Hello, my name is Mahan Mathur, and the following will be an introduction to radiology. And over the course of this video series, we're going to be covering conventional radiography, we'll follow that up with computed tomography, CT imaging, then ultrasound, then finish out with magnetic resonance imaging. And the objectives are fourfold, for the conventional radiography portion of this lecture, the objective is to be able to distinguish the five basic radiographic densities on radiographs. So we'll start off with conventional radiography, we'll dive a little bit into historical context before going into the five basic densities, the techniques that we use, and the uses for it from a clinical perspective. So this gentleman over here is the founder of radiology in some sense. His name is Wilhelm Conrad Rontgen. He was a German physicist and at 8th of November of 1895, he discovered x-rays. And for this, he was awarded the first ever Nobel Prize in physics, and this was in 1901. He actually never sought patent protection for this discovery and we're so indebted for that because it really has revolutionized the way we practice medicine. So how did this all come about? Well back in 189, Rontgen and a whole bunch of physicists were experimenting with something called cathode tubes, particular one he uses something called a Crookes tube. And what it was is essentially like a big large light bulb. And inside of it there was cathode end which is connected to a negative portion of a power source, a very high voltage power source, and anode which was connected to a positive portion of that same power source. And when you switch on this power source, there would be bluish hue that would emanate from inside this structure, and those were known as cathode rays. And there was some theories that in addition to cathode rays, there were other multiple additional rays that were being emitted, they were yet to be discovered. So on that day in November of 1895, he went to his lab, he connected his Crookes tube into a high voltage power source and put actually a black cardboard box over the tube, switched off the lights and switched on the tubes. And what he found was that everything was dark except there was a piece of paper about a meter away, which happened to be coated with some fluorescent material barium platinum cyanide that actually started glowing. And when he switched off the power source, he realized the glow went away. When he switched it on, it would switch back on, so he investigated this a little bit further because he had put a black cardboard box over this that eliminated the theory that this fluorescent screen could be shining due to the presence of ultraviolet rays or visible right light rays. And also cathode rays themselves are eliminated because they would only travel about less than 10 centimeters, and this was placed much further away from that. So from that, he introduced that there was probably something else, some other mysterious ray that was being emanated as a result of this interaction. And he named that x-rays for the algebraic symbol for the unknown was X. And so he didn't know what it was until he named it x-rays. Now in reality, would happen is something close to what I'm showing you over here. You certainly have a cathode on which there's a filament that's tied up over here. And when you connect it to a high voltage power source, it actually boils off a bunch of electrons. These electrons had an anode on the opposite side and they produce the x- rays, that interaction. A lot of that interaction actually gets dissipated heat, but about 1% will produce x-rays. And those are those mysterious rays that cause that screen in 1995 to shine and become fluorescent. So this supposedly is one of the first ever x-rays that was ever produced. And it said that this is the hand of Rontgen's wife. And as you can see, some of the x-rays certainly pass through her. And you can see that fluorescent screen in the back being very bright or white. And some of the x-rays don't pass through her, not through her bones over here, which are dark and not through her ring as well, which is very, very dark. And so when you take these x-rays and you actually then project them onto a photographic film, the areas that are bright on the fluorescent screen were black in photographic film. While the areas that are dark on the fluorescent screen will actually be white on that photographic film. And so essentially, that's what an x-ray that we know it looks like. So this is what it would look like if you just invert those color scheme. The key idea here is that x-rays when produced will interact with objects in different ways. Some will go through the objects in which case they'll blacken the photographic film placed behind it. While some will not go through the object, it will be attenuated, in which case they'll be various degrees of gray or white that we see on that photographic film, so this is a key concept. As a result of this interaction, we basically have five densities that we can identify in conventional radiographs. They are air, fat, fluid and soft tissues bundled into one, bone, and metal. Now with air, everything goes through and so that will blacken the film or the cassette that we place behind patient, while metal, nothing will go through. So it will be a very bright white, and everything else in between will be different shades of gray. So if we look at this radiograph of the abdomen, just to orient everybody, up here will be the head of the patient, down here will be feet of the patient, that's the right side, that's the left side. Have a look and see if you can name the following densities on this. The answers, I'll show you here, this darkest stuff in the left upper quadrant is going to be a air. The brightest stuff here is going to be metal. Bones can be the next brightest density, that's going to be white, but not as bright as the metal. Soft tissue, which is anything from the subcutaneous fat to the organs to fluid that's contained in the body will all have a relatively white appearance. And fat will be somewhere in between the densities of soft tissue and air. So you can see that it's relatively dark but certainly not as dark as air. So that little strip up there is going to be fat. And if you look there are other evidence or metal on this radiograph. You can see surgical clips in the left groin area of this patient, as well as these markers that say supine and left side indicating how the patient is positioned in which is the right side which is the left side of the patient. In terms of technique, this is also a key concept. For any x-ray that's taken and ideally you'd want to take