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Overestimation of the LVEF by Quantitative Gated SPECT in Simulated Left Ventricles

Nuclear Medicine Section, Department of Radiology, Baylor College of Medicine, Houston; Department of Nuclear Medicine, St. Luke’s Episcopal Hospital, Houston; and Texas Heart Institute, Houston, Texas

View larger version (44K): [in a new window]   FIGURE 1. Short-axis and long-axis slice examples of digitally created left ventricles.

View larger version (45K): [in a new window]   FIGURE 2. Graphs of QGS LVEF for unsmoothed (A) and smoothed (B) datasets vs. targeted LVEF (tLVEF) and average end-diastolic volume (EDV) clearly show that QGS LVEF is greater than tLVEF when EDV is small.

View larger version (33K): [in a new window]   FIGURE 3. Passing–Bablok graphs of smoothed data’s QGS LVEF vs. tLVEF for smallest (A) and largest (B) volumes. (Same data are present at ends of graph in Fig. 2B.) Slope and y-intercept are calculated with their 95% confidence interval. Confidence intervals are used to determine whether there is only a chance difference between slope and 1 and between y-intercept and 0. Plots show poor agreement when volume is small and good agreement with larger volumes.

View larger version (17K): [in a new window]   FIGURE 4. Plot of slopes from linear fits of QGS LVEF vs. tLVEF for each given volume. With perfect agreement, slope values would equal 1.

View larger version (35K): [in a new window]   FIGURE 5. Residual plots show differences of expected and observed values vs. corresponding expected value. If fit was adequate, a normal distribution with mean of 0 would be found. Graphs show divergence of QGS LVEF from tLVEF when EDV is low and ejection fractions are in upper range for unsmoothed (A) and smoothed data (B), worse for smoothed data.

View larger version (31K): [in a new window]   FIGURE 6. Plots of differences of measured EDV vs. mean EDV for unsmoothed (A) and smoothed data (B). Anticipated plot would show no variance because maximal volume was set in model and then intermediate values were calculated.