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Wise And Gentle Imaging
Recent articles in both the scientific literature and lay press have detailed the increasing use of diagnostic imaging – most significantly CT – and the potential health risks caused by the associated ionizing radiation. Since 2007 medical imaging has represented the single largest source of radiation exposure to the US population. The value of diagnostic imaging for making important and sometimes life-saving diagnoses is well known, with a newly published study showing that the use of CT changes the leading diagnosis for nearly half of all Emergency Department patients. Nonetheless, the radiation doses involved are not trivial, and the Diagnostic Radiology community has come together in an effort to ensure that this important medical imaging is used appropriately.
Image Wisely is an awareness program introduced toward the end of 2010 by the American College of Radiology, the Radiological Society of North America, the American Association of Physicists in Medicine and the American Society of Radiologic Technologists. Sharing the philosophy of the Image Gently pediatric radiation reduction campaign initiated in 2008, Image Wisely's objective is to encourage practitioners to avoid unnecessary ionizing radiation scans and to use the lowest optimal radiation dose for necessary studies. Both web sites contain valuable information for physicians and patients about radiation safety and the use of medical imaging.
Northwest Community has pledged to be part of these campaigns, and the Radiology Department has made important changes to lower radiation doses in recent years. Specific steps have included using bismuth shields to protect radiation sensitive organs such as the cornea, thyroid and female breast during CT scanning. We also have adjusted the energy utilized by our CT scanners to provide the lowest amount of radiation required to obtain diagnostic quality images.
Imaging During Pregnancy
Fetal exposure to ionizing radiation can be alarming to prospective parents and is dealt with by the general public with less objectivity than is almost any other noxious agent. The risks are greatest during the first trimester, with potential adverse effects falling into three categories: lethal, teratogenetic and carcinogenetic, with the development of childhood leukemia the greatest concern. As a causal relationship between a radiation dose of up to 10 rad (ie, approximately 15 abdominal CT examinations) and a specific deleterious effect in humans has never been directly established, exposure during pregnancy to the ionizing radiation doses used in diagnostic imaging is not considered an indication for therapeutic abortion.
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Two of the most common reasons that diagnostic imaging studies are obtained during pregnancy are to evaluate chest and abdominal pain. If pulmonary embolism is a concern, both nuclear medicine ventilation/perfusion (V/Q) scanning and contrast-infused chest CT can be performed with minimal radiation exposure to the fetus. While the literature has no clear consensus on which test to use, we prefer CT to V/Q scanning. While iodinated contrast media do cross the placenta, they do not remain in the fetal circulation long and are not contraindicated. It is advised that lower extremity venous Doppler testing - which does not use any ionizing radiation - be performed first, as a positive test may obviate the need for additional imaging.
For pregnant women with abdominal pain, ultrasound should be the initial examination. However, sonography will often not be diagnostic, particularly when appendicitis and renal colic are clinical concerns. In these circumstances MR imaging is then advised. There have been no documented adverse fetal effects from MR imaging, but FDA guidelines require labeling of MR imaging devices to indicate that safety with respect to the fetus has not been established. The theoretical concerns relate to both the high magnetic field strengths and radiofrequency energy pulses. Like their CT counterparts, gadolinium-based MR contrast media cross the placenta, but they are contraindicated as they remain within the fetal circulation substantially longer than do iodine agents and their long-term effects are not known.
Uninfused coronal T2-weighted image showing a dilated appendix with adjacent fluid (arrow) in this 25-year-old female with early acute appendicitis. Note the gravid uterus (U).
Uninfused axial T2-weighted image showing a 3 mm calculus (arrow) in the proximal left ureter in this 32-year-old female with left flank pain and ipsilateral hydronephrosis. Note the gravid uterus (U).
If you wish to discuss imaging risks and algorithms for your patients, please do not hesitate to call 847.618.5850.
Thanks to Dr. Kenneth Spero for his assistance and advice.
For more information about Northwest Radiology Associates, the services we provide and how to contact individual radiologists, please visit our web site: northwestradiologyassociates.com. You can also follow us on Twitter at: twitter.com/northwestrads .
If you wish to be added to our distribution list, please email: ckalbhen@nch.org. We always welcome your questions and comments as well.
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