Patient Basis

 
In the FT group, overall sensitivity and specificity were both 88% (14 of 16 and 30 of 34 patients, respectively), with positive and negative predictive values of 78% (14 of 18 patients) and 94% (30 of 31 patients), respectively. All lesions larger than 10 mm were correctly identified. In 6–9-mm lesions, sensitivity and specificity were 92% (11 of 12 patients) and 97% (37 of 38 patients), respectively; positive and negative predictive values were 92% (11 of 12 patients) and 97% (37 of 38 patients), respectively. For lesions 5 mm or smaller, sensitivity and specificity were 56% (nine of 16 patients) and 88% (30 of 34 patients), respectively. Positive and negative predictive values were 69% (nine of 13 patients) and 81% (30 of 37 patients), respectively.

Comparison of the obtained sensitivity and negative predictive values in the FT and non-FT groups showed that the observed differences were minimal and not statistically significant. Comparison of specificities and positive predictive values between groups showed a strong tendency toward improvement in the FT group. However, as was expected with such a small number of patients, the difference was not statistically significant.

Cleanliness and Tagging
Assessments of colonic cleanliness are listed in Table 8. In the non-FT group, there were 24 segments with fecal residue (Fig 3). In the FT group, fecal residue was noted in 96 segments. Thus, the non-FT group had the cleanest colons, with 43 patients obtaining a score of 4 or 5 versus 22 patients in the FT group.


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  		TABLE 8. Evaluation of Fecal Residue

 


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  		Figure 3. Reduced cleanliness: larger and smaller tagged fecal residues. Zoomed transverse two-dimensional CT colonographic image obtained with the patient supine shows multiple small and one large (arrow) nodular lesion. The lesions are tagged, which is indicative of fecal residue.

 
In all but one patient, all lesions larger than 10 mm were labeled. In that patient, a 13-mm untagged fecal residue was detected in the sigmoid colon. This lesion was easily identified as fecal residue, since air was included in the lesion. All 6–9-mm lesions were labeled. The results for the smallest (<=5 mm) fecal residues are listed in Table 8. The average labeling score varied between 89% for the ascending colon and 75% for the sigmoid colon. There was no fecal residue left in the rectum, which is explained by application of the bisacodyl suppository.


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES
 
Compliance, sensitivity, and specificity are major factors to consider in the evaluation of a screening strategy, with compliance being paramount (10,38).

Brenes and Paskett (39) showed that barriers to screening and physician recommendation were the only significant multivariate predictors of compliance with screening guidelines. The barriers mentioned included the following: "The examination is uncomfortable and can hurt," "It is embarrassing," and "It takes too much time and too much effort to use the enemas."

Thus, the challenge in CT colonography is to reduce the perception of pain related to the examination and the perception of a taxing preparation. It has already been shown that potential patients prefer CT colonography over conventional colonoscopy because of its noninvasive nature (40). The postprocedural perception of pain has also been reported as reduced for CT colonography, as compared with that for conventional colonoscopy (41).

The perception of a taxing preparation can be related to nutritional (eg, diet) and physical (eg, cathartics) cleansing. In the current study, we evaluated whether nutritional as well as physical cleansing could be optimized by using dietary FT.

With respect to diet, we found that a majority of the patients liked the different components of the kit. With respect to physical cleansing, we found significantly reduced discomfort in the FT group. A major factor that explains this finding is the replacement of PEG by magnesium citrate. Magnesium citrate offers several advantages over PEG: fewer side effects, reduced disruption of daily patient activity, reduced volume, and no salty taste (30,33,36,42–45). The taste and considerable volume were reported to especially reduce compliance in patients receiving PEG (36,45). The cathartic volume to be ingested was further reduced by adding bisacodyl. Use of bisacodyl to reduce the amount of fluid to be ingested has previously been reported by Adams et al (29). For the same reason, bisacodyl had already been added in the patients receiving PEG.

Our technique thus reduced discomfort by reducing colonic cleansing and eliminated the need for electronic cleansing. Other authors (25–27,46), however, have used electronic colonic cleansing to reduce or even replace colonic cleansing. It is anticipated that electronic cleansing of the unprepared colon will further increase patient compliance. However, to our knowledge, no comparative studies were available at the time this article was written.

