Today on the Doc On The Run Podcast, we’re talking about MRI essentials for runners, slice size matters.
In this series on how you can learn some of the basics about MRIs so that you can actually look at your own MRI if you had an injury, you went and your doctor got you an MRI, you got the report, you’re trying to figure out what all this gibberish means when you’re looking at the report and you take the disc, you put it in your computer, or you go on their online portal and you’re looking at those images and you’re trying to make sense of it, and you’re trying to figure out if it really picked up your injury or not. This episode on the size of the slices might help you. It will also help you a lot if you’re going in to get an MRI because you have a injury and your doctor is going to order an MRI.
If you don’t understand the difference of size of the slices, don’t feel bad. When I lecture on this at medical conferences, I almost always get at least one doctor who asks me about how big the slices should be, if it should be four millimeters or three and a half millimeters, or one and a half millimeters or two or whatever. And it depends on the specific injury you have.
So the first thing is why would somebody get a big sliced MRI? And what I mean by that is that if we look at your foot, for example, if this is the side view of your foot and you get an injury and they send you for an MRI and the doctor has no idea what’s going on, absolutely no clue. Well, they could get a couple of different kinds of MRIs. They could get one with big slices or they could get one with small slices.
If your foot, basically, if this is the two basic views of your foot, if the doctor said, “I have no idea what’s going on, we’re going to get big slices.” Why would they do that? Well, there’s an image grid that’s going to look at your foot. It’s not going to look at all of it, but it has a set number of slices that are going to actually look at your foot. And those set slices could be anything from a millimeter, millimeter and a half, all the way up to four millimeters. So there’s a big difference between one and four.
Let’s say they put the grid on your foot like this and they do slices. Well, you’re going to look there, you’re going to look there, you’re going to look there, there, there, and there. And in this view, you’re going to look there, there, there, and there.
Same thing here. They put the grid on your foot, and let’s say they’re just looking at the fore foot, they put the grid on here and they take it and they look at these slices in these places here. If they take the grid instead and they make it bigger so that’s your whole foot and you got the same number of slices, but they’re further apart, well, you may miss stuff. In fact, this is an exaggerated example, as you can see, but obviously when we’re looking at this, if we have your first metatarsal bone, for example, or let’s say it’s your second toe, just to make things simple, we’ll use a plantar plate as an example.
Let’s say this is a cross-section of your second toe, not your big toe, and you have the plantar plate down here. So how much of that do you get? Well, if you look at the way I drew this, this slice actually goes through the plantar plate. This slice does not go through the plantar plate. That doesn’t go through it, and that doesn’t go through it. But if you had smaller slices, if they were closer together, you would get a lot better picture of the plantar plate because you get more views of it.
When we look at it from this attitude here, this is your second metatarsal bone, and the plantar plate is right under there. Well, this one’s going to look at it, but the more slices you have in this area, the more visual detail you get on the plantar plate ligament. Some of these things in your foot are really, really small. A plantar plate ligament is really small. If you have four millimeter slices, you might miss it entirely. So four millimeters is really kind of a long way in the foot when you’re looking at things like a neuroma, when you’re looking at a plantar plate injury, even a thing like a sesamoid bone. And as a good example, we’ll look at a sesamoid bone, an MRI, I’ll have images on the show notes page as well as in the video version.
But when you look at the sesamoid bones, you have two of them. They’re like tiny little kneecaps, but they’re not that big. So when you look at them and you see how big the sesamoid bone is from one side to another, and then you think about if you had four millimeter slices, well, how much of it are you going to see? You don’t see the whole thing. It looks like you’re seeing the whole thing when you look at the MRI, but you’re only looking at little slices or windows of imaging, little parts of it that are very isolated views. It just looks like it’s all comprehensive because you have so many images.
If the radiologist has no idea what’s going on with you, they might do a much broader grid, spread it out. So those slices are farther apart. I do not particularly like that. I’m not looking for some maybe tumor in there. I’m usually looking for a very specific injury. So if you have a specific injury like a peroneal tendon injury, you’re better off getting small slices. If you know, have a plantar plate injury, get small slices, try to get them closer together, focused in that area so that you can get better imaging detail, and then your doctor can make a better decision about what’s going on with you. But that’s the difference between big slices and small slices on an MRI when you’re a runner.
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