CT scans and radiation exposure



The NY Times ran an article called

With Rise in Radiation Exposure, Experts Urge Caution on Tests at

http://www.nytimes.com/2007/06/19/health/19cons.html?_r=1&adxnnl=1&oref=slogin&adxnnlx=1182254102-vQpytpx6W/Z9gvAaNPDZvA



“This is an absolutely sentinel event, a wake-up call,” said Dr. Fred A. Mettler Jr., principal investigator for the study, by the National Council on Radiation Protection. “Medical exposure now dwarfs that of all other sources.”


Where do CT heart scans fall?

Let's first take a look at exposure measured for different sorts of tests:



Typical effective radiation dose values

Computed tomography Milliseverts (mSv)

Head CT 1 – 2 mSv
Pelvis CT 3 – 4 mSv
Chest CT 5 – 7 mSv
Abdomen CT 5 – 7 mSv
Abdomen/pelvis CT 8 – 11 mSv
Coronary CT angiography 5 – 12 mSv

Non-CT Milliseverts (mSv)

Hand radiograph Less than 0.1 mSv
Chest radiograph Less than 0.1 mSv
Mammogram 0.3 – 0.6 mSv
Barium enema exam 3 – 6 mSv
Coronary angiogram 5 – 10 mSv
Sestamibi myocardial perfusion (per injection) 6 – 9 mSv
Thallium myocardial perfusion (per injection) 26 – 35 mSv

Source: Cynthia H. McCullough, Ph.D., Mayo Clinic, Rochester, MN


If you have a heart scan on an EBT device, then your exposure is 0.5-0.6 mSv, roughly the same as a mammogram or several standard chest x-rays.

A heart scan on a 16- or 64-slice multidetector device, your exposure is around 1.0-2.0 mSv, about the same as 2-3 mammograms, though dose can vary with this technology depending on how it is performed (gated to the EKG, device settings, etc.)

CT coronary angiography presents a different story. This is where radiation really escalates and puts the radiation exposure issue in the spotlight. As Dr. Cynthia McCullough's chart shows above, the radiation exposure with CT coronary angiograms is 5-12 mSv, the equivalent of 100 chest x-rays or 20 mammograms. Now that's a problem.

The exposure is about the same for a pelvic or abdominal CT. The problem is that some centers are using CT coronary angiograms as screening procedures and even advocating their use annually. This is where the alarm needs to be sounded. These tests, as wonderful as the information and image quality can be, are not screening tests. Just like a pelvic CT, they are diagnostic tests done for legimate medical questions. They are not screening tests to be applied broadly and used year after year.

Always be mindful of your radiation exposure, as the NY Times article rightly advises. However, don't be so frightened that you are kept from obtaining truly useful information from, for instance, a CT heart scan (not angiography) at a modest radiation cost.



Detail on radiation exposure with CT coronary angiograms on multidetector devices can be found at Hausleiter J, Meyer T, Hadamitzyky M et al. Radiation Dose Estimates From Cardiac Multislice Computed Tomography in Daily Practice: Impact of Different Scanning Protocols on Effective Dose Estimates. Circulation 2006;113:1305-1310, one of several studies on this issue.

Comments (8) -

  • Anonymous

    6/20/2007 1:13:00 AM |

    I had a calcium score scan on a 64-slice machine at the Morristown Hospital in New Jersey. No contrast was injected. The technician did three separate scans that included the lung, even thought I didn't for a lung scan. I wonder why three scans were taken. Does it mean that I had three times the radiation?

  • Dr. Davis

    6/20/2007 1:22:00 AM |

    Hi,
    Of course I can't comment specifically on what was done, but it is common practice to perform 1) a "scout" film for the technologist to identify the location of important "landmarks" like the sternum and the top and bottom of the heart to minimize the window of exposure, and 2) lung imaging as a routine part of  heart imaging, not necessarily an additional scan.

    If an additional and unrequested lung scan was performed, you may want to call and ask why this policy is in operation.

  • Anonymous

    6/21/2007 4:35:00 AM |

    What do you feel about yearly nuclear stress tests for people with CAD?  The radiation exposure seems high and the ability of a stress test to pick subtle changes in flow is low.  In the absence of symptoms it would appear that the common practice of nuclear stress tests for people with CAD is a questionable practice.

  • Dr. Davis

    6/21/2007 12:14:00 PM |

    I agree. The radiation is excessive. I tend to follow that route only when nothing else is possible. An alternative for stress testing is stress echocardiogram in its various forms, none of which involve radiation. They still suffer the other pitfalls of stress testing, of course, but do not involve radiation.

