When a patient’s coronary artery disease symptoms appear to be coming from more than one source, physicians need the best picture possible to fully understand the root of the problems. Research suggests that new techniques in cardiac MRI may help narrow down which vessels are culprits even better than before.
The ability to image the heart is changing. While recent innovations aren’t global yet, cardiac magnetic resonance imaging techniques are taking understanding multivessel disease to a whole new level. Increased speed of MR image capture and coding allows physicians the option to improve their view through either 3D or high-resolution technology (Circ Cardiovasc Imaging 2013;6:339-348). While these techniques are still in their infancy, what they reveal holds significant promise. And many in the field are looking forward to even more changes to come.
With speed comes innovation
With extra speed, a team of researchers were able to compare traditional and advanced cardiac MR techniques to get a better look inside coronary arteries. Sebastian Kozerke, PhD, a professor with the Institute for Biomedical Engineering at the University and ETH Zurich in Switzerland, Manish Motwani, PhD, a cardiologist formerly of University of Leeds in the U.K., lead the research teams.
“One of the problems with imaging multivessel disease or three-vessel disease is that sometimes the whole heart is ischemic,” says Motwani. “The whole heart doesn’t get a lot of blood and, therefore, it can be difficult to pick out normal areas from ischemic areas.” Improving cardiac MR’s resolution from 3 mm down to 1 mm, he notes, provides more detail into which vessels may specifically be part of the problem.
“MRI has high spatial resolution,” Motwani says, and by increasing that resolution further, “we found that technique was able to pick out areas of the heart with a low blood supply even better than standard cardiac MRI.”
While, as Kozerke states, the techniques are still being refined, these techniques and the increased speed could make a powerful tool even more so. Improved resolution, “helps a lot when looking at triple vessel disease because then you can see perfusion gradients across the myocardium which couldn’t be detected with coarser resolution,” he says. And when looking at the effected heart in three dimensions, it allows a physician to see perfusion defects in the apex, which can be missed with the standard three-slice 2D CMR. However, at present, “it’s a compromise between coverage and resolution.”
Both techniques were developed to overcome the limitations in using standard 2D CMR imaging to quantify ischemic burden and overall affected myocardial area. In particular, high resolution provides more minute detail, while 3D provides a greater area of coverage and better understanding of ischemic burden (Circ Cardiovasc Imaging. 2014 Jul;7:647-654), allowing physicians to see more as recommended by current guidelines (Circ Cardiovasc Imaging 2015;8).
With resolution down to 1 mm, physicians also have noticed fewer artifacts, like dark rim artifacts, which previously led to increased false positives. Other details that are clearer with improved resolution include the difference between primary stenosis and areas of the myocardium still receiving some blood flow through peripherals and subtle perfusion defects in the endocardium “that are very difficult when you have very course resolution. That’s what people are seeing now with the higher resolution techniques,” Kozerke says
At present, however, it’s important to note that cardiac MR imaging allows for either 3D, whole heart coverage or higher resolution imaging, but not both, barring further innovation.
Cardiac magnetic resonance imaging does have its advantages and limitations, however.
As Daniel S. Berman, MD, chief of cardiac imaging and nuclear cardiology and professor of imaging and cardiac medicine at Cedars Sinai Medical Center in Los Angeles, Calif., points out, the advantages already inherent in cardiac MR lie in the high resolution of the images and the ability to provide these images without exposing a patient to radiation. “It is the only technique to really accurately be able to do tissue characterization; to look at multiple different processes within in the myocardium or heart muscle, such as scaring or inflammation or edema that can occur in various cardiac diseases,” he says.
Berman argues that cardiac MR trumps SPECT and others, “providing a