Chapter 1: Clinical Overview of Contemporary Myocardial Perfusion Imaging with Cardiac Positron Emission Tomography (PET)

INTRODUCTION

Cardiac PET myocardial perfusion imaging has gained considerable acceptance in the clinical world of Nuclear Cardiology for many reasons. One driving force has been the substantial expansion of PET oncology, which has led to widespread availability of PET scanners in hospital settings. However, the burgeoning literature has also provided a demonstration of the incremental clinical value of cardiac PET, which has resonated in the marketplace and resulted in a gradual but steady growth of this modality into office-based and hospital settings. Finally, the sustained availability of radiotracers in the form of generator-produced ⁸²Rb and cyclotron-produced ¹³N-ammonia has provided a stable milieu for the growth of cardiac PET myocardial perfusion imaging. This chapter describes the latest documentation of the important aspects of cardiac PET that makes this a compelling story for the present and future of nuclear cardiology. Sections include: brief history of cardiac PET, description of available tracers, diagnostic accuracy, image quality, unique aspects of PET MPI data, including myocardial blood flow (MBF), risk stratification, radiation exposure, protocols, and patients best suited for evaluation and tracers in development.

History of PET/CT Scanners

William Sweet and Frank Wren used positron-emitting radionuclides in the 1950s to localize brain tumors.^1,2 This was achieved by using two opposing gamma-ray detectors. Subsequently, in the 1970s, using multidetector systems, Burnham et al³ were able to map out a 2-dimensional distribution of positron-emitting radionuclides. The first PET scanner for use in humans was developed by Michael Phelps and Ed Hoffman in 1976.⁴ Short-lived radionuclides, such as carbon-11, nitrogen-13, and oxygen-15, however, were used mainly in neurology.

Detectors used in PET scanners changed from Bismuth Germinate (BGO) in 1985⁵ to a new scintillation material called lutetium oxyorthosilicate (LSO). The faster decay time of LSO meant that it could handle higher count rates, which allowed dynamic image acquisition. The first commercial scanner with LSO crystals was introduced in 2001 by Siemens. Initially, attenuation correction (AC) on PET systems was performed using a radioactive source. It was only during the early 21st century that CT was integrated into PET systems that led to more accurate AC, which enabled accurate quantification of tracer distribution and along with LSO crystal technology made quantifying myocardial perfusion in mL/gm/min feasible.

It was not long after thallium-201 was seen as a viable myocardial perfusion tracer for gamma camera imaging in the mid- to late 1970s, that ¹³N-ammonia was among the first radioactive tracers to be investigated for use in myocardial PET (Figure 1-1). In 1979, Schelbert et al⁶ demonstrated images of myocardial perfusion in humans, with the quantitation of MBF in normal volunteers at stress and rest in 1989.⁷ The use of ¹³N-ammonia for cardiac imaging, however, was only approved by the US Food and Drug Administration (FDA) in 2007.