Many patients with chest pain are put through a series of tests, including electrocardiograms and stress tests that are time consuming and expensive: In the U.S. alone, such testing costs $10 billion to $12 billion a year. Other patients go on to have an invasive angiography, or a cardiac catherization to look at the arteries, even though as many as 20% to 40% of these cases reveal no clinically significant narrowing of the arteries.Well, maybe not, Dr. Hecht. A relatively recent article on CT scanning from Circulation demonstrated that such high resolution scanners still could only make a diagnosis 75% of the time at best, since coronary calcium and even a single irregular heart beat could distort an acquired image. But companies want to market to the worried well, offering piece of mind that a heart scan will reassure them they are not at risk of heart disease, and turn a profit.
"Because stress tests are not perfect, there are many patients who go to cath lab who don't need it," said Harvey Hecht, chief of cardiovascular computer tomography at Lenox Hill Hospital in Manhattan. "All of those will be eliminated by doing cardiac CT."
But what these companies also fail to mention is the radiation exposure these scans supply to the average man and woman. (Yes, ladies, women get much more radiation than men with these scans).
So, in the interest of public disclosure, I thought I'd assemble here some interesting data that I culled from various sources regarding radiation exposures and cancer risks with common diagnostic cardiovascular tests. Hopefully this will serve as a wake-up call to patients considering these tests. It should be mandatory that radiation dose be disclosed with these tests, especially as the number of x-ray elements grows from 64-slice to 128-slice scans. From the FDA's website:
The effective doses from diagnostic CT procedures are typically estimated to be in the range of 1 to 10 mSv. This range is not much less than the lowest doses of 5 to 20 mSv received by some of the Japanese survivors of the atomic bombs. These survivors, who are estimated to have experienced doses only slightly larger than those encountered in CT, have demonstrated a small but increased radiation-related excess relative risk for cancer mortality.So to update the FDA's table, I added a few lines regarding average radiation doses of current cardiovascular tests for comparison:
Radiation dose from CT procedures varies from patient to patient. A particular radiation dose will depend on the size of the body part examined, the type of procedure, and the type of CT equipment and its operation. Typical values cited for radiation dose should be considered as estimates that cannot be precisely associated with any individual patient, examination, or type of CT system. The actual dose from a procedure could be two or three times larger or smaller than the estimates. Facilities performing "screening" procedures may adjust the radiation dose used to levels less (by factors such as 1/2 to 1/5 for so called "low dose CT scans") than those typically used for diagnostic CT procedures. However, no comprehensive data is available to permit estimation of the extent of this practice and reducing the dose can have an adverse impact on the image quality produced. Such reduced image quality may be acceptable in certain imaging applications.
The quantity most relevant for assessing the risk of cancer detriment from a CT procedure is the "effective dose" . Effective dose is evaluated in units of millisieverts (abbreviated mSv; 1 mSv = 1 mGy in the case of x rays.) Using the concept of effective dose allows comparison of the risk estimates associated with partial or whole-body radiation exposures. This quantity also incorporates the different radiation sensitivities of the various organs in the body.
|Diagnostic Procedure||Typical Effective Dose (mSv)||Number of Chest|
X rays (PA film) for Equivalent Effective Dose
|Time Period for Equivalent Effective Dose from Natural Background Radiation|
|Chest x ray (PA film)||0.02||1||2.4 days|
|CT head||2.0||100||243 days|
|CT abdomen||10.0||500||3.3 years|
|Coronary Angiogram||3.4||170||1.1 years|
|64-slice CT (male)||15.2||760||5.1 years|
|64-slice CT (females)||21.4||1070||7.1 years|
|Dual-isotope (3.0mCi Tl-201+30mCi Tc-99) Thallium scan||27.3||1365||9.1 years|
So think about this when you get your next CT scan "just to find out" your coronary disease risk: is it worth the radiation exposure?
12:21 PM CST: Data for mammogram and dual-isotope Thallium test added. Reference: Thompson RC and Cullom SJ. J Nucl Cardiol 2006; 13: 19-23.