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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Conventional therapy vs. alternative therapy

Conventional therapy vs. alternative therapy

11. March 2008 William Davis (5)
Rose is a 75-year old woman, mother of four, grandmother of many more.

Rose's story started after a heart attack 18 months ago that resulted in two stents. She was advised to follow an American Heart Association diet and take Lipitor. However, some months later, after her fourth stent, she became disilluioned in the conventional approach to heart disease and sought alternative therapies to help reduce or reverse her heart disease.

She found an alternative health practitioner who advised chelation, antioxidant vitamins for "excessive oxidation," and several homeopathic preparations.

Nothing was said about diet or exercise. Nothing was said about the baked flour products and pastries that occupied at least two meals every day. Nothing was said about the candies she indulged in several times per day, nor the soft drinks. Nothing was said about the wildly fluctuating blood sugars, poorly controlled by an oral diabetes agent. Thirty pounds of weight gain over the past 5 years with no exercise or physical activity? No comment here, too.

In short, Rose was the "graduate" of the conventional approach, as typically offered nationwide thousands of times a week. She was also the recipient of the insight of at least one alternative health practitioner, eager to reject conventional notions of how to achieve heart health.

So I then met her. She was experiencing chest pains every day, several times per day. Blood pressure over 200. At 5 ft, 3 inches, weight: 186 lbs.

Initial laboratory results:

HDL cholesterol 42 mg/dl
LDL 132 mg/dl
Triglycerides 263 mg/dl
Blood sugar 173 mg/dl


You can fill in the rest. In short, Rose was a disaster. Despite the attentions of several professionals from both the conventional as well as alternative camps, she was careening rapidly towards failure. She'd been given various crutches, Band-Aids, and salves, none of which resulted in any possibility of long-term relief from her aggressive disease.

My point: As I've said previously, all we want is truth. We want effective, rational approaches that yield real benefit. A stent? All that provides is temporary restoration of blood flow. Statin agents? They do indeed reduce LDL cholesterol. But what if Rose has 8, 9, or 10 other causes of heart disease unaffected by the statin drug? It will do little or nothing.

Nobody had addressed many of the root causes of Rose's disease: insulin resistance, high triglycerides, inactivity, obesity, hypertension (and identifying the reasons why her blood pressure was so high), vitamin D deficiency (virtually guarantted to be severe), junk foods including the ones known as "whole grains."

My message: Success in heart disease, as well as all aspects of health for that matter, doesn't necessarily have to come from an "alternative" approach, nor a "conventional" approach. It comes from applying what is truly effective, regardless of what label someone applied to it.

I would no sooner trust my health and life to an alternative health practitioner hawking unusual herbs and remedies than I would submit to a heart catheterization, three stents, followed by a statin drug. There's small benefit in both approaches, but none are the best. You've got to look elsewhere for that.


Copyright 2008 William Davis, MD
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Comments (5) -

  • Sue

    3/10/2008 11:19:00 PM |

    I'm really dismayed that the alternative practitioner did not look at diet (most do) but if they did I'm sure they would have recommended the usual low fat. Herbs can be very useful but only if combined with appropriate diet.

  • mike V

    3/10/2008 11:53:00 PM |

    Re: Rose

    Please follow up on Rose's TYP progress from time to time.
    We can find all kinds of studies and other info. Only your blog provides us with real world practical feedback on results with real patients.

    Thanks
    MikeV

  • Danimal

    3/11/2008 12:45:00 AM |

    I hear ya, Dr. Davis. My dad just had his 2nd bypass during an aortic pseudo-aneurism operation. He had a rock the size of my thumb knuckle removed from his aorta, his chest cracked, and still has massive occlusion of his arteries. Still, my RN-having stepmadre insists on him pursuing an AHA-approved low-fat, high-carb diet, and won't even consider putting him on Vitamin D and Niacin. How can you fight against the experts of the AHA?

  • Sravana

    3/11/2008 6:51:00 PM |

    As an alternative healthcare provider (acupuncturist/herbalist), you can BET that I would be talking to her about diet and exercise. I would've taken her BP, and probably sent her to an MD immediately to get that taken care of.

    Now, given that she was a wreck, what kind of exercise program would you put her on? I'm thinking a 20 minute walk every day, at whatever pace she could manage without chest pain - but she's already *having* chest pain! I'm curious how you handle that.

  • Anonymous

    8/31/2008 12:09:00 AM |

    "There is a clear need for a rapid, simple, safe, and sensitive method of determining the type and intensity of inflammation in the gut mucosa in clinical practice. In this study, we have evaluated the potential of a new method, the mucosal patch technique, in patients with and without apparent gut inflammation, as assessed by conventional diagnostic procedures.

    http://www.ncbi.nlm.nih.gov/pubmed/15542519

    "In 18 of 20 patients gluten challenge induced neutrophil activation defined as increased [myeloperoxidase] MPO release and increased NO synthesis. Ten of these 20 patients showed a similarly strong inflammatory reaction to CM challenge."

    http://www.ncbi.nlm.nih.gov/pubmed/17302893

    "Molecular chlorine generated by the myeloperoxidase-hydrogen peroxide-chloride system of phagocytes converts low density lipoprotein cholesterol into a family of chlorinated sterols."

    Myeloperoxidase, a heme protein secreted by phagocytes, is a potent catalyst for LDL oxidation in vitro, and active enzyme is present in human atherosclerotic lesions. ... Our observations suggest that Cl2 generation in acidic compartments may constitute one pathway for oxidation of LDL cholesterol in the artery wall.

    http://www.ncbi.nlm.nih.gov/pubmed/8798498

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