MR Colonography With Fecal Tagging

Rationale and Objectives

Both magnetic resonance (MR) and computed tomographic (CT) colonography are useful for colon examination. With sensitivities close to those for conventional colonoscopy (CC) for polyps, colonography has been proposed as an alternative to diagnostic CC. MR colonography (MRC) with fecal tagging may be a method of gaining further patient acceptance and widespread use, but the method has to be optimized. The aim of our study was to evaluate the quality of a new contrast agent mixture and to validate a new method for evaluating the tagging efficiency of contrast agents.

Materials and Methods

Twenty patients referred to CC underwent dark lumen MRC prior to the colonoscopy. Two groups of patients received two different oral contrast agents (barium sulfate and barium sulfate/ferumoxsil) as a laxative-free fecal tagging prior to the MRC. After MRC, the contrast agent was rated qualitatively (with the standard method using contrast-to-wall ratio) and subjectively (using a visual analog scale [VAS]) by three different blinded observers.

Results

Evaluated both qualitatively and subjectively, the tagging efficiency of barium sulfate/ferumoxsil was significantly better ( P < .05) than barium sulfate alone. The VAS method for evaluating the tagging efficiency of contrast agents showed a high correlation (observer II, r = 0.91) to the standard method using contrast-to-wall ratio and also a high interclass correlation (observer II and III = 0.89/0.85). MRC found 1 of 22 (5%) polyps <6 mm, 2 of 3 (67%) polyps 6−10 mm, and 2 of 2 (100%) polyps >10 mm.

Conclusion

MRC with fecal tagging using barium sulfate/ferumoxsil as contrast agent will give better overall assessment of the colon wall compared to barium sulfate alone. Furthermore, the VAS method of evaluating fecal tagging efficiency correlated with the standard method of calculating the contrast-to-wall ratio.

Ever since the development of magnetic resonance (MR) and computed tomographic (CT) colonography, the techniques have been labeled as promising new methods for examining the colon. It has been argued that with the high sensitivities of both CT and MR colonography, the techniques now stand as realistic alternatives or supplements to conventional colonoscopy (CC), which so far has remained the gold standard for colon examination. Considering the drawbacks of colonoscopies (colonic cleansing, pain, need for sedation, complication rates, mortality, etc.) and especially considering that studies have shown a potential decrease in mortality from colorectal cancer between 15% and 33% with screening of an asymptomatic population ( ), many have followed the development of MR and CT colonography with high expectations.

So far, several studies have been published describing MR colonography (MRC) with fecal tagging ( ), and some have suggested that that colonography with little or no colonic cleansing would improve patient acceptance, the rationale being that colonic cleansing for a majority of patients subjected to colonic examination is rated as one of the most uncomfortable parts of the procedure ( ).

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Materials and methods

Study Group

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Patient Preparation

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MR Imaging

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Data Analysis

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Contrast=(Istool−Iwall)/(Istool+Iwall), Contrast

stool

−

wall

)

(

stool

wall

)

where I stool and I wall are correspondingly mean intensities of region of interest (ROI) placed in the stool and in the wall, respectively. Signal intensity was measured using a circular ROI of 100 mm 2 in the stool and using free-hand ROI of 50 mm 2 in the colonic wall. The circular ROI was placed by the evaluators in the stool that was judged to be representative for the whole segment. The free-hand ROI was placed in the proximity of the circular ROI. For polyps and tumors and location/size of lesions, the six segments of the colon were evaluated by consensus decision by V.B.L. and M.P.A.

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Conventional Colonoscopy

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Results

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Table 1

Subjective Evaluation of Tagging Efficiency and Diagnostic Confidence for All Observers

Tagging Efficiency VAS Diagnostic Confidence VAS Rectum Sigmoid Colon Descending Colon Transverse Colon Ascending Colon Cecum Rectum Sigmoid Colon Descending Colon Transverse Colon Ascending Colon Cecum Group A ⁎ 4.4 4.3 4.3 4.0 4.3 4.5 7.2 6.8 7.0 6.7 6.7 5.9 Group B † 8.0 8.0 8.0 7.7 7.2 7.1 8.2 8.6 8.6 7.9 7.5 6.9P -value ‡ <.001 <.0001 <.0001 <.0001 <.0001 <.001 <.003 <.0001 <.0001 <.006 <.27 <.076

Tagging efficiency and diagnostic confidence was evaluated using VAS, a continuous scale from 0 to 10 (0 = no tagging, 10 = optimal tagging).

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Table 2

Qualitative Evaluation of Tagging Efficiency for All Observers

Tagging Efficiency VAS Rectum Sigmoid Colon Descending Colon Transverse Colon Ascending Colon Cecum Group A ⁎ 0.19 0.17 0.18 0.23 0.21 0.29 Group B † 0.42 0.64 0.43 0.54 0.45 0.42P -value ‡ <.002 <.0001 <.0001 <.0001 <.0002 .05

Tagging efficiency and diagnostic confidence was evaluated using VAS, a continuous scale from 0 to 10 (0 = no tagging, 10 = optimal tagging).

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Table 3

Interclass Correlation of Subjective and Qualitative Evaluation

Quantitative Evaluation ⁎ Qualitative Evaluation † ICC ‡ P -value § ICC ‡ P- value § Observer II vs. I 0.74 <.0001 0.83 <.0001 Observer II vs. III 0.85 <.0001 0.89 <.0001

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Discussion

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References

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MR Colonography With Fecal Tagging

Rationale and Objectives

Materials and Methods

Results

Conclusion

Materials and methods

Study Group

Patient Preparation

MR Imaging

Data Analysis

Conventional Colonoscopy

Results

Discussion

References

Further Reading

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Abstracts of Funded National Institutes of Health Grants

Assessing Diagnostic Confidence