MODEL FOR RADIONUCLIDE EVALUATION OF LEFT-TO-RIGHT DUCTAL SHUNTS

A model for radionuclide evaluation of left-to-right ductal shunts was designed. It was a generalization of the standard Maltz-Treves method , accounting for the possibility that distribution of the shunt flow b etween the two lungs differs from that in the right ventricular (RV) o utput (F-s). This yields a new formulation in which the ratio of ducta l now to pulmonary flow (F-d/F-p) equals a weighted average of F-d/F-p Obtained separately for the right lung (RL) and the left lung (LL), i .e. F-d/F-p=R(F-d/FpP)(RL)+(1-R) (F-d/F-p)(LL); where R is the fractio n of the RV output going to the right lung. Separate shunt-flow ratios can be obtained by conventional analysis of the respective lung radio histogram, while R can be determined from the upslopes of these curves . Formulas were derived rigorously from basic principles, so that the ultimate clinical validity of the method depends on radioangiographic assessment of R, (F-d/F-p)(RL) and (F-d/F-p)(LL). Due to asymmetry of flows there is no true referent method for patients with ductal shunts . Therefore a simulation study, using quasi-real data, was utilized, y ielding satisfactory performances of the algorithm: (F-p/F-s)(calculat ed)=0.92 (F-p/F-s)(simulated)+0.15 (r=0.878).