Measurement of myocardial blood flow with oxygen-15 labelled water: comparison of different administration protocols

Positron emission tomography (PET) in conjunction with (CO2)-O-15 or (H2O)-O-15 can be used to measure myocardial blood flow (MBF) and tissue fraction (TF), i.e, the fraction of the tissue mass in the volume of the region of interest. However, with (CO2)-O-15 inhalation, the tissue fraction in the septum is overestimated. Bolus injection of (H2O)-O-15 together with arterial cannulation gives very precise results but is invasive. The purpose of this study was to develop a method which circumvents these problems. A four-parameter model with parameters for MBF, TF and spill-over fractions from both left and right ventricular cavities was developed. This method was compared with a three-parameter model (no right ventricular cavity spill-over) in both septal and non-septal regions of interest for three different administration protocols: bolus injection of (H2O)-O-15, infusion of (H2O)-O-15 and inhalation of (CO2)-O-15. It was found that MBF can be measured with intravenous administration of (H2O)-O-15 without the requirement for arterial cannulation. The four-parameter protocol with bolus injection was stable in clinical studies. The four-parameter model proved essential for the septum, where it gave highly significantly better fits than did the three-parameter model (P<0.00003 in each of 15 subjects). Administration of (H2O)-O-15 together with this four-parameter model also circumvented the problem of overestimation of TF in the septum seen with (CO2)-O-15 inhalation. In addition, the radiation dose of (H2O)-O-15 protocols is lower than that of (CO2)-O-15 inhalation. Using a left atrial input curve instead of a left ventricular cavity input curve gave the same mean MBF and TF.