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Diagnosing strokes with imaging CT, MRI, and Angiography

Visit us (http://www.khanacademy.org/science/healthcare-and-medicine) for health and medicine content or (http://www.khanacademy.org/test-prep/mcat) for MCAT related content. These videos do not provide medical advice and are for informational purposes only. The videos are not intended to be a substitute for professional medical advice, diagnosis or treatment. Always seek the advice of a qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read or seen in any Khan Academy video. Created by Vishal Punwani.

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Video transcript

- [Voiceover] So, we know that once a stroke is suspected immediate diagnosis and treatment is really really important, so that if a stroke has actually occurred than treatment can get underway to save as much brain tissue as possible. So, what are the parts of diagnosis? Well, the health care team will sort of interview the patient about their symptoms and do some physical exams. And that's to test the patient's neurological system to look for any compromise due to the stroke. But an extremely important part of diagnosing stroke is doing imaging tests to actually look at the brain and actually see what's going on in there. So, what sorts of imaging, what sorts of scans can be done to look at the brain? Well, let's go through a few of the more common and important ones. So, first up, you'd likely get an immediate CT scan or Computerized Tomography Scan which is basically a special type of x-ray that takes lots of images from lots of different levels and angles. And the end result is that you get to look at the brain in lots of different views. So, this is a view of the brain here that was generated with a CT scan and we're looking at this brain as if it's been cut from front to back, what's known as an axial view. So this is a normal brain, right? No stroke or anything has happened to this brain, and I just want to point out a few things. And actually, let me also say that we're looking at this brain from the bottom up, so that makes this the left side and this the right side. And that'll be the case for all the images we see, so keep that in mind. So, what are some of the features of normal brain on CT? Well you can see the nice, fairly well delineated curves of the brain tissue here, and you can also see that the edges, right, the surface of the brain look a little different from just below the surface, and that's a reflection of the gray matter on the outside of the brain and the white matter on the inner parts of the brain. And one more thing I might mention is that you can see this normal brain looks nice and symmetrical, right? Everything is pretty even about the left and the right sides. But, what about a brain that's had a stroke? Well that's where things get a little bit more interesting because you actually can't immediately tell, like even if you took a CT scan of a person's brain a few minutes or even like an hour after they've had a stroke, it would look pretty much like this normal CT scan here, and that's because the changes that happen in the brain during and after a stroke, they take time to develop and sometimes you can't see any brain changes on CT until about half a day after the stroke has occurred. Usually about 12 to 18 hours after is when you can start seeing some changes on CT. Having said all of that, even though you might not be able to see any brain tissue changes right after a stroke, at least not on a CT scan, as I keep mentioning, you might be able to see a clot that caused it. So, here's a CT scan taken pretty quickly after a stroke, like within a few hours, and what you might notice is this thing here which is actually the Left Middle Cerebral Artery. It certainly stands out doesn't it? One might even say it looks "hyper dense", and in fact, this is called the MCA Hyperdense Sign. And that signifies that there's possibly a clot there. So, in some cases, that may be one of the things that you can see early on a CT, but let me bring up another CT. So, this scan here is from 48 hours after a stroke. So, let's see how things have evolved. You can see some swelling developing here, and remember neurons have been swelling up and dying off and inflammation in this brain region result in all this swelling that you see here, right? And notice where it is. It's on the outside, sort of the side bit of the brain here on the left. And remember the outer sides of the brain are primarily supplied with blood by the Middle Cerebral Artery. So, just to jump back a bit in the diagnosis timeline, by this point, you'd have already done your physical exam on this person, and you probably discovered some problems on the right side of their body, maybe some weakness of their right-sided limbs or something like that. So, you'd already be suspecting that there's a problem on the left side of their brain, and this CT scan certainly adds some evidence to your diagnosis now. So, a few other things to notice. In our stroke brain, our nice well-delineated curves of the surface of the brain are not really so present anymore because of the swelling. And notice that the surface of the brain is starting to look pretty similar to what's underneath in contrast to the normal side over here where there's good differentiation between gray matter on the outside of the brain and white matter