Abstract 17862: Radiation Dose and Downstream Testing from Coronary CT Angiography (CTA) versus SPECT Myocardial Perfusion Imaging (MPI) for the Evaluation of Chest Pain in the Emergency Department (ED)

Abstract

Background: While recent CTA studies have suggested lower radiation dose and faster study time than MPI, this comparison has been to older Na-I SPECT cameras using traditional rest-stress protocols. We compared CTA to modern SPECT MPI using high efficiency CZT (cadmium-zinc-telluride) cameras and newer stress-first protocols in an ED Chest Pain Unit (CPU) population.

Methods: In a retrospective, non-randomized study all patients who underwent CTA or Tc-99m sestamibi SPECT MPI as part of their ED CPU assessment in 2010-2011 driven by ED attending preference and equipment availability were evaluated for their radiation dose and subsequent diagnostic testing. CTA was performed on a 64-slice scanner (GE Lightspeed VCT) and MPI was performed on either a CZT SPECT camera (GE Discovery 530c) or a conventional SPECT camera. Effective dose from CTA was estimated from scanner-reported dose-length product using a published scanner-specific conversion factor and from MPI from recorded administered activity using updated ICRP Publication 103 tissue weighting factors and dosimetry tables.

Results: Over the 2 year period 192 patients underwent CTA and 939 MPI. The CTA patients were a lower risk cohort based on age, cardiac risk factors, and known heart disease. In the MPI group, 708 (75%) underwent stress-only imaging, 184 (20%) rest-stress, and 47 (5%) stress-rest with 853 (91%) imaged on a CZT camera. While there was no significant difference in the proportion of subsequent angiograms, there were more follow-up stress tests in the CTA group. The effective dose of 13.5 mSv for the CTA group was significantly higher than 5.0 mSv for stress-only MPI and 10.4 mSv for rest-stress MPI studies.

Conclusions: CZT SPECT MPI and stress-only imaging used in a majority of patients had significantly lower patient radiation dose and less follow-up diagnostic testing than CTA. As published, stress-only imaging can be completed within 90 minutes which compares favorably with the 1 hour length of a CTA.