MRI studies demonstrate
pre-emptive usefulness of imaging
By Jan Jarvis
Researchers at UT Southwestern Medical Center are using MRI of the aorta to help predict the risk of cardiovascular events such as heart attacks and vascular diseases in the brain.
In one study, published in the June issue of Radiology, researchers found that increased abdominal aortic wall thickness and plaque buildup correlated with a greater risk of all types of cardiovascular events. Also in that issue, researchers in a separate study used MRI to measure aortic arterial stiffness, a strong independent predictor of diseases of blood vessels that supply the brain.
Both studies involved participants from the Dallas Heart Study, which was designed to detect early disease, said Dr. Ronald Peshock, Assistant Dean of UT Southwestern Medical School and Professor of Radiology and Internal Medicine. In the new and ongoing studies, researchers are looking at the progression of disease.
Predicting cardiovascular events
In the first study, researchers used MRI to measure very subtle but significant differences in two distinct measures of aortic atherosclerosis: aortic plaque buildup and thickness of the aortic wall.
Both measurements are predictors of cardiovascular events, but there’s an important difference between accumulation of plaque and the thickness of the aortic walls, said Dr. Amit Khera, Associate Professor of Internal Medicine and senior author of the study.
“Accumulation of plaque tells us there is increased risk for peripheral vascular occlusion, stroke, and abdominal aortic aneurysms, but not all forms of cardiovascular events, including heart attacks and death from cardiovascular disease,” he said. “In contrast, thickening of the aortic walls is more likely to be predictive of all forms of cardiovascular disease.”
Those with the thickest aortic wall have almost a twofold higher risk of a future adverse event as does someone who has a thin aortic wall, Dr. Khera said.
The size of the aorta also contributes to the ease of using MRI as a predictive tool for cardiovascular events, said Dr. Christopher Maroules, a diagnostic radiology resident at UT Southwestern and lead author of the study.
“The aorta is the largest artery of the body and is relatively fixed in position, making it an ideal target vessel to interrogate with MRI,” he said. “The coronary arteries, in contrast, are a fraction of the size and undergo constant respiratory and cardiac motion, making them more challenging to image.”
In addition, the abdominal aorta often is incidentally imaged during routine MRI exams of the spine and abdomen.
“Radiologists may be able to infer prognostic information from these routine exams that could benefit patients by identifying subclinical cardiovascular disease,” Dr. Maroules said.
Predicting vascular disease in the brain
In the other study, the relationship between aortic arterial stiffness and cerebral microvascular events was evaluated.
Researchers found aortic arch pulse wave velocity – a measure of arterial stiffness – was a stronger predictor of cerebrovascular disease later in life than were traditional clinical risk factors.
While measuring arterial stiffness using pulse wave velocity is believed to be more accurate than other methods, it is not widely used because the technique requires special equipment and training, said Dr. Kevin S. King, Assistant Professor of Radiology and lead author of the study. A common clinical method to estimate arterial stiffness is measuring pulse pressure through the traditional arm blood pressure test, but this is insufficient, he said.
“MRI measurements, on the other hand, can provide important information on the stiffness of the aorta among patients already being evaluated with MRI, without a significant increase in scan time and at a minimal cost,” Dr. King said.
In the study – which showed that arterial stiffness is the strongest predictor of age-related elevations in the brain’s white matter hyperintensities, which are the marker of cerebral microvascular disease – the aortic arch pulse wave velocity was measured using MRI. Then, seven years later, researchers measured the volume of white matter hyperintensities, which appear as bright spots on MRI and are associated with accelerated motor and cognitive decline, Alzheimer’s disease, and stroke.
The information could lead to clinical tests that better predict the risk for some brain diseases, Dr. King said.
“A lot of attention is being given as to how to protect the brain from aging,” he said. “Given the aging population, there’s a lot of interest in how people can live longer, healthier lives.”
Dr. Khera holds the Dallas Heart Ball Chair in Hypertension and Heart Disease.