Today on the Doc On The Run podcast, we’re talking about whether an MRI or CT of your foot is better when you have a running injury.
Yesterday I was talking to a runner who had an ankle sprain that didn’t improve. After about a year of not be able to run, having pain when walking and becoming really frustrated with not being able to run, he called me for a second opinion.
During that discussion he asked me whether or not it would be better to get an MRI or a CT scan to evaluate the bone, joint and surrounding soft tissue to determine what was really going on and preventing him from getting back to running.
This is an unfortunate, but common scenario with injured runners and overtraining injuries.
The story typically goes like this…
A runner is deep in the build phase of training. Something gets off with your training schedule and you extend your work out or stack a couple of workouts to try to make up for the lost work out on the schedule.
The next day you wake up and realize you have an overtraining injury.
Something hurts. But you’re not foolish so you take some off and stop running for a few days.
You feel a little better, so you go for a run. But it gets worse. Fear of not making it your event pours in. You call to schedule an appointment, and find out you will have to wait for a few days or a week.
Then you go to see the doctor. The doctor says, “its an overtrianing injury…you have been running too much.”
The doctor tells you to stop running.
You are instructed to ice it, wear a brace try some inserts (most of which you already tried). Nothing seems to be helping so the doctor gives your prescription for physical therapy.
You take time off of work and go to physical therapy for a few weeks, but it doesn’t get better.
A month or so later you go back to the doctor explain you’ve had basically no improvement and you still can’t run without this aching sensation in your foot.
The doctor gets some x-rays of your foot and ankle but she sees nothing.
So you start thinking maybe you need an MRI or a CT scan. You start reading on running forums about how injured runners limp along with an aching injury for months until they finally got an MRI or a CT scan. And the question comes to mind, Which is better?
It maybe helpful to understand a little bit about MRI and CT scan so see you can best make a decision about which study would give you the information you really need.
MRI vs. CT Imaging. How they work.
Both use computers. But the imaging process is very different.
How does an MRI make images of running injuries?
MRI basically makes on a image of your body using a big magnet. You get a range of black and white based on the amount of water content in the tissues.
Here’s an example: Bone marrow is on the inside of your bones. Bone marrow is mostly fat, which is mostly oil. There is normally very little water inside the bone. When you get a stress fracture in a bone, it becomes inflamed and irritated. The inflammatory fluid that collects inside bone when it becomes injured is mostly water. That water lights up bright white on the MRI.
So when you have a stress fracture in your second metatarsal bone, you see a bunch of bright white color on the inside of that one second metatarsal bone. When you look at all the other metatarsal bones (the first, third, fourth and fifth metatarsals), they are dark. They are normal. So the non-injured metatarsal bones have no bright white signal. That difference in the amount of white vs. black shows us how much inflammation is in the tissue.
And of course, when you have an overtraining injury such as a stress fracture in the foot, tendinitis, or a sprained ligament, your body tries to heal it. That healing begins with inflammation. The MRI gives an excellent picture of the inflammation at work wherever the tissue is injured.
How does an CT scans make images of running injuries?
A CT scan uses a computer and takes a series of x-ray images and then creates a set of tissue images that appears very similar to the images produced from an MRI. The primary difference between these two imaging modalities is that CT scans use x-rays, and hence radiation to obtain the imaging. The speed at which x-ray particles move through bone is very different than the speed at which x-ray particles move through soft tissue. For that reason CT scans are the best imaging modality to look at injuries in bone.
Many years ago CT scans were used to look at bony abnormalities but weren’t really that effective in evaluating the soft tissues. But the soft tissue imaging capabilities of CT scans has improved dramatically over the past few decades. At some institutions where the radiologists and radiology technicians are used to running certain protocols to evaluate soft tissue injuries they can do something called “soft tissue windowing” that modifies the protocol in a way hat provides excellent detail of soft tissues like tendons, ligaments and joint capsules.
Because x-rays and CT scans all happen very quickly a CT scan is a very short study. For that reason you can often get one of those CT scans very quickly where it may take longer to get scheduled for an MRI.
So the bottom line is there used to be a huge difference between the two studies and you may still read something that says “MRI is for soft tissue” and “CT scan is for bone.”
But that line is really blurry in an age of modern medical imaging. Now you can get much of the same information on an MRI and CT scan. But there are still differences.
Here are the advantages of an MRI
An MRI will give you more detail been a CT scan on tendons, ligaments and joint capsules. An MRI only uses a magnet and does not use x-rays. So there is no radiation exposure within MRI.
Here are the advantages of a CT scan
If you have a suspected fracture in the bone the CT scan will give you more detail, and more accuracy in the anatomic detail of the fracture then you will get on an MRI.
Here are the disadvantages of MRI:
MRI is a much longer study. It takes about a half an hour or so to actually complete the exam. You have to lay still during the MRI study. It’s often hard for athletes to sit still for that long.
