Image intensifier basics and nomenclature (sneak preview #3)

Coronary angiographic views and terms like LAO cranial or RAO caudal can sometimes be pretty confusing. But they are not that difficult after all. This short video will bring you up to speed on image intensifier basics. You will learn what the C-arm is and how it can move around in the 3-dimensional space to acquire the optimal image of each coronary artery and stenosis. 

 

[00:00:00] So let's take a moment to look at how we acquire an angiographic image and also discuss some of the terminology that we use. Like any procedure that involves ionizing radiation, we need an x-ray source and that's shown here on the diagram. This emits x-rays and it's detected, here, on something we call an image intensifier. In the cath lab, the x-ray source and the image intensifier are connected together by this structure.

[00:00:30] We call it a C arm because it looks like a letter C. We position the patient in the x-ray beam centering on the heart. The C arm is then able to move around the patient in a number of different directions or planes, to take different angiographic views. These are described in two anatomical planes. We're going to use the same key throughout the whole of this course. The first plane, in the top right-hand corner, here,

[00:01:00] shows the plane looking from the patient's feet towards the patients head. In the second anatomical frame, shown in the bottom picture, here on the right, we're going to look at the patient from the side on position. Starting with the first anatomical plane, looking from the feet of the patient towards the patient's head. If the x-ray source is situated directly below the patient, with the image intensified directly above the patient, this is

[00:01:30] referred to as a standard starting position or 0 degrees. You can see that the image intensifier can then rotate around the patient towards the right, known as the right anterior oblique or RAO view. The image intensifier can also rotate to the left, known as the left anterior oblique or LAO. As you can see from the diagram, the image intensifier can rotate right around to 90 degrees,

[00:02:00] in either a right or a left direction. If it rotates over here, to 90 degrees, it's known as the right lateral. If it rotates over here, to 90 degrees, it's known as the left lateral. Here are two example views. Using our key, you can see that in this picture, the image intensifier has rotated 30 degrees to the right, and so we named this RAO 30 degrees or RAO 30 for short. In the bottom image,

[00:02:30] the image intensifier has rotated 40 degrees to the left of the patient, we note that as LAO 40 degrees or LAO 40 for short. Moving on to the second plane, we can now see that the image intensifier can move towards the head of the patient, known as a cranial angulation or towards the feet of the patient, known as a caudal angulation. There's a physical limitation here that isn't apparent in the other plane. All modern image

[00:03:00] intensifier devices are fitted with proximity monitors. These are essentially devices to ensure that the machine does not collide with a patient to cause injury. As you can see in the diagram, there is a limit to how far the image intensifier can move, in a cranial direction, before it comes into contact with the patient. Similarly, there is a limitation to how much the image intensifier can move in the caudal position for the same reasons. Looking at two example images, on the right again,

[00:03:30] you can see in the first top right picture, the image intensifier has moved to 30 degrees, angulated towards the head of the patient. This is described as cranial 30 degrees or cranial 30 for short. In the bottom image, the image intensifier has been angled 20 degrees towards the feet of the patient, caudal 20 degrees or caudal 20 for short. Let's look at a common angiographic view, LAO

[00:04:00] cranial view. You'll now know from our previous slides that this means that the image intensifier must be towards the left of the patient, in one anatomical plane, LAO. And at the other anatomical plane, it must be towards the head of the patient, cranial. What you don't know is the specifics of how much it's moved, in either of these different angulations, in either plane. It's very important to know exactly where the image has been acquired from,

[00:04:30] in terms of the angulations, so that it can be reproduced. If we now add an angulation to both of the different planes, and change LAO cranial into LAO 40 degrees, cranial 25 degrees, you can quite clearly understand now the image intensifier is 40 degrees to the left-hand side of the patient, LAO 40 and 25 degrees towards the head of the patient, cranial 25.