ORIGINAL ARTICLE Compensation for spill-in and spill-out partial volume effects in cardiac PET imaging Yong Du, PhD, Igal Madar, PhD, Martin J. Stumpf, MA, Xing Rong, MS, George S. K. Fung, PhD, and Eric C. Frey, PhD Background. Partial volume effects (PVEs) in PET imaging result in incorrect regional activity estimates due to both spill-out and spill-in from activity in neighboring regions. It is important to compensate for both effects to achieve accurate quantification. In this study, an image-based partial volume compensation (PVC) method was developed and validated for cardiac PET. Methods and Results. The method uses volume-of-interest (VOI) maps segmented from contrast-enhanced CTA images to compensate for both spill-in and spill-out in each VOI. The PVC method was validated with simulation studies and also applied to images of dog cardiac perfusion PET data. The PV effects resulting from cardiac motion and myocardial uptake defects were investigated and the efficacy of the proposed PVC method in compensating for these effects was evaluated. Results. Results indicate that the magnitude and the direction of PVEs in cardiac imaging change over time. This affects the accuracy of activity distributions estimates obtained during dynamic studies. The defect regions have different PVEs as compared to the normal myocar- dium. Cardiac motion contributes around 10% to the PVEs. PVC effectively removed both spill-in and spill-out in cardiac imaging. Conclusions. PVC improved left ventricular wall uniformity and quantitative accuracy. The best strategy for PVC was to compensate for the PVEs in each cardiac phase independently and treat severe uptake defects as independent regions from the normal myocardium. (J Nucl Cardiol 2013;20:84–98.) Key Words: Partial volume compensation Æ spill-in and spill-out Æ cardiac PET imaging INTRODUCTION Cardiac PET imaging allows non-invasive quanti- tative assessment of cardiac function and regional blood flow. Quantitative measures from PET images are of clinical importance since the degree of abnormality is directly related to patient prognosis and outcome. 1-3 In addition, quantitative kinetic analysis of dynamic car- diac PET data provides unique information that improves discrimination between healthy and diseased tissue compared to static images. In research studies, compartmental analysis has provided quantitative mea- sures that have allowed discrimination between these tissues. 3-6 However, the finite spatial resolution of PET images results in partial volume effects (PVE) that can reduce the accuracy of quantitative measurements obtained from the images. 7 This is especially true for images used in kinetic analysis where the PVEs result in mixing of the time-activity curves (TAC) of different tissues. PVEs include both spill-out and spill-in of activity to and from a region- or organ-of-interest. 8 In sequences of dynamic cardiac images, PVEs will affect measured activities in the myocardium, blood pool (BP), and neighboring organs in a complex way that varies with time. 9 Myocardial activities are usually underestimated due to the spill-out of counts to neighboring regions with lower activity, such as the ventricular chamber. The spill-out of the myocardial counts can also cause overestimation of activity in neighboring regions such as the BP. In addition, adjacent regions with high From The Russell H. Morgan Department of Radiology and Radiological Sciences, School of Medicine, Johns Hopkins Uni- versity, Baltimore, MD. Received for publication Mar 25, 2011; final revision accepted Oct 22, 2012. Reprint requests: Yong Du, PhD, The Russell H. Morgan Department of Radiology and Radiological Sciences, School of Medicine, Johns Hopkins University, 601 N Caroline St, JHOC 4263, Baltimore, MD 21287; duyong@jhu.edu. 1071-3581/$34.00 Copyright Ó 2012 American Society of Nuclear Cardiology. doi:10.1007/s12350-012-9649-z 84