Computed tomography: beam hardening and environmental density artifact.

Phantoms designed to simulate cysts or avascular masses and other material encountered in computed tomographic (CT) body and head scanning were used to evaluate the effect of beam hardening in a GE CT/T 8800 scanner. The phantoms were scanned before and after the addition of iodinated contrast material to various compartments within the phantoms. The results indicate that in general the addition of contrast material in the CT body phantom resulted in a decrease in the CT numbers recorded from the cyst phantoms. Conversely, the addition of contrast material in a concentric peripheral cylinder (simulating the addition or presence of the calvarium in CT head scanning) resulted in a generalized inhomogeneous increase in CT numbers of specimen materials contained in that ring.