Direct 4D Parametric Imaging in Dynamic Myocardial Perfusion PET

yocardial perfusion (MP) PET provides improved diagnostic quality, certainty, and accuracy over conventional MP SPECT imaging [1-5]. The prognos-tic value in predicting adverse cardiac outcomes has also been demonstrated in an increasing number of studies [6-8]. In particular, dynamic MP PET imaging followed by tracer kinetic analysis (e.g. compartmental modelling applied to Rb-82 [9-15]), provides a powerful mean to estimate the tracer transport rate K1, and subsequently myocardial blood flow (MBF) which when measured under rest and stress used to calculate the coronary flow reserve (CFR). The CFR has been shown to be related to the Purpose: Dynamic myocardial perfusion (MP) PET imaging followed by tracer kinetic modeling allows quantification of myocardial blood flow, thus enabling computation of the coronary flow reserve, with considerable clinical potentials. Nonetheless, utilization of short dynamic frames can lead to noisy flow estimates, an issue that is further amplified in parametric imaging at the voxel level. Our purpose is to utilize an enhanced image reconstruction framework to better address this issue. Methods: We implemented a novel 4D reconstruction scheme to directly estimate MP parametric images from the measured dynamic datasets. This included formulation of a 4D log-likelihood objective function relating the kinetic parameters to the projection datasets, and implementing numerical methods to optimize the objective function. We also utilized the technique of optimization transfer to enable more convenient and reliable parametric imaging. We simulated MP Rb-82 PET projection datasets based on the XCAT phantom utilizing patient-based time activity curves for the various organs and clinically realistic noise levels, followed by noise vs. bias analysis. Results: The proposed direct 4D methodology was shown to outperform conventional indirect parametric imaging, reducing noise by over 50% (matched bias), with further reductions of 15% in noise and a factor of five speed-up when optimization transfer was additionally utilized. Conclusion: Direct 4D PET image reconstruction is a viable and very promising approach towards robust parametric MP PET imaging at the individual voxel level. M degree of coronary artery stenosis (CAS) [16]. It thus allows for non-invasive assessment of the functional importance of CAS and may aid identification of patients with either diffuse, nonocclusive luminal coronary artery narrowing or a balanced reduction in coronary artery blood flow (extensive multi-vessel coronary disease) [17, 18]. CFR has also been shown to be reduced as a function of various coronary risk factors before the onset of clinically overt disease (e.g. in asymptomatic men with …