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This model has been developed by Hermannsen et al. [27] for cardiac PET studies using H215O water bolus injection. It incorporates two spill-over terms from blood in the left and the right ventricles which are relatively displaced in time. So the operational equation which is fitted to the measured data is
where TF = tissue fraction, Vlv = spill-over fraction from the left ventricle, Vrv = spill-over fraction from the right ventricle. In practice, the left ventricular time-activity curve is also used as the input curve Cp(t).
Implementation Notes
As opposed to standard PKIN models a tissue fraction is used rather than a strict geometrical correction for compliance with the original model. The right ventricle curve is only used for spillover correction of septal TACs. It must be loaded as the Total blood curve. The left ventricle curve serves both as the input curve as well as for spillover correction of all myocardial TACs. It must be loaded as the Input curve.
The right ventricle spill-over fraction Vrv is automatically fixed to zero if the string "Sep" is not contained in the name of the region. The assumption is that such a TAC is not from septal tissue and should thus be modeled with single spill-over from the left ventricle. The reason of this behavior is the usage of this model in the PCARDP tool.
Abstract [27]
"Positron emission tomography (PET) in conjunction with C15O2 or H215O 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 H215O 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 H215O, infusion of H215O and inhalation of C15O2 . It was found that MBF can be measured with intravenous administration of H215O 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 H215O 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 H215O 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."