Answer to Question #12033 Submitted to "Ask the Experts"

Category: Medical and Dental Patient Issues — Diagnostic X Ray and CT

The following question was answered by an expert in the appropriate field:

Q

I will be having a discogram on my lumbar area soon, and I believe they also include a lumbar computed tomography (CT) scan after the procedure. I have not been able to find out how much radiation exposure I would get from these two studies. I have had an extensive amount of imaging studies over my life for various issues, and so I am somewhat concerned.

I am 50 years old. I had abdominal/pelvic CT with and without contrast a number of years ago, as well as an extensive number of x rays, epidural steroid injections for my lumbar disc issue, dental x rays, and back x rays. I know this discogram would potentially add a lot more exposure.

Can you tell me how much radiation exposure I will get from the discogram and CT scan? Can I assume that fluoroscopy used during an epidural steroid injection results in less exposure than the fluoroscopy used during a discogram, which I think is a longer procedure? I have had a lot of anxiety over the many exposures I've had over the years, and I know I need to take it all in perspective.

A

Discography exams are performed to determine if intervertebral discs are damaged and contributing to spinal nerve pain. Generally, this involves one, or possibly two, x-ray procedures: a fluoroscopic procedure to inject a contrast fluid into the suspect discs and then a follow-up CT scan to examine the anatomy of the discs and to identify if they are causing pressure to be exerted on the spinal nerves. Sometimes, the injection can be performed during the CT scan and without the fluoroscopic procedure.

Generally, before the exams are conducted, your doctor will have conducted a physical exam to locate the specific discs that may be responsible for your symptoms. Usually, this is only one or two discs. As such, the fluoroscopic field and CT scan volume should be limited to just this target area. Consequently, in your case, only a limited area of the body will be exposed to the x-ray fields. Your doctor may be able to limit the exams to x ray only the particular suspect lumbar discs instead of performing a full lumbar scan. Because of this, the dose you will receive should be a fraction of a standard lumbar fluoroscopy/CT scan series quoted below.

The mean effective dose for a standard lumbar spine fluoroscopic procedure is 1.5 millisieverts (mSv), and for a lumbar CT it is 6 mSv. So the estimated total you could receive from both procedures is 7.5 mSv. This is equivalent to the natural radiation exposure that you would receive every 2.5 years. While I understand that you are concerned about x-ray exposures you have received previously, this is not a radiation level that would place you in a measurably increased risk group. It is also comparable to 2.5 years of the average annual medical dose received by the U.S. population, which is about 3 mSv each year (Smith-Bindman 2012).

An epidural steroidal injection procedure is performed to inject a medication into the spinal column to hopefully alleviate the swelling around the nerve and relieve pain. Since the goal is to place the medication in the right place, the x-ray exposure should be somewhat less than that from a discography exam. In a discography exam, they inject a contrast dye into the same area, but they also take additional views, in an attempt to fully visualize the anatomy of the lumbar disc and surrounding anatomy. Consequently, the total exposure time may be greater for a discography exam than for an epidural steroidal injection procedure.

However, I would stress that it is highly unlikely that the radiation risk from even multiple procedures would exceed the benefits of achieving relief from a condition of chronic back pain. Chronic back pain causes serious quality-of-life issues, and the pain medications used to control chronic back pain are usually powerful narcotics with serious side effects.

Consequently, is the benefit to you in identifying a damaged disc and possibly being able to correct your current condition worth the very small risk from the radiation? In your case, I believe it is.

Michael J. Bohan, RSO

Reference

Smith-Bindman R. Appendix F: Ionizing radiation exposure to the U.S. population, with a focus on radiation from medical imaging. In: Institute of Medicine. Breast cancer and the environment: A life course approach. Washington, DC: The National Academies Press; 2012. Available at: https://www.nap.edu/read/13263/chapter/15. Accessed 18 July 2017.

Editor's Note: The Health Physics Society's position statement Radiation Risk in Perspective states that "below levels of about 100 mSv above background from all sources combined, the observed radiation effects in people are not statistically different from zero." In other words, the risk, if it exists, is too small to be seen.

Ask the Experts is posting answers using only SI (the International System of Units) in accordance with international practice. To convert these to traditional units we have prepared a conversion table. You can also view a diagram to help put the radiation information presented in this question and answer in perspective. Explanations of radiation terms can be found here.
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