Abstract
Positron emission tomography provides quantitative measurements of radio-tracer concentrations in vivo to study physiological and molecular processes with radio-labelled compounds of biological affinity. Its application in Cardiology includes the measurement of myocardial blood flow. Quantification of regional blood flow across the myocardium may provide insight in the understanding of the physiological mechanisms involved in ischaemia. However, such measurements are restricted by scanner resolution and sensitivity and the influence of organ motion during data acquisition. Significant improvements in sensitivity in 3D mode of acquisition allow the exploitation of the inherent spatial resolution of the latest generation of PET tomographs. In addition, the acquisition of individual events in list mode makes possible the implementation of motion correction schemes. The problem of obtaining accurate attenuation correction factors, in the absence of septa, was addressed by using single photon transmission measurements and an image segmentation technique, the Local Threshold Segmentation of the attenuation coefficients. This approach was found to provide accurate attenuation coefficients and a scheme for generating attenuation correction factors for absolute quantification could be defined. The influence of motion on the spatial resolution on a current generation 3D PET scanner was assessed with experimental measurements at typical levels of respiration- related motion and was found to be significant for quantitative imaging of the myocardium. Simultaneous electrocardiographic and respiratory gating of list-mode data was implemented and validated. This dual gating approach can be used in data of high counting statistics for the elimination of motion within a single image frame. For count-limited measurements of myocardial blood flow, a method for compensating for respiratory motion, at no loss of total counts, was presented. Validation results showed a generally good accuracy and the technique was applied to 18FDG and C15O patient data. Improvement in the recovery coefficient for accurate tracer concentration assessed against well-counter measurements of blood sample tracer concentration was found for the C15O data.