Thoracic Imaging 2003 - Society of Thoracic Radiology

Cardiac MRI: New Developments
Gautham Reddy, M.D.
Coronary artery disease (CAD) is the leading cause of death
in the United States and other industrialized countries. Although
a reduction in the prevalence of CAD has been noted over the
past 2 decades, the increasing age of the population will result
in more patients developing coronary artery disease. The number
of Americans older than 65 years is approximately 25 million
and over the next 50 years is expected to exceed 65 million.
Cardiac MRI is a rapidly evolving modality that can be applied
to the evaluation of ischemic heart disease, including the
appraisal of perfusion, left ventricular function (wall motion),
viability, and coronary obstruction.
Perfusion. Myocardial perfusion imaging can be assessed by
MRI, which offers several advantages over other imaging methods.
MRI uses no ionizing radiation, offers high spatial resolution
(which allows delineation of the subendocardial layer) and
good temporal resolution, and allows assessment of left ventricular
function during the same examination. A recent study has
shown that MRI perfusion examination can detect coronary
lesions with a sensitivity of 90% and a specificity of 83%.
Left ventricular function / Wall motion. Pharmacological
stress MRI with high-dose dobutamine can be used to detect
areas of ischemic myocardium. Stress MRI is safe and has
greater diagnostic accuracy than dobutamine stress echocardiography.
A recent study has shown that stress MRI has greater
sensitivity (86% vs 74%), specificity (86% vs 70%), and accuracy
(86% vs 73%) than stress echocardiography. The most
important clinical indication is the assessment of stress-induced
wall-motion abnormalities in patients whose stress echocardiography
examination is of moderate or poor quality.
Viability. In patients with ischemic heart disease, it is important
to differentiate between viable and non-viable myocardium,
independent of ventricular function in response to stress.
Contrast-enhanced MRI can differentiate between viable and
non-viable myocardium independent of the age of infarction,
and without regard to ventricular function. MRI viability studies
can detect acute and chronic infarcts with high sensitivity
(100% acute, 91% chronic) and can precisely localize the area
of infarction.
Coronary MRA. Invasive x-ray coronary angiography
remains the gold standard for the identification of clinically significant
CAD. Although numerous noninvasive tests have been
developed to assist in the identification of patients with coronary
artery disease, a substantial minority of patients referred
for elective diagnostic x-ray coronary angiography are found not
to have clinically significant coronary stenosis (defined as a
reduction in the luminal diameter of at least 50 percent).
Recently, Kim et al performed a prospective, multicenter
study to determine the clinical usefulness of free-breathing coronary
MR angiography in the diagnosis of native-vessel coronary
artery disease. A total of 636 of 759 proximal and middle segments
of coronary arteries (84%) were interpretable on MR
angiography. In these segments, 78 (83%) of 94 clinically significant
lesions (>50 luminal stenosis on x-ray angiography) were
detected by MR angiography. Overall, coronary MR angiography
had an accuracy of 72% for diagnosing coronary artery disease.
The sensitivity, specificity, and accuracy for patients with disease
of the left main coronary artery or three-vessel disease were
100%, 85%, and 87%, respectively. The negative predictive values
for any coronary artery disease and for left main artery or
three-vessel disease were 81% and 100%, respectively. In effect,
free-breathing MR angiography can reliably identify or rule out
left main coronary artery or three-vessel disease.
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3. Simonetti OP, Kim RJ, Fieno DS, et al. An improved MR imaging
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4. Wu E, Judd RM, Vargas JD, et al. Visualization of presence,
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