  • Mike

    12/20/2008 11:40:00 AM |

    I just launched a webiste that may answer some of your questions.  www.xrayrisk.com. It allows you to calculate your cancer risk based on studies you have had and answers some faq on radiation exposure and cancer.

  • Anonymous

    12/6/2009 12:52:26 AM |

    There are several ways to estimate your cancer risk - the best site for background information is probably the Image Gently campaign.

    The American College of Radiology has similar information pages for patients and the general public.

    To track your exposure, as Mike said there's the xrayrisk website.
    There's also a program for the iphone called Radiation Passport that tracks all of your radiation exposure and gives you the associated risk of developing cancer from your radiation exposure.

  • buy jeans

    11/3/2010 6:33:12 PM |

    CT coronary angiography presents a different story. This is where radiation really escalates and puts the radiation exposure issue in the spotlight. As Dr. Cynthia McCullough's chart shows above, the radiation exposure with CT coronary angiograms is 5-12 mSv, the equivalent of 100 chest x-rays or 20 mammograms. Now that's a problem.

  • Medical CT

    11/29/2010 4:34:03 AM |

    The CT scanner was originally designed to take pictures of the brain. Now it is much more advanced and is used for taking pictures of virtually any part of the body.

    The scanner is particularly good at testing for bleeding in the brain, for aneurysms (when the wall of an artery swells up), brain tumours and brain damage. It can also find tumours and abscesses throughout the body and is used to assess types of lung disease.

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Another Ornish casualty

Another Ornish casualty

Barry's lipoproteins were nearly all corrected to perfection: LDL 64 mg, HDL 57 mg, triglycerides 45 mg. He was approaching the Track Your Plaque goal of 60/60/60, the levels we find tip the scales heavily in your favor for achieving plaque reversal.

But one problem still prominently persisted: small LDL. Of Barry's 64 mg of total LSL, 90% of his LDL were small.

Barry was already on niacin (Slo-Niacin; Upsher Smith)1000 mg per day and fish oil, 4000 mg per day, both of which contribute to correction of this pattern. He had added occasional raw almonds and oat bran to his daily habits, both of which also help suppress small LDL. "I thought you told me that small LDL should go away if I did all this!" he lamented in frustration.

We probed Barry's diet choices more closely. "I eat really healthy foods, just like an Ornish program." Uh oh.

"What do you mean?" I asked.

"For breakfast, I have two slices of whole wheat toast--no butter or margarine, of course! I'll have Shredded Wheat with skim milk. That's it. My typical lunch is low-fat turkey--no mayonnaise!--on whole wheat. I'll add some low-fat whole wheat crackers or pretzels. That's pretty much my habit."

"How about dinner?"

"Dinner varies a lot. I'll usually have a low-fat meat like chicken or turkey, never beef, a vegetable, and a potato. I love rolls but I try to make them whole wheat. I don't use gravy. I love ice cream, so I've been having low-fat frozen yogurt instead. I guess that's about it."

Barry had indeed been counseled on how we approach nutrition. We, of course, do not endorse the low-fat approach of the Ornish program. Low saturated and hydrogenated fat, yes, but not the super-strict low-fat, "all fat is bad" approach of Dr. Dean Ornish.

Barry's diet is typical of someone on a low-fat restriction. When I asked him why he was eating this way, he admitted that he'd seen Dr. Ornish on a TV program in which he persuasively proclaimed that he reversed heart disease in his patients over the past nearly 20 years using this low-fat approach.

That explained it. Barry's nearly pure carbohydrate diet was triggering high blood sugar responses after meals, causing his insulin to skyrocket and magnifying the small LDL pattern.

I advised Barry to dramatically reduce his carbohydates like breads, pretzels, low-fat yogurt, crackers, etc. Instead, he could increase his lean proteins like eggs, egg whites, Egg Beaters, raw nuts and seeds, low-fat (yes, low-fat!) dairy products like yogurt and cottage cheese (both high protein), and healthy oils.

I've seen this happen with many people over the years: A severe low-fat restriction becomes a high-carbohydate diet. It's not uncommon for many people to have more than 70% of calories from carbohydrates on these programs.

The low-fat approach worked in the era of high-fat diets in the 1980s. In 2006, where convenience foods made with carbohydrates, especially wheat, predominate and pack 80% of supermarket shelves, low-fat is now a distorted nutritional mistake that leads to problems like Barry's uncontrolled small LDL, and often pre-diabetic or overt diabetes.
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