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

What is a CT scan?

A CT scan, or Computed Tomography scan, to give its full name, is essentially a more sophisticated X-Ray scan. X-ray scans use radiation fired at an area of the body - the rays that are not absorbed are captured and an image is formed. A CT scan is a more complex version of this process, where a large number of scans are taken from different angles.

The resulting images are combined to generate a three dimensional image of the area of the body being scanned. So whereas a standard Xray only generates a 2-D slice, a CT scan (previously known as a CAT scan) is able to generate a much fuller picture.

A patient undergoing a CT scan lies on a platform which is passed through a cylindrical machine. The process lasts no longer than 30 minutes, is sometimes as short as 5 minutes, and is totally painless.

What is an MRI?

A CT scan is most beneficial for observing bone structure, and is less useful for scanning soft tissues in the body. To scan these tissues more effectively, a doctor will usually suggest an MRI scan. MRI stands for Magnetic Resonance Imagery. Rather than using radiation, this procedure exposes the body to a strong magnetic field, which affects the molecules in the body in such a way that a detailed picture can then be produced.

An MRI is performed in a similar way to a CT scan - the patient usually enters a cylindrical machine. However, an MRI scan tends to last longer, and can last up to 45 minutes. An MRI machine also makes a rather loud noise. In some cases, the patient will be injected with a dye, helping the technician to make the image even clearer.

Differences between the two

One of the major reasons for the increase in use of MRI scans is that they are far superior for collecting images for areas of the body apart from bone. They are also more versatile, and are used for help in diagnosing a wide variety of conditions.

Another benefit to an MRI scan is that it does not expose either patient or technician to potentially harmful radiation. Although the length of time of exposure is relatively short, CT scans still have this risk; there are no known adverse affects to the patient from an MRI scan.

The cost of an MRI scan tends to be higher than for a CT scan, although this can vary according to the patient's needs.

One reason why a patient might opt for CT is if they have metal implants in their body, since these often mean that an MRI is impossible.

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