Abstract 1637: Radiation Dose Measurements on Subjects Undergoing Combined CT Perfusion and CT Angiography Imaging with a Prototype 256-row MDCT Scanner

Abstract

Introduction: The purpose of this study was to directly measure the radiation dose on subjects undergoing combined CT Perfusion (CTP) and CT Angiography (CTA) imaging on a 256-row MDCT scanner. Methods: Fifteen patients underwent combined CTP and CTA imaging on a prototype 256 row MDCT scanner (Toshiba, Nasu, Japan). The prototype 256-row MDCT scanner consists of 256 rows of 0.5 mm size detectors with the capability to scan 12.8 cm length in the axial plane per CT gantry rotation in 0.5 secs. The protocol included a scout scan and test bolus scan followed by adenosine stress CTP (120 kVp, 200 mA, gantry rotation speed of 0.5 secs for 3 rotations, 128x1.0 mm) and rest CTA (120 kVp, 350 mA, gantry rotation speed of 0.5 secs for 3 rotations, 256x0.5 mm) in an axial scan mode. Direct dose measurements were performed using a custom vest worn by the patient fitted with 15–25 thermoluminiscent dosimeters (TLDs) (Landauer, IL) placed in AP and lateral locations. An anthropomorphic phantom was also scanned with the same protocol with TLDs positioned on the surface and inside the phantom at various organ locations. Effective doses were estimated based on the maximum surface dose according to previously validated methodology. Results: The effective dose from TLD measurements ranged from 22 to 32 mSv for the entire protocol. This is based on direct dose measured on subjects and not based on dose derived from phantom measurements as done routinely. Conclusions: The doses reported in this study are comparable to similarly measured doses from 64-slice MDCT coronary angiography alone. This prototype scanner uses 3 gantry rotations and a 1.5 second exposure time in it current configuration. Since, 256-row MDCT can cover the entire heart in a single rotation, it eliminates the need for tissue overlap from low pitch values. Efforts are currently underway to develop a prospective ECG-gated protocol that can limit radiation exposure to a single rotation for both stress and rest CTA scans. With a single rotation, the effective dose can be reduced to nearly one-third of the dose measured with this prototype, or approximately 7–11 mSv for a combined CTP and CTA imaging.