Ionizing Radiation in Cardiac Imaging

Abstract

A preliminary report on medical radiation exposures to the US population based on publicly available sources of data estimated that the collective dose received from medical uses of radiation has increased by Ͼ700% between 1980 and 2006. 1 Computed tomography (CT) has had an annual growth rate of Ͼ10% per year and accounted for Ϸ50% of the collective dose in 2006. Approximately 65% of the collective CT dose is from studies of chest, abdomen, and pelvis. In 2006, cardiac CT accounted for 1.5% of the collective CT dose; however, utilization of cardiac CT is expected to rise, with the potential to further increase exposure to the population. 1 Nuclear medicine studies in the United States have increased by 5% annually to 20 million in 2006 and accounted for Ϸ25% of the 2006 collective medical radiation dose. Among nuclear medicine studies, cardiac imaging represented 57% of the number of studies and Ϸ85% of the radiation dose. 1 A number of publications on imaging with CT, fluoroscopy, or radioisotopes have emphasized the risks that may be associated with exposure to ionizing radiation. [2][3][4] To make informed decisions concerning the use of medical radiation in imaging procedures, the following are important components: (1) A working knowledge of the principles and uncertainties of the estimation of patient dose and biological risk; (2) a comparison of the risks of radiation exposure with the risks of activities in daily life; and (3) recognition of the potential risk of failing to make important diagnoses or treatment decisions if imaging is not performed because of safety concerns.There is no federal regulation of patient radiation dose, with the exception of mammography. Most federal and state regulations are aimed at equipment performance or the handling of nuclear materials. Therefore, appropriate utilization of the equipment or nuclear material in cardiac imaging, to maintain the dose as low as reasonably achievable, is the responsibility of the imaging physician and facility. The purpose of this Science Advisory is to provide a conceptual framework and make general recommendations for the safe use of cardiac imaging that relies on ionizing radiation. Parameters of Dosimetry CT and FluoroscopyThe parameters by which ionizing radiation is quantified differ among imaging modalities. 4 The amount of radiation produced by an imaging device can be described using exposure, expressed in International System of Units (SI) units of coulombs per kilogram (C/kg), or air kerma, expressed in SI units of milligrays (mGy). This document will use the term exposure, which refers to the amount of ionization produced in air by photon irradiation. Exposure can be measured for CT and fluoroscopy with ionization chambers within test objects (phantoms) or at body surfaces with minimal difficulty. Measurable or easily derived parameters, such as entrance skin exposure in radiography and fluoroscopy and the weighted CT dose index (CTDI w ) in CT, are useful to establish diagnostic reference levels for radioThe American Heart Ass...

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