March 31, 2011 by dailybolusoflr
Coronary CT Angiogram to evaluate patients with CP in the ED
· This is a relatively new modality used to evaluate patients in the ED with chest pain.
· From a radiation standpoint, there is a range of radiation exposure to patients based on how the CT is performed.
There are two approaches for CCTA:
Retrospective ECG Gating (which delivers about 10-15mSv)
◦ Segments cardiac cycle (R-R Interval) into 10 phases (0-90%)
◦ Scans the entire time, but uses information obtained during certain times to form the images.
Best time to obtain information is 40-80%
◦ Tube Modulation is possible which decreases the radiation output during the less useful times in the cycle. So, for phases 0-39% the radiation output would be deceased, increased during phases 40-80% and then decreased again until 90%.
Prospective ECG Gating (2.5-7mSv)
◦ Approximates location of the 10 phases in the cardiac cycle from estimate based on HR and RR interval
◦ Collects data only from certain phases- the radiation output is OFF during the less useful cycles
◦ This significantly decreases the radiation dose but due to the lack of imaging for the entire cycle, does limit information obtained
LVEF cannot be calculated from prospectively gated ECG CCTAs
◦ These images can be compromised by patients with ectopy or irregular HRs.
· Rest-stress (sestamibi) 9.4 mSv
· Rest-stress (thallium) 40 mSv
· Angio 7 mSv
· Angio with stent or angioplasty 15 mSv
· CCTA retrospective gating 10-15 mSv
· CCTA prospective gating 2.5-7 mSv
The ‘what, when, where, who and how?’ of cardiac computed tomography in 2009: guidelines for the clinician. The Canadian Journal of Cardiology 25, 135-139.
Linda Regan, MD FACEP
Program Director, Emergency Medicine Residency
Johns Hopkins Medical Institutions