COMPUTER-ASSISTED MYOCARDIAL THICKENING ANALYSIS OF GATED MIBI SPECT IMAGES

RATIONALE AND OBJECTIVES. The purpose of this study is to use the rela tionship between the partial volume effect, count density, matrix size , and reconstruction filter in gated single photon emission computer t omography (SPECT) to recover myocardial thickness, and to validate mea surements generated using a computer-assisted automatic contour method with a phantom model and with thickness changes measured by echocardi ography. METHODS. Regional myocardial contour was defined automaticall y using shape constraints, gray level thresholding, and a gradient met hod applied to gated technetium-99m (Tc-99m)-methoxy-isobutyl-isonitil e (MIBI) SPECT images. A heart phantom with wall thickness ranging fro m 0.8 cm to 1.3 cm was constructed. SPECT images were acquired and rec onstructed using different matrix sizes, count densities, and filters, Wall thickness determinations derived from the reconstructions made w ith each combination of matrix size, type of filter, and cutoff freque ncy were correlated with the measured thicknesses. The best combinatio n was applied to the gated MIBI SPECT images of 55 patients who also h ad echocardiography and coronary arteriography, Count density measurem ents were made across each regional myocardial segment to evaluate wal l thickness at end-diastole and end-systole, Systolic wall thickening measurements made with this automated computer-assisted contour techni que were compared with echocardiographic measurements made from segmen ts with normal perfusion and from regions containing infarcted tissue. RESULTS. Different reconstruction filters and cutoff frequencies affe cted the accuracy of measurements of myocardial wall thickness determi ned from gated myocardial SPECT images. A matrix size of 64 x 64, with a minimum of 10 counts/pixel/frame, and use of a Hanning filter with 0.5 cyc/cm cutoff frequency gave the best combination for myocardial t hickness determination and spatial resolution, Application of these fa ctors to the phantom yielded results that correlated very well with th e thickness measurements (r = 0.986, P < 0.001), Application of the te chnique to the clinical SPECT studies yielded measurements of myocardi al wall thickening that were not significantly different from that det ermined by echocardiography, CONCLUSION. Computer-assisted contour ana lysis of gated SPECT images enables accurate determination of regional wall thickening using the count density changes within each myocardia l segment.