Noninvasive Quantitative Assessment of Segmental Myocardial Wall Motion Using Technetium-99m 2-Methoxy-Isobutyl-Isonitrile Scintigraphy

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Abstract
Technetium-99m methoxy-isobutyl-isonitrile (MIBI) has been recently introduced to trace regional myocardial perfusion; the first-pass and the equilibrium-gated images have been also used to assess myocardial function. In the present study, a quantitative index of regional myocardial wall motion obtained from perfusion electrocardiogram-gated images is proposed. The assumption of the study is based on the partial volume effect, i.e. changes in radioactivity counts correlated with variations in the object size. On this basis, changes in the detected radioactivity reflect changes in myocardial wall thickness during the cardiac cycle. Twenty patients with coronary artery disease and regional wall motion abnormalities and 10 normal subjects were studied by MIBI scintigraphy and contrast ventriculography; regional wall motion was analyzed by a radial method applied to both techniques. In each patient, absolute systolic changes in radioactivity and its ratio to normal reference values were determined in 9 anatomical cardiac regions according to the formula: (end-systolic counting profile - end-diastolic counting profile/ end-diastolic counting profile) X 100. These values were compared with the quantitative wall motion of corresponding segments obtained from contrast ventriculography. The overall agreement between radioisotopic and ventriculographic techniques was 88% (158 of 180 segments). The intra- and interobserver variations in the measurements of the scintigraphic wall thickening index were ± 5.4 and ± 4.1 %, respectively. Normal, hypokinetic and akinetic ventriculographic segments showed wall thickening index values of 1.1 ± 0.19, 0.82 ± 0.2 and 0.45 ± 0.3, respectively (p < 0.001). Thus, the count-based wall thickening index, reflecting systo-diastolic transmurai radioactivity changes, provides an alternative means for the complementary evaluation of regional myocardial wall motion during perfusion studies with MIBI.

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