Saturday, April 24, 2010

CT scan vs MRI scan

I saw a recently published piece of news in the Zao Bao about CT scan giving an increased risk of cancer and should not be recommended for routine use in health checks. CT scan is known to be one of the best tools for studying the lungs and abdomen. It is also used in cancer diagnosis, and is the preferred method for diagnosing lung, liver, and pancreatic cancer.

So I checked out the differences between CT scan and MRI, and their associated risks...

HOW CT SCAN WORKS:

CAT (Computerized Axial Tomography) scans are similar to conventional X-ray imaging, but instead of imaging the outline of bones and organs, a CAT scan machine forms a full three-dimensional computer model of the inside of a patient's body. Doctors can even examine the body one narrow slice at a time. The X-ray beam moves all around the patient, scanning from hundreds of different angles, and the computer takes all that information to compile a 3D image of the body.

HOW MRI WORKS:

Magnetic resonance imaging uses radiofrequency waves and a strong magnetic field instead of X-rays to provide clear and detailed pictures of internal organs and tissues. These radio waves are directed at protons in hydrogen atoms -- one of the most abundant atoms in the human body, because of the body's high water content. The waves "excite" the protons, and when they "relax," they emit strong radio signals. A computer can turn those signals into a high-contrast image showing differences in the water content and distribution in various bodily tissues. It is becoming increasingly popular as an alternative to traditional X-ray mammography for the early diagnosis of breast cancer because women aren't exposed to the same radiation they experience with X-rays. [Source: ScienceDaily 2006]

What are the risks of MRI?

  • Because MRI uses low-energy, non-ionizing radio waves, there are no known risks or side effects. In fact, since the technique uses no radiation, it can be repeated with no known adverse effects.
  • While there are no known hazards, MRI is not proven to be safe during pregnancy. If a pregnant woman must undergo an MRI, she will be asked to sign a special consent form.
  • The magnet at the center of the procedure may affect, or be affected by, any person fitted with a pacemaker, hearing aid, or other electrical device. People with such devices should advise the physician or technician. They are generally advised not to have an MRI.
    [Source: ehealth MD, oct 2009]

As the studies done on CT scan and cancer risk were only carried out in US, the results may not be generalised to other regions.

Related readings:

CT scans and cancer risk - 16 Dec 09

CT scans 'could raise the risk of cancer' - 15 Dec 09

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