Tuesday I ran a post: Alarmist Article About CT Scans–As Cancer Patients, What Choice Do We Have?

The article got me thinking: What are the radiation risks when one undergoes these tests? I concluded my post this way:

I’m sure it is always best to avoid any medical test if possible. But this article does seem a bit alarmist. I am curious to find out the difference in radiation levels between a CT scan, full body x-ray bone survey and MRI, since I get a bone survey and MRI’s fairly regularly. I will do a little research and report back.

One of our regular readers, Nick from California, seemed interested in the same thing. He commented Wednesday:

Pat –
While you’re at it, can you please differentiate between a PET scan and a CT scan? I do believe they are different.

MRIs should pose no health risk, by the way — that much I did research since I have to do so many of them! 🙂

Sounds like a plan—so let’s get to work! Here is a review of the basic imaging tests from Neurologychannel.com:

CT Scan
Computerized tomography (CT scan) uses x-ray technology to produce multiple cross-section images. In addition to providing images of the brain and nervous system, they can be used to identify broken bones, tumors, blood clots, heart disease, and internal bleeding.
MRI Scan
Magnetic resonance imaging (MRI scan) uses a powerful magnet combined with radio waves to examine organs, soft tissues, and skeletal structures. MRI scans are especially valuable in finding brain and spinal cord abnormalities. They may also be used to help diagnose torn ligaments, tumors, circulation (blood flow) problems, inflammation (e.g., arthritis), and infection.
PET Scan
Positron emission tomography (PET scan or PET imagery) uses radiation from the emission of positrons (extremely small particles discharged from a radioactive substance) to create images that can help detect and evaluate cancer and the effects of cancer therapy. This test also can be used to diagnose a variety of neurological conditions, including memory disorders, tumors, and seizure disorders.
Benefits/Risks
The primary benefit of positron emission tomography is that it can detect minor changes in biochemical levels, even before these changes show up as tumors or other abnormalities. In addition, the radiation exposure is lower than x-rays or CT scans.
There are some risks, however, primarily to women who are pregnant or nursing, due to the injection of the radioactive substance into the body. The potential risks to the fetus must be weighed against the benefits of the PET scan. Women who may be pregnant should inform the PET technicians before the procedure.

This is a very basic review. For example, whenever I get an MRI, it is without contrast, which is contraindicated for a multiple myeloma patient. There are similar variations with these other tests as well.

But what about the radiation risks? Here is part of a standard radiation dose table, comparing average x-ray and CT radiation exposure:

U.S. average effective radiation dose compared with equivalent period of time exposed to natural background radiation for conventional X-ray, CT, fluoroscopy, interventional procedures (Reference: Mettler FA, et al: Effective Doses in Radiology and Diagnostic Nuclear Medicine: A Catalog, Radiology 2008 248:254-263).

Conventional Radiology
Chest
0.1
Abdominal AP
0.7
Upper Back X-ray
1.0
Lower Back X-ray
1.5
Neck X-ray
0.2
Skull (4 films)
0.1
Pelvis/Hip X-ray
0.7
Extremity (arm, leg, etc.)
0.01
Mammogram
0.4
Dental X-ray
0.01
CT Scans
Head/Brain CT
2.0
Neck CT
6.0
Chest CT (Standard)
7.0
Chest CT (R/O PE)
15.0
Cardiac CT
16.0
Cardiac CT (calcium scoring only)
3.0
Abdomen CT
8.0
Abdomen and Pelvis CT
14.0
Chest, Abdomen and Pelvis
18.0
Pelvis CT
6.0
Virtual Colonoscopy CT
10.0

Here are examples of average radiation exposure for US citizens yearly:

Radiation Exposure
Typical Effective Radiation Dose mSv
Natural Background Radiation
3.1
Average Medical in U.S.
3
Total Average Exposure in U.S. (with Medical)
6.2
Domestic Pilots
3
Occupational Radiation Workers
2-5

As you can see, CT scans do expose patients to an unusually high amount of radiation. Is it worth the risk? Obviously, most physicians believe so.

As Nick mentioned in his comments, MRI’s and PET scans work in a different way. The Health Physics Society answers the question this way:

Do magnetic resonance imaging (MRI) and ultrasound use radiation?
MRI and ultrasound procedures do not use ionizing radiation. If you have either of these types of studies,
you are not exposed to radiation

But what about PET scans? No one seemed too concerned in the literature I reviewed. This excerpt from the Cleveland Clinics was typical:

Does the PET scan pose any risks?
Although a radiotracer chemical is used in this test, the amount of radiation you are exposed to is low. The dose of tracer used is so small that it does not affect the normal processes of the body. However, the radiotracer may expose the fetus of patients who are pregnant or infants of women who breastfeed to the radiation. You and your doctor need to consider this risk compared with the need for and potential information to be gained from the PET scan.

Bottom line: Radiation from a PET scan is far less than a CT scan. The radiation exposure comes from the contrast, not the test itself.

I wasn’t aware a CT scan exposed patients to so much radiation! Is it worth the risk? I’m not a physician, but the other tests, MRI, PET and conventional x-rays don’t concern me much. CT scans are another matter! But if our doctors suspects we have a brain tumor or other disorder which can only be identified and located using a CT scan, what choice do we really have?

Feel good, keep smiling and avoid CT scans unless absolutely necessary! Pat

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