CT Perfusion Imaging in Cerebral Ischemia

Abstract

To the Editor: We read with interest the Guidelines and Recommendations for Perfusion Imaging in Cerebral Ischemia by the Writing Group on Perfusion Imaging, from the Council on Cardiovascular Radiology of the American Heart Association.1 The authors have succeeded admirably in summarizing the important recent developments of perfusion imaging and their relevance to clinical investigations of cerebral ischemia. We have been involved in the development of the First-Pass Bolus Tracking Methodology of CT Perfusion for over a decade and would like to comment on a few issues raised by the authors concerning this particular methodology. The Table is a comparison of the effective dose equivalent2 (HE) of each of the three perfusion imaging methods discussed in the Guidelines that involve the use of ionizing radiation. The effective dose equivalents for the 2 computed tomography (CT) techniques are estimated using the methodology published by Huda et al 3 based on the CT dose index values published for LightSpeed QXi scanners (General Electric Medical Systems). For CT scanners of other models or from other manufacturers, the values in the Table can be scaled proportionally according to the computed tomography dose index value of the scanner relative to the LightSpeed QXi scanner. View this table: The Table shows that CT perfusion (CTP) imaging does not necessarily give a higher radiation dose to the subject than XeCT and SPECT perfusion imaging. In comparison, a screening head CT scan has an effective dose equivalent of 1.5 mSv.3 With the recent interest in using a saline chaser to shorten the duration of the first transit of the contrast bolus through the brain, the scan duration for CTP can be reduced to around 25 to 30 s resulting in an even lower dose of 1.8 to 2.2 mSv. While xenon-enhanced computed tomography (XeCT) and single photon …