Gul Moonis: What is the Difference Between a CT Scan and an MRI?

The “CT” in “CT scan” stands for “computed tomography,” while MRI stands for “magnetic resonance imaging.” These techniques are similar in that they both produce detailed images of internal structures in the body, generally in a series of two-dimensional “slices,” although three-dimensional imaging is becoming a possibility. The CT scan does this by detecting the differences between how different tissues absorb x-ray radiation. Magnetic resonance imaging, by contrast, uses a powerful magnetic field to align free protons in the body, and by detecting their differing amounts in different tissues, creates detailed two-dimensional or three-dimensional images.

Computed tomography scanning uses ionizing radiation and may result in slight increase in cancer risk, especially with repeated use. Magnetic resonance imaging can be more detailed and does not carry the same risks. However, the magnetic resonance imaging machine can be quite claustrophobic and is not suited to those with implanted medical devices such as pacemakers and cochlear implants.

Gul Moonis is a radiologist at the Beth Israel Deaconess Medical Center in Boston and the author of several papers on the subject of radiology.


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