Chapter 7: Radiation Reduction Strategies in Myocardial Perfusion Imaging

INTRODUCTION

Patient radiation exposure during medical procedures is a growing concern among health care providers, professional organizations as well as the general public. Medical radiation (of all subtypes) has increased by over 700% since 1980. Because of its value in diagnosis and prognosis in patients with known or suspected obstructive coronary disease, radionuclide myocardial perfusion imaging use has also increased over the last 25 years. Nuclear imaging accounts for approximately 25% of medical radiation. Cardiac imaging represents ~50% of all nuclear imaging procedures but is responsible for nearly 85% of all nuclear radiation doses.^1–4

Optimizing radiation exposure for patients is of considerable importance for patient safety and should be taken into account when ordering tests. For the nuclear cardiologist, this impacts choices in testing protocols, equipment, and even tracers. Radiation-reduction strategies should also take into account the value of the testing procedure and should not be performed at the expense of image quality, and thus the value of the examination itself. This chapter will present concepts of the consequences of radiation exposure, methods of measuring radiation exposure in medical imaging and in particular, nuclear cardiology, describe current radiation exposure in common cardiovascular single-photon emission computed tomography (SPECT) and positron emission tomography (PET) myocardial perfusion imaging (MPI) procedures, and discuss methods of reducing radiation exposure through instrumentation changes, protocol changes, and tracer choice.

Radiation Exposure: The Data

The exact consequences of radiation exposure are uncertain. The deterministic effects of direct radiation to an organ system, such as epidermal reactions, are well studied. However, understanding the consequences of radiation exposure to an individual is more obscure and difficult to assess. These stochastic effects of radiation exposure acquired during medical imaging are indeed difficult to apply to an individual's lifetime risk of developing cancers. This is in part due to variations in radiation types, exposure rates and quantities, and tissue susceptibilities as well as timing of procedures. In addition, malignancy generated by radiation exposure is often indistinguishable from those occurring from other causes.² Data estimated from the coronary computed tomography (CT) literature suggest that a 10-mSv radiation exposure increases lifetime risk of developing a fatal malignancy by 0.0005%.⁴ This represents a small, but measureable increase in lifetime risk, but is difficult to quantify when considering an individual patient. For perspective, Table 7-1 illustrates comparative risks of death from both radiation sources and other causes.⁴