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Let's examine the fluoroscopy imaging mode.

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There are a variety of modes available for any user in

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fluoroscopy. Among them, the most common one is the

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normal fluoroscopy mode. That includes also

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magnification mode, which is the most commonly done across the board.

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Then there is also option called high-dose fluoroscopy mode,

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which is used in certain circumstances, and

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these days it is used less and less.

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In addition, fluoroscopy system also has the capability to record,

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such as spot film, photo spot, and digital

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photo spot.

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For a system which is typically configured for cardiology,

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you also have the capability to do a conventional and

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digital cine.

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In addition, most fluoroscopy system, especially in the interventional system,

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also have the capability to do digital subtraction angiography,

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also called as DSA.

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So let me go through some of these things.

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Why this makes such an important in which mode we are

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operating, and that has an implication on image quality,

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and more so on the patient radiation dose exposure.

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These are the typical skin entrance exposure rate.

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This is one way we measure in

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fluoroscopy what is the radiation exposure rate on the

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skin surface. Because if we do a fluoroscopy for

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a very long time, the same skin surface get lot of

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radiation can trigger skin injury.

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In fluoroscopy, the normal fluoroscopy means

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if it is operating in a normal fluoroscopy mode on an

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average size patient, the radiation exposure to the skin

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surface is one to five rads per minute.

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That is 10 to 50 milligray per minute.

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The reason why I'm showing this and the importance of it will be discussed later

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part when we talk about the deterministic effect and stochastic

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effect. But here is the different mode.

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When it's operating in the normal fluoro, it is one to five rads per

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minute if the system is set properly.

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If the system can be set very high, and the radiation dose can be very

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high, too. And that's also one of the reason why

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we advocate any new fluoroscopy system to

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be evaluated by a medical physicist to make sure they're

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operating in this reasonable radiation dose level.

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If the system is operated in a high dose fluoro mode,

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the radiation typical dose rate is 10 to 20 rads per minute.

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That can accumulate 100 to 200 milligray per minute.

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So in interventional fluoroscopy, for example, if

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it is done for one hour of radiation exposure,

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that can lead to 60 to 300 rads of

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exposure to the normal fluoroscopy mode or

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600 to 1,200 rads with high-dose fluoro mode.

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And that has an implication on the radiation injuries to the patient.

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In the United States, based on the FDA, there are

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some limitations on the equipment, which means

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when you're operating under fluoroscopy system,

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the maximum exposure rate cannot exceed

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10 R per minute. This is defined at what's the

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radiation dose measured at 30 centimeter from the

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image receptor, assuming the patient size is 30 centimeter,

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and there are defined system. For this particular lecture, it

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suffice to say, for normal fluoroscopy mode, it

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cannot operate more than 10 R per minute.

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So because of that, when the patient is very obese,

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larger,

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and the system cannot go beyond 10 R per minute, the

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image is very noisier and difficult to view, and

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that's when the system can be operated on a high-dose fluoro mode.

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If we turn it to the high-dose fluoro mode, the radiation limit now can

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go up to 20 R per minute, basically

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allowing for the physicians to visualize with

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much lesser image noise.

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At the same time, there are no radiation limit for cine and digital,

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and that's why it's important for a medical physicist to

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evaluate before they start using on the patient, because they can be

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set unnecessarily very high.

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One of the other point of interest is when you are

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operating in a high-dose fluoro, the system is required to

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give a very high audible signal,

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basically indicating that you're operating on a high-dose fluoro and you

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are not unnecessarily exposing the patient.

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This is a busy slide. I just want to give a relative comparison

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between a typical standard fluoro versus high-dose

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fluoro, cine, DSA, and typical radiograph.

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We're going to show this image. I'm going to show this again later in the image

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radiation dose. But just want to show you if the system is

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operating properly. You don't need more than one and a half to

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two and a half micro R per frame to give a good

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image quality.

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In a high-dose fluoro, it's usually double, three to six

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micro R per frame, and cine is

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10 to 15 micro R per frame, and DSA is 500 to

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1,000 R,

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micro R per frame. How does that translate to typical number of

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radiograph?

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This is a back of the envelope calculation, basically showing the

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radiographic equivalence

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for the various imaging mode.

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If someone operate normal fluoro for one minute based on

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30 frame per second,

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compared to a radiograph at 400 frame per second,

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which require about 300 micro R per frame

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A normal fluoroscopy for one minute, which is at two microamp per

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image,

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is equivalent to approximately 12 radiographs.

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And the high fluoro for one minute is two, which is six

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microamp per frame,

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is equivalent to taking 36 radiograph.

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A DSA run of 10 runs at 10 images

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per run can yield up to 333

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frames or radiographs.

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So just to give you an example how the scalable and how much the

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variation between the different operating modes.

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A salient feature of a fluoroscopy system is automatic brightness control

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or automatic exposure control, called AEC.

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The purpose of this one is increased radiation is needed to

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penetrate thicker body parts,

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bone, instrumentation, and so forth.

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So the X-ray tube automatically adjusts to keep the

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image brightness same. That is why it's called automatic

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brightness control or automatic exposure control, and

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it automatically matched with respect to what amount of X-rays

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reaching the image receptor, automatically adjusts the X-ray tube

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techniques to deliver the same amount of brightness.

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The automatic exposure adjustment versus X-ray

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response is to patient thickness is as follows.

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Basically showing here is a thin versus a thick patient,

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and on the bottom X-axis is a tube voltage and the tube

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current. For a thin patient, if this is the amount of technique

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used for radiation dose, which is delivered here,

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if the mA is increased,

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that automatically means it is higher dose

7:54

and more contrast because you're using it at low kV.

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On the other hand, if the kV is increased, it can decrease the lower dose

8:02

to the skin, but it also can provide less contrast.

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So there is a trade-off between thin and thick patient and how the tube current and

8:10

tube voltage can be adjusted.