Assessment of RV function using gated blood pool SPECT.

Dysfunction of the right ventricle (RV) can occur in several aspects of cardiovascular disease (CVD) such as pulmonary hypertension (PH), congenital heart disease, left-sided heart failure (HF), coronary artery disease, and RV myocardial infarction, or valvular heart disease. The independent prognostic value of RV function is most strongly established for HF and PH, but the role of the RV in CVD has thus far remained relatively neglected. Cardiac magnetic resonance (CMR) imaging is often considered the gold standard in RV function assessment because it provides high-resolution images of the RV cavity and myocardium. This allows for RV measurements without the need for geometric assumptions required with 2D echo-based techniques or planar radionuclide ventriculography (PRNV). An important advantage of CMR is the high spatial and temporal resolution of the images, while the lack of fully automated processing introduces operator dependence and therefore increases interand intra-observer variability. In this issue of the Journal of Nuclear Cardiology , Dercle et al report on the use of three algorithms for the assessment of RV function using gated blood pool SPECT (GBPS) and compare the results of these methods with CMR-derived values. GBPS offers several potential advantages over other imaging modalities for RV analysis; notably, the acquisition is fast and technically simple, the resulting images are fully threedimensional (3D, or rather 4D if one includes gating), and processing is comparatively operator-independent due to the availability of automatic or semi-automated analysis algorithms. The ability to automatically and reproducibly analyze 3D images of the RV is important given its complex geometry, characterized by a triangular shape in horizontal long-axis view and a crescent shape in short-axis view. While the left ventricle (LV) can adequately be modeled by an ellipsoid clipped by a singular plane that represents both the mitral and aortic valves, RV segmentation is further complicated by the fact that the tricuspid and pulmonary valves are not coplanar and are separated by the ventriculoinfundibular fold, as opposed to the fibrous continuity of the LV valves. Given the anatomy of the RV, the main drawbacks of GBPS are the absence of tissue differentiation and the low resolution of the images (typically in the order of 6 mm/voxel, isotropically). This low resolution in turn leads to several challenges: partial volume effect renders segmentation error-prone when the apical portion of the RV cavity contracts, count spillover complicates visualization and segmentation of the interventricular septum, and the lack of fine anatomical detail virtually eliminates the ability to accurately locate the pulmonary valve. These effects are often exacerbated by the use of a low cutoff (smooth) reconstruction filter, a common occurrence in laboratories that primarily perform myocardial perfusion studies where such filter settings may be advisable and are generally the default for cardiac SPECT. The results described by Dercle et al confirm the impact of such challenges: while RV end-diastolic volumes (EDV) correlate moderately to well with CMR Reprint requests: Serge D. Van Kriekinge PhD, AIM Program, Department of Medicine, Cedars-Sinai Medical Center, 8700 Beverly Blvd, Ste A047N, Los Angeles, CA 90048; vankriekinges@cshs.org J Nucl Cardiol 2015;22:493–5. 1071-3581/$34.00 Copyright 2015 American Society of Nuclear Cardiology.