The sensitivity for stenosis/obstruction ranges from 87% to 92% with high specificities; detection performance remains high for abscesses, with sensitivity ranging from 86% to 100%. As with CT, the detection for fistulas is more variable, ranging from 40% to 100%. Because of the superior soft-tissue contrast, perianal disease, including fistulation to the perineum, is best evaluated with MRI, using a small field of view, focused examination [74-76]. Standard MRI without IV contrast has been investigated because of emerging concerns with IV gadolinium use and potential long-term accumulation in the body and brain. Noncontrast techniques such as DWI have been used to evaluate evidence for CD. There is growing literature examining its promise in detecting active disease versus quiescent disease, for complication evaluation, and disease monitoring, although many of the studies involve DWI in the context of enterography technique [77]. One study without enterography technique [48] reported a sensitivity of 49% to 82% and specificity of 85% to 93% for DWI, although lower specificities have been reported at meta- analysis [78] Overall, DWI appears to have moderate sensitivity but low specificity, leading to increased false positives for disease activity [77]. Thus, the current consensus is that noncontrast-only techniques such as DWI can be done, but there is likely improved performance with the information gained from post-IV contrast series. In this specific variant, MR may be limited. Acutely ill patients are less likely to be able to hold still for the duration of an MRI examination, leading to increased artifact and poorer image quality. In these instances, other options may be preferable, particularly CT enterography or standard abdomen and pelvic CT. However, patient factors such as obesity and guarding may not allow adequate compression with the US probe or large amounts of shadowing gas may obscure bowel, preventing an optimal examination.
Crohn Disease. The sensitivity for stenosis/obstruction ranges from 87% to 92% with high specificities; detection performance remains high for abscesses, with sensitivity ranging from 86% to 100%. As with CT, the detection for fistulas is more variable, ranging from 40% to 100%. Because of the superior soft-tissue contrast, perianal disease, including fistulation to the perineum, is best evaluated with MRI, using a small field of view, focused examination [74-76]. Standard MRI without IV contrast has been investigated because of emerging concerns with IV gadolinium use and potential long-term accumulation in the body and brain. Noncontrast techniques such as DWI have been used to evaluate evidence for CD. There is growing literature examining its promise in detecting active disease versus quiescent disease, for complication evaluation, and disease monitoring, although many of the studies involve DWI in the context of enterography technique [77]. One study without enterography technique [48] reported a sensitivity of 49% to 82% and specificity of 85% to 93% for DWI, although lower specificities have been reported at meta- analysis [78] Overall, DWI appears to have moderate sensitivity but low specificity, leading to increased false positives for disease activity [77]. Thus, the current consensus is that noncontrast-only techniques such as DWI can be done, but there is likely improved performance with the information gained from post-IV contrast series. In this specific variant, MR may be limited. Acutely ill patients are less likely to be able to hold still for the duration of an MRI examination, leading to increased artifact and poorer image quality. In these instances, other options may be preferable, particularly CT enterography or standard abdomen and pelvic CT. However, patient factors such as obesity and guarding may not allow adequate compression with the US probe or large amounts of shadowing gas may obscure bowel, preventing an optimal examination.