If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content
Current time:0:00Total duration:9:30

Diagnosing strokes with imaging CT, MRI, and Angiography

Video transcript

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 then treatment can get underway to save as much brain tissue as possible so what are the parts of diagnosis well the healthcare team will sort of interview the patient about their symptoms and do some physical exams and that's the tests 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 the more common and important ones so first up you'd likely get an immediate CT scanner 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 and 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 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's 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 norm 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 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 hyper dense 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 the 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 the 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 then 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 is 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 right because of the swelling and notice that the surface of the brain is starting to look pretty similar to what's underneath right 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 a 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 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 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 cerebrospinal fluid your CSF that 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 this subtype of CT scanning this one that we'll talk about now it's 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 a stroke because 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 well houston we have a problem this bit looks abnormal this is where our blockage is which likely caused our stroke in 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 in your meninges etc so what you're left with is just the cerebral blood vessels and it's pretty cool right you can 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 what blockage sudden stop here right so Bloods not going through here and then that's a problem for the tissue on the other side so the last type of scan will look at is probably something you've already heard of called the MRI scanning or magnetic resonance imaging this is the one that dr. house probably has right in his office because for some reason all these patients seem to get one right away which is kind of interesting anyways these use magnetic fields and radio waves to provide some really high resolution images of the body and 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 taking 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 right 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 right 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 detects stroke and the last image will look at is another type of MRI called flare 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 flare 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 workup CT angiography and MRI