Reduced discomfort resulted in an improved final opinion in the FT group. Willingness to repeat the examination also improved, but this was not a significant finding. This finding is explained by postprocedural perception of benefit (eg, to not worry anymore), which was the same for both the FT and the non-FT group. This has also been reported by Brenes and Paskett (39).

Other issues reported to improve patient compliance are short duration of therapy, availability of written information, and single-blister packaging of the medication (47). In the current study, therapy was brief for both groups, and patients were provided with extensive oral and written information. In the FT group, the preparation kit was provided in a single package, which therefore might also have contributed to better patient compliance, according to Murphy and Coster (47).

In addition to compliance, a screening examination must also be of acceptable sensitivity and specificity for clinically important lesions (48). In recent publications (18,20,49), CT colonography has been advocated as potentially meeting these requirements. The preparation without tagging was slightly modified in that colonic cleansing was performed with PEG 1 day before the examination to reduce the amount of residual fluid. Residual fluid may result in drowned colonic segments in both supine and prone positions, hampering lesion diagnosis (50). In the non-FT group, there were no drowned segments. We presume this to be the result of cleansing 1 day before CT colonography. It is possible that this also explains our encouraging results in this group. In fact, all lesions larger than 10 mm were detected, and in the 6–9-mm group, 16 (89% success rate) of 18 lesions were detected. This was comparable with findings in the FT group, in which all lesions larger than 10 mm and 12 of 13 6–9-mm lesions were detected.

There was, however, a contrast with the false-positive findings. Although magnesium citrate is known to leave more fecal residue (42), resulting in a less-clean colon (as was also found in our study), FT reduces the number of false-positive results. In fact, in the non-FT group, 13 lesions were falsely diagnosed because of fecal residues, with four lesions in the 6–9-mm range. In the FT group, the number of false-positive results due to fecal residue was reduced to four, with no false-positive findings resulting from fecal residue larger than 6 mm. This resulted in improvement of overall specificity from 77% to 88%. As such, although more fecal residue was found in the FT group, tagging facilitated differentiation from polyps. In addition to the previously mentioned increase in patient compliance, this brings us to a possible second advantage of stool tagging: increase in specificity in lesion detection. In the current study, no additional and superfluous conventional colonoscopy would have been necessary for false-positive lesions larger than 6 mm, which has been proposed by Rex (48) as the cutoff size for polyp detection. This is explained by the good labeling (eg, tagging) of fecal residue larger than 6 mm. In fact, labeling was successful in all but one lesion larger than 6 mm. For the largest (>10-mm) lesions, FT was inhomogeneous (Fig 4) but clearly detectable. Therefore, no confusion with polypoid lesions occurred.



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  		Figure 4a. Transverse two-dimensional CT colonographic images obtained with the patient supine at the levels of the (a) sigmoid, (b) descending, (c) transverse, and (d) ascending colon show FT (arrow in a and b; arrow and arrowhead in c; arrow in d) as homogeneous in the sigmoid and descending colon and inhomogeneous in the transverse and ascending colon.

 


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  		Figure 4b. Transverse two-dimensional CT colonographic images obtained with the patient supine at the levels of the (a) sigmoid, (b) descending, (c) transverse, and (d) ascending colon show FT (arrow in a and b; arrow and arrowhead in c; arrow in d) as homogeneous in the sigmoid and descending colon and inhomogeneous in the transverse and ascending colon.

 


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  		Figure 4c. Transverse two-dimensional CT colonographic images obtained with the patient supine at the levels of the (a) sigmoid, (b) descending, (c) transverse, and (d) ascending colon show FT (arrow in a and b; arrow and arrowhead in c; arrow in d) as homogeneous in the sigmoid and descending colon and inhomogeneous in the transverse and ascending colon.

 


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  		Figure 4d. Transverse two-dimensional CT colonographic images obtained with the patient supine at the levels of the (a) sigmoid, (b) descending, (c) transverse, and (d) ascending colon show FT (arrow in a and b; arrow and arrowhead in c; arrow in d) as homogeneous in the sigmoid and descending colon and inhomogeneous in the transverse and ascending colon.

