Reliability of enhanced gated SPECT in assessing wall motion of severely hypoperfused myocardium: Echocardiographic validation

Background. A method has been described for improving myocardial visibility on ^99mTc-labeled sestamibi gated tomograms, even in the presence of severe hypoperfusion. It is essential to verify that images transformed in this manner truly depict the myocardium and do not contain image artifacts. This is especially important if transformed images are to be used to aid in the discernment of regional wall-motion abnormalities. Methods and Results. All radially detected maximum counts were mapped automatically to the same brightness level for each cinematic frame. This produced tomographic cine images strongly suggestive of myocardium that appeared to translate but not to brighten from diastole to systole. Transformed scintigrams were compared with echocardiographic cine images of horizontal long axis and short axis views for 40 patients. Echocardiograms were of sufficient quality to allow comparison of radial distances from left ventricular center to midmyocardium for 15 short axis images and 25 horizontal long axis images. Readings were graded independently for 10 territories on a five-point scale (normal, mild-to-moderate hypokinesis, severe hypokinesis, akinesis, dyskinesis) of regional wall motion of original and enhanced scintigrams and echocardiograms. Comparison of echocardiographic and single photon emission computed tomographic (SPECT) locations of midmyocardial horizontal long axis points yielded a root-mean-square error value of 1.5 ± 0.6 pixels (average absolute error, 11% ± 5%). SPECT versus echocardiographic wall-motion readings were compared by means of contingency table analysis. The log-likelihood ratio (G²) was 109.3 (n = 364; df = 16) with probability of no association < 10^-6. Although readings of unenhanced SPECT cine images agreed well with those of echocardiograms (G² = 94.3; n = 350; df = 16; P < 10^-6), Pearson-corrected contingency coefficients indicated stronger association with echocardiograms of transformed tomograms than with readings of original scintigrams (0.57 versus 0.51). The McNemar χ² test indicated this improvement to be significant. The strongest associations were found between readings of unenhanced and enhanced scintigrams. Overall, similar results were obtained for horizontal long axis and short axis territories when analyzed separately. Linear regression analysis indicated strong correlations (r = .80 to r = .92) of ejection fractions from unenhanced gated SPECT images, enhanced gated SPECT images, echocardiograms, and first-pass radionuclide angiograms with no significant differences among correlations. Conclusions. Regional image enhancement succeeded in revealing shapes that genuinely represented myocardium in this population with hypoperfusion. Wall-motion conclusions were similar whether drawn from original or enhanced scintigrams, although enhancement significantly improved agreement with echocardiographic readings. Enhanced SPECT cine images allowed sensitive discrimination of regional wall-motion abnormalities, even in areas of severely hypoperfused myocardium, in excellent agreement with visual echocardiographic assessment for which myocardial visualization is independent of perfusion.