Imaging the Heart
Heart disease is often thought of as a “man’s” disease. However, every year, about the same number of men and women die from heart disease. Moreover, heart disease is the leading cause of death for women in the United States. A woman has about a one in four chance of dying of heart disease. By comparison, chances of dying from breast cancer are about one in thirty.1 In the US, we screen for breast cancer through mammography.
Unlike mammography, there is no simple screening imaging test for heart disease. Despite this, imaging does play a significant role in the assessment and treatment of our biggest killer. Modalities include nuclear medicine, echocardiography, cardiac catheterization, computed tomography (CT scans) and magnetic resonance imaging (MRI).
The two most commonly used nuclear medicine studies of the heart are the “stress” test and the MUGA scan. For a stress test, a patient is injected with a small dose of radioactive tracer that accumulates in active heart muscle, both at rest and after exercise, most often on a treadmill. After each injection, the patient gets scanned on a special camera. The “stress” and rest scans are compared, and a difference could indicate ischemia.
The MUGA (multigated acquisition) scan uses the patient’s own red blood cells tagged with radioactivity to accurately measure how much blood the heart can pump.
This is an ultrasound exam of the heart. High frequency sound waves are produced and their reflections off tissues are detected by the same transducer. A computer generates images based on the echo pattern. This allows the doctor to see the anatomy of the heart in real-time and to examine the function of the heart valves and heart chambers.
In this procedure, a small catheter is placed in an artery, usually in the thigh, and advanced backwards through the aorta to the left side of the heart.
The arteries that supply the heart muscle (the coronary arteries) take origin just where the aorta meets the heart. The catheters are placed in these vessels, and x-ray dye is squirted through them, while the x- ray camera rapidly films the passing dye. This is a coronary angiogram, and it is the gold standard for looking at these arteries. Diseases of these vessels cause chest pain and heart attacks. Multiple interventions, including stenting open narrowed coronary arteries, can be done at catheterization.
The recent advent of fast, multidetector CT scanners have allowed doctors to take CT pictures fast enough to “stop” the action of the heart and see the anatomy clearly. On older scanners, the heart was a blur. With appropriate timing of x-ray dye, images can be made of the heart chambers, and even the coronary arteries, using intravenous injections rather than the more invasive and expensive cardiac catheterization.
The patient is placed in a large magnet, aligning the body’s hydrogen molecules along the magnetic field. Radio waves pulsed at the patient then affect this polarity differently in different tissues, and a computer can generate images of the anatomy from maps of these effects. This method has several special uses for the heart, including examination of heart muscle, scarring and valve function.
Heart disease is our number one killer. While no simple imaging screening exam exists, imaging of the heart is integral to the diagnosis and treatment of heart disease. All of the above cardiac imaging modalities are available, by referral, at one or more of the local Novant affiliated hospitals, imaging centers or cardiology offices.
By Kevin M. Spangler, M.D., Ph.D. Staff Radiologist, Neuroradiology and Cardiac CT, Triad Radiology Associates
- United States. Women and Heart Disease Fact Sheet. Atlanta: Center for Disease Control and Prevention, 2010. Web. 2 Jan 2011.