underneath. So, in the brain with the stroke developing, you actually start to lose this gray-white differentiation and things start to look a little bit more the same as each other, and that's another sign of stroke on a CT scan. And maybe the last thing I'll mention is the disruption of the left and right sided symmetry that we talked about earlier. So in this stroke brain, you can pretty quickly see that there's some bulging of this left side over to the right. And again that's caused by swelling over on this side, and it's referred to as a Mass Effect. And this is an extra bad sign because it can cause compression of other parts of the brain from them being pushed on, and that can be fatal. And you can actually already see an example of this Mass Effect by the swollen area here pushing on and reducing the volume of these brain ventricles. These ventricles, by the way, they produce your Cerebral Spinal Fluid, your CSF that bathes and nourishes your brain. And actually just one more thing. These images are of the most common type of stroke, Ischemic Stroke. But here's a CT image of the less common type of stroke: Hemorrhagic Stroke. And CTs are really good for diagnosing these hemorrhagic strokes because blood leaking out of your cerebral circulation and into your head space, they show up really well on CT as an abnormal, bright area. So, that's blood there. So, maybe we'll leave this normal type of CT scanning now and just take a brief look at another kind of CT imaging you can do. So, I just wanted to spend a bit of time on this basic CT technique though because they're pretty much the first scan you order, and they can give you a lot of information about what's going on. So this sub-type of CT scanning, this one that we'll talk about now, is called CT Angiography, and it can give you a lot of useful information as well, and it's actually pretty cool. So, a special dye gets injected into your bloodstream, and it makes your blood vessels sort of light up on a CT scan. So then it's really easy to see where in your cerebral blood vessels the problem is that caused the stroke cause everything's all lit up. So, look here. Here's our blood vessels, right? Nicely lighting up, and we're following along, and we're following along, and everything looks good, it's good. Whoa. Houston we have a problem. This bit looks abnormal. This is where our blockage is which likely caused our stroke, and this scan made it a lot easier to pinpoint that. And in another type of angiography, you can use computer software to hide the image of the actual brain tissue and surrounding structures in your head, like your skull and your meninges, etc. So, what you're left with is just these cerebral blood vessels. And it's pretty cool, right? You can actually see that everything that is not a blood vessel has been hidden using a computer and now this image here can give us a pretty clear idea of what caused the stroke. Everything looks good, looks good, good, good... Whoa. Blockage. Sudden stop here, right? So, blood's not going through here, and that's a problem for the tissue on the other side. So the last type of scan we'll look at is probably something you've already heard of called MRI scanning or Magnetic Resonance Imaging. This is the one that Dr. House probably has right in his office because for some reason all of his patients seem to get one right away which is kind of interesting. Anyway, these use magnetic fields and radio-waves to provide some really high resolution images of the body. In our case, they let us see the tissues of the brain and the surrounding structures pretty well. And they're actually more sensitive in detecting brain ischemia than CT scans are, but they're less available and they take a lot longer to do than a quick, sort of readily available CT scan which is still really, really good. But let's actually look at these MRI images. So, remember how I said that it can take up to a day almost for brain changes to appear on a CT scan? Yeah, that's not the case with MRI. These images were taken a mere half hour after the patient started having their stroke symptoms, just incredible. So, you can see that there's already ischemic brain changes happening in the right MCA territory here. And these next set of images, these look pretty fun and colorful. These are special MRI images that measure how much blood flow is running through your brain. So, this right half of the brain in this patient is normal, right? This is how normal blood flow looks, but on the left here, you can see that there's a lack of blood flow going on. That's what a lack of blood flow looks like. So, it would make you think of a clot in the left Middle Cerebral Artery because the MCA is what serves this area here on the left. And these were only taken actually an hour after symptom onset in this patient. So, you can see how quickly MRI can detect stroke. And the last image we'll look at is another type of MRI called the Flair MRI in which pictures of the brain are taken but then computer software removes any fluid in the brain from showing up in the final image. So, what you end up with is just a super clear image of just the brain tissue. So you can see in this high resolution, crisp Flair image that there's a lesion. There's some damage happening in the left half of the brain here. So, those are some of the more important imaging tests that happen as part of a stroke work-up. CT, Angiography, and MRI.