Hello, welcome back. This is the section where I want to talk about the different types of Imaging. We hear a lot about CAT scan, MRI's scans, PET scan, all kinds of scans, and what I wanted to do was give you a way to categorize the different types of imaging so that you could understand them and sort of keep them straight in your head. So the best way that I thought of to do that was to categorize the different types of imaging body energy that actually produces the imaging and that there's really just four basic types of energy. We have X-rays, of course, which everyone's heard of and X-rays are used to produce the plain films or radiographs and also CT scans and then several other different types of images. A magnetic field is used to produce MRI, which a lot of people don't realize, and they think that, that gives radiation as well, which it does not. Sound waves are used, of course, to produce ultrasound images, and radioisotopes are used to produce nuclear medicine. The first type of imaging that we'll talk about are X-rays. They're the most common. And the definition of X-rays are that they are short wavelength electromagnetic radiation, which I know is a little bit of a mouthful. So what does that mean? A lot of times we just call electromagnetic radiation And what it does, it will consist of an electrical field and a magnetic field that are together. When they're combined, they produce synchronized waves called electromagnetic waves, and the waves are characterized by their wavelength. And they form a spectrum which is seen at the bottom of the slide here. The spectrum is called the Spectrum. And on this spectrum here you see on the left you have electromagnetic radiation with longer wavelengths. For example, you have radio waves, which are several meters in length. And then, as you move to the right on the spectrum, the wavelengths become shorter and since they're shorter they have more energy. And that means that they can be more penetrating. So on the far right, you have X-rays. Which takes us back to the definitions which they are short wavelength electromagnetic radiation. They penetrate the body because they have the short wavelength. And that's why we're able to use them to produce X-rays. And what happens is, when they pass through the body, to take a film we talked about it a little bit earlier. When they go through thicker areas they move more slowly, and they're more absorbed as a opposed to when they go through more thin areas, like the lungs that are full of air. So this results in the image of varying densities, which you can see a little bit on the top right of the spectrum. How exactly are X-rays used to produce images? We have a device which is the source of the energy and that's the X-ray tube. We have X-rays that come out in a beam and they strike an object, which in our case for medical imaging is a patient. And the object will absorb the X-rays differentially, depending on the tissue thickness, which we talked about a little bit earlier. And then, there are remnant X-rays that exit out of the body. And they're what expose the image and show us the different densities. And now we're moving on to another type of imaging, and this is ultrasound. And we're going to talk a little bit about how sound waves are used to produce images. On the left, you'll see, I actually have this numbered, is number one, the device is an ultrasound transducer. And what that does is it emits energy, which are sound waves. And then, the ultrasound transducer's actually placed right up against the body part that we want to image. And the sound waves are released, and they go through the tissue that you want to image. In this case, this is a fetal ultrasound, so the images are directed toward the fetus. Some of the waves are absorbed by the tissue, many of them bounce back and the waves that bounce back do so at varying transmissions so that information is taken back up by the transducer and it's converted into an image which you see in the top right. This is our third type of imaging that we want to discuss and this is MRI where we use a magnetic field to produce images. Here, I have shown on the left. And this is the first thing that you need to know is all the tissues in the body that have hydrogen atoms, which are most of them, those atoms in their natural state are randomly aligned. So that's represented by the image on the left where you see some of the arrows are pointing up and some are down. It just shows that the alignment is a little bit different for all of the atoms. And then, the device which is the next picture moving over, the MRI is a magnet. And what that does, is that creates a large, strong magnetic field and then, when that's supplied to the body the hydrogen atoms and the tissues become polarized. What happens when the polarize is thin, they then all line open the same direction. And you can see that in the second figure from the right where all the arrows are now pointing in the same direction indicating that the atoms have been polarized. Then, once the field is turned off, then the hydrogen atoms depolarize. And when they depolarize, they do so differentially depending on the tissue that they reside in. So since the hydrogen atoms are depolarizing, based upon the tissue that they reside in, they create different signals. And those difference signals are used to create an image, which you see on the far right. Which is a sagittal MRI of the head. And you can certainly appreciate how the different densities that are represented there. And this is our final type of imaging that we'll go over. This is nuclear medicine. In a nuclear medicine, radionuclides are used to produce the images. A radionuclide is simply a radioactive drug and it's administered to the patient. So here on the left, you see a radionucleotide, in its shielded container. So it's the very small blue object there, and the entire container is lead. In the background of the picture you see a detector that's measuring the radioactivity. And the front is the ledge shield which is actually you can see through so you can work with the device. And then, moving to the right, you see that the radionucleotide is being given to the patient. You'll notice that the person giving it is giving the radionucleotide with a shield around it as well. Similar to, as we discussed with the other types of imaging, different tissues respond differently to the energy. Here, as well the radionucleotide is taken up differentially in various tissues. And once it's taken up, then it begins to decay or lose its radioactivity, and then as it's decaying the energy is emitted, and that's converted into an image which shows hot spots as we call them in areas where the tissue took up the radionucleotide. On the slide second from the right is the picture of a patient in a camera after they've been given the radionuclide. And then, the picture on the right is the end product that's the bone scan of a patient with prostate cancer with a metastatic disease to the bones that's outlined there. So that concludes the end of our section on the different types of imaging. Hopefully that was helpful, so that you can sort of keep everything organized in your mind as to the types of images that you may see.
