A practical method for measuring right ventricular ejection fraction using gated SPET

Full text: Measurement of right ventricular (RV) ejection fraction (EF) can provide important clinical information but is difficult to obtain. Although potentially accurate, first-pass imaging is technically difficult. More usually, RVEF is estimated from planar equilibrium gated heart pool scans (GHPS). These EFs are known to be highly unreliable because of substantial overlap between the RV and the right atrium. We have developed an alternative means for measuring RVEF from equilibrium GHPS, using SPET instead of planar studies. Gated SPET images were acquired (16 bins, 180 deg rotation, 64 stops) and reconstructed into short-axis views. A single region of interest (ROI) was drawn to exclude the left ventricle from the short-axis slices, which were then reprojected to produce horizontal long-axis images. A ROI was drawn around the RV on the end diastolic (ED) long-axis image. Time-activity curves (TACs) were generated from successive rows of pixels in the ED ROI, starting at the basal end. Each TAC was checked for the presence of increased activity at end systole (ES). When two consecutive TACs showed no sign of increased activity at ES, that row was considered to mark the valve plane. Another ROI was then drawn on the ES image and EF was calculated as usual. A group of 18 patients were injected with 900 MBq of 99Tcm and both planar (45 deg LAO, 32 bins) and SPET GHPS were acquired. SPET EFs were easily generated and reasonably consistent (mean standard deviation was ± 5, over 6 repeats). RVEFs from the two techniques show a broad general agreement (slope = 0.5, CC = 0.5). The next step is to compare SPET RVEF with a more accurate technique, such as first-pass, and with clinical outcome