Magnetic resonance imaging (MRI) provides additional information about the inside of a patients body and the tissue structures and organs within. In some cases, depending on which area of the body is being imaged, dynamic contrast enhancement (DCE) may be added to the scan. During cardiac magnetic resonance (CMR), which as the name suggests is an MRI exam performed to look at the cardiovascular system, contrast may be used to provide further information. The contrast can be especially useful for studies conducted to determine myocardial viability.
Why does myocardial viability matter?
Myocardial viability is used to determine the viability of the myocadium tissue in a patient's heart. The myocardium is the muscular layer of the heart and lies between the epicardium and endocardium.1 The myocardium controls the heart's pumping action, pushing blood out of the heart and then letting blood in. It requires the most oxygen, meaning it is affected by ischemia, which is characterized by decreased blood flow.
In order to determine the viability of myocardial tissue, certain tests can be conducted by radiologists. These tests are aimed at evaluating whether revascularization is an option rather than cardiac transplant.2 Imaging tests, such as electrocardiography (ECG), positron emission tomography (PET), computed tomography (CT) and magnetic resonance imaging (MRI). Each test offers its own information about the myocardium.
Types of imaging tests2
- ECG: ECG may help detect myocardial viability using different techniques, including resting or contrast ECG. In some case, the left ventricular (LV) ejection fraction (EF) may show improvement with low-dose dobutamine.
- PET: This technique uses a special kind of contrast agent that enters the patient's system and may be integrated into biochemical molecules. Once the radionuclides in the contrast begin to enter the biochemical molecules, the uptake can be monitored and quantified, which can lead to the ability to monitor a variety of functions, including oxidation and oxygen consumption. PET scans use ionizing radiation to produce the images.
- SPECT: For our purposes, the type of CT that is most useful is single-photon emission-computed tomography (SPECT). This test uses a radiotracer that helps radiologists monitor uptake (like with PET). SPECT may be used to obtain images of viable myocardium pinpointed by quantification of uptake. This method exposes the patient to ionizing radiation.
- MRI: This technique helps to assess viable and infarcted myocardium using multiple techniques. MRI may help to assess small infarcts, including some that would be missed on SPECT. Some techniques that may be used in resting MRI, dobutamine MRI, and contrast enhanced MRI. MRI does not involve any sort of ionizing radiation, since it creates the images using electromagnetic fields.
How does MRI help with the detection of ischemia-induced cardiac fibrosis?3
Phase sensitive (PS) myocardial delayed enhancement (MDE) can be completed using MRI. PS MDE helps to suppress healthy myocardium signal, which could lead to a decrease in rescanning due to poorly suppressed healthy myocardium signal. This could allow radiologists and physicians to plan patient care pathways and the benefit of angioplasty.
One patient, a 60-year-old male, was referred for a myocardial viability MR exam.3 His exam included function, perfusion, and qualitative analysis of myocardial viability. The results of the study showed an EF of about 24%, abnormality with delayed and reduced contrast enhancement and systematic cardial fibrosis. However, the team found it was possible to detect myocardial necrosis, as well as myocardial ischemia.3 The patient was able to successfully have angioplasty to recover some of their cardiac function.
Patients, like this man, may find that the additional information provided by PS MDE can help their physicians to decide the potential value of angioplasty, which potential could help to improve the outcomes for these patients. Myocardial viability provides valuable information, and MRI may provide the necessary data. Physicians may wish to consider using cardiac magnetic resonance to determine the value of their treatment options.
- Myocardium. Heart.org. https://atgprod.heart.org/HEARTORG/Encyclopedia/Heart-Encyclopedia_UCM_445084_ContentIndex.jsp?title=myocardium. Last accessed July 26, 2019.
- Myocardial Viability: What We Knew and What Is New. Cardiology Research and Practice. https://www.hindawi.com/journals/crp/2012/607486/. Last accessed July 26, 2019.
- Detecting ischemia-induced cardiac fibrosis with phase sensitive MDE. SIGNA Pulse. http://www.gesignapulse.com/signapulse/spring_2019/MobilePagedArticle.action?articleId=1488826&app=false#articleId1488826. Last accessed July 26, 2019.