Cardiac Nuclear Medicine
Cardiac Nuclear Medicine
Hossein Jadvar (Doctor) gives expert video advice on: How can I prepare for a cardiac nuclear medicine test? and more...
What is 'cardiac nuclear medicine'?
Cardiac nuclear medicine is basically used to diagnose diseases of the heart. The two major areas of detection are what we call myocardial ischemia, and that is the shortage of the blood to the heart muscle in relation to coronary artery disease. The second major area is in the detection of myocardial viability. Those are areas of the heart muscle which are hibernating. They are not dead yet but they are hibernating, and they're not contracting. So we need to detect those areas of the heart so that we know if we need to restore the blood flow to those areas of the heart, so they come back and contract and contribute to normal cardiac function.
What is an 'ECG'?
ECG stands for electrocardiogram. Essentially, it's a record of the electrical activity of the heart. It is obtained by placing electrodes into the appropriate places on the surface of the body and connecting it to an electrocardiograph, which records this electrical activity of the heart.
What is 'myocardial perfusion scanning'?
Myocardial perfusion scanning is basically a nuclear medicine technique where we inject the patient intravenously with appropriate tracer designed for looking at perfusion or blood flow to the cardiac muscle. For example, we can give technetium nitro ionine system maybe or tetrofosmin, or thallium -201-chloride which basically go to the coronary artery into the heart muscle and tells us how the muscle is being perfused. That's what's called the cardiac perfusion imaging.
What are the benefits and risks of myocardial perfusion scanning?
The benefits of myocardial perfusion imaging is tremendous. Basically it's a very time tested procedure for corneal artery disease in patients. That's the major benefit for us, to establish which patients who are presenting with chest discomfort actually have cardiac origin disease, as opposed to other causes of chest discomfort. The risks of myocardia perfusion scanning are basically similar to what we discuss with general local medicine. They are very small in relation to the radioactivity which is administered to the patient. So the benefit to risk ratio is huge.
What is 'cardiac gating'?
Cardiac gating is when we connect a patient and use the electrocardiogram (ECG) to synchronize the imaging acquisition from the camera system when we're doing cardiac imaging tests. The reason for that is we can actually look at the function and beating of the heart during imaging acquisition. This is important because we can get information about cardiac function with such indices as, for example, left ventricular ejection fraction; which is an important parameter for us to know. So gating is used in conjunction with imaging to give us functional data on the heart.
What is a 'stress thallium test'?
People usually call it a stress thallium test, because previously thallium was one of the most common tracers used, but basically it refers to the procedure of doing a cardiac profusion imaging study, and in that, we normally have a patient imaged after or during a type of cardiac stress. Most commonly, it's when a patient runs on a treadmill or on a bicycle ergo meter, but it can also be done pharmacologically, and not necessarily through some sort of a dynamic exercise. That's the stress portion of it and the thallium really refers in general to the tracer that is administered. It could be cystamibi or tretramospine or thallium and that's basically what is within that term of stress thallium.
What does the equipment used in a cardiac nuclear medicine test look like?
The equipment are basically what we call single-photon emission computed tomography, or SPECT systems. These are usually gamma camera systems that have what we call two heads or three heads. The heads are basically the detectors which surround the patient, and they are able to acquire or record the gamma rays that come off of the patient, and that data is used by the computer to form an image of the heart.
How is a cardiac nuclear medicine test performed?
The cardiac nuclear medicine test is performed after the patient arrives in the clinic. Basically they are interviewed again making sure that the test is appropriate. The patient has been prepared adequately and appropriately. Then they usually receive what we call a rest scan and that is that the patient is injected interveneously with an appropriate radio tracer. And then, after a few minutes, they are placed into a scanner and images of the heart are obtained. These are called the "rest images." Then after that's finished, a second phase of this study will be performed, and that is the stress portion of the image. In the stress portion the patient is connected to an actual cardiogram by placing electrodes on their body. Depending upon what type of a stress is performed, the patient is prepared appropriately for that. For example, in most common cases, the patient is goes onto a treadmill and they start exercising on a treadmill according to a specific protocol. When the heart rate of the patient gets to some point, which is considered the peak for injection of radio tracer that radio tracer is administered at that point at the appropriate cardiac and stress level. During all this time, the patient's blood pressure is also recorded. The electrocardiogram is dynamically recorded to make sure to look at the electrocardiogram for any systemic changes. After the radio tracer's injected at peak stress, the treadmill, for example, is slowed down and the patient is taken off the treadmill. They relax for some time and then after that, the patient is taken to the camera system for taking additional images. And those additional images are called "stress images." Finally the "stress images" are compared to the "rest images" by a nuclear medicine physician to determine if there was, in fact, a stress induced ischemia, because isocheimal shortage of blood to the heart usually occurs when the heart is under stress and needs to work harder. If the coronary artery that is supplying some area of the heart is narrowed, it is unable to deliver the adequate amount of blood or that radio tracer and that we can see when we compare it to a rest study.
What will I experience during a cardiac nuclear medicine test?
The procedure itself doesn't really cause any specific types of sensations. Again, there may be a little pain at the time when the radio tracer is administered intravenously, but other than that, there are really no side effects associated with the radio tracers themselves. Very rare, that we talked about in the past. The patient just lies down, or sometimes in some cases they sit down in a chair, and the camera system is around them, and they take the pictures. There is really no specific sensation associated with that. On the treadmill they may get tired, because they're running for example or they're doing exercise. And of course, if they have coronary disease, they may get their usual chest pain, or angina, with increasing cardiac workload during the procedure. That is really not specific to nuclear medicine, but it's a side issue in relation to the stress that the patient is undergoing for us to appropriately perform the protocol. If the patient is stressed with pharmaceuticals, for example dobutamine, dipyridamole, adenosine, they may also get some specific side effects. For example, they may get headache with some of the pharmaceuticals, such as dipyridamole. Or they may have some chest pain which may or may not be the same as angina that they have outside of the hospital.