Transient hepatic attenuation differences at biphasic spiral CT examinations.

Transient hepatic attenuation difference (THAD) is a perfusion disorder that can sometimes be observed in hepatic arterial phase of a biphasic spiral CT examination. The involved site of liver by THAD appears as an area of high attenuation on the hepatic arterial phase image and returns to normal attenuation on portal venous phase image. The knowledge of the shape, distribution and causes of THAD is essential to differentiate the THAD from other pathologies such as neoplasm.