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Department of Radiology, Stedelijk Ziekenhuis, Bruggesteenweg 90, Roeselare B-8800, Belgium.
Received July 22, 2004;
accepted after revision September 28, 2004.
Address correspondence to P. Lefere.
Abstract
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MATERIALS AND METHODS. The study consists of a review of 200
patients examined in a clinical setting. Conventional colonoscopy and CT
colonography or follow-up were used as the gold standard. All patients
prepared for CT colonography the day before the examination with a dedicated
low-residue diet. Fecal tagging was performed with 50 mL of barium. The
residual feces and fluid were evaluated on a segmental basis. The residual
feces was divided in two categories (< 6 mm and 
6 mm). The amount of
fluid was assessed on the axial slices. The efficacy of tagging was evaluated
visually.
RESULTS. For the study, 1,200 segments were evaluated. Residual feces was present in 413 segments (34.41%), with feces less than 6 mm in 210 segments (17.5%) and feces 6 mm or greater in 203 segments (16.92%). There was residual fluid in 527 segments (43.91%). Nontagged feces 6 mm or greater was present in 49 segments (4.08%) and nontagged fluid in 178 segments (14.83%). All nontagged feces 6 mm or greater was easy to assess. All fluid redistributed with dual positioning. A total of 65 lesions 6 mm or greater were correctly diagnosed on primary CT colonography. In two patients, two lesions adjacent to each other were misinterpreted as being only one. Another 8-mm lesion was missed.
CONCLUSION. In the present study, CT colonography after fecal tagging with 50 mL of barium combined with a reduced cathartic cleansing was feasible.
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The purpose of the present study was to evaluate dietary fecal tagging before CT colonography using only a total of 50 mL of a 40% weight/volume (w/v) barium suspension administered with meals. This preparation was performed the day before CT colonography in combination with a reduced cathartic colon cleansing based on magnesium citrate and bisacodyl and a commercially available dedicated low-residue diet. To evaluate the feasibility of this method, we reviewed the data sets of 200 patients to assess the efficacy of fecal tagging.
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The indications for CT colonography were screening for colorectal cancer in patients older than 50 years; a history of previous polypectomy or colorectal cancer; a history of familial colorectal cancer or polypectomy before the age of 60; positive fecal occult blood test; frail and elderly patients; patients unable or unwilling to undergo conventional colonoscopy; and patients with incomplete conventional colonoscopy. Red anal blood loss and acute abdominal complaints were not considered indications for CT colonography. In cases of red anal blood loss, patients were immediately sent to conventional colonoscopy.
Preparation
The preparation started 2 days before CT colonography. The patients were
asked to avoid food rich in fiber or pulp: flavored cheese, condiments,
whole-grain bread, crackers, cereal, popcorn, raw fruit, mustard, raw fruit,
jam, and garlic. One day before CT colonography, patients received a
commercially available preparation kit providing food and beverages for
breakfast, lunch, and dinner the day before CT colonography (Nutraprep,
E-Z-EM). This kit contained powdered drinks with vanilla flavor, orange juice,
soups, nutrition bars, crackers, and apple sauce. Fecal tagging was performed
with a 40% w/v barium suspension (Tagitol V, E-Z-EM) not commercially
available at the time the examinations were performed. This barium suspension
had an apple flavor. The patients had to drink 25 mL of this suspension at
breakfast and 12.5 mL at lunch and dinner, respectively. Patients were asked
to ingest the barium in the first 15 min after their meal. At 6:00 pm,
cathartic cleansing of the colon was started with 16.5 g of magnesium citrate,
followed by the ingestion of four tablets of bisacodyl at 7:00 pm. Patients
were instructed to drink an additional glass of water at 8:00 and 9:00 pm. The
morning of the CT colonography examination, the patients had to insert a
bisacodyl suppository in the rectum at 7:00 am. CT colonography was performed
in the morning.
For patient compliance to be improved, patients received a folder to encourage them and to provide them with ample information about the preparation and the need to detect the adenomatous precursors of colorectal cancer.
CT Technique
One hundred fifteen patients were scanned with single-detector technique.
