MRI Offers High Resolution for Cardiovascular Diagnosis
MRI meets an expanded range of imaging needs in a noninvasive manner.
Magnetic resonance imaging can explore anatomy and function with superior resolution and enables clinicians to diagnose cardiac conditions that may not be detectable by other imaging modalities, according to Steven D. Wolff, MD, PhD, Director of Cardiovascular MRI and CT for the Cardiovascular Research Foundation.
When imaging cardiac function and anatomy, cardiologists need details on valvular, coronary and cardiac morphology; ventricular function; perfusion; and viability. Among the tools available are cardiac catheterization and transesophageal echocardiography (TEE), which are more invasive; computed tomography (CT), which is noninvasive but limited to cardiac imaging; and single photon emission computed tomography (SPECT) and positron emission tomography (PET), which are lower resolution than MRI.
MRI can address a wider range of imaging needs in a noninvasive manner with high resolution, Wolff said, but is limited for imaging the coronary lumen.
Large field of view
MRI offers a large field of view, high spatial resolution and excellent image contrast between air, fat, muscle and blood. MRI has arbitrary imaging planes, so it is not limited to specific windows as ultrasound is. Its contrast agent is non-nephrotoxic, making it safe in patients with renal insufficiency.
By employing a 3-D volumetric technique, MRI may be the most accurate modality for determining end-diastolic and end-systolic volume, stroke volume and ejection fraction, Wolff said. In patients with heart failure, MRI can be used to monitor treatment success, as it can detect a decrease in ventricle size and is highly reproducible to determine efficacy over a period of weeks instead of months.
MRI can also quantify cardiac function in terms of flow volume. In patients with aortic insufficiency, MRI can monitor and quantify aortic flow and mitral regurgitation.
Anatomic imaging capability
With its superior anatomic imaging capabilities, MRI can enable a clinician to differentiate conditions such as myxoma from lung cancer. High-resolution infarct imaging can be used to differentiate between dead and viable tissue to identify whether patients are candidates for revascularization. In addition, left and right ventricle infarcts may not be detectable by other modalities.
In another example, Wolff showed a patient with heart failure and normal ejection fraction. An MRI image of the epicardium showed unusual thickness that led to a diagnosis of pericardial constriction. In this case, MRI revealed an anatomic abnormality as well as a functional abnormality.
Although MRI lacks the spatial resolution of CT, its field of view is not affected by calcium, making it invaluable in heavily calcified vessels.
Use of both modalities can provide the best comprehensive noninvasive evaluation, Wolff said.