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Abstract
Despite knowing the importance of maintaining steady blood flow to the vulnerable neonatal brain, there is currently no reliable way to quantify regional brain perfusion at the bedside