Radionuclide equilibrium ventriculography in infants and children using converging collimator

In infants and young children, the radionuclide cardiac blood-pool images obtained with a general-purpose (GP) parallel-hole collimator are often too small to provide accurate delineation of the left ventricle (LV), especially the interventricular border. In order to obtain magnified cardiac images, a radionuclide gated equilibrium study was performed with a converging (CV) collimator. We compared these two methods in terms of image quality and estimation of LV ejection fraction (EF). Twenty-five children (age, 10 months to 6 years, mean 2.5 years; weight, 5.5 to 20 kg, mean 12 kg) with various heart diseases were studied with administration of 3-7 mCi 99mTc human serum albumin. The GP collimator was used in 15 subjects and the CV collimator in 16. The CV collimator provided optimal magnification and better resolution than the GP type. Cardiac images obtained with the CV collimator facilitated precise delineation of the entire interventricular border in all 16 cases. Those obtained with the GP collimator showed poor delineation of the interventricular border in four subjects. Both GP and CV collimations enabled LVEFs to be calculated, and the values correlated well with those obtained by cine-angiography. The correlation coefficient, however, was higher with the CV collimator (r = 0.787 vs. 0.861, p less than 0.001). Radionuclide cardiac blood-pool study with CV collimator has clinical significance because it provides sufficiently magnified cardiac images with high resolution, enabling accurate estimation of LVEF in infants and young children.