Chapter 9: SPECT Myocardial Perfusion Imaging Protocols

INTRODUCTION

Single photon-emission computerized tomographic (SPECT) myocardial perfusion imaging (MPI) remains the dominant noninvasive functional imaging perfusion method for the diagnosis as well as prognosis of epicardial coronary artery disease (CAD). The advent and advances of other methods used for similar purposes (cardiac positron emission tomography [PET], stress echocardiography, coronary computerized tomography [CTA], and magnetic resonance imaging [MRI]) have all contributed to recent re-examination of traditional MPI protocols to optimize its use.¹ This task was facilitated by introduction of high-efficiency cadmium zinc telluride (CZT) nuclear cameras and innovative software. With changes in society and concern of radiation exposure, emphasis has shifted from "one size fits all" to patient-centered imaging with individualized approach to each patient's unique constellation of reasons and urgency of testing, comorbidities, age, body habitus, physical ability, and results of previous tests and procedures.² In-depth knowledge of the advantages and disadvantages of available radionuclide tracers and stressors by those who perform stress testing and imaging is paramount. Patient participation in decision making becomes desirable, as well.

With an acknowledgment of possibly harmful effects of low radiation doses used at times frequently over an extended period of time due to the chronic nature of CAD, attention has shifted to dose reduction³ and potentially mandatory tracking of all received radiation doses.⁴

In view of competing noninvasive imaging modalities, cost effectiveness has also been addressed. The length of "traditional" MPI is almost ½ a day, which poorly compares to on average 1 hour to completion and diagnosis using CTA, stress echo, or PET. Many of the newer imaging protocols therefore address the need for increased throughput and improved productivity of a Nuclear Cardiology Laboratory. This chapter will describe protocols for SPECT MPI for the two primary imaging agents, thallium-201 and technetium-based products.

SPECT PROCEDURES

The primary indication for a SPECT MPI study is the assessment of the relative distribution of coronary flow in patients with suspected or known CAD. Since this distribution of coronary flow both at rest and stress is equal in all segments of the left ventricle, the presence of perfusion defects suggests intraluminal coronary obstruction, and if worse at stress than rest, ischemia. An increase in coronary flow is needed for the detection of significant coronary artery stenosis (>50% of luminal narrowing) since rest flow distribution is even unless prior infarction is part of the history. Coronary flow can be increased most physiologically with physical effort (treadmill exercise), or in patients who are unable to exercise adequately, using coronary vasodilators (adenosine, dipyridamole, and regadenoson) or dobutamine (for a more complete description, see Chapter 8).

Evaluation of left ventricular size and function became possible with the development of gating algorithms used in conjunction with MPI. The combination of perfusion and function data improved both the diagnostic and the prognostic value of SPECT studies. ECG-gated SPECT imaging is a powerful tool for ...