Coronary artery disease (CAD) is the leading cause of death in the United States for both men and women [1
]. Therefore, detecting the presence of CAD is an important endeavor. Obstructive CAD can cause cardiac regions to become ischemic, as a result of reduced blood flow through the associated coronary artery. Myocardial perfusion imaging (MPI) provides visual representations of the atrial and ventricular blood pools and perfusion of the myocardium, and abnormalities observed on the MP images are indicative of ischemic regions and thus, obstructive CAD.
For more than thirty years, single photon emission computed tomography (SPECT) and its predecessor, planar imaging, have been almost exclusively used with 201
Tc-sestamibi, and 99m
Tc-tetrofosmin for MPI [2
]. Despite two major disadvantages, prohibitive cost and complicated logistics, positron emission tomography (PET) can be a reasonable alternative to SPECT for MPI due to several factors, including: improved sensitivity, specificity, and quantitative accuracy, as well as improved evaluation of multi-vessel CAD and obese patients [13
]. Furthermore, PET possesses a much better ability to analyze biophysical kinetics, including myocardial blood flow (MBF).
Rb Positron Emission Tomography (82
Rb-PET) has been used to evaluate patients with suspected or known ischemia and CAD [3
]. For accurate clinical assessment of MBF, time activity curves (TACs), which are derived from delineated regions in the myocardium, must be compared to arterial input functions (AIFs) using first-order kinetics analyses [4
]. Coronary flow reserve (CFR), which is the ratio of MBF with and without physical or pharmacologic stress, has been applied to MPI studies to detect
ischemic regions and stenotic coronary vessels. Specifically, CFR values have been used to: define stenotic vessels [5
]; identify triple-vessel CAD [6
]; assess severity and risk of stenoses [7
]; detect atheroschlerosis before onset of obstructive CAD and detect microvasculature disease [10
Electrocardiogram-gated (ECG-gated) studies are performed to calculate the left ventricular ejection fraction (LVEF), which is the ratio of stroke volume to end diastolic volume. Unlike CFR, LVEF is not able to localize ischemia and identify stenotic vessels; it is only able to detect the presence of CAD [11
]. However, prior detection of CAD (by LVEF) may be used in combination with CFR values to determine the relevance and risk of individual stenoses [9
]. Furthermore, we surmise that comparing LVEF values with CFR values may reduce diagnostic uncertainty associated with several modes of CAD.
PET scanners with list-mode capability need only a single acquisition for clinicians to determine LVEF and CFR [12
]. However, PET data acquired by list-mode require extra processing time to create and reconstruct dynamic multiframes and ECG-gated volumes [11
]. Thus, for scanners at many clinical practices where physics support is inadequate, or those that do not have list-mode capability, dynamic PET acquisitions followed by ECG-gated acquisitions are needed to determine LVEF and CFR. Such a procedure generally requires twice the dose
and acquisition time as individual dynamic or gated acquisitions and is usually not implemented in favor of gated-only protocols
]. Thus, CFR is not calculated at many clinics and physicians there must formulate diagnoses based upon a suboptimal amount of physiologic information. Perhaps most importantly, differentiating
between single- and multi- vessel disease can have implications for treatment
. For example, a study in 2004 by the American Heart Association states that coronary artery bypass grafting (CABG) is the preferred treatment for triple-vessel disease and diffuse disease not amenable to angioplasty [27
]. Angioplasty, usually with stenting, is preferred for single vessel disease, because it is less invasive than CABG [28
]. Thus, our method may also have bearing on treatment decisions.
In this study, we investigated whether dynamic and ECG-gated studies could be combined into a single protocol of length equal to one typical gated scan. The advantage of such a protocol is that it would afford clinicians the flexibility to order dynamic and ECG-gated studies by minimizing dose, cost, and acquisition time. However, the mutual exclusivity that often exists between dynamic and ECG-gated acquisitions eliminates important frames from the dynamic study. In our validation study of this protocol, uncertainty was estimated by comparing MBF and CFR values calculated from AIFs and TACs with missing frames to MBF and CFR values calculated from AIFs and TACs with all frames. We believe that our technique, if validated, would enable the routine determination of MBF, CFR, and gated LVEF on imaging systems without the capability for list mode processing or acquisition. In this way, complete diagnostic information could be known and treatment decision-making may be improved.