Mass General Hospital
APRIL 2010
ISSUE 26

 
 
CT Angiography with Reduced Radiation - The Dawn of a New Era
Wilfred Mamuya, MD, PhD, Shawn Gregory, MD, Waleed Ahmed, MD, Brian Ghoshhajra, MD, MBA, and Suhny Abbara, MD
 
  Clinical History
A 46-year-old woman with a history of supraventricular tachycardia, benign positional vertigo, and a meningioma was admitted after being found unresponsive at the bottom of a stairway. During her index hospitalization, no arrhythmias were noted; and a technically difficult transthoracic cardiac ultrasound revealed mild to moderate mitral regurgitation, inferior hypokinesis, and an estimated left ventricular ejection fraction of 44%. The initial neurological workup was unremarkable, and the patient refused any further cardiovascular workup. Following discharge, she consented to a cardiac CTA evaluation, and was scanned at MGH with a latest generation high-pitch, dual source ("Flash") CT scanner.

Figure 1: Volume Rendered 3D views of high pitch dual source (“flash“) CTA show normal right and left coronary arterial systems.
Figure 1

Figure 2: Multiplanar reformation of flash coronary CTA  shows normal right coronary artery.
Figure 2
Figure 3: Curved multiplanar reformations of flash coronary CTA  shows normal left anterior descending (LAD) and circumflex (LCX) coronary arteries.
Figure 3

(Click on images to enlarge)

Figure 1: Volume Rendered 3D views of high pitch dual source (“flash“) CTA show normal right and left coronary arterial systems.

Figure 2: Multiplanar reformation of flash coronary CTA  shows normal right coronary artery.

Figure 3: Curved multiplanar reformations of flash coronary CTA  shows normal left anterior descending (LAD) and circumflex (LCX) coronary arteries.


Findings
Cardiac CTA revealed no evidence for anomalous coronary arteries. There was right coronary artery dominance, without evidence of any coronary artery disease. There was no evidence of aortic dissection or aneurysm, and her pulmonary vasculature was unremarkable.

Discussion

The evaluation of coronary arteries by cardiac CTA in patients with a cardiomyopathy of unclear etiology is an established indication1 and has a negative predictive value of 98% in excluding coronary artery disease as a potential etiology2. Our patient was scanned in the "Flash" mode using the new  high-pitch CT scanner, which has a scanning speed of up to 43 cm/s and a temporal resolution of 75 ms. Therefore, an entire chest examination can be completed in just 0.6 seconds. The "Flash" mode can be used reliably in patients with a heart rate of less than 65 and regular rhythm3. Our patient's examination lasted 0.43 seconds, and her total radiation exposure was 1.07 millisieverts (mSv), compared to an average effective dose of 7 mSv for a diagnostic cardiac catheterization and an average effective dose of 15.6 mSv for a myocardial perfusion imaging study (SPECT)4.


 
 
REFERENCES
1. Hendel RC et al. ACCF/ACR/SCCT/SCMR/ASNC/NASCI/SCAI/SIR 2006 Appropriateness Criteria for Cardiac Computed Tomography and Cardiac Magnetic Resonance Imaging. JACC 2006, 48:1474-1497
2. Ghostine S et al. Non-invasive diagnosis of ischaemic heart failure using 64-slice computed tomography. Eur. Heart J. 2008;29:2133-2140
3. Achenbach S et al. Coronary computed tomography angiography with a consistent dose below 1 mSV using prospective electrocardiogram-triggered high-pitch spiral acquisition. Eur Heart J. 2010;31:340-346
4. Fazel R et al. Exposure to low-dose ionizing radiation from medical imaging procedures. NEJM 2009;361:849-57
   

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Editors:
Suhny Abbara, M.D.
MGH Department of Radiology
Wilfred Mamuya, M.D., Ph.D.
MGH Division of Cardiology

Phone: 617-726-5954