Why do I need a CT AND an MRI?
If you go to a doctor or a hospital with a complaint of pain, any pain really, chances are you will get imaged. This imaging ranges from a simple x-ray to cardiac catheterizations. Often, you will get more than one and more than one kind. If you go to one hospital and they transfer you to another one, chances are the second hospital will repeat the imaging studies of the first. Why do you need more than one? Why two kinds of imaging of the same body part? Why repeat them?
The simplest form of imaging is the X-ray. If you come to the doctor and say you fell and now your ankle hurts, you might get an ankle film. If you go to the same doctor and say you fell 6 months ago and it still hurts, chances are you’ll get an MRI. Do you need an MRI? Probably not. MRI tells your doctor alot more about the ligaments and soft tissue in your ankle, much less about the bone. So if you have a torn tendon, say, the MRI will show it better. But MRIs cost a couple of thousand bucks. Unless you’re a professional athlete or are going to have surgery on said tendon, skip the MRI and get some physical therapy. This is especially true for back pain. Doctors do all these MRIs for back pain and yep, they might find something, but I’d opt for PT over surgery every day of the week and twice on Sundays. Don’t bother.
If you come into the ER with severe headache or head trauma, you will probably not get an X-ray of your head. This is because X-rays just shoot radiation straight through the body part, and any bone trauma would be either hard to see or hard to locate. For head stuff most people start with a CT scan. CT are like X-rays but they can take pictures in slices through your body, thus giving your doctor a better idea of where the problem is if there is one. CT is also good for bone stuff, so if you have major sinus issues (sinuses and nasal passages being full of small bones), you may get a CT. CT is also good for following a problem over time, so if you get admitted with head trauma you’ll likely get multiple head CTs. If your CT scan is negative or equivocal, you might also get an MRI. MRI again shows soft tissues better, and it is especially good for visualizing arteries and veins. If you’ve had a stroke, your CT may initially be normal but show damage in a certain area of the brain later on, whereas an MRI might show you damage earlier. If you come in with a headache, or worse yet, dizzyness, you’ll get a head CT but it will mostly likely be negative. This is because most causes of headaches and dizzyness have nothing to do with your brain at all.
Why will a doctor in one hospital repeat an image done in another? Some of it is a comfort thing. Doctors at one hospital are comfortable with the radiologists they usually use and are used to their way of reading things. Imaging studies are usually up to some degree of interpretation and clinical correlation, meaning sometimes a radiologist will find something that’s really nothing, but he doesn’t know the whole story so he will ask your doctor to take the finding and correlate it with your symptoms. These days, most imaging studies go up on a hospital-wide imaging network that can be accessed by your doctor, but these systems are hospital-based and usually cannot be accessed by outside hospitals, so unless the first hospital sent a hard copy of the films with you, they’ll likely get repeated. Surgeons won’t usually be satisfied with just a radiology report, that is a verbal or written report of what the radiologist has found. They’ll want to look at the images directly.