Quantitative radionuclide angiocardiography: determination of Qp: Qs in children.

A new method of determining pulmonary-to-systemic flow ratios (Qp/Qs) in patients with left-to-right shunts using radionuclide angiocardiography is described. It involves the analysis of pulmonary time-activity histograms using a gamma-variate model. It appears to be simple, relatively atraumatic, and superior to the methods using C2/C1 ratios because, in addition to accurately detecting the presence of left-to-right shunts, it permits precise quantitation. In the 35 patients studied, it was found that Qp/Qs < 1.2 could be separated from Qp/Qs > 1.2 and that when the Qp/Qs is between 1.2 and <3 the shunts could be accurately quantified. Additional Indexing Words: Left-to-right shunt Ventricular septal defects Atrial septal defects Gamma variate Radionuclide angiocardiography ALTHOUGH detection of left-to-right shunts using nontraumatic technics may be possible, accurate quantitation of left-to-right shunts requires cardiac catheterization with oximetry or dye-dilution methods. The technics for detection used in the past included intravenous dye injection with arterial or capillary sampling and analysis of the resulting curves,14 and intravenous injection of radionuclides with analysis of precordial or pulmonary time-activity histograms.'19 None of these technics permitted quantitation. A new nontraumatic technic of quantifying left-to-right shunts is described. This method consists of intravenous injection of a radionuclide with external detection by a gamma camera. Pulmonary time-activity histograms are generated and the analysis is done using a computer program based on a least-squares fit to a gamma variate which directly generates a pulmonary-systemic flow ratio.20' 24 Ejection fractions Materials and Methods Thirty-five patients whose diagnosis was established by previous cardiac catheterization were studied. They ranged in age from 4 months to 21 years. Among 13 without left-to-right shunts, 10 had pulmonic stenosis with pressure gradients ranging from 10 to 100 mm/Hg, and three had aortic stenosis with gradients ranging from 10 to 80 mm/Hg. Twenty-two patients had left-to-right shunts with pulmonary-to-systemic flow ratios ranging from 1.05 to 3.0 as determined by oximetry data. A gamma scintillation camera* with a 15,000 parallel-hole collimator 2.5-cm deep was used.t The data from the camera were recorded on a magnetic tape system, in a 256 x 256 matrix format which permitted quantitative analysis.t The system was interfaced to a small on-line digital computer system. § This computer can acquire and store information on a 64 x 64 matrix directly from the gamma camera or from the video tape system. The data stored can be analyzed off-line. All patients were prepared for the study with sodium or …