Radiologist Questions Mri

What's the difference between an MRI and a CT scan?

I'm scheduled to have a CT scan of my lungs. My friends are asking me why I'm not getting an MRI instead. What exactly is the difference between an MRI and a CT scan?

6 Answers

Different technology. CT is best for lungs.
While MRI is better for its great soft tissue contrast and multi-sequences providing significant additional information, CT is much better for the thorax, especially the lungs due to its high spatial resolution. It is perfect for evaluation of nodules and masses and pneumonia. MRI is more of a problem solver and is useful for the heart, aorta and great vessels. CT is very quick, even if contrast is used. The downside is radiation exposure which one does not get with MRI. This is X-ray exposure is nominal in the broad scheme of things.
MRI is excellent in looking at soft tissues of the body. Lungs are composed mostly of air, and are much better seen on CT scans than MRI. Incidentally, CT scans are also less expensive and much faster.
A CT scan uses X-rays, whereas MRI uses magnetic fields. CT scan gives a dose of ionizing radiation to the patient. There is no dose of ionizing radiation in MRI. MRI is good for  brain and nervous system studies.
A CT scan uses radiation (x-rays) to produce images whereas an MRI uses magnetism and radiofrequency waves (no radiation). A CT scan is fast, usually lasting 2 to 5 minutes. An MRI can take much longer (15 or more minutes) depending on the body part being scanned. Anyone can get a CT scan. There are some conditions that prohibit the use of an MRI scan due to the strong magnetic fields required for the test, the most common being presence of a pacemaker, metallic foreign bodies (especially in sensitive areas like the eyes or near vital organs or vessels), and brain aneurysm clips.

In the case of an exam for the lungs, a CT scan is the best type of scan for the resolution needed for evaluating the lungs. An MRI is usually not used for evaluating the lungs.

A CT scan uses radiation which allows tissues such as your lungs to be better seen and evaluated where MRI uses high strength magnets that is better for other tissues like the brain and muscles.


Dr Cox