Detection of colorectal polyps: comparison of multi-detector row CT and MR colonography in a colon phantom.
OBJECTIVE
To compare multi-detector row (four- and 16-section) computed tomography (CT), including a low-dose protocol, with high-field-strength (1.5- and 3.0-T) magnetic resonance (MR) imaging for reader detection of colorectal polyps in a colon phantom.


METHODS
A colon phantom with simulated haustral folds and 10 polyps of varying size (2.0-8.0 mm) was imaged at four- and 16-section CT (section thicknesses of 1.25 and 0.75 mm, reconstruction increments of 0.8 and 0.7 mm, and 100 and 10 mAs, respectively, and 120 kV for both) and at 1.5- and 3.0-T MR imaging (three-dimensional gradient-recalled echo sequence, section thickness of 1.4 mm). Three-dimensional endoluminal images were assessed by 10 reviewers for each modality regarding polyp detection. Comparisons of sensitivities were performed by using logistic regression.


RESULTS
Overall, polyps were detected with a sensitivity of 87% (95% confidence interval [CI]: 80%, 94%) at four-section CT, 92% (95% CI: 87%, 97%) at 16-section CT, 56% (95% CI: 46%, 66%) at 1.5-T MR imaging, and 55% (95% CI: 45%, 65%) at 3.0-T MR imaging. The detection of polyps at least 4 mm in diameter was not influenced by the modality or radiation dose (sensitivity of 100%). CT performed in low-dose mode depicted all polyps with a diameter of at least 3 mm. Polyps smaller than 3 mm in diameter were detected with a sensitivity of 7.5% (1.5-T MR imaging), 22.5% (3.0-T MR imaging), and 20% (low-dose CT); detection rates were significantly greater (P < .001) with normal-dose CT (four section, 67.5%; 16 section, 82.5%). Increased spatial resolution (with CT) and higher field strength (with MR imaging) had no significant effect on polyp detection.


CONCLUSIONS
With both multi-detector row CT and MR imaging, readers detected polyps above the clinically relevant threshold diameter of 6 mm, with similar sensitivities.
Wessling
Johannes
J
Department of Clinical Radiology and Medical Informatics and Biomathematics, University of Muenster, Albert-Schweitzer-Str 33, 48149 Muenster, Germany. weslingj@uni-muenster.de
Fischbach
Roman
R
Borchert
Alexandra
A
Kugel
Harald
H
Allkemper
Thomas
T
Osada
Nani
N
Heindel
Walter
W
D003111:Colonic Polyps / Q000175:diagnosis* / Q000000981:diagnostic imaging; D015179:Colorectal Neoplasms / Q000175:diagnosis* / Q000000981:diagnostic imaging; D019047:Phantoms, Imaging; D014057:Tomography, X-Ray Computed / Q000379:methods*