two views in order to best visualize everything and they should be done orthogonal to one another at the very least. So here you have a patient, this is going to be the x-ray source, this is a film that's placed in front of the patient over here. So that's one view of the patient standing up and this is another view of the patient lying down. So we have to radiographs over here, one of them is upright, one of them is supine, how can you tell? Well the first clues always on the radiographs which I've actually cropped. So you don't get the answer here, is that they'll always be labeled. This is going to be the upright, this is going to be the supine, these are metallic markers that are just placed on the machine to make sure that you know which one is upright and supine. But there are also clues on the images that can help. For example, in this image, we can see multiple air fluid levels, these straight lines that are contained in the bowel, suggesting that this patient is actually standing up to have the water lie dependably within the bowel loops and you don't see those over here on the supine radiographs. Now why do we get multiple views? Well, let me show you. So this is an x-ray of the distal extremity, the right lower extremity, the ankle area and somebody who fell down and had some pain. And if you look at this, this is the fibula, this is the tibia, it looks pretty okay. Maybe subtly, there's a little bit more thickening of the skin or the soft tissue in this region versus this region, so that could suggest that maybe there's been some injury there. But it certainly looks like everything's intact if you follow the contours of all the bones. We can take in a little bit more oblique manner and here again, for the most part, it looks pretty good. Maybe there's a little bit of a subtle lucinschi here, but it'd be very hard pressed for you to call that a true fracture. And finally, if you get a lateral view, you can see very clearly there's a crack in this bone, this obliquely oriented dark line and this is going to be a fracked, very, very difficult to detect on the frontal or oblique radiographic views. Now in terms of the terminology, this is important. We call a radiograph, particularly this is when we're talking about chest x-rays, PA versus AP. PA refers to postero-anterior and AP is antero-posterior. When refers to how the x-ray is first entering the patient, so if it's entering it, so it goes to the patients back first, we call it a postero-anterior x-ray. Well, if it's entering the patient, so it's going from the frontal side of the patient to the back, we call an antero-posterior x-ray. And this is important because this can have effect on how things look. Here's an x-ray generator that's similar in concept to what was shown earlier. This is the cathode, this is the anode, there'll be electrons that boil off the cathode, go to the anodes, will produce x-rays. And as you produce x-rays, you can see with the PA technique, the x-rays hit the back of the patient first and the heart in this case is closer to the film. With the AP technique, the x-rays hit the frontal aspect of the patient first and you can actually see that the heart is away from the film. And so this is an important concept and that the closer that the object is to the film, the less prone it will be to have magnification blurry edges. If you take that object away from the film, it'll actually magnify and have more blurry edges. And you can actually do this experiment on your own. If you take your finger and you shine a light source behind it, perhaps from your smartphone if you have a light source and you shine it on top of your finger and you project your finger onto a piece of paper. The closer that finger is to the piece of paper, the more accurate the size of the shadow that it casts in terms of what the finger looks like. The further you move that finger away from that piece of paper, more magnified and blurry edge you will get. So how does this work practically? If you look at these two chest x-rays on the same patient, taking a few minutes apart, one of these is a PA projection, the other is an AP projection. So have a look and see if you can figure out why. As you can see here, this will be the PA projection, this was the AP projection. The heart here looks much larger. If you follow the edges around the middle of this radiograph, it look very blurry, certainly on the lateral aspect of the air radiograph look very, very blurry. Here looks much sharper, much crisper. If you were to look at this x-ray, this would be a normal x-ray, if you were to look at this, this may seem like the patient has that too much fluid, maybe a pulmonary edema. So what is conventional radiography useful for? One of the prime reasons is to use it to detect fractures in patients with trauma. It's a quick modality, it's cheap, there's less radiation and can depict fractures very well. In this instance, you can see a fibula fracture with multiple complex components. It's also very useful when you want to place lines in patients whether it's in the arterial venous structures or in the stomach or in different locations. You can get the final location of lines, it's a very cheap modality, quick modality. In order to look at that, and if it's in the wrong position, look at this line over here, it's supposed to be in the stomach. Where do you think it's placed? This was actually placed in the airways. And so it's important to be able to detect that so you don't initiate feeding and cause damage to the lungs. It's great for some abdominal emergencies, for example free air. So you should never have air inside your abdominal cavity, it should be located in the bowel. If that air escapes the bowel, that goes inside the abdominal cavity and causes the appearance of free air as you can see over here. So this is abdominal emergency and this patient would have to go to the operating room very quickly. And finally it's very useful in day to day chest imaging, particularly in patients who are placed in the intensive care unit. Often they get pneumonias, they get aspiration, they have too much fluid, overload and so chest x-rays are a very good way to look at that on a day to day basis. This patient has a lot of whiteness in their lungs, suggesting there's some fluid or infection that has infiltrated the lungs. So in summary, for conventional radiography, these are the five basic radiographic densities, air, fat, water and soft tissue, bone, and metal. And it's also important to understand the different techniques that are done. You need multiple views to see pathology, and PA and AP is also important as it has a effect on the way things look.
