The purpose of this proposed research is to implement and test a method for mitigating errors in x-ray CT scanners due to beam hardening in iodine. The central focus is the electron beam tomography (EBT) machine made by Imatron, which because it can produce a two dimensional image in as little as 50 milliseconds can be used for stop action imaging of the heart. Ideally, one would like to be able to give a patient an intravenous injection of standard iodine contrast agent, then image the flow of the agent through the myocardium in real time. The degree of CT number enhancement in the myocardium should be closely related to blood flow, so that perfusion defects could be seen and quantitated. However, the major impediment to this goal is the presence of artifacts due to scattered photons and beam hardening, especially beam hardening in the injected iodine. The latter effect is especially significant when there is substantial quantities of iodine in the cardiac chambers and can actually depress the CT number in the myocardium. We propose a systematic solution based on the physics of scattered photons and spectrum hardening in bone and iodine. Preliminary work has demonstrated a useable scattered photon correction which can still be improved. The method for hardening correction identifies bone and iodine in the uncorrected image and uses an algorithm previously developed by the author for hardening in bone. Detailed physiologic tests of the accuracy using a canine model are included.
| Joseph, P M (1998) Sampling errors in projection reconstruction MRI. Magn Reson Med 40:460-6 |
