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The topic I'm going to talk today is physics of fluoroscopy.

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My name is Mahesh. I'm a professor of radiology and radiological science

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at the Johns Hopkins University School of Medicine, and I'm a

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board-certified medical physicist.

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I'm going to talk on the following outline.

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In this particular part, fluoroscopy versus

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radiography, equipment configuration,

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X-ray generator and collimation,

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fluoroscopy imaging modes,

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image intensifier versus flat panel detectors,

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magnification and field of view, and pulse fluoroscopy.

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So let's look in the difference between fluoroscopy and

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radiography.

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Fluoroscopy radiation exposure rate is much lower than

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radiography. That's the first thing,

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and fluoroscopy is a dynamic imaging versus radiography is

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a static imaging.

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For example, here, for an abdominal entrance radiation

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exposure rate for a fluoroscopy, it's about 45

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milligray per minute.

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For radiography, it's 3 milligray,

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and at 200 milliseconds, that accounts to about

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900 milligray a minute. So there is an order of 20 times

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magnitude between radiography and fluoroscopy.

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The low exposure rates is required to avoid

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radiation injury to patient. We're going to discuss later why fluoroscopy

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is done at such a lower radiation exposure rate.

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But we don't do one frame, but we do multiple frame.

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Because of that, the fluoroscopy detectors, the image

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receptor, requires a very high gain.

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When I say high gain, means the conversion of imaging from

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X-ray exposure to actual digital image.

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That receptor does all these things.

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It requires a high optimal or high gain.

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Compared with radiography, fluoroscopy imaging have

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significantly greater noise.

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It also reduced spatial resolution.

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If you just compare one frame of fluoroscopy image

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versus a radiographic image, the image of fluoroscopy is

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slightly higher noise. However, that is integrated with the number of

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frames we do.

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With respect to fluoroscopy, the fluoroscopy at a typical image

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receptor is, for fluoroscopy, is one line pair

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per millimeter,

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whereas radiography can go as high as up to 10 line

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pair per millimeter.

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So when I say the line pair per millimeter, that is the way the

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physics we quantify the spatial

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resolution in any of the X-ray imaging.

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This is a schematic diagram of a fluoroscopy imaging chain.

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You look here on the left-hand side is a photograph of a

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mobile C-arm,

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which is an image intensifier based on the top and

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image flat panel detector at the bottom.

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The fundamental components of an imaging chain are as

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follows. One is the X-ray tube is common.

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Then there is a collimator housing, which allows

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user to adjust the beam size.

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You have then the table where the patient is lied, and the

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table is made up of a material such that it has least

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amount of absorption of the X-rays.

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Then radiation passing through the patient is now then captured

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by an image receptor. In this case, I'm

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showing an image intensifier.

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At the entrance surface, there is a grid.

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The purpose of the X-ray grid is to block off any

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scatter radiation. Then you have the electrical, such

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as optical coupling and video camera for image intensifier,

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slightly different for flat panel, but these are the fundamental

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components of a fluoroscopy imaging chain.

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Historically, fluoroscopy began to be used right from the time when

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X-rays were discovered.

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Radiologists were using this even in the absence of image

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intensifier, wherein the radiologist used to go into the room

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of a fluoroscopy system,

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turn the lights off, get their eyes adjust to the darkness, and then

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move very close to the patient. And this is a

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screen through which the X-ray would pass through the patient

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and allow the radiologist to see a very fuzzy image.

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And we can only see that the person is not wearing an apron, of course, and

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then the amount of radiation required is very high.

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Therefore, the patient dose was also high, and so was the exposure to

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the radiologist in the early days, 1920s and '30s.

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From the time an image intensifier discovered, then at the beginning, the

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radiologist used to stand very close to the image intensifier because there's

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only one eyepiece they used to see the image.

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So early generation fluoroscopy radiologist was

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required to observe directly onto the screen,

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and it is only possible one person view at a time.

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Later development led into a TV, monitors which multiple

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people can see. These images, which are photograph images,

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you can see in the historical museum in the US, at Smithsonian

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Museum. These are very early stage.