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INTRODUCTION

The use of radionuclides for the assessment of cardiovascular disease is well-established as a very low-risk, high-sensitivity, and specificity technology for establishing the presence of coronary disease, hibernating myocardium, and other cardiac and cardiovascular syndromes.1,2 Recently societies and professional medical organizations have expressed concern for radiation exposure to patients undergoing nuclear cardiology procedures.3 It is important in addressing concerns of radiation exposure that the quality of nuclear cardiology procedures not be sacrificed for the purposes of reducing the patient's radiation dose alone. Nuclear cardiology procedures can confer life-saving benefits; however, the application of sensible radiation reduction techniques can maintain and even improve the diagnostic quality of nuclear cardiology images while reducing the patient dose.3–6

Current understanding of the influence of radiation on the patient's long-term risk assumes the effect of ionizing radiation is cumulative over a patient's lifetime. More recent genomic studies of double strand breakage and repair mechanisms may indicate a simple linear; no threshold model for the influence of radiation may overestimate the risk of carcinogenesis from diagnostic radiation.7 Despite this, each procedure must take into account radiation-reducing steps to have an impact on the overall patient dose. However, radiation-reduction strategies should not come at the expense of diagnostic quality.

Imaging societies encourage nuclear laboratories and health-care providers to consider patient needs when prescribing imaging tests.8 For example, elderly patients with known coronary disease have a different risk-to-benefit relationship than younger patients at a lower likelihood for coronary disease. Customizations of imaging protocols should take into account patients' needs for an accurate assessment of cardiovascular disease in addition to their own sensitivity to ionizing radiation, as well as the frequency of testing procedures being ordered.

Cardiac PET offers some unique advantages over SPECT by simultaneously providing improved image quality, diagnostic accuracy, and reducing patient dosage.9 This chapter investigates the trade-offs of reducing patient dose, specific advantages of cardiac PET, and recommends strategies for optimizing patient dose and image quality with a cardiac PET procedure.

RADIATION EFFECTS

Photon ionizing radiation interacts with cells by depositing energy in a focal region, disrupting the cell's machinery. Of greatest concern is changes in the cell's DNA that could lead to carcinogenesis. At lower photon energies (ultraviolet radiation), radiation can cause focal breakages of DNA base pairs, resulting in pyrimidine dimers that then can be sites of incorrect or incomplete DNA repair.10 These incomplete repairs have the potential for producing viable cancerous cells as is the case of melanoma.

At higher photon energies, the mechanism for carcinogenesis is the production of hydroxyl radicals.11 When gamma radiation interacts with molecules inside of a cell, the result is a Compton scattered electron that thermalizes in the medium. This thermalization process produces free electrons that break the hydrogen-hydroxide bond leading to free hydroxyl radicals inside of the cell. These ...

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