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

Abstract

Positron emission tomography (PET) in conjunction with C¹⁵O₂ or H₂ ¹⁵O 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 C¹⁵O₂ inhalation, the tissue fraction in the septum is overestimated. Bolus injection of H₂ ¹⁵O 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 H₂ ¹⁵O, infusion of H₂ ¹⁵O and inhalation of C¹⁵O₂. It was found that MBF can be measured with intravenous administration of H₂ ¹⁵O 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 H₂ ¹⁵O together with this four-parameter model also circumvented the problem of overestimation of TF in the septum seen with C¹⁵O₂ inhalation. In addition, the radiation dose of H₂ ¹⁵O protocols is lower than that of C¹⁵O₂ inhalation. Using a left atrial input curve instead of a left ventricular cavity input curve gave the same mean MBF and TF.