Another disadvantage is that you simply cannot turn on that gigantic magnet and get good images if you have implanted hardware like plates from a previous ankle fracture or screws from a tendon or ligament repair. The metal creates this starburst a pattern on the imaging it really makes it less valuable. You just can’t see anything with all that scatter.
You also cannot have an MRI if you have vascular clips holding blood vessels together from some prior vascular surgery. Obviously you don’t want the magnet to rip those little metal clips out of your blood vessels. You also can’t have an MRI if you have a pacemaker because it could move the electrodes or kill the battery.
You also cannot have an MRI if you are claustrophobic. You have to lay in a tube during the exam. To combat this they’re are other kinds of MRIs called an open MRI or an extremity MRI that do not require you to lay inside a tube. But nothing is free and medicine. You pay for not laying in the tube. And the way you pay is by getting much lower resolution images that do not give you anywhere near the same amount of anatomic detail. In short those pictures are much less effective and much less useful for you and your doctor.
Here are the advantages of a CT scan
The CT scan provides excellent detail for suspected fractures and cystic lesions in bone. A cystic lesion is basically just a benign bone tumor where you have a little collection of fluid or fat or some other kind of cells inside the bone that makes it weaker. Sometimes runners have these cystic lesions and they get symptoms that seem to be like a stress fracture. CT scan provide excellent detail for all of these kinds of abnormalities in bone.
The CT scan is very fast and only takes a few minutes. So it’s a lot easier for an athlete to sit still for CT scan.
A CT scan can give you some of the same information about soft tissue that MRI would give you, often lower cost than MRI. In a sense CT scans are older technology and the use of older technology is generally less expensive than new, fancy cutting-edge technology.
Another advantage of the CT scan is that if you have a particular timeline because you’re trying to stay on track with your training to stay on course for making it to the starting line of a specific race you probably don’t have a lot of time to waste. Because a CT scan doesn’t take as long as an MRI imaging centers that have both a CT scan and an MRI can do a lot more CT scans in one day and a lot fewer MRIs. It is usually easier to schedule a CT quickly since the study itself takes much less time to run.
Here are the disadvantages of a CT scan:
The disadvantage most doctors talk about it is that a CT scan doesn’t show inflammation the way MRI does. Stress response, stress reaction and mild stress fractures don’t show up as well on a CT scan as they do on MRI.
In terms of your overall health, the bigger disadvantage is probably radiation. The CT scan uses x-rays and so you do get exposed to radiation when you have a CT scan.
Should I get an MRI or a CT scan for running injury?
If you don’t really know if it is a bone issue, cartilage issue or some other soft tissue issue like a tendon or ligament, and nothing shows up on X-ray, you may start thinking about getting an MRI or CT scan.
So, which is best?
It all depends on your circumstances and preferences.
Whether or not an MRI or a CT scan will be better for you depends on your story. When any doctor asks you all of these questions about how you responded to treatment it really helps us determine what kind of tissue has been injured.
For example if you really have a mild stress fracture or a stress response in one of the metatarsal bones, that typically calms down pretty quickly when you just reduce your activity.
The amount of discomfort and pain you have when you apply impact such as jumping rope or running or doing box jumps helps us determine whether or not it’s a bone or soft tissue injury. And even the positioning of your foot, and the relief you get when you hold your foot in a different position can tells a lot about whether or not an MRI or CT scan will be helpful for you.
Whether or not an MRI or a CT scan will be better for you depends on your exam. Does it really seem more likely to be a tendon or a ligament? Does it hurt when you push it, stretch it, etc.?
But if all things are equal and you could actually get the information you need with either of the two studies than the choice boils down to your personal preferences.
If you are extremely claustrophobic and you won’t be able to sit still inside a tube for half an hour you’re probably better off getting a CT scan instead of an MRI.
But if you’re extremely paranoid about radiation, if you worry about the amount of radiation you get on transcontinental flight, if you would never in a million years live near a cell phone tower or high tension power lines, if you refuse to eat fish caught in the Pacific ocean near Southeast Asia for fear of radiation still poisoning fish from the Fukushima nuclear power plant disaster, you probably don’t want to get exposed to the radiation from CT scan. In that case you would probably opt for an MRI.
What you really need to understand is there are differences between the exams and if you can keep really close track of your symptoms, and the improvement or lack thereof from all of the treatments you have tried from that time the injury occurred until the time you meet with your doctor to consider MRI or CT scan you will have a much better chance of getting the best study for you.
Make sure you keep track of your pain. Log it. Record it. Share it with your doctor and you and your doctor will both be better equipped to decide whether or not an MRI or a CT scan will be most helpful in making the diagnosis that puts you on the path to healing and getting back to running.
Pain is the best tool to help an injured runner decide when run. You don’t have to figure out what to write down. We made a simple Pain Journal PDF for you.
If you have a question that you would like answered as a future addition of the Doc On The Run Podcast, send it to me PodcastQuestion@docontherun.com. And then make sure you join me for the next edition of the Doc On The Run Podcast!