Thoracic Imaging 2003 - Society of Thoracic Radiology
Thoracic Imaging 2003 - Society of Thoracic Radiology
Thoracic Imaging 2003 - Society of Thoracic Radiology
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Cardiac MRI: New Developments<br />
Gautham Reddy, M.D.<br />
Coronary artery disease (CAD) is the leading cause <strong>of</strong> death<br />
in the United States and other industrialized countries. Although<br />
a reduction in the prevalence <strong>of</strong> CAD has been noted over the<br />
past 2 decades, the increasing age <strong>of</strong> the population will result<br />
in more patients developing coronary artery disease. The number<br />
<strong>of</strong> Americans older than 65 years is approximately 25 million<br />
and over the next 50 years is expected to exceed 65 million.<br />
Cardiac MRI is a rapidly evolving modality that can be applied<br />
to the evaluation <strong>of</strong> ischemic heart disease, including the<br />
appraisal <strong>of</strong> perfusion, left ventricular function (wall motion),<br />
viability, and coronary obstruction.<br />
Perfusion. Myocardial perfusion imaging can be assessed by<br />
MRI, which <strong>of</strong>fers several advantages over other imaging methods.<br />
MRI uses no ionizing radiation, <strong>of</strong>fers high spatial resolution<br />
(which allows delineation <strong>of</strong> the subendocardial layer) and<br />
good temporal resolution, and allows assessment <strong>of</strong> left ventricular<br />
function during the same examination. A recent study has<br />
shown that MRI perfusion examination can detect coronary<br />
lesions with a sensitivity <strong>of</strong> 90% and a specificity <strong>of</strong> 83%.<br />
Left ventricular function / Wall motion. Pharmacological<br />
stress MRI with high-dose dobutamine can be used to detect<br />
areas <strong>of</strong> ischemic myocardium. Stress MRI is safe and has<br />
greater diagnostic accuracy than dobutamine stress echocardiography.<br />
A recent study has shown that stress MRI has greater<br />
sensitivity (86% vs 74%), specificity (86% vs 70%), and accuracy<br />
(86% vs 73%) than stress echocardiography. The most<br />
important clinical indication is the assessment <strong>of</strong> stress-induced<br />
wall-motion abnormalities in patients whose stress echocardiography<br />
examination is <strong>of</strong> moderate or poor quality.<br />
Viability. In patients with ischemic heart disease, it is important<br />
to differentiate between viable and non-viable myocardium,<br />
independent <strong>of</strong> ventricular function in response to stress.<br />
Contrast-enhanced MRI can differentiate between viable and<br />
non-viable myocardium independent <strong>of</strong> the age <strong>of</strong> infarction,<br />
and without regard to ventricular function. MRI viability studies<br />
can detect acute and chronic infarcts with high sensitivity<br />
(100% acute, 91% chronic) and can precisely localize the area<br />
<strong>of</strong> infarction.<br />
Coronary MRA. Invasive x-ray coronary angiography<br />
remains the gold standard for the identification <strong>of</strong> clinically significant<br />
CAD. Although numerous noninvasive tests have been<br />
developed to assist in the identification <strong>of</strong> patients with coronary<br />
artery disease, a substantial minority <strong>of</strong> patients referred<br />
for elective diagnostic x-ray coronary angiography are found not<br />
to have clinically significant coronary stenosis (defined as a<br />
reduction in the luminal diameter <strong>of</strong> at least 50 percent).<br />
Recently, Kim et al performed a prospective, multicenter<br />
study to determine the clinical usefulness <strong>of</strong> free-breathing coronary<br />
MR angiography in the diagnosis <strong>of</strong> native-vessel coronary<br />
artery disease. A total <strong>of</strong> 636 <strong>of</strong> 759 proximal and middle segments<br />
<strong>of</strong> coronary arteries (84%) were interpretable on MR<br />
angiography. In these segments, 78 (83%) <strong>of</strong> 94 clinically significant<br />
lesions (>50 luminal stenosis on x-ray angiography) were<br />
detected by MR angiography. Overall, coronary MR angiography<br />
had an accuracy <strong>of</strong> 72% for diagnosing coronary artery disease.<br />
The sensitivity, specificity, and accuracy for patients with disease<br />
<strong>of</strong> the left main coronary artery or three-vessel disease were<br />
100%, 85%, and 87%, respectively. The negative predictive values<br />
for any coronary artery disease and for left main artery or<br />
three-vessel disease were 81% and 100%, respectively. In effect,<br />
free-breathing MR angiography can reliably identify or rule out<br />
left main coronary artery or three-vessel disease.<br />
REFERENCES:<br />
1. Al-Saadi N, Nagel E, Gross M, et al. Noninvasive detection <strong>of</strong><br />
myocardial ischemia from perfusion reserve based on cardiovascular<br />
magnetic resonance. Circulation 2000; 101:1379-<br />
1383.<br />
2. Nagel E, Lehmkuhl HB, Bocksch W, et al. Noninvasive diagnosis<br />
<strong>of</strong> ischemia-induced wall motion abnormalities with the use<br />
<strong>of</strong> high-dose dobutamine stress MRI: comparison with dobutamine<br />
stress echocardiography. Circulation 1999; 99:763-770.<br />
3. Simonetti OP, Kim RJ, Fieno DS, et al. An improved MR imaging<br />
technique for the visualization <strong>of</strong> myocardial infarction.<br />
<strong>Radiology</strong> 2001;218:215-223.<br />
4. Wu E, Judd RM, Vargas JD, et al. Visualization <strong>of</strong> presence,<br />
location, and transmural extent <strong>of</strong> healed Q-wave and non-<br />
Q-wave myocardial infarction. Lancet 2001:357;21-28.<br />
5. Kim WY, Danias PG, Stuber M, et al. Coronary magnetic<br />
resonance angiography for the detection <strong>of</strong> coronary<br />
stenoses. N Engl J Med 2001; 345:1863-1869.<br />
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