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Crohn Disease: Mural Attenuation and Thickness at Contrast-enhanced CT Enterography—Correlation with Endoscopic and Histologic Findings of Inflammation¹

¹ From the Mayo Clinic College of Medicine, Rochester, Minn (K.D.B.), Department of Radiology (J.G.F., C.D.J., J.L.F., J.M.B., M.R.B., C.H.M.), Division of Gastroenterology, Department of Internal Medicine (C.A.S., W.J.S., E.V.L.), and Department of Health Sciences Research, Section of Biostatistics (W.S.H., B.S.C.), Mayo Clinic Rochester, 200 First Street SW, Rochester, MN 55905. Received July 9, 2004; revision requested September 14; revision received January 14, 2005; accepted February 16; final version accepted, March 16. Address correspondence to J.G.F. (e-mail: fletcher.joel{at}mayo.edu).

View larger version (139K): [in a new window]   Figure 1a: Small-bowel phantom simulating normally enhancing bowel that was used to validate automated attenuation measurements. (a) Transverse CT image shows 2-mm wafer of "solid liver" (white arrow) that simulates the attenuation of normally enhancing bowel. This wafer was placed between a polystyrene block with the attenuation of perienteric fat (black arrow) and surrounding water, which mimicked the attenuation of intraluminal fluid. (b) Enlarged transverse CT image shows how line tool (thick white bar) was placed perpendicularly across the solid liver wafer. The line tool acquired maximal attenuation measurements at 1-mm increments in the direction of the black arrow.

View larger version (139K): [in a new window]   Figure 1b: Small-bowel phantom simulating normally enhancing bowel that was used to validate automated attenuation measurements. (a) Transverse CT image shows 2-mm wafer of "solid liver" (white arrow) that simulates the attenuation of normally enhancing bowel. This wafer was placed between a polystyrene block with the attenuation of perienteric fat (black arrow) and surrounding water, which mimicked the attenuation of intraluminal fluid. (b) Enlarged transverse CT image shows how line tool (thick white bar) was placed perpendicularly across the solid liver wafer. The line tool acquired maximal attenuation measurements at 1-mm increments in the direction of the black arrow.

View larger version (112K): [in a new window]   Figure 2a: Semiautomated measurement of terminal ileal attenuation. (a) Transverse CT image of inflamed ileal loop shows that the gut lumen is transected parallel to the transverse cut plane. The green box indicates the portion of the image that is cropped to isolate the bowel segment to be analyzed. (b) Within the cropped image, the line tool (red line) was placed over the bowel wall to obtain measurements of mural attenuation and wall thickness every 1 mm along a 3.0-cm bowel segment (along the blue line, in the direction of the open arrow). (c) Graph corresponding to ileal measurements in b. The numbers on the y-axis are Hounsfield units; those on the x-axis represent distance in millimeters. The red curve plots CT attenuation versus distance, with values corresponding to the red line traversing the bowel wall in b. Graph shows maximum mural attenuation (arrow), the automated mural thickness measurement obtained by using a full width at half maximum technique (H-shaped measurement), and attenuation values corresponding to luminal fluid (large arrowhead) and perienteric fat (small arrowheads). (d) Transverse CT image demonstrates analysis of another ileal segment in which the gut lumen is transected perpendicular to the transverse cut plane, with the line tool (green and red line) placed in the center of the bowel lumen to obtain measurements of mural attenuation and wall thickness at 15° increments rotating around the central axis of the bowel. (e) Graph corresponding to ileum in d shows maximum mural attenuation (arrow), the automated mural thickness measurement obtained by using a full width at half maximum technique (H-shaped measurement), and attenuation values corresponding to luminal fluid (large arrowhead) and perienteric fat (small arrowheads).

View larger version (132K): [in a new window]   Figure 2b: Semiautomated measurement of terminal ileal attenuation. (a) Transverse CT image of inflamed ileal loop shows that the gut lumen is transected parallel to the transverse cut plane. The green box indicates the portion of the image that is cropped to isolate the bowel segment to be analyzed. (b) Within the cropped image, the line tool (red line) was placed over the bowel wall to obtain measurements of mural attenuation and wall thickness every 1 mm along a 3.0-cm bowel segment (along the blue line, in the direction of the open arrow). (c) Graph corresponding to ileal measurements in b. The numbers on the y-axis are Hounsfield units; those on the x-axis represent distance in millimeters. The red curve plots CT attenuation versus distance, with values corresponding to the red line traversing the bowel wall in b. Graph shows maximum mural attenuation (arrow), the automated mural thickness measurement obtained by using a full width at half maximum technique (H-shaped measurement), and attenuation values corresponding to luminal fluid (large arrowhead) and perienteric fat (small arrowheads). (d) Transverse CT image demonstrates analysis of another ileal segment in which the gut lumen is transected perpendicular to the transverse cut plane, with the line tool (green and red line) placed in the center of the bowel lumen to obtain measurements of mural attenuation and wall thickness at 15° increments rotating around the central axis of the bowel. (e) Graph corresponding to ileum in d shows maximum mural attenuation (arrow), the automated mural thickness measurement obtained by using a full width at half maximum technique (H-shaped measurement), and attenuation values corresponding to luminal fluid (large arrowhead) and perienteric fat (small arrowheads).

