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.
Tags :

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.

Add comment

Loading
Stenosis detection vs. plaque detection

Stenosis detection vs. plaque detection

22. November 2007 William Davis (5)
One of the most common misunderstandings encountered by both physicians and the public is that, to create an effective heart disease prevention program, we need tools for atherosclerotic plaque detection. What we do not need is a tool for stenosis detection. (Stenosis means percent blockage. A 50% stenosis means 50% of the diameter of an artery is reduced by atherosclerosis.)

This issue came to mind recently with the ongoing conversation at Heart.org forum, in which the conversation predictably degenerated into a "what good are heart scans when there are better tests to detect blockage" sort of mentality.
They are right: There are better tests to detect stenoses or blockages, such as stress tests, heart catheterization, and CT coronary angiography. If someone is having chest pain or breathlessness, these tests are useful to help understand why. These tests are preludes to stents, bypass surgery, and the like. They are the popular tools in hospitals, the ones that provide entry into the revenue-yielding world of heart disease procedures.

Plaque detection, on the other hand, is principally a tool for the person without symptoms. In this regard, it is more like cholesterol testing. I doubt my colleagues would bash cholesterol because it doesn't reveal blockages. Plaque detection identifies the person who has already started developing atherosclerosis.

Dr. William Blanchett of Colorado articulates this idea well:

EBT calcium imaging not only identifies the vast majority of individuals at risk, it also identifies individuals with minimal risk. In other words, it distinguishes those who are likely to benefit from treatment . . .and it identifies those unlikely to benefit from treatment. Furthermore, the greatest value of EBT calcium imaging is that with serial imaging you can determine who is and who is not responding to treatment.

Those patients not responding to the initial treatment are identified by progression of their calcified plaque on a subsequent scan are then placed on additional therapies. The net result is a remarkable reduction in heart attack rates.

Ahh, the voice of reason. Plaque detection empowers you in your prevention program. If you know how much plaque your begin with, you can track that value to know whether you have having a full effect or not. Stenosis detection, on the other hand, empowers your doctor and provides the irresistible impulse to stent.

Another common objection raised to plaque detection is "why bother if you're going to give everybody a statin anyway?" We know the origins of that argument, don't we? If the only strategy known to your doctor is cholesterol reduction with statin drugs, then perhaps that's right. But, with awareness of all the things that go beyond statin drugs, often make them unnecessary, then knowledge of who should engage in an intensive program of prevention or not is enabled by plaque detection.
Tags :

Comments (5) -

  • BarbaraW

    11/23/2007 3:30:00 AM |

    Happy Thanksgiving to you and your family.  One of the things I am thankful for is that you and others are blogging about these important health and nutrition issues.

  • jpatti

    11/23/2007 11:35:00 PM |

    Since I've already had a bypass, a heart scan is unlikely to give me useful info.  So I'm kind of in the place where understanding tests other than heart scans is more important.  

    Is heart.org a good place to learn things like how to interpret an echocardiogram?  I've got a report in the mail to me right now so I can try to figure it out.

    If not, where would you recommend for the "advanced" post-prevention type of information?

  • Dr. Davis

    11/24/2007 1:18:00 AM |

    jpatti--

    Sorry, I don't know of any such sites that focus on these sorts of tests.

    Have you considered reading a general cardiology text? Most provide more than you will need to know, but a visit to your medical bookstore or library will yield a number of "entry-level" texts that might help you navigate through the maze.

  • Anonymous

    8/20/2010 10:54:26 AM |

    Dear Dr. Davis,

    I'm new to your blog, which I find very interesting and full of what appears to be insightful comments and recommendations. I also find your "unorthodox" stance on many issues very refreshing. I would like to know:
    1.have you published research backing the advice you give on your blog?
    2. has your work been peer reviewed?
    3. could you, please, let me know where I can find them?

    Thanks in advance for your help.

  • buy jeans

    11/3/2010 3:49:24 PM |

    Ahh, the voice of reason. Plaque detection empowers you in your prevention program. If you know how much plaque your begin with, you can track that value to know whether you have having a full effect or not. Stenosis detection, on the other hand, empowers your doctor and provides the irresistible impulse to stent.

Add comment

Loading