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X-Ray and CT/MRI Scan Imaging – Instrument Based Diagnostic Techniques

by Joseph Alpert, MD
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    00:01 that can get out and cause a stroke or other damage.

    00:01 X-ray and CT/MRI are magnificent imaging techniques that give us very detailed pictures of the inside of the body. So let’s look at each of the kinds of x-ray or radiation techniques used: the plain x-ray, the CAT scan or CT scan, the fluoroscopy sometimes with angiography – with an invasive test – or the lung scan using nuclear-medicine techniques. Let’s look at each of these.

    00:33 So let’s look at the plain x-ray. This uses x-rays – electromagnetic radiation – that penetrate the body. And in fact the first x-rays were done here in Germany by a man called Roentgen. And that’s why we talk about Roentgen rays or x-rays. It shows the internal structure of the body. The x-ray generator produces a similar and smooth beam of x-rays that projects towards the body. Organs and bones absorb certain amount of the x-rays and lungs and so forth where air absorbs less. And then there’s a photographic plate or a screen that’s very sensitive to the x-rays behind and it gives us a two-dimensional image of the body’s internal structures. You can see on the example that there is the heart and the lungs and the ribs.

    01:31 The CAT scan is a more sophisticated x-ray machine. It uses the same form of electromagnetic radiation but it does it in a three-dimensional manner. And also using a computer program reconstructs two and even eventually three-dimensional images. So you can see here what’s going on. There are images. X-rays are given from different angles and they produce a cross-sectional or so-called tomographic image. And these virtual slices can be put together even to show us a three-dimensional reconstruction. This is very good for looking also at the soft tissues. It doesn’t just show the bones. There are very specific areas inside the body that can be displayed such as the various heart chambers. It shows, at times, the extent of occlusion in coronary arteries when dye is administered. So in a sense it’s a sort of non-invasive technique at angiography. The patient’s injected with an intravenous iodine dye and the heart is scanned using a very high speed CT scanner. And we can actually image the blood vessels in the heart, the arteries. And here is a picture of an actual CT scanner.

    02:54 Fluoroscopy is very much like the plain x-ray except that we’re looking at a fluoroscope and we can actually see the heart moving and sometimes even the blood vessels pulsating with the fluoroscope. We use the fluoroscope when we’re also doing invasive testing so that we can guide the catheters into the right place to inject dye so that we can see pictures, for example, of the coronary arteries. Fluoroscopy uses the same x-rays as I said before and it gives us moving images of the body’s interior.

    03:27 With angiography – we’ll mention that later – that’s an invasive technique where catheters are placed into the body and dye is injected directly into various arteries.

    03:38 And we can visualise the channel to see if there are obstructions. This can be done both for the arteries and for the veins when we want to see if there’s obstruction in either of those areas and we can also see if there is obstruction within the heart chambers.

    03:54 The lung scan consists of an injection as well as inhalation of radioactivity. What we do first is to have the patient take a deep breath. And in that breath there is radioactive xenon gas and it shows us the distribution of the air in the lung. Then a different radioactive substance – there’s a variety of different ones, one of the commonest is radioactive technetium – is attached to albumin molecules. And it’s injected intravenously and it goes where the blood flow goes in the lung so that we get a picture of where the air is with the xenon inhalation, so-called ventilation scan. We get a picture of where the blood itself is going in the perfusion scan below. And we make a comparison. In patients with clots in the lung – pulmonary embolism – such as this example, the aeration is normal but there are multiple areas where the blood flow is abnormal because there’s obstruction in the pulmonary circulation from clots.


    About the Lecture

    The lecture X-Ray and CT/MRI Scan Imaging – Instrument Based Diagnostic Techniques by Joseph Alpert, MD is from the course Introduction to the Vascular System.


    Author of lecture X-Ray and CT/MRI Scan Imaging – Instrument Based Diagnostic Techniques

     Joseph Alpert, MD

    Joseph Alpert, MD


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