The introduction of routine absolute myocardial blood flow assessments for cardiac PET adds unique information that is difficult, if not impossible, to acquire using other noninvasive modalities. Specifically, the assessment of absolute myocardial blood flow with cardiac PET improves the determination of normalcy,1,2 detection of multivessel disease,3 detection of balanced flow reduction,4 detection of microvascular disease,5 and risk stratification.6–8 These benefits can only be obtained if the quantitative values are accurate.9
The assessment of myocardial blood flow with PET uses the measurement of the transport of tracer from the blood pool into the myocardium10–13 to calculate the blood flow in the coronary arteries. First, this requires an accurate dynamic scan across a wide range of count rates. In many systems, the count rate can be 10 times the activity of a conventional perfusion scan, with the entire, undecayed bolus in the field of view at once. In the case of 82Rb, that activity will decay to near background levels during the course of the study. This complex, quantitative study must be accomplished without adding to significantly the radiation dose or compromising the quality of the clinical study.14,15
The choice of the radiotracer used to measure blood flow, in principle, should not have an impact on the blood flow. However, protocols and flow models for measuring blood flow are typically specific to the radiotracer used and have challenges particular to that agent.10–13 In addition, quality control and data processing steps depend heavily on the choice of radiotracer. Clinicians must carefully assess data quality for patient motion,16 accuracy of the placement of the blood pool region of interest (ROI),17,18 and the accuracy of myocardial boundaries. Quality control in the assessment of myocardial blood flow carries a greater importance than in visual analysis of perfusion data because quantitative flow can correctly contradict visual assessment.
Ultimately, the assessment of myocardial blood flow with cardiac PET can greatly increase the diagnostic information available to the cardiologist; however, this information may complement, complicate, or even contradict the visual assessment of the study. Because of this, the utility of absolute blood flow assessment requires an understanding of the entire acquisition, processing, and quality control procedures by both the technologist and the interpreting nuclear cardiologist. This chapter describes the scientific foundation of myocardial blood flow assessment, methods for optimizing myocardial blood flow measurements, and strategies for assessing the quality of myocardial blood flow PET studies.
ACQUISITION AND PROCESSING
The assessment of myocardial blood flow with PET is made possible because of two characteristics of PET imaging: (1) all PET studies are attenuation and scatter corrected, and (2) PET studies are always acquiring a full 360 degrees of data. This constant collection of tomographic data allows for the creation ...