RELIABILITY OF ENHANCED GATED SPECT IN ASSESSING WALL-MOTION OF SEVERELY HYPOPERFUSED MYOCARDIUM - ECHOCARDIOGRAPHIC VALIDATION

Background. A method has been described for improving myocardial visib ility on Tc-99m-labeled sestamibi gated tomograms, even in the presenc e of severe hypoperfusion. It is essential to verify that images trans formed in this manner truly depict the myocardium and do not contain i mage artifacts. This is especially important if transformed images are to be used to aid in the discernment of regional wall-motion abnormal ities. Methods and Results. All radially detected maximum counts were mapped automatically to the same brightness level for each cinematic f rame. This produced tomographic cine images strongly suggestive of myo cardium that appeared to translate but not to brighten from diastole t o systole, Transformed scintigrams were compared with echocardiographi c cine images of horizontal long axis and short axis views for 40 pati ents. Echocardiograms were of sufficient quality to allow comparison o f radial distances from left ventricular center to midmyocardium for 1 5 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, dyskinesi s) of regional wall motion of original and enhanced scintigrams and ec hocardiograms, Comparison of echocardiographic and single photon emiss ion 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 echocardio graphic wall-motion readings were compared by means of contingency tab le analysis. The log-likelihood ratio (G(2)) was 109.3 (n = 364; df = 16) with probability of no association <10(-6). Although readings of u nenhanced SPECT cine images agreed well with those of echocardiograms (G(2) = 94.3; n = 350; df = 16; P < 10(-6)), Pearson-corrected conting ency coefficients indicated stronger association with echocardiograms of transformed tomograms than with readings of original scintigrams (0 .57 versus 0.51). The McNemar chi(2) test indicated this improvement t o be significant, The strongest associations were found between readin gs of unenhanced and enhanced scintigrams. Overall, similar results we re obtained for horizontal long axis and short axis territories when a nalyzed separately, Linear regression analysis indicated strong correl ations (r = .80 to r = .92) of ejection fractions from unenhanced gate d SPECT images, enhanced gated SPECT images, echocardiograms, and firs t-pass radionuclide angiograms with no significant differences among c orrelations. Conclusions. Regional image enhancement succeeded in reve aling shapes that genuinely represented myocardium in this population with hypoperfusion. Wall-motion conclusions were similar whether drawn from original or enhanced scintigrams, although enhancement significa ntly improved agreement with echocardiographic readings. Enhanced SPEC T 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.