Figure 1: Cardiac catheterization lab setup

Figure 1: Cardiac catheterization lab setup

In this picture, we see the table that the patient lies supine on during the procedure. The image intensifier (which detects the X-rays to form an image) is anterior to the patient, and the X-ray source is posterior to the patient. The concept of backlighting is very important in developing an intuitive understanding of the images.

Because the image intensifier is what collects X-rays to create an image, we will represent it with a camera. Similarly, the X-ray source will be represented by a light bulb.

Figure 2: Schematic illustration of C-arm

Figure 2: Schematic illustration of C-arm

Because of this backlighting, we are really looking at “shadow puppets” of the coronary arteries.

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The further an object is from the image intensifier, the closer it must be to the x-ray source. Counterintuitively, this means images that are further from the image intensifier actually appear larger!

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This key concept is illustrated with the graphics below:

Figure 3: Object far from light source appears relatively small

Figure 3: Object far from light source appears relatively small

First, the blue star is relatively far from the light source, resulting in a relatively small shadow.

Figure 4: Object near to light source appears relatively large

Figure 4: Object near to light source appears relatively large

Next, we move the blue star relatively closer to the light source, resulting in a larger shadow, even though it is further from the source

To see this concept in action, consider the following cineangiogram:

Video 1: Left anterior oblique caudal angiography

Video 1: Left anterior oblique caudal angiography

Here is a still image with the LAD and LCx labeled.

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For some, this intuitively appears as if the proximal LAD and LCx are close to the viewer and move further away (i.e. “dive into” the screen) as the vessels course toward the apex. However, this image is actually obtained by viewing the heart from the apex. Therefore, the left main, proximal LAD, and proximal LCx are actually the furthest from the viewer, and the distal vessels are closest (i.e. they are “emerging from” the screen).