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Detection of Colorectal Polyps: Comparison of Multi–Detector Row CT and MR Colonography in a Colon Phantom¹

¹ From the Departments of Clinical Radiology (J.W., R.F., A.B., H.K., T.A., W.H.) and Medical Informatics and Biomathematics (N.O.), University of Muenster, Albert-Schweitzer-Str 33, 48149 Muenster, Germany. Received February 20, 2005; revision requested April 19; revision received August 3; accepted September 1; final version accepted January 3, 2006. Address correspondence to J.W. (e-mail: weslingj{at}uni-muenster.de).

View larger version (115K): [in this window] [in a new window] [Download PPT slide]   Figure 1a: (a) Elastic plastic phantom placed in the center of a lard-filled acrylic cylinder. (b, c) The cross sections display the locations of the 10 sessile spherical polyps of varying sizes on or near the haustral fold, at the base of the fold, on the fold, and on the wall of the colon apart from the fold.

View larger version (97K): [in this window] [in a new window] [Download PPT slide]   Figure 1b: (a) Elastic plastic phantom placed in the center of a lard-filled acrylic cylinder. (b, c) The cross sections display the locations of the 10 sessile spherical polyps of varying sizes on or near the haustral fold, at the base of the fold, on the fold, and on the wall of the colon apart from the fold.

View larger version (98K): [in this window] [in a new window] [Download PPT slide]   Figure 1c: (a) Elastic plastic phantom placed in the center of a lard-filled acrylic cylinder. (b, c) The cross sections display the locations of the 10 sessile spherical polyps of varying sizes on or near the haustral fold, at the base of the fold, on the fold, and on the wall of the colon apart from the fold.

View larger version (122K): [in this window] [in a new window] [Download PPT slide]   Figure 2a: Endoluminal views of the colon phantom obtained with 16-section CT (left) and 3.0-T MR imaging (right) (three dimensional turbo-field-echo sequence, 3.0/1.44, 15° flip angle, acquired matrix of 192 x 123 x 60 over a field of view of 350 x 262.5 x 168 mm). Large polyps of 6 and 8 mm (in the background) are seen equally well with either 16-section CT or 3.0-T MR imaging. Smaller (2–4-mm) lesions (arrows) seen at CT tend to disappear or are almost not delineated with MR imaging.

View larger version (117K): [in this window] [in a new window] [Download PPT slide]   Figure 2b: Endoluminal views of the colon phantom obtained with 16-section CT (left) and 3.0-T MR imaging (right) (three dimensional turbo-field-echo sequence, 3.0/1.44, 15° flip angle, acquired matrix of 192 x 123 x 60 over a field of view of 350 x 262.5 x 168 mm). Large polyps of 6 and 8 mm (in the background) are seen equally well with either 16-section CT or 3.0-T MR imaging. Smaller (2–4-mm) lesions (arrows) seen at CT tend to disappear or are almost not delineated with MR imaging.

View larger version (21K): [in this window] [in a new window] [Download PPT slide]   Figure 3: Graph of size-dependent polyp detection with CT and MR imaging. Detection of polyps 4 mm or larger was not influenced by modality or radiation dose. CT depicted all polyps as small as 3 mm, even with a low-dose mode. Detection of polyps smaller than 3 mm diminishes for all modalities. Whereas sensitivity was low for MR imaging (sensitivity of 7.5% at 1.5 T and 22.5% at 3.0 T) and low-dose CT (sensitivity of 20%), depiction rates were significantly higher for CT at normal dose (P < .001). Although there was a substantial difference between four- and 16-section CT in this size range, the difference was not statistically significant.

View larger version (33K): [in this window] [in a new window] [Download PPT slide]   Figure 4: Graph of size-dependent contour definition scores for CT and MR imaging. Good (score of 2) to excellent (score of 1) depiction of polyps 4 mm or larger was achieved independently of modality and radiation dose. Whereas depiction of 3-mm polyps was rated equally good for CT (mean score, 1.2) in a normal- and low-dose setting, quality of polyp delineation decreased substantially for both MR imaging modalities for polyps 3 mm or smaller. Delineation of polyps as small as 2 mm was not reliable with either MR imaging or low-dose CT.

View larger version (19K): [in this window] [in a new window] [Download PPT slide]   Figure 5: Graph shows number of false-positive (FP) and false-negative (FN) findings for CT and MR imaging; numbers are given as mean per reader. All false-positive and false-negative results affected polyps smaller than 6 mm. There was a substantial difference in false-positive results, with an average of 0.5 lesion per reader for four-section CT and 0.9 lesion per reader for 16-section CT. The number of false-positive results in a small size range tended to be irrelevant for low-dose CT and for MR imaging. Corresponding to the rate of detection, the number of overlooked lesions smaller than 6 mm was significantly higher for MR imaging compared with CT at normal and low dose (P < .001).