Magnetic Resonance Imaging, also known as MRI, is a powerful medical imaging tool used to produce detailed pictures of the interior of the human body. An MRI scanner uses an extremely strong magnet to generate a magnetic field around a patient. This magnetic field, combined with radio wave pulses, activates and energizes the hydrogen atoms in the body. Once energized, the hydrogen atoms emit a signal that is interpreted by a computer and communicated as a high-contrast and high-resolution image.
MRI is used when images are needed of organs, soft tissues, bone and other internal body structures. The most common uses of MRI are to evaluate the brain and spine, pelvic organs, blood vessels, and organs of the chest and abdomen. However, over the past decade physicians have begun exploring MRI’s role in evaluating and monitoring cholesterol and reversing atherosclerosis in patients.
What is atherosclerosis?
Atherosclerosis is a condition of the heart that is characterized by the hardening and narrowing of the arteries. In most cases, the arteries are slowly blocked by the buildup of plaque, putting blood flow at risk. Atherosclerosis is the most common cause of heart attacks, strokes, and peripheral vascular disease, and it is the leading cause of death and disability in both the U.S and Europe.2
High cholesterol is one of the leading causes of atherosclerosis. Not all cholesterol is harmful, however high levels of low-density lipoproteins (LDL) in a patient can collect in the walls of blood vessels in the form of plaque and cause blockages. These higher levels of LDL and plaque formation raise the odds of heart disease and put patients at risk for health concerns throughout their entire body.1
Statins are a common prescribed medication used to lower cholesterol and shrink plaques.3 However, very little is known about the responses of different types of plaques to the various types of medications currently available.
When evaluating the effects of therapy on plaques, the focus should be on assessing plaque tissue composition, inflammatory activity, and plaque burden assessment. Many medical imaging modalities, including X-ray, ultrasound, and computed tomography (CT) scans are capable of assessing the severity of atherosclerosis and studying the arterial walls. However, none of these imaging methods is capable of completely characterizing the composition of plaques.2
Over the past decade, advancements in MRI technology have made it possible for radiologists to directly assess the composition of plaque tissue. Many studies have confirmed that MRI exhibits high contrast for internal plaque features, and that combined information from multiple contrast weightings is critical for distinguishing all plaque components.2
What’s the danger of plaque?
There are different types of plaque tissue composition, and not all plaques are equally dangerous. Some plaques in the artery wall grow to a certain size and then stop. This plaque does not block blood flow and may never cause any symptoms. In other cases, plaque can grow in a slow and controlled way into the path of blood flow. This will eventually cause significant blockages and typically manifests with pain in the chest or legs. The most dangerous plaques will rupture suddenly, allowing blood to clot inside an artery.
The role of MRI in assessing plaque
In order to study plaque morphology in vivo, physicians need an imaging method that can provide an accurate assessment of plaque tissue components and activity. MRI offers a major advantage over other modalities because it can be performed noninvasively and without radiation. Therefore, researchers have begun using MRI’s unique abilities to reveal differences in plaque composition and behavior in an effort to determine what health risks individual blockages present, and how to best treat them.3
In a study featured in the Journal of the American College of Cardiology, researchers followed 51 people who were recently diagnosed with high cholesterol. All of the participants had plaque lesions of the major vessel appear on their initial MRI scans. They were then prescribed either 20 or 80 milligrams daily of Zocor, a popular statin. After being treated for a year and a half, the follow up MRI scans showed that both groups ended up with similar reductions in plaque size, regardless of the strength of the statin dose. Furthermore, this study concluded that monitoring LDL cholesterol can also be used to gauge the effectiveness of statin therapy. The group that received the higher statin dose experienced a 46% reduction in LDL levels, compared to a 36% reduction in LDL among those with 20 milligram doses.4
Another study conducted by researchers at Johns Hopkins resulted in being able to detect the early benefits of a statin much earlier in treatment. Researchers used MRI to measure the success of Zocor in reducing plaque formation in patients with atherosclerosis, and to monitor how well initial cholesterol lowering therapy work for patients with advanced-stage cardiovascular disease in need of quick results.5
During this three-year study, the Johns Hopkins team studied plaque levels in 29 patients. Using a standard MRI scanner, researchers measured calcium deposits at the start of therapy to establish a baseline reading of plaque volume. After six months, they then took another reading to gauge if statin therapy and reduced levels of lipids were correlated to reduced plaque volume.
The results showed that after only six months of therapy, plaque volume levels were significantly reduced on average, by nine percent. The study’s lead author and cardiologist Joao Lima, M.D, associate professor of medicine and radiology at The Johns Hopkins University School of Medicine, believes that their results show the benefits of statins much earlier than before, and how physicians can use MRI to more closely monitor the progress of patients under therapy. Furthermore, he explained how eventually it may be possible to use MRI measurements of plaque volume levels as a predictor to selecting the best statin therapy when treating a patient with atherosclerosis.5
In 2013, a study by Patrick Colletti, professor of radiology at USC and chief of MRI at LAC+USC Medical Center launched a six-year project studying the long-term effect of statins drugs on arterial blockages associated with atherosclerosis. Colletti hopes to learn how plaques in arteries respond to various statins, and to better understand the relationship between medications and the health risks related to atherosclerosis. He believes that MRI scans will give physicians the information they need to tailor therapeutic intervention for individual patients.3
Colletti has been working in conjunction with researcher Zhao Xue-Qiao, a professor at the University of Washington School of Medicine in Seattle. Zhao believes that the study of atherosclerosis has been revolutionized by MRI, as it is capable of providing information about the makeup of plaque deposits and the level of inflammation.3
Moreover, MRI scans are capable of showing lipids depositing in arteries to form a new plaque over time, the healing period known as fibrosis, and calcification, when plaques are less dangerous. This is valuable information allowing doctors to determine patient therapy accurately and accordingly. With the evidence that Colletti and his team are collecting from MRI, they are hoping to use this imaging to predict which plaques will be stable for the long-term, and which patients will need more aggressive therapy. 3
While research continues regarding MRI’s ability to assess and monitor cholesterol, preliminary evidence clearly indicates that MRI is capable of identifying unique characteristics in plaque. MRI of atherosclerosis can depict changes in plaque in cases that are undetectable by other modalities, but still threaten a patient’s survival. As research proceeds, physicians hope to better monitor cholesterol and positively impact the development of heart disease.
- “What is Atherosclerosis?” Web. 4 September 2018. <https://www.webmd.com/heart-disease/what-is-atherosclerosis#1>.
- Zhao, Xue-Qiao and Kerwin, William S. “Examining the Potential of MRI for Monitoring Cholesterol Therapy.” 2012. Web. 4 September 2018. < https://www.medscape.com/viewarticle/767759>.
- Karon, Paul. “MRI helps doctors examine effects of cholesterol meds.” 2 December 2013. Web. 4 September 2018. <https://news.usc.edu/57627/mri-helps-doctors-examine-effects-of-cholesterol-meds/>.
- “MRI Scan Reveals How Cholesterol Drugs Work.” 5 July 2005. Web. 4 September 2018. < https://www.webmd.com/cholesterol-management/news/20050705/mri-scan-reveals-how-cholesterol-drugs-work>.
- “MRI can Measure Early Benefits of Cholesterol-Lowering Drugs.” Johns Hopkins Medicine. 11 October 2004. Web. 4 September 2018. <https://www.hopkinsmedicine.org/Press_releases/2004/10_11_04.html>.