MRI vs CT

  1. can anyone explain to me the indications for the two? what i mean is, why is sometimes an MRI ordered and sometimes a CT?
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  2. 15 Comments

  3. by   MS._Jen_RN
    It all depends on what you are trying to image in what organ/tissue. Ultimately it often becomes the radiologist's call. (In my facility) That's what they went to school for afterall. There are known things that one or the other is better for. For example MRI for soft tissue/hemmorage issues, r/o CVA's that weren't seen on the CT. Hope that helps.
    ~Jen
  4. by   platon20
    Ultimately, MRI is better than CT for just about any kind of imaging you want to do. Its better for brain bleeds, fractures, soft tissue injury, muscle damage, sprained ligaments, acute stroke, chronic stroke, neurodegenerative disease, etc

    The only reason CT is still used is because:

    1) Its cheaper
    2) Its faster
    3) Every hospital has a CT scanner

    You can get a CT scan in 40 seconds flat. The fastest MR scan is about 5 minutes long, and most radiologists want studies that last half an hour or longer.

    Radiologists would actually rather have an MRI for everything, but that wont happen because of the reasons I listed above, plus the fact that the bore size is much smaller and longer than CT and some people get claustrophobic.

    Teh open MR scanners are available that are not as claustrophobic but their magnet strength is less than 1 tesla which means the image quality is not as good.
  5. by   all4schwa
    Quote from platon20
    Ultimately, MRI is better than CT for just about any kind of imaging you want to do. Its better for brain bleeds, fractures, soft tissue injury, muscle damage, sprained ligaments, acute stroke, chronic stroke, neurodegenerative disease, etc

    The only reason CT is still used is because:

    1) Its cheaper
    2) Its faster
    3) Every hospital has a CT scanner

    You can get a CT scan in 40 seconds flat. The fastest MR scan is about 5 minutes long, and most radiologists want studies that last half an hour or longer.

    Radiologists would actually rather have an MRI for everything, but that wont happen because of the reasons I listed above, plus the fact that the bore size is much smaller and longer than CT and some people get claustrophobic.

    Teh open MR scanners are available that are not as claustrophobic but their magnet strength is less than 1 tesla which means the image quality is not as good.
    very good answer, that puts things in perspective, thank you!!
  6. by   gauge14iv
    And not every patient can be MR'd - for instance those with metal implants of some sort or who are on certain types of drips that can't be taken off the pump.

    In most cases - CT is the "quick look" - MRI is definitive
  7. by   all4schwa
    Quote from gauge14iv
    In most cases - CT is the "quick look" - MRI is definitive
    that's a good way of looking at it!
  8. by   platon20
    Quote from gauge14iv
    And not every patient can be MR'd - for instance those with metal implants of some sort or who are on certain types of drips that can't be taken off the pump.

    In most cases - CT is the "quick look" - MRI is definitive
    Yes, fortunately if their implant was done within the last 15 years or so most of them are MRI-compatible. Metals are fine in the MR scanner, as long as they are not ferromagnetic. Iron, nickel, steel, and cobalt are the bad guys. The rest of the metals are OK. So if the patient knows for sure they have a titanium implant then its no problem.

    Pacemakers are contraindicated as well..... but even with pacers if you have a cardiologist who can wave his magic wand and reprogram the pacemaker into "safe" or "nonpaced" mode for the scan, then its fine. MRIs dont cause permanent damage to pacemakers, they just increase the risk of an unneeded discharge.
  9. by   augigi
    Really? I didn't know that titanium was okay for MRIs - interesting!
  10. by   all4schwa
    Quote from platon20
    Yes, fortunately if their implant was done within the last 15 years or so most of them are MRI-compatible. Metals are fine in the MR scanner, as long as they are not ferromagnetic. Iron, nickel, steel, and cobalt are the bad guys. The rest of the metals are OK. So if the patient knows for sure they have a titanium implant then its no problem.
    valuable info, i've wondered why some people with known metal in their bodies where okay.
  11. by   VickyRN
    All patches should be taken off before going to MRI, also. Otherwise, can sufffer burns, since some patches contain metals.
  12. by   platon20
    Tattoos can also be a problem because some of the tattoo inks have ferromagnetic metals.

    Another thing to watch out for is people who work with welding equipment. It turns out that very small particles of iron can get embedded in your cornea if you do welding over a long period of time. Normally the iron filaments dont bother you and your eyes are fine.

    In the MR scanner, the RF pulses cause the iron filaments to start rotating, effectively boring out your cornea like swiss cheese.
  13. by   Daytonite
    MRIs provide a better contrast between normal tissue and pathological tissue and for that reason are a better choice than a CT scan in many instances. CT scans will show bone artifact that will obscure other structures. This does not happen with MRI scanning. The larger blood vessels can be visualized with MRI scanning. This is not possible with CT scanning. With MRI scanning it is possible to image the transverse, sagittal and coronal planes of the body directly because the magnetic fields can be manipulated. This is not possible with CT scanning. MRI scanning is superior to CT scanning in showing the response of cancer to radiation and chemotherapy. In general, when soft tissue needs to be examined, MRI scanning is usually the test of choice over the CT scan.

    Disadvantages and problems with MRI scanning include difficulty scanning patients who weigh over 300 pounds, are pregnant, claustrophobic, require constant monitoring equipment that they cannot be disconnected from or patients with implanted metal objects which result in the MRI image degradation or movement of these objects within the body by the magnet.
  14. by   Catscanman
    Platon20,
    Ultimately, you're incorrect! MRI is NOT better for just about anything than CT. Visit www.ct-scan-info.com and click on CT vs MRI for the correct information, that comes from a registered and certified CT Technologist. CT has it's area of image superiority and so does MRI; they're not interchangeable and one is not better than the other for all things.

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