Predictive Model for ⁸²Rb Generator Bolus Times as a Function of Generator Lifetime

Abstract

⁸²Rb cardiac PET is largely used to study myocardial perfusion with function and to calculate myocardial blood flow (MBF) and coronary flow reserve or myocardial flow reserve. Although the dosing activity of ⁸²Rb is determined by the patient weight, the infusion volume and activity concentration varies with the age of the ⁸²Rb generator. We sought to predict the needed bolus volume of ⁸²Rb to help evaluate the accuracy of MBF findings. Methods: Data were collected from deidentified tickets of an ⁸²Rb generator, including the instantaneous eluted activity flow rate. The times to reach 4 activity levels—740, 1,110, 1,480, and 1,665 MBq (20, 30, 40, and 45 mCi, respectively)—were also calculated. The activity flow rate for the largest bolus was fitted to determine the functional form. The time to reach each bolus level was fitted as a function of the generator age, and 95% CIs were created. Results: The activity flow rate was fitted with a growth-saturation model, allowing a calculation of bolus volume. The amplitude of the fit was observed to also be influenced by the time since the last elution and possibly other clinical factors. Elution times to reach the 4 activity levels were plotted versus generator age. The linearized data were fitted, and 95% CIs were created symmetrically around the fit. The 95% CI band allowed a prediction of elution time to achieve each bolus size for future generators, as a function only of generator age. Conclusion: A predictive model was created for elution times from this brand of ⁸²Rb generator as a function of generator age. The value of this model is in determining whether the necessary amount of activity can be extracted from a generator before reaching one of the backup infusion settings, such as volume limits per administration, given a generator age. Some sites may also control the bolus duration for better MBF calculations, since predicting the time for the injection to complete may determine whether MBF and coronary flow reserve calculations are meaningful.