CT scans and radiation exposure

19. June 2007 William Davis (8)


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.
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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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The wheat-free life

The wheat-free life

30. June 2007 William Davis (10)
"There's nothing else I can do with my diet," declared Whitney, a 53-year old university faculty member.

"I don't eat meat. I never eat fried foods. I can't remember the last time I used butter. My idea of having a treat is a handful of blueberries. What else can I do?"

Whitney was clearly frustrated. With a CT heart scan score of 264, she was worried that trouble was just around the corner. Her lipoprotein panel had demonstrated a severe small LDL pattern, with 70% of all LDL particles in the small category. HDL was also low at 41 mg/dl.

"What did you eat for breakfast?" I asked.

"Same as always: Either Fiber One cereal or Shredded Wheat. No sugar, just skim milk. Sometimes I have some orange juice, fresh-squeezed of course."

"How about lunch?"

"If I brown-bag it, I'll usually have a reduced-fat turkey breast sandwich on whole grain bread. About once a week, I'll have a whole wheat bagel--no cream cheese, of course."

"Dinner?"

"Sometimes I have chicken--skinless--with a vegetable, corn, or salad. I love pasta, but I always use whole wheat."

"How about snacks?"

"I try not to snack. But, when I'm desperate, I usually grab some Triscuits or pretzels."

The problem with Whitney's diet was clear: Too many sugar-equivalents, otherwise known as wheat. I suggested that her diet was far too heavily laden with wheat products. She seemed skeptical. "But this is as low-fat as I can get! Now you're going to take away wheat?"



What happens when you eliminate wheat from your diet?

Several predictable, consistent changes can be observed:


--HDL cholesterol goes up.

--Triglycerides go down.

--Small LDL particles are reduced.

--LDL cholesterol drops (the amount dropped depends on the proportion of small LDL pattern)

--Blood sugar drops.

--Blood pressure drops.

--C-reactive protein (an index of imperceptible inflammation) drops.


In addition to these measurable changes, several perceptible improvements often develop: more energy, less afternoon "slump," better sleep, sometimes less rashes.

Since Whitney was skeptical, I suggested a simple 4 week "experiment": Eliminate wheat products entirely for 4 weeks and see for herself what happens. I also warned her that, while I believe that elimination of wheat is a great strategy, she could negate the benefits by indulging in candy, soft drinks, and other junk products. It would therefore be necessary to maintain an otherwise healthy diet.

So Whitney gave it a try for 4 weeks. To make up for the dropped calories, she increased her reliance on vegetables, fruits, lean proteins, nuts, seeds, and healthy oils.

After losing 6 lbs over the 4 weeks without otherwise trying, she was convinced. She was further convinced when we reassessed her laboratory work: HDL went up 10 mg/dl; triglycerides down 120 mg/dl; blood sugar dropped from 112 mg/dl (pre-diabetic) to 95 mg/dl (normal). Several months later, we checked her lipoproteins. Small LDL had dropped to around 30% of total LDL--a big improvement.

It's contrary to conventional wisdom. It's counter to the USDA Food Pyramid. It's certainly not what the American Heart Association says. It could potentially disrupt the economics and politics of the enormously powerful food industry.

But, more often than not, the results are impressive to phenomenal.
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Comments (10) -

  • Darwin

    6/30/2007 8:00:00 PM |

    Saw this in my RSS reader.  Are they correct, and if so, can you recommend any other non-wheat whole grains we should consume?

  • Dr. Davis

    6/30/2007 9:52:00 PM |

    "Your arteries are happy when you eat whole grains" is patent nonsense, imy view. There are indeed subgroups of people who can do fine eating whole grains, but the majority of people do miserably.

    Oats and flaxseed are the only grains that I would recommend. Otherwise, more than sufficient fiber and nutrients come from vegetables, fruit, and raw nuts and seeds.

  • JT

    7/1/2007 12:44:00 AM |

    Avoiding wheat is something I'm familiar with.  I never thought I'd be on a wheat free diet for heart health though.  Having had a sever intestinal problem for most of my  life, gastrologists have prescribed a gluten free (wheat, barely, rye free) diet many many times.  

    Being on a wheat free diet is easier today than in the past.  That's because it used to be believed that celiac sprue was a rare condition, with possibly 1 in 3000 having the condition.  Now with DNA testing it has been found that as many as 1 in 100 have the condition.  Happly, food processors have noticed, and label more foods as being gluten free.    

    It used to be believed that only thin people with diarrhea had celiac, but now it is known that over weight constipated patients can have the genetic condition too.  This has led to some to suggest that celiac might be one of the most under-diagnosed conditions in America.  

    I've read that celiacs are much more likely to have heart disease compared to the general public.  So reading this bog makes me wonder if those that do much better on a wheat free diet for heart health could also be undiagnosed celiac.

  • Darwin

    7/1/2007 5:02:00 AM |

    Thanks Dr. Davis.  I really appreciate your advice and your blogging.

  • Ortcloud

    7/1/2007 11:53:00 PM |

    regarding the article

    "Your arteries are happy when you eat whole grains"

    It is odd that they dont say  compared to what ? compare to no wheat ? compared to refined wheat ?

    It is all relative, so maybe they are comparing refined grains, compared to whole grains ? They leave that out. Maybe on purpose as  an intententional form of manipulation to imply that eating grains is healthy.

    It would be like saying "organic mercury is healthy for you" when they compare it to methyl mercury, but leaving out the part about the methyl mercury. Both are extremely toxic, but someone reading it might think the less evil form is healthy for you. Pure deception.

  • Anne

    7/2/2007 11:51:00 PM |

    I have been gluten free for the past 4 years. I had heart bypass 7 years ago. Before I went gluten free I was having pitting edema in my legs, fatigued and shortness of breath. I stopped eating gluten and those symptoms, along with many others. disappeared. In fact, I feel my best when I stay away from all grains - especially processed grains.

    I don't know how happy my arteries are now, but I am much happier. I think they are too.

  • jpatti

    10/6/2007 8:55:00 AM |

    The article on whole grains is typical of how I see this terms used.  Some studies show that a diet in whole grains is healthier than a diet in refined grains (never mind they can't compare to vegetables).

    First thing I notice on that page is a picture of a bowl of cereal, looks like flaked wheat.  Does anyone even KNOW that the word "whole" means?  

    You cannot take a flaked wheat out in the yard and plant it and have it grow.  This is cause it's not a whole grain.  Everyone does this silliness, the AHA, the ADA, etc.  

    General Mills would freak out if people REALLY started eating wheat berries instead of Cheerios.

  • jpatti

    10/6/2007 8:57:00 AM |

    Besides oats and flaxseeds, barley is a very good grain too.

  • Anonymous

    3/27/2010 6:58:10 PM |

    about 1950, the drug lords made it practically illegal in the usa for doctors to learn about, study, and use (and tell people about) vitamin c which did, does and will prevent heart disease. big pharma so much prefers profit to health, they will simply let millions die if it means more $$$ for them.  See a spanish document translated by google for the verification, et al such as m.salaman and max gerson and linus pauling. signed jeff elohim

  • buy jeans

    11/2/2010 8:54:59 PM |

    It's contrary to conventional wisdom. It's counter to the USDA Food Pyramid. It's certainly not what the American Heart Association says. It could potentially disrupt the economics and politics of the enormously powerful food industry.

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