Single-detector helical CT (Tomoscan AV/EU, Philips) was performed with a 5-mm
slice thickness, 7-mm table feed (pitch of 1.4), and 2-mm slice reconstruction
index. Eighty-five patients were scanned with MDCT (HiSpeed, GE Healthcare)
using a 2.5-mm collimation, 120 kVp, 70 mA, a pitch of 1.35, and 0.6-sec
gantry rotation. According to Stuart et al.
[4], smooth-muscle relaxation
was achieved with IV administration of 20 mg of hioscin buthylscopolamine
(Buscopan, Boehringer Ingelheim). The colon was inflated with carbon dioxide
until patient tolerance using a mechanical inflator delivering a continuous
pressure varying between 20 and 35 mm Hg (Protoco2l, E-Z-EM). Colonic
distention was assessed on the scout view. The entire colon was scanned with
the patient in the supine and prone positions. If the patient was not able to
lie in the prone position, the patient was scanned in the left decubitus
position [5].
The obtained images were sent to a workstation equipped with endoluminal software (InnerviewGI, E-Z-EM). The colon was examined with primary 2D read with 3D problem-solving by two radiologists with experience in CT colonography. A final diagnosis was made after consensus interpretation.
Evaluation of the Colon
The colon was evaluated per patient and on a segmental basis. To do so, the
interpreting radiologists divided the colon in six segments: cecum, ascending
colon, transverse colon, descending colon, sigmoid colon, and rectum
[6]. The segments were examined
with the patient in the supine position and in the prone or left decubitus
position.
Fecal Residue
Residual feces.—The residual feces was divided in two groups
according to its size measured on the axial slices: less than 6 mm and 6 mm or
greater. If both sizes were present in one segment, the segment was considered
to have residual feces of 6 mm or greater. The feces was measured on a
magnified image using a caliper. The residual feces of 6 mm or greater was
also assessed on efficacy of tagging. This assessment was done on a visual
basis: tagged or nontagged. The rationale for making the distinction between
less than 6 mm and 6 mm or greater was that it is generally accepted that
polypoid lesions less than 6 mm can be ignored
[7]; therefore, nontagged feces
less than 6 mm did not cause any concern. Partially tagged residual feces was
considered as nontagged.
At the same time, the number of segments with only one nontagged fecal ball 6 mm or greater was evaluated. The feces was also evaluated on its morphologic aspects: moving after dual positioning, floating in a pool of barium, a hyperdense peripheral ring with a hypodense center, a hooked appearance, and a foamy appearance (i.e., nontagged material mainly consisting of air bubbles and minimal solid feces). One morphologic aspect did not exclude any other one.
Residual fluid.—The residual fluid was evaluated on axial slices according to its proportion to the maximal anteroposterior diameter of the segment of the colon where it was detected [8]. In this way, four groups were generated: 0%, less than 25%, 25-50%, and greater than 50%. In segments presenting with different fluid levels, only the largest fluid level was considered. The tagged appearance was assessed on a visual basis: tagged or nontagged. Segments with fluid of mixed density (e.g., barium settling down) were categorized as nontagged. Patients with nontagged fluid were also reviewed to detect fluid in the small bowel. In cases of nontagged fluid, the supine images were compared with the prone or left decubitus images to assess whether the entire colonic wall was visualized.
Polyp Detection
Patients with a suspicious lesion of 6 mm or greater were sent to
conventional colonoscopy. The lesion was measured and mapped according to its
segmental localization. Conventional colonoscopy was performed in the first 2
weeks after CT colonography. The endoscopists were not blinded to the results
of CT colonography. Each lesion detected on conventional colonoscopy was
carefully mapped and measured and was compared with an open biopsy forceps. At
each time, an anatomopathology examination was performed. In case of
incomplete colonoscopy, patients with a suspicious lesion 1 cm or more beyond
the reach of the colonoscope were reexamined with CT colonography within the
next 6 months. If the suspected lesion was confirmed, surgery was
performed.
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The preparation failed in two patients. These patients presented with an abnormal amount of fecal residue. These examinations were not excluded from the study. The fecal residue was easily recognizable in these patients because it had air inclusions. The cause of failure of the preparation was noncompliance of these patients with both the low-residue diet and the cathartic cleansing. In one patient with a stenosing adenocarcinoma in the sigmoid, there was more fecal residue when compared with the average patient; however, this did not hamper evaluation of the colon.