View larger version (19K): [in a new window]   Figure 2c: Semiautomated measurement of terminal ileal attenuation. (a) Transverse CT image of inflamed ileal loop shows that the gut lumen is transected parallel to the transverse cut plane. The green box indicates the portion of the image that is cropped to isolate the bowel segment to be analyzed. (b) Within the cropped image, the line tool (red line) was placed over the bowel wall to obtain measurements of mural attenuation and wall thickness every 1 mm along a 3.0-cm bowel segment (along the blue line, in the direction of the open arrow). (c) Graph corresponding to ileal measurements in b. The numbers on the y-axis are Hounsfield units; those on the x-axis represent distance in millimeters. The red curve plots CT attenuation versus distance, with values corresponding to the red line traversing the bowel wall in b. Graph shows maximum mural attenuation (arrow), the automated mural thickness measurement obtained by using a full width at half maximum technique (H-shaped measurement), and attenuation values corresponding to luminal fluid (large arrowhead) and perienteric fat (small arrowheads). (d) Transverse CT image demonstrates analysis of another ileal segment in which the gut lumen is transected perpendicular to the transverse cut plane, with the line tool (green and red line) placed in the center of the bowel lumen to obtain measurements of mural attenuation and wall thickness at 15° increments rotating around the central axis of the bowel. (e) Graph corresponding to ileum in d shows maximum mural attenuation (arrow), the automated mural thickness measurement obtained by using a full width at half maximum technique (H-shaped measurement), and attenuation values corresponding to luminal fluid (large arrowhead) and perienteric fat (small arrowheads).

View larger version (96K): [in a new window]   Figure 2d: Semiautomated measurement of terminal ileal attenuation. (a) Transverse CT image of inflamed ileal loop shows that the gut lumen is transected parallel to the transverse cut plane. The green box indicates the portion of the image that is cropped to isolate the bowel segment to be analyzed. (b) Within the cropped image, the line tool (red line) was placed over the bowel wall to obtain measurements of mural attenuation and wall thickness every 1 mm along a 3.0-cm bowel segment (along the blue line, in the direction of the open arrow). (c) Graph corresponding to ileal measurements in b. The numbers on the y-axis are Hounsfield units; those on the x-axis represent distance in millimeters. The red curve plots CT attenuation versus distance, with values corresponding to the red line traversing the bowel wall in b. Graph shows maximum mural attenuation (arrow), the automated mural thickness measurement obtained by using a full width at half maximum technique (H-shaped measurement), and attenuation values corresponding to luminal fluid (large arrowhead) and perienteric fat (small arrowheads). (d) Transverse CT image demonstrates analysis of another ileal segment in which the gut lumen is transected perpendicular to the transverse cut plane, with the line tool (green and red line) placed in the center of the bowel lumen to obtain measurements of mural attenuation and wall thickness at 15° increments rotating around the central axis of the bowel. (e) Graph corresponding to ileum in d shows maximum mural attenuation (arrow), the automated mural thickness measurement obtained by using a full width at half maximum technique (H-shaped measurement), and attenuation values corresponding to luminal fluid (large arrowhead) and perienteric fat (small arrowheads).

View larger version (19K): [in a new window]   Figure 2e: Semiautomated measurement of terminal ileal attenuation. (a) Transverse CT image of inflamed ileal loop shows that the gut lumen is transected parallel to the transverse cut plane. The green box indicates the portion of the image that is cropped to isolate the bowel segment to be analyzed. (b) Within the cropped image, the line tool (red line) was placed over the bowel wall to obtain measurements of mural attenuation and wall thickness every 1 mm along a 3.0-cm bowel segment (along the blue line, in the direction of the open arrow). (c) Graph corresponding to ileal measurements in b. The numbers on the y-axis are Hounsfield units; those on the x-axis represent distance in millimeters. The red curve plots CT attenuation versus distance, with values corresponding to the red line traversing the bowel wall in b. Graph shows maximum mural attenuation (arrow), the automated mural thickness measurement obtained by using a full width at half maximum technique (H-shaped measurement), and attenuation values corresponding to luminal fluid (large arrowhead) and perienteric fat (small arrowheads). (d) Transverse CT image demonstrates analysis of another ileal segment in which the gut lumen is transected perpendicular to the transverse cut plane, with the line tool (green and red line) placed in the center of the bowel lumen to obtain measurements of mural attenuation and wall thickness at 15° increments rotating around the central axis of the bowel. (e) Graph corresponding to ileum in d shows maximum mural attenuation (arrow), the automated mural thickness measurement obtained by using a full width at half maximum technique (H-shaped measurement), and attenuation values corresponding to luminal fluid (large arrowhead) and perienteric fat (small arrowheads).

View larger version (21K): [in a new window]   Figure 3: ROC curves for the performance of absolute terminal ileal attenuation (dotted line) and the ratio of terminal ileal attenuation to control ileal attenuation (dashed line) in predicting abnormal ileal biopsy results. Note the similar performance of both quantitative measures.

View larger version (28K): [in a new window]   Figure 4: Scatterplot of terminal ileal enhancement versus normal ileal enhancement (in Hounsfield units) in 96 patients who underwent CT enterography. Although there was a wide range of attenuation values in the terminal ileum, all but two patients had attenuation values of less than 109 HU in the normal-appearing control ileal loop.

View larger version (156K): [in a new window]   Figure 5a: Transverse CT enterographic images in 34-year-old man with abnormal ileal enhancement and no endoscopic or histologic evidence of ileal inflammation in whom abnormal bowel enhancement possibly arose from abnormalities in mesenteric venous circulation show (a) an enhancing terminal ileum (arrow) with attenuation of 118 HU, (b) a chronic portal vein clot (arrows) with cavernous transformation of the portal vein, (c) intraluminal esophageal varices (arrow) that indicated portal hypertension, and (d) evidence of previous small bowel resection, with mural hyperenhancement (arrows) and wall thickening consistent with active recurrent Crohn disease near the anastomosis. The mild dilatation of proximal small bowel (arrowhead) in d indicates partial small-bowel obstruction.

View larger version (152K): [in a new window]   Figure 5b: Transverse CT enterographic images in 34-year-old man with abnormal ileal enhancement and no endoscopic or histologic evidence of ileal inflammation in whom abnormal bowel enhancement possibly arose from abnormalities in mesenteric venous circulation show (a) an enhancing terminal ileum (arrow) with attenuation of 118 HU, (b) a chronic portal vein clot (arrows) with cavernous transformation of the portal vein, (c) intraluminal esophageal varices (arrow) that indicated portal hypertension, and (d) evidence of previous small bowel resection, with mural hyperenhancement (arrows) and wall thickening consistent with active recurrent Crohn disease near the anastomosis. The mild dilatation of proximal small bowel (arrowhead) in d indicates partial small-bowel obstruction.

View larger version (77K): [in a new window]   Figure 5c: Transverse CT enterographic images in 34-year-old man with abnormal ileal enhancement and no endoscopic or histologic evidence of ileal inflammation in whom abnormal bowel enhancement possibly arose from abnormalities in mesenteric venous circulation show (a) an enhancing terminal ileum (arrow) with attenuation of 118 HU, (b) a chronic portal vein clot (arrows) with cavernous transformation of the portal vein, (c) intraluminal esophageal varices (arrow) that indicated portal hypertension, and (d) evidence of previous small bowel resection, with mural hyperenhancement (arrows) and wall thickening consistent with active recurrent Crohn disease near the anastomosis. The mild dilatation of proximal small bowel (arrowhead) in d indicates partial small-bowel obstruction.

View larger version (107K): [in a new window]   Figure 5d: Transverse CT enterographic images in 34-year-old man with abnormal ileal enhancement and no endoscopic or histologic evidence of ileal inflammation in whom abnormal bowel enhancement possibly arose from abnormalities in mesenteric venous circulation show (a) an enhancing terminal ileum (arrow) with attenuation of 118 HU, (b) a chronic portal vein clot (arrows) with cavernous transformation of the portal vein, (c) intraluminal esophageal varices (arrow) that indicated portal hypertension, and (d) evidence of previous small bowel resection, with mural hyperenhancement (arrows) and wall thickening consistent with active recurrent Crohn disease near the anastomosis. The mild dilatation of proximal small bowel (arrowhead) in d indicates partial small-bowel obstruction.

View larger version (96K): [in a new window]   Figure 6: Transverse CT images in 28-year-old woman with endoscopically normal-appearing terminal ileum (for a distance of 15 cm) and normal ileal mucosa at random ileal biopsy show terminal ileal mural hyperenhancement and stratification (large arrow) and an ileocolic fistula (small arrows).