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Nuclear Tests – Instrument Based Diagnostic Techniques

by Joseph Alpert, MD
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    00:00 the body dissolve it.

    00:00 Nuclear tests: I’ve already shown you one. That was the lung scan. But there are also nuclear tests to show us abnormalities in the blood flow in the heart. So we already talked about the first one which was lung scanning for pulmonary embolism. The ones that are used for the heart are several.

    00:21 There’s one called the technetium pyrophosphate scanning than can show damaged or dying heart muscle.

    00:30 Thallium imaging can show us abnormality in heart blood flow.

    00:34 A MUGA scan can show us how well the heart contracts.

    00:41 And a less common test – the positron emission tomogram – can actually show us areas of the bodies where there are abnormal structures such as cancers. This is a test commonly used by the oncologists – by the cancer experts – to pick up metastases, that is spread of cancer. The positron emission tomogram can also be used to measure blood flow in the heart to find areas of abnormal blood flow secondary to atherosclerosis.

    01:11 One of the commonest tests done is the so-called stress test. Usually, this test is done with an electrocardiogram but it can also be done with radioactive injection, both of which show us abnormal blood flow in the heart.

    01:26 During the stress test, one exercises the patient. You can see the little cartoon here.

    01:33 It shows the patient with the EKG electrodes on. There are technicians and a cardiologist monitoring the test, watching on a TV screen the EKG complexes, the electrical activity in the heart – looking for abnormalities that might develop that would show there are areas of the heart not getting enough blood flow. One can do this on a treadmill walking or pedalling on a bicycle. And you keep increasing the vigour with which the patient exercises.

    02:05 So you, in a sense, stress the heart. You push the heart and look to see how the heart responded to exertion. Are there areas of abnormal blood flow suggested? Finally, I showed you an example before of a transoesophageal echo. That’s an echo probe placed on a device that actually is threaded down into the oesophagus. But you can also do this test from externally on the chest wall. We do this test all the time for heart disease. It tells us if the valves are normal, if the muscle is working well, is the heart dilated or not. And, as I showed you before with the transoesophageal echo, we can actually identify blood clots in the heart that are at risk for breaking off and causing trouble.

    02:50 A piece of blood clot that breaks off and travels in the body is called an embolus.

    02:57 We already talked about clots breaking off from the veins in the leg causing pulmonary embolism. But you can also have arterial embolism where a clot breaks off from the left atrium in a patient with atrial fibrillation and causes a stroke.

    03:12 We get a very quick assessment of heart valves and heart contraction with the transthoracic test. We get an idea of how vigorously the heart is contracting. And this helps us detect heart attacks, enlargement or weaknesses in the heart and even cardiac tumours.

    03:31 The transoesophageal as I already mentioned is an alternative way. It gives us even better pictures than the transthoracic. A specialised probe is passed down the oesophagus. And you already saw an image of a blood clot in the left atrium in a patient with atrial fibrillation.

    03:50 Finally, the invasive tests. I’ve mentioned them before. In the invasive tests, a catheter is threaded into a blood vessel and dye is usually injected with this catheter so that this dye appears white to the x-ray. And we actually make x-ray movies showing us the channel of a blood vessel to see whether it has been narrowed or not. One also makes certain measurements of blood flow and pressure in the heart that also help tell us something about how accurate the heart is. The overall technique is called a catheterisation.

    04:27 We can also do blood tests when we’re in the different chambers of the heart to see what the oxygen level is, just to make sure it’s normal. And we can even take a little piece of the heart muscle and send it to pathology to be examined under the microscope if we think there’s a tumour there or if we think there’s some other material that’s been deposited in the heart and that’s hurting it.

    04:48 And these are all of the techniques that are done invasively. We can do an angiogram of the carotid arteries. Usually, as I said, we start with a non-invasive test but if we see a critical narrowing and we think about angioplasty – that is the balloon and stent opening of the vessel – or surgery, often an angiogram will be done to give us a better picture of the anatomy before surgery. And carotid stenting actually place a little metal cage in the artery and expands the area of narrowing and holds it open.

    05:25 We can also do electrophysiological studies inside the heart. The electrocardiogram just shows us the heart electrical activity from the surface. When we put catheters in the heart, we can get a lot more information about the electrical activity in the heart.

    05:41 And then finally we can also put a little ultrasound probe on the tip of a catheter and we can use that to show us the thickness of a blood vessel and areas of atherosclerosis.

    05:53 And then finally, only occasionally, we can take a piece of heart muscle with a biopsy to send, as I said, to pathology for examination under the microscope.


    About the Lecture

    The lecture Nuclear Tests – Instrument Based Diagnostic Techniques by Joseph Alpert, MD is from the course Introduction to the Vascular System.


    Author of lecture Nuclear Tests – Instrument Based Diagnostic Techniques

     Joseph Alpert, MD

    Joseph Alpert, MD


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