Studies explore MR for myocardium, SPECT perfusion, and automated echo

Selected peer-reviewed studies published from mid-December to mid-January added additional credence to the ability of delayed-enhancement MR angiography to assess myocardial infarction. Research expanded the list of cardiovascular capabilities of 64-slice CT to include predicting the future risk of coronary artery disease and uncovering the causes of unexplained chest pain. Artificial intelligence promises to make ejection fraction measurement with echocardiography faster and easier, and near-infrared fluorescence imaging creates a new dimension to thrombus imaging.

Myocardial necrosis

Diagnostic value of contrast-enhanced magnetic resonance imaging and single-photon emission computed tomography for detection of myocardial necrosis early after acute myocardial infarction

J Am Coll Cardiol 2007(1);49:208-216

Delayed-enhancement MRI may be a better diagnosis choice than technetium-99m sestamibi SPECT for detecting myocardial necrosis after reperfusion to treat myocardial infarction. By studying 78 patients with acute myocardial infarction, Dr. Tarq Ibrahim and Dr. Martin Breuer from Munich's German Heart Center and Dr. Markus Schwaiger and colleagues at the Technical University of Munich found that DE-MRI was significantly more sensitive than SPECT for detecting and evaluating the extent of MI. Using x-ray angiography for comparison, the overall sensitivities of DE-MRI and SPECT were 97% and 87%, respectively (

p

= 0.008). The authors credited the higher in-plane resolution of CMR for its ability to detect small subendocardial infarcts missed by SPECT regardless of their location. Randomized single and multisite trials are needed to confirm the findings.

Prognosis for patients with suspected CAD

Prognostic value of multislice computed tomography coronary angiography in patients with known or suspected coronary artery disease

J Am Coll Cardiol 2007;49(2):62-70

Dutch researchers have shown that 64-slice CT angiography adds insight to the probability of future myocardial infarction and other major cardiac events for patients with suspected coronary artery disease. Under the direction of Dr. Jeroen J. Bax, Dr. Gabija Pundziute of Leiden University Medical Center found connections between the severity of coronary artery stenosis identified with multislice CTA and cardiac events that arose during 16 months after imaging. Coronary plaques were detected in 80 of 100 patients. About two-thirds (63%) of patients with obstructive disease had events, and 30% of patients with some evidence of CAD had a future event. All patients who were free of disease on their MSCT scans lived through at least the next year without incident. Further study is needed to confirm the preliminary findings.

Differential diagnosis of acute chest pain

AJR 2007:188:76-82

A preliminary study of the triple rule-out protocol indicates that contrast-enhanced 64-slice CT angiography can track down the cause of unexplained chest pain for patients who arrive in the emergency room with chest pain complaints. The investigation by Dr. Thorsten R.C. Johnson and colleagues at the University of Munich in Germany correctly identified the cause of chest pain for 37 of 55 patients. Pulmonary embolism, high-grade coronary stenosis, and aortic aneurysm accounted for 25 of the findings. Others included bypass graft occlusion, pneumonic consolidation, atelectasis, mediastinal mass, aortic dissection, cardiac tumor, lung tumor, hiatal hernia, and pulmonary metastasis. CTA triple rule-out did not explain the cause of pain for 14 patients. Of these, four involved pathology that was either overlooked or inaccurately interpreted. Ten were true negatives. Another four patients were excluded because of breath-hold problems. CE-CTA produced a detailed 3D volume of the entire chest in about 22 seconds of scan time. Radiation exposure was estimated at 6.9 mSv. Beta blockers were not administered. Clinical follow-up was performed five months after initial evaluation. With the test's sensitivity estimated at about 93%, the results encouraged Johnson to move ahead with larger trials.

Artificial intelligence

A novel two-dimensional echocardiographic image analysis system using artificial intelligence-learned pattern recognition for rapid automated ejection fraction

J Am Coll Cardiol 2007;49(2):217-226

Physicians frustrated with time-consuming process of acquiring left ventricular performance measures with echocardiography will find solace in the promise of artificial intelligence to perform the task for them. Under the guidance of Dr. John Gorcsan III, Dr. Maxime Cannesson calculated ejection fractions on 218 patients using a 2D echocardiographic image analysis system featuring artificial intelligence-learned pattern recognition. Completely automated EF calculations were performed on 77% of the patients, while 23% needed manual editing of the endocardial tracing. Automated EF results correlated well with manual EF calculations and helped improve the performance of visual EF assessments by novice readers. The automated technique took less than half as much time as the manual approach to complete.

NIR fluorescence imaging

Localization and quantification of platelet-rich thrombi in large blood vessels with near-infrared fluorescence imaging

Circulation 2007;115(1);84-93

Dr. John Frangioni's group in the radiology department at Beth Israel Deaconess Medical Center and colleagues in the division of hematology/oncology and the cardiovascular research center at Massachusetts General Hospital are making progress toward a real-time optical imaging technique using fluorescence-labeled platelets to light up intravascular thrombi. The fluorescence then fades as the occlusion breaks up, again in real-time, during thrombolyis. Platelets in the experiment on six pigs were labeled with IR-786, a lipophilic cationic indocyanine-type near-infrared fluorophore. Thrombi were induced using ferric chloride in the femoral veins of the animals. Fluorescence appeared at the injured sites within minutes after IR-786 infusion. The agent's accumulation was observed during open surgery with an intraoperative NIR fluorescence system suspended on an articulated arm over the field-of-view. The NIR fluorescent light was pseudocolored in lime green and fused to anatomic images captured with a video camera. The technique also displayed the presence and extent of thrombi induced with embolization coils in the femoral veins of pigs. Streptokinase and heparin were infused after the thrombi stabilized. The dissolution of the thrombi could be seen in real-time, with thrombolysis resulting in a 22.5% decrease in fluorescence signal. Frangioni envisions using NIR imaging for drug research and improvement of the visualization of thrombus formation during vascular surgery.