A computed tomography (CT) scan, AKA a computed axial tomography (CAT) scan, is a medical imaging method that uses many X-ray measurements taken from different angles to produce tomographic (cross-sectional) images of specific areas of the part of the body that was scanned. It can restructure images in various planes and even as three-dimensional (3D) or volumetric representation of body structures. Because CT scans are created by several X-ray measurements, it exposes the body to ionized radiation.

Magnetic resonance imaging (MRI) is a non-invasive imaging technique used in hospitals and clinics to produce detailed soft tissue anatomical images, through emission and absorption of energy of the radiofrequency range of the electromagnetic field by employing powerful magnets that produce a strong magnetic field around the area to be imaged, without exposing the body to ionized radiation. It is a medical application of nuclear magnetic resonance (NMR).

CT scans and MRI are similar in the way that both show cross-sectional images of the body which is accomplished with different techniques, thereby showing the same parts of the body in different ways. They differ mostly in the following:

Radiation: because CT scans are made up by several X-rays, the body is exposed to ionized radiation, which is not usually appropriate in some contexts, like pregnancy.  MRI does not expose the body to ionized radiation

Uses: CT scans are excellent for bone structures and soft tissues, but MRI is better for the latter because it detects very slight differences in soft tissues, like the brain

Cost: CT scans are less expensive than MRI

Time: CT scans are taken in about 5 minutes, while MRIs are obtained in 15 minutes up to 2 hours, depending of the body part being examined

Patient comfort: The narrow tube of the MRI machine can cause anxiety. CT machines are very open, so concerns about confined space are rare.

Limitations: since MRI uses an electromagnetic field, patients having metal implants/objects in their body (such as pacemakers or prosthetics) are unable to undergo this method of examination.

Learn more about CT scanners, MRI costs, and PET scanner costs

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