Fecal Residue
Residual feces.—The results concerning the residual feces
are listed in Table 1. There
were 787 segments (65.58%) without feces and 413 segments (34.41%) presenting
with feces. Most feces was located in the cecoascending colon: 183 segments
representing 15.25% of the total number of segments or 44.3% of the segments
with feces. There were 203 segments with feces 6 mm or greater (16.92% of the
total number of segments) (Fig.
1). Nontagged feces 6 mm or greater was detected in 49 segments
(4.08%) with nontagged feces in the rectum of 19 patients (38.77% of segments
with Nontagged feces). In 34 segments (69.38% of the segments with nontagged
feces), there was only one nontagged fecal ball (Figs.
2A, and
2B).
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The nontagged feces moved to the nondependent part of the colon after the patient moved into the supine and prone position, respectively, in all segments making it easily recognizable. It was floating in a pool of barium in 21 segments. In 10 segments, the nontagged feces presented as a single nodule with a hyperdense peripheral ring and a hypodense center (Figs. 3A, and 3B). The nontagged feces presented with a hooked appearance in 12 segments and with an air inclusion in 15 segments. A foamy appearance was detected near the ileocecal valve in five patients.
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The nontagged fluid covered less than 25% of the colonic lumen of the axial slices in 79.5% of the segments with nontagged fluid (144 segments) representing 84 patients (73.7% of patients with nontagged fluid) (Fig. 5). Nontagged fluid covering greater than 50% of the colonic lumen on the axial slices was detected in five segments (0.42%). In all of these segments, the fluid redistributed with dual positioning. Nontagged fluid was exclusively present in the rectosigmoid region of 38 patients. Of the other 76 patients with Nontagged fluid, 49 (64.5%) presented with a combination of nontagged fluid in the right hemicolon (cecum, ascending colon, and transverse colon) and nontagged fluid in the small bowel. Of the 86 patients with tagged fluid in the colon, 25 (29.06% of patients with tagged fluid) presented with nontagged fluid in the small bowel.
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Lesion Detection
In the group of patients undergoing primary CT colonography, a total of 71
lesions 6 mm or greater were suspected, which resulted in 42 patients being
sent to conventional colonoscopy. CT colonography correctly diagnosed 65
lesions (Figs. 6A, and
6B) and produced six
false-positive findings in five patients. The false-positives were caused in
four patients because of diverticulosis with severe luminal narrowing and
thickening of the folds. In these cases, a differential diagnosis that
included carcinoma was made. In one case, an additional polypoid lesion of 9
mm was detected only when the patient was in the prone position. This lesion
was detected at conventional colonoscopy. Biopsy revealed edematous and
hemorrhagic mucosa consistent with a polyp simulating mucosal prolapse
syndrome. A thickened fold at the level of the splenic flexure caused a
false-positive in another patient.
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In the group of patients referred after incomplete conventional colonoscopy, two patients, referred because of redundancy, presented with a lesion: a suspicious flat lesion 1 cm or larger in the cecum and a saddle-shaped lesion with malignant characteristics in the transverse colon, respectively. Both patients underwent repeat CT colonography after 3 months. At each examination, the lesion was confirmed. Both patients underwent surgery, and the lesions were in fact reconfirmed. The first lesion was an adenoma, and the second was an adenocarcinoma. Four patients were referred because of an obstructive tumor. CT colonography confirmed these lesions and showed three true-positives—one that was 6 mm or larger and two that were 1 cm or larger, with one malignant-appearing lesion—proximal to the obstructive tumor in one patient. These lesions were confirmed in the postoperative period. There were two adenomatous polyps and one adenocarcinoma.
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In a previous study, effective labeling of fecal residue was achieved the day before CT colonography by administering 750 mL of a 2.1% w/v barium suspension as the sole tagging agent. This corresponded to a total barium intake of 15.75 g. In this way, CT colonography accurately detected tumoral lesions [2]. In an effort to reduce the volume of contrast material and of barium in particular, the concentration of the barium suspension was increased to 40% w/v. This enabled a reduction of the total volume of the barium suspension to be ingested from 750 to 50 mL and still resulted in a total barium load of 20 g.
