Iowa Radiology Blog

Wise and Safe Diagnostic Imaging: Understanding Radiation Dose

May 31, 2014 10:59:00 AM

Posted by Diane Campbell

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What is Radiation Dose?

We are exposed to various forms of radiation every day. Solar radiation (sunlight) and radon, which occurs in varying concentrations around the world, are the most common sources.  Radiation dose is typically measured in millisieverts (mSv). Other dose measurement units include rad, rem, roentgen, sievert, and gray. The average natural annual dose of radiation from the environment in the U.S. is about 3 mSv. The dose is higher in areas of high elevation and lower in areas closer to sea level.  A round trip coast-to-coast flight results in an additional .03 mSv because of increased exposure to cosmic rays.  Understanding how the radiation dose involved in a given procedure compares to radiation exposure from the natural environment can help to make sense of information you receive about dose.  Some modalities like ultrasound and Magnetic Resonance Imaging (MRI) are helpful diagnostic tools which do not deliver any radiation.

Understanding the Radiation Dose Delivered During a Procedure provides a helpful guide to understanding the radiation dose involved in various radiological procedures.  For example, an abdominal CT scan delivers a dose comparable to 3 years of natural exposure, while a bone density scan results in the equivalent of about 3 hours of natural radiation exposure. In addition, radiation dose is dependent on many factors including patient size and organs imaged. The following chart shows the approximate doseages for commonly ordered exams and the additional lifetime risk of fatal cancer from examination. 

For this procedure:

* Your approximate effective radiation dose is:

Comparable to natural background radiation for:

** Additional lifetime risk of fatal cancer from examination:


Computed Tomography (CT)-Abdomen and Pelvis

10 mSv

3 years


Computed Tomography (CT)-Abdomen and Pelvis, repeated with and without contrast material

20 mSv

7 years


Computed Tomography (CT)-Colonography

10 mSv

3 years


Intravenous Pyelogram (IVP)

3 mSv

1 year


Radiography (X-ray)-Lower GI Tract

8 mSv

3 years


Radiography (X-ray)-Upper GI Tract

6 mSv

2 years



Radiography (X-ray)-Spine

1.5 mSv

6 months

Very Low

Radiography (X-ray)-Extremity

0.001 mSv

3 hours



Computed Tomography (CT)-Head

2 mSv

8 months

Very Low

Computed Tomography (CT)-Head, repeated with and without contrast material

4 mSv

16 months


Computed Tomography (CT)-Spine

6 mSv

2 years



Computed Tomography (CT)-Chest

7 mSv

2 years


Computed Tomography (CT)-Chest Low Dose

1.5 mSv

6 months

Very Low


0.1 mSv

10 days



Coronary Computed Tomography Angiography (CTA)

12 mSv

4 years


Cardiac CT for Calcium Scoring

3 mSv

1 year



Bone Densitometry (DEXA)

0.001 mSv

3 hours



0.4 mSv

7 weeks

Very Low

Note for pediatric patients: Pediatric patients vary in size. Doses given to pediatric patients will vary significantly from those given to adults.

* The effective doses are typical values for an average-sized adult. The actual dose can vary substantially, depending on a person's size as well as on differences in imaging practices.

** Legend:

Risk Level

Approximate additional risk of fatal cancer for an adult from examination:


less than 1 in 1,000,000


1 in 1,000,000 to 1 in 100,000

Very Low:

1 in 100,000 to 1 in 10,000


1 in 10,000 to 1 in 1000


1 in 1000 to 1 in 500

Note: These risk levels represent very small additions to the 1 in 5 chance we all have of dying from cancer.

Why Should I Understand My Radiation Dose?

Radiation is a concern because the energy of these waves is strong enough to knock electrons out of their orbits, creating ions. When this happens inside the body, it results in the creation of hydroxyl radicals, which can damage nearby DNA strands, or the direct ionization of DNA.  Most of this damage is quickly repaired by the body, but it can occasionally lead to changes in cells that increase the risk of cancer formation.

Radiation overexposures have received media attention in the past few years because some clinics failed to monitor safety protocols. There are legitimate concerns about the radiation safety protocols involved in various imaging procedures.  Because computerized tomography (CT or CAT) scans deliver a significantly higher dose of radiation than conventional X-rays, this modality has received more scrutiny.   CT scans can provide valuable information about health conditions, which allows health care providers to offer more beneficial treatment, but limiting a patient’s radiation dose should always be a factor when considering radiologic procedures. It is important to understand the risks and benefits of any medical procedure you may undergo. 

Radiation dose is cumulative over a person's lifetime. The risk of cancer associated with radiation exposure decreases with age, both because children are more sensitive to radiation and because they have more years in which cancer could develop. As adults age, radiation exposure is less of a concern because a patient's tissues are less sensitive to radiation.  Given the slightly increased cancer risk associated with radiation exposure, radiologic imaging should be performed only when the benefits of the knowledge obtainable by the procedure outweigh this risk. 

How Does Iowa Radiology Ensure Wise and Safe Imaging? 

At Iowa Radiology, we work as your advocate and ally in this respect.  We work with referring providers to ensure that the appropriate test is ordered to ensure that we will get the information we need at the lowest possible dose for the patient.

Because we are concerned about reducing CT radiation levels, we were leaders in the acquisition of SAFIRE dose radiation reduction technology.  This new generation of image reconstruction technology has been shown to reduce the radiation dose to our patients by up to 60% and improves image quality. Because a lower dose directly translates to lower risk, the use of SAFIRE technology ensures safer imaging for our patients.  Additionally, we use CT protocols to adjust the radiation dose according to patient size, the relevant body part, and the reason for imaging.  Specific pediatric protocols minimize radiation dose for children. In all cases, we follow the principle of “ALARA” (“as low as reasonably achievable”) in terms of radiation dose. If it is possible to obtain the desired clinical information using ultrasound or MRI, which deliver no radiation dose, we will recommend it.  Extensive personnel training and the use of low-dose methods were necessary steps to receiving American College of Radiology (ACR) accreditation for our CT scanners.

We also use shielding to reduce the radiation dose to organs whenever possible. In a general X-ray procedure, we use collimation to carefully restrict the X-ray beam to the specific area of clinical interest.  Our regularly scheduled quality control procedures ensure that all X-ray devices are functioning properly and safely.

These initiatives are all part of a larger mission to remain on the cutting edge of technology and leaders in quality patient focused care. 

At Iowa Radiology, your health and comfort are important to us.  We always explain procedures before they are performed and answer any questions that arise. If you ever have any questions or concerns about a procedure scheduled at our office, please contact us.


The health-related information on the Iowa Radiology website is meant for basic informational purposes only. It is not intended to serve as medical advice or to be used for diagnosing or treating a disease. Users of this website are advised to consult with their health care providers before making any decisions concerning their health.

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Iowa Radiology was founded in 2001 by a group of well-known central Iowa diagnostic professionals who wished to emphasize the personal side of diagnostic care as much as the technical side.


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