 
The importance of fecal residue causing false-positive findings has already been addressed by Macari and Megibow (24). In two of the series (18,20) published thus far, Fenlon et al (18) obtained a specificity of 94% for lesions larger than 10 mm and 92% for lesions of 6–9 mm, whereas Yee et al (20) achieved a specificity of 72% for polyps and 57% for adenomas. Both Fenlon et al and Yee et al explained that fecal residues are the major cause of false-positive diagnoses as follows: Fenlon et al (18) reported 19 false-positive polyp diagnoses (including eight 6–9-mm lesions and two >10-mm lesions), with nine located in segments of colon containing residual solid stool; Yee et al (20) found 185 false-positive polyps in 113 patients, with 77% (including 21 lesions larger than 10 mm) in poorly prepared segments. In an earlier article, Fenlon et al (51) also reported two false-positive findings of polyps (6 and 8 mm) caused by fecal residue. Tagging of fecal residue offers the possibility of at least reducing those causes, as found in the current study. A possible drawback of tagging is attachment of barium to a polypoid lesion, causing a false sense of residual stool. This was, however, not the case in the present study. A possible explanation for this is physical cleansing with bisacodyl and magnesium citrate. Labeling is, however, incomplete for the smallest fecal residue (<=5 mm), which still results in false-positive findings. Lesions 5 mm or smaller are, however, not considered clinically important (48) and would therefore not prompt unnecessary conventional colonoscopy.

There were several limitations of this study. Both patient groups were small. This decreased the possibility of detecting statistically significant differences in diagnostic performance. Although our results are encouraging, especially for specificity in the FT group, studies of larger patient populations are needed. The patients were not strictly randomized because of interrupted availability of the preparation kit. Comparing preparations is difficult because combinations of preparation and examination are frequently compared. We tried to avoid this by interviewing patients twice, prior to CT colonography and 2 weeks later. We did not find significant changes in reported discomfort, which suggests that the preparation, not the examination, causes the most discomfort. This finding has also been reported by Debatin et al (52). However, the controversy about possible placebo effects points out the difficulty of addressing subjective symptoms (53). Therefore, assessment of reported discomfort should be addressed with care, and more extensive comparative studies are needed. Moreover, comparing lesion detection with CT colonography and conventional colonoscopy is difficult, since it is well recognized that conventional colonoscopy is less accurate than CT in predicting the relative intraluminal location of polyps.

Dietary FT with use of the preparation kit was compared with preparation with PEG and bisacodyl. We did not compare the preparation kit with oral sodium phosphate, which is reported to reduce discomfort, and preparation with PEG (44,50). The reason for not using oral sodium phosphate in our department rests with a concern about possible adverse biochemical effects in an outpatient population, as discussed by Toledo and Di Palma (54) in a recent review article. Instead, as previously reported by Adams et al (29), we reduced the possible discomfort caused by PEG by reducing the volume, with addition of bisacodyl as a cathartic. To reduce increased fluid levels known to be associated with the use of PEG, preparation in the non-FT group had to be started at 1:00 PM. Since fluid levels, as well as patient discomfort, are known to be optimized with use of sodium phosphate, a comparative study would be of interest.

In conclusion, dietary FT appears feasible, allowing reduced colonic cleansing, which results in improved patient compliance, and improving specificity by reducing false-positive results caused by fecal residue.


   ACKNOWLEDGMENTS
 
We thank Steffen Fieuws, MS, from the Biostatistical Centre, Leuven, Belgium, for help with statistical analysis.


   FOOTNOTES
 
Abbreviations: FT = fecal tagging, PEG = polyethylene glycol

Author contributions: Guarantors of integrity of entire study, all authors; study concepts and design, all authors; literature research, all authors; clinical studies, P.A.L., S.S.G., J.D.; data acquisition, P.A.L., S.S.G.; data analysis/interpretation, all authors; statistical analysis, P.A.L., S.S.G.; manuscript preparation and definition of intellectual content, all authors; manuscript editing, P.A.L., S.S.G.; manuscript revision/review and final version approval, all authors.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
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