Although the volume to label fecal residue was clearly diminished, effective tagging of residual feces was obtained in all patients. Only 4.08% of segments presented with Nontagged feces 6 mm or greater. Furthermore, the nontagged feces 6 mm or greater was restricted to one fecal ball in 69.38% of the segments with nontagged feces. The nontagged feces was easily recognizable because it moved with dual positioning, was floating in a pool of barium, or presented with the typical characteristics of feces: an air inclusion, a hyperdense peripheral ring with a hypodense center, or a hooked appearance. Because some of the nontagged fecal balls were floating in barium pools, it remains questionable whether this feces could ever be tagged.
No particular effort was made to perform fluid tagging. This could be a matter of debate because 14.83% of the segments presented with nontagged fluid. However, the Nontagged fluid was mostly negligible: In 73.7% of the patients with fluid, it covered less than 25% of the colonic lumen in the segments where it was detected. In only 0.42% of the segments, the nontagged fluid covered more than 50% of the colonic lumen. In these cases, this fluid was redistributed with dual positioning, thus enabling visualization of the entire colonic wall.
The good results of tagging are reflected in the results of polyp detection. In fact, there were no false-positive findings caused by Nontagged feces. Three false-negatives of a total of 68 lesions 6 mm or greater were reported. Only one lesion of 6 mm or greater was overlooked, and it was detected retrospectively. The two other lesions were adjacent to another lesion and were hence misinterpreted as being a bilobulate rather as being two separate lesions. Furthermore, in this clinical setting with a wide mix of patients this method of tagging seemed to be robust. There were eight patients with a stenosing adenocarcinoma, representing a possible burden for colonic preparation or tagging. However, only one of these patients presented with more fecal residue when compared with the average. The preparation failed in only two patients. Both patients admitted they were not compliant with the instructions of the preparation. These cases underscore the importance of providing detailed instructions to the patients.
These good results offer the opportunity to use only barium as the tagging agent and hence to use the strict minimum of contrast material to obtain efficient tagging. Moreover, barium has the advantage of being a cheap medium and it produces few side effects. Another advantage is that the use of only one contrast agent simplifies the preparation for the patient. Of course the nontagged residue can be considered a disadvantage. In fact, this approach of tagging necessitated a primary 2D read with 3D problem. This allowed some fecal residue not being tagged. In case a primary 3D read is preferred, improvement to almost optimal dietary fecal tagging will be required to perform fecal subtraction [1]. A valuable alternative is offered by the use of translucency rendering. With this software technique, information is provided concerning the attenuation of a lesion detected on the 3D images. This enables differential diagnosis between a true lesion and tagged fecal residue [10].
What could be the causes of the suboptimal fecal tagging? First of all, the use of the bisacodyl suppository has to be questioned. In fact, it is striking that 38.77% of the Nontagged feces 6 mm or greater was located in the rectum. Because the bisacodyl suppository was inserted into the rectum only shortly before CT colonography and this is Nontagged material, the bisacodyl suppository could be the cause of the large amount of Nontagged fecal residue in the rectum. Thus, elimination of the suppository could improve the efficacy of tagging. Furthermore, if this would prove efficient, patient compliance would probably also improve.
Another reason of imperfect fecal tagging might be caused by the fact that patients were drinking too much regular fluid the day before CT colonography or even the morning before CT colonography. In 64.5% of patients with nontagged fluid, there was nontagged fluid in both the right hemicolon and the small bowel. This could be an indication that these patients had too much regular drinks the day before CT colonography, more especially after ingesting the cathartic agents. It could also be an indication that some patients were not compliant with the preparation instructions and had a drink the morning of CT colonography. It is also clear that the dietary fecal tagging could still be improved by adjusting the barium regimen.
Finally, nontagged residue could also be more frequent in patients with irritable bowel syndrome or constipation. This study is faced with the important limitation that, because not all cases were controlled by conventional colonoscopy, there is a probability that significant lesions could have been missed.
We can conclude that in the present study promising results with efficient tagging were obtained with only a total of 50 mL of a 40% w/v barium suspension and a reduced cathartic cleansing. Further research is needed to optimize fluid tagging to enable fecal subtraction and a primary 3D read.
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