Chapter 3: Interpretation of Cardiac PET Myocardial Perfusion Imaging Studies

INTRODUCTION

Cardiac positron emission tomographic (PET) myocardial perfusion imaging offers patients and referring health-care providers a superior product with high diagnostic accuracy and risk stratification. As with SPECT, the interpretation of the images is extremely important to the resulting product. Physicians with experience in interpreting single-photon emission computed tomography myocardial perfusion imaging (SPECT MPI) are familiar with the imaging artifacts that reduce confidence in the interpretation of SPECT MPI studies (eg, soft tissue attenuation, gastrointestinal (GI) tracer activity in close proximity to the heart, and patient motion). Interpretation of PET MPI studies requires an understanding of the fundamental differences between PET and SPECT (Table 3-1) and the imaging artifacts unique to PET MPI. As rubidium-82 (⁸²Rb) is the most commonly used radionuclide tracer for PET MPI, the discussion pertains primarily to interpretation of ⁸²Rb PET MPI studies. This chapter examines key aspects to successful interpretation, including differences in interpretation between SPECT and PET, artifacts unique to PET, approaches to interpretation, and, finally, reporting.

As a result of the robust methods for correction for soft tissue attenuation and photon scatter, a normal PET MPI study will generally appear "more normal" than a normal SPECT MPI study. That is, in normal subjects, image quality will typically be good to excellent¹ and myocardial tracer activity will be more homogeneous with PET MPI than SPECT MPI. Unlike SPECT MPI (in which breast attenuation results in variability in normal perfusion patterns for women and men), normal PET MPI perfusion patterns for women and men are similar to one another. Owing to the superior myocardial uptake kinetics of PET MPI tracers and the ability to measure left ventricular systolic function at peak stress, an abnormal PET MPI study will appear "more abnormal" than an abnormal SPECT MPI study. Therefore, interpretative confidence is higher for PET MPI studies than for SPECT MPI studies.¹ However, confident interpretation of PET MPI studies requires that the PET MPI study is performed properly and that study quality is confirmed with automated quality control software. The use of quality control software is mandatory for PET MPI, because it is impossible to exclude artifacts related to patient motion or incorrect attenuation correction (misregistration of transmission and emission datasets) solely by reviewing the reconstructed tomographic slices. Unlike traditional SPECT MPI in which the angular projections are acquired sequentially and the rotating raw planar images are available for review, PET MPI images are acquired simultaneously by ...