What is the effect of an air-filled bowel obstruction on abdominal subject contrast?

What is the effect of an air-filled bowel obstruction on abdominal subject contrast?

• A. Decreased subject contrast
• B. No change in subject contrast
• C. Increased subject contrast
• D. Variable effect on subject contrast

Answer: (C)

Subject contrast comes from differences in X-ray attenuation between adjacent tissues. Air has very low attenuation, so interfaces between gas and soft tissue create a large grayscale difference on radiographs. When a bowel obstruction is filled with gas, there are many gas-filled loops throughout the abdomen. Each gas-soft tissue interface adds to the overall contrast seen on the image, making the abdominal outlines and bowel walls more conspicuous. In short, more air in the abdomen increases the differential attenuation between structures, so subject contrast is increased.

Subject contrast comes from differences in X-ray attenuation between adjacent tissues. Air has very low attenuation, so interfaces between gas and soft tissue create a large grayscale difference on radiographs.

When a bowel obstruction is filled with gas, there are many gas-filled loops throughout the abdomen. Each gas-soft tissue interface adds to the overall contrast seen on the image, making the abdominal outlines and bowel walls more conspicuous. In short, more air in the abdomen increases the differential attenuation between structures, so subject contrast is increased.