64-slice cardiac CT reaches beyond coronary arteries

Sixty-four-slice cardiac CT may be the most disruptive technology to hit coronary artery imaging since the introduction of SPECT. And its influence does not end at the diagnosis of atherosclerotic coronary artery disease.

A Tuesday morning scientific session featured studies demonstrating that multislice CCT is well suited for several applications:

• diagnosing nonvalvular thrombi and masses in the left atrium and left ventricle

• detecting and characterizing anomalous coronary arteries

• measuring the therapeutic affect of statins on coronary artery plaque

• assessing coronary bifurcation lesions

• performing a triple rule-out protocol on patients with acute chest pain

Dr. Gregory Gladish, an assistant professor of radiology at M. D. Anderson Cancer Center, presented results based on imaging experience with 102 symptomatic patients suggesting that 64-slice CCT may become an alternative to transesophageal echocardiography for assessing left heart thrombi before cardioversion.

CCT revealed left-sided masses in 11 patients, while such masses were diagnosed for seven patients with TEE. Sensitivity of 64-slice CCT was 100%, and specificity was 97%. The prevalence of left-sided nonvalvular masses or thrombi was 3.9%.

Dr. Lan Song of the Peking Union Medical College Hospital in Beijing found in a retrospective study of 1894 patients that volume-rendered images acquired with 64-slice CT are superb for detecting the origin and course of anomalous coronary arteries. Her results indicated that ECG-gated MSCT is also more sensitive to the presence of myocardial bridge than conventional angiography.

The potential of CCT to evaluate the effect of cholesterol-lowering drugs was demonstrated in Dr. Masae Uehara's year-long study of 21 patients treated with lipid-lowering atorvastatin (Lipitor). After 12 months of treatment, the average LDL cholesterol levels of the subjects fell from 122 mg/dL before baseline scanning to 96 mg/dL when follow-up imaging was performed.

A comparison of pre- and post-treatment scans revealed that the areas of noncalcified coronary plaques, manually measured from axial or multiplanar reconstructions, did not change significantly between scans, but plaque density increased. The average measurement before treatment was 55 HU. It rose to 62 HU after 12 months of therapy.

Dr. Carlos van Mieghem of Erasmus Medical Center in Rotterdam, the Netherlands, demonstrated how 64-slice CT angiography can provide a comprehensive assessment of complex coronary bifurcation lesions to aid interventional planning. Coronary bifurcation lesions were identified using cardiac CTA in 44 of 313 consecutive patients. The sensitivity, specificity, positive predictive value, and negative predictive value of CTA for this role were 96%, 99%, 85%, and 99%, respectively. In 40 of 42 cases, CTA correctly reproduced the luminal classification of the main vessel and side branch.

Dr. Thorsten Johnson of Ludwig-Maximilians University in Munich showed that the triple rule-out protocol can be applied in practice for patients with acute chest pain when performed with the help of ECG-gated 64-slice CT imaging. His study of 45 patients revealed that 64-slice imaging generates enough resolution to rule out aortic dissections, pulmonary emboli, and the presence of coronary artery disease.

The findings are made by evaluating and manipulating a single 3D volume rendering encompassing the upper abdomen, including the lungs, major arteries, and heart.

Johnson noted that adequate contrast enhancement of the pulmonary vessels, coronary arteries, and aorta was achieved in all subjects. One exam was deemed nondiagnostic, and inconsequential motion artifacts appeared in nine studies.

The cause of the chest pain was correctly identified in 34 patients, according to Johnson. Findings included eight pulmonary emboli, seven coronary stenoses, and three aortic dissections. The cause of pain was not found in nine cases.

The CCT exams achieved a sensitivity, specificity, and accuracy rate of 94%, 78%, and 89%, respectively. Follow-up scans performed three months later to identify the cause of acute chest pain indicated that CTA achieved 94% sensitivity.

Additional studies performed at the University of Munich suggest that the triple rule-out protocol will become even more sensitive to the source of chest pain when performed on a dual-source CT scanner, Johnson said.