The contraction fraction (CF) in myocardial studies with Technetium-99m-isonitril (MIBI) ? correlations with radionuclide ventriculography and infarct size measured by SPECT

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Abstract
Criteria for the detection of coronary artery disease in nuclear cardiology include visualization of perfusion defects and functional impairment of contraction. The purpose of this study is to combine both methods in one procedure with the new myocardial perfusion tracer, 99mTc-methoxy-isobutyl-isonitril (MIBI), reducing time and radiation burden to the patient. Following an uncomplicated recovery, ten patients with first myocardial infarction participated in this study. Radionuclide ventriculography (RNV) was performed at rest and during exercise. Within 2–3 days, 370 MBq 99mTc-MIBI were injected and SPECT acquisition commenced 1 h later. Data processing included a scar image in polar coordinates. Areas of significantly reduced tracer uptake were expressed as a percentage of the total myocardial area. Directly following SPECT, resting and maximum exercise gated planar LAO images were recorded and the contraction was quantified. The concept of the contraction fraction (CF) rested on the end systolic change in count distribution: their increase in density and their centripetal concentration. For comparison, geometrical inner edge detection techniques were also applied. All algorithms for describing an EF equivalent were verified by computer simulations, showing a perfect correlation over a wide range of preset EFs. When applied to the patient studies only the non geometric methods revealed a good correlation with the ejection fraction (EF) obtained by RNV, and with the infarct size measured by SPECT. The corresponding correlation coefficients (r), standard errors (SEE) and the regression lines read as follows (in %): CF=0.56×EF+24.8; r=0.87; SEE=4.98; CF=-0.53×SPECT+71.5; r=0.93; SEE=4.19. Thus, estimation of the left ventricular function by the above defined CF is feasible, easy to perform and clinically meaningful. In one procedure with 99mTc-labelled MIBI not only the perfusion abnormalities were detectable, but also any reduction in function by a valied EF equivalent. Although the monochromatic gamma spectrum of the radionuclide provided better tissue penetrating power, the inner edge of the left ventricle was poorly outlined (especially in the stress studies) and does not lend itself to clinical routine practice.

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