Radiation Exposure from X-ray and CT Examinations

Evan Lum

What is an X-ray• An x-ray is a form of electromagnetic radiation

which falls in between gamma rays and ultra violet rays on the electromagnetic spectrum.

• They have a wavelength of anywhere between 0.01 nm and 10 nm.

• Corresponds to an energy of 0.1 to about 123 keV (kiloelectron volts)

What is a CT scan?

• CT stands for computed tomography which is a medical imaging method employing tomography (imaging in sections) created by computer processing.

• Using a series of x-ray images about a single axis of rotation, CT produces volume data such as 3D images of internal organs which can be manipulated through a process called “windowing”.

Medical Uses for X-ray

• Plain x-rays are mostly used to detect pathology in the skeletal system.

• Sometimes used for soft tissue:– Chest x-ray to identify lung

diseases like pneumonia or lung cancer.

– Abdominal x-ray to detect intestinal obstruction, free air or free fluid.

Medical Uses for CT Scan

• Head – detect infarction, tumors, hemorrhage, bone trauma.

• Lungs – shows internal aspects of the lungs which plain x-ray can not.

• Cardiac – excellent imaging of coronary arteries• Abdominal/Pelvic – sensitive method for

diagnoses of abdominal diseases.• Extremities – can image complex fractures,

especially around joints. Also ligament injuries and dislocations can be seen.

Radiation Exposure

• The Sievert is the SI unit for radiation dose which is equivalent to one joule per kilogram.

• The average American is exposed to about 3 mSv per year from naturally occurring radioactive materials and cosmic radiation from outer space.

• This amount of radiation exposure over such a long period of time is basically harmless to us.

Radiation from X-rays• Extremities – 0.001 mSv per x-ray (not

harmful)• Spine – 1.5 mSv per x-ray (about 6 months

worth of natural exposure)• GI tract – 6-8 mSv per x-ray (2-3 years worth

of natural exposure)• Each of these are considered not to be

relatively harmful

• Head – 2 mSv per CT scan (under 1 year)• Spine – 6 mSv per CT scan (2 years)• Chest – 7 mSv per CT scan (over 2 years)• Abdomen/Pelvis – 15 mSv per CT scan (5

years)• Abdomen/Pelvis without contrast material –

30 mSv per CT scan (10 years)• Coronary Computed Tomography

Angiography (CTA) – 16 mSv (5 years)

Radiation from CT Scan

Why is this dangerous?

• Although radiation can be used to treat cancer, it can also cause it.

• The delivery of energy waves through our body can alter atoms’ molecular structure causing cells in our body to mutate and become cancerous.

• Higher risk procedures can leave patients with up to a 1 in 500 chance of getting cancer.

• The united states gives over 60 million CT scans per year.

• It has been estimated recently that CT scanning has been the cause of about 30,000 cases of cancer yearly.

Statistics

What Can We Do?

• Due to their major contribution to the medical field, the benefits of x-ray imaging and CT scanning usually outweigh the risks from radiation exposure.

• Something we can do to avoid this is avoiding unnecessary procedures.

• This decision should only be made by a professional not a patient!

Sources• http://www.usatoday.com/news/health/2009-12-15-r

adiation15_st_N.htm• http://en.wikipedia.org/wiki/X-

ray_computed_tomography• http://www.radiologyinfo.org/en/pdf/sfty_xray.pdf• http://www.worldculturepictorial.com/blog/content/

ct-scan-study-shows-increased-radiation-exposure-cancer-risks-tests-often-unnecessary

• http://www.hanskellner.com/2005/06/27/left-shoulder-xray/

• “The Physics of Medical Imaging”, by S. Webb, New York: Adam Hilger, 1990.

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