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CME Released: 2/5/2010
Valid for credit through: 2/5/2011
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February 5, 2010 — Computed tomography (CT) is a better noninvasive imaging test than magnetic resonance imaging (MRI) for detecting and ruling out coronary artery disease, according to the results of a new meta-analysis [1]. The newer CT scanners are also more sensitive than older scanners and involve less iodinated contrast agent but higher radiation exposure, report the researchers.
"Our meta-analysis suggests that CT has better sensitivity and specificity than MRI and is therefore advantageous for detecting and ruling out clinically relevant coronary stenoses," according to lead investigator Georg Schuetz (Charité Medical School, Berlin, Germany) and colleagues. "CT should be considered the foremost noninvasive alternative to coronary angiography" in selected patient populations.
The results of the study are published online February 2, 2010 in the Annals of Internal Medicine.
Up Against the Gold Standard
As the authors point out, including senior investigator Dr Marc Dewey (Charité Medical School, Berlin, Germany), CT and MRI are attractive alternatives to invasive coronary angiography for clinical decision making. Although conventional angiography is the gold standard, noninvasive coronary angiography with CT and MRI are used to rule out coronary artery disease in patients with a low pretest likelihood of disease, such as patients with inconclusive stress tests and atypical angina.
The meta-analysis included 89 CT studies and 19 MRI studies directly comparing the noninvasive imaging test with conventional coronary angiography. Most of the studies were performed in Europe at university hospitals and included only state-of-the-art CT scanners and MRI approaches. Significant coronary artery stenosis was defined as a reduction of 50% or greater in the coronary artery for CT, MRI, and conventional angiography.
The sensitivity and specificity for CT was 97.2% and 87.4%, respectively, and 87.1% and 70.3%, respectively, for MRI. An analysis restricted only to CT studies used to rule out coronary artery disease resulted in a similar sensitivity and specificity to the overall findings, whereas a subgroup analysis of scanners with more than 16 detector rows resulted in a significantly higher sensitivity than that for scanners with a maximum of 16 rows.
Diagnostic Accuracy for CT and MRI
| Imaging test | Mean sensitivity (95% CI) | Mean specificity (95% CI) |
| MRI | 87.1 (83.0–90.3) | 70.3 (58.8–79.7) |
| CT | 97.2 (96.2–98.0) | 87.4 (84.5–89.8) |
| Used to rule out coronary artery disease (45 studies) | 97.6 (96.1–98.5) | 89.2 (86.0–91.8) |
| Used to rule out acute coronary syndrome (7 studies) | 95.6 (87.2–98.6) | 76.6 (50.9–91.2) |
| CT scanners >16 rows | 98.1 (97.0–99.0) | 89.4 (86.0–92.0) |
| CT scanners 12 to 16 rows | 98.1 (94.0–97.0) | 84.7 (80.0–89.0) |
The researchers note that although technical advances have improved image quality for CT and MRI, multislice CT is more sophisticated and easier to perform, particularly since the CT examination is shorter than MRI, requires reduced breath-hold time, and doesn't constrain the patient to the same extent as MRI. "Thus, CT is more accepted, more widely available, and more favored by patients, and it has become reasonably cost-effective," write Schuetz and colleagues.
Commenting on the results of the study, Dr Roger Blumenthal (Johns Hopkins University, Baltimore, MD) agreed that CT angiography is much more accessible to clinicians than coronary magnetic resonance angiography. "The database with CT angiography is rapidly growing, and the amount of ionizing radiation associated with CT angiography in academic centers is steadily coming down," he said.
In the meta-analysis, the mean amount of contrast agent required was 37.8 g for the studies of CT scanners with <16 rows and 31.3 g for those with >16 rows. The mean radiation exposure, however, was significantly less, 9.4 mSv vs 13.0 mSv, for scanners with 16 rows or fewer compared with those with more than 16 rows, respectively.
Blumenthal noted that most clinicians consider only a standard coronary angiogram or noninvasive CT angiography in a patient with a low probability of obstructive coronary artery disease. He referred to the COURAGE trial, however, a study in patients with predominantly mild angina, and noted that "in many cases a treadmill stress echo can rule out significant inducible ischemia, and the clinician does not need to proceed with an angiogram."
References
Coronary artery disease is a major cause of morbidity and mortality in the United States. Although coronary artery disease is usually diagnosed through conventional coronary angiography, this test is invasive and is associated with potential harms.
There are several options for less invasive imaging procedures to visualize the coronary arteries. However, CT and MRI offer image quality superior to that of other noninvasive modalities. These noninvasive tests may be particularly helpful to reliably exclude coronary artery disease in patients with a low to moderate likelihood of the disease, thereby avoiding an unnecessary invasive test.
