Gonzalo T. Chua

Imaging of small bowel Crohn's disease: can abdominal CT replace barium radiography?

Objectives: To analyze imaging features and compare the diagnostic information provided by abdominal computed tomography (CT) and enteroclysis to see whether CT can replace barium examinations in the assessment of patients with small bowel Crohns disease. Methods: The abdominal CT studies and enteroclysis of 33 patients with small bowel Crohns disease who underwent both examinations within a 2-week time period were retrospectively reviewed and scored for the presence and severity of the following features: mural edema, ulceration, small bowel obstruction, stricture, sinus tract formation, fistula, abscess, extraintestinal manifestations, and total number of intestinal sites involved. The statistical significance of the differences for each variable was calculated. Results: A total of 37 case sets were reviewed. CT demonstrated 10 (27 %) abscesses compared to 7 (19 %) shown by enteroclysis. Three extraintestinal sites shown by CT were not demonstrated by enteroclysis. Enteroclysis detected a larger number of intestinal sites of involvement (54 vs. 47) and more cases of ulceration (78 % vs. 19 %), small bowel obstruction (46 % vs. 16 %), stricture (38 % vs. 11 %), fistula formation (24 % vs. 8 %), and sinus tract formation (27 % vs. 5 %). The two modalities were similar in characterizing and grading the severity of mural thickening (CT showed 41 %, enteroclysis 46 %). Conclusion: Abdominal CT and enteroclysis provide unique and complementary diagnostic information in patients with Crohns disease of the small bowel. Both methods may be required for the accurate assessment of the severity and extent of Crohns disease of the small bowel. The choice of initial examination will depend on the clinical issue in question.

Correction of helical CT attenuation values with wide beam collimation: in vitro test with urinary calculi.

RATIONALE AND OBJECTIVES Urinary calculi are now commonly detected with helical computed tomography (CT), and it has been proposed that stone composition can be determined from CT attenuation values. However, typical scans are made with a beam collimation of 5 mm or more, resulting in volume averaging and reduction in accuracy of attenuation measurement. The authors tested a model for correction of errors in attenuation values, even at section widths larger than the width of the object. MATERIALS AND METHODS Human urinary stones were scanned with helical CT at different beam collimation widths. A computer model was used to predict the effect of beam width and stone size on accuracy of measured attenuation. RESULTS At 3-mm collimation, the model corrected the attenuation readings with an underestimation of 12% +/- 1 (compared with values at 1-mm collimation; 127 stones; diameters of 1.7-11.3 mm). With attenuation measured at 10-mm collimation, the model underestimated the true value by 34% +/- 3 (103 stones), with a significant negative correlation with stone diameter on magnitude of error (diameters of 3.0-11.3 mm). Correlation of data from patient scans with subsequent in vitro scanning of the same stones confirmed the validity of the model, but corrected in vivo scans consistently yielded lower values for the stones than in vitro. CONCLUSION Volume averaging effects on attenuation in helical CT are predictable in vitro for urinary calculi--and presumably for other roughly spherical structures--as long as section width does not excessively exceed the diameter of the structure.

Effect of Radiographic Contrast Material Exposure on Spiral CT Attenuation of Renal Calculi

RATIONALE AND OBJECTIVES The authors performed this study to determine whether exposure of renal calculi to radiographic contrast material has an effect on the attenuation values at computed tomography (CT) performed with varying collimation widths. MATERIALS AND METHODS Renal calculi (23 stones of various composition) were scanned with 1-, 3-, and 10-mm collimation. Stones were then exposed to a solution of radiographic contrast material for 5 minutes, washed with water, and rescanned 36 hours later. The reproducibility of the CT attenuation measurements on different days was evaluated by obtaining measurements in a subset of 16 renal stones on 4 different days. RESULTS There was no statistically significant change in attenuation after contrast material exposure at narrow collimation. At wider collimation, statistically significant increases were noted in both attenuation and standard deviation. A small amount of variability between readings was noted on different days, with a minimal increase in attenuation each day. Correlation between readings remained very high. CONCLUSION Exposure of stones to a radiographic contrast material had a statistically significant effect on CT attenuation values only at wide collimation. This may be related to technical factors including volume averaging. Absence of an effect at narrow collimation suggests that the attenuation values of renal stones do not significantly change after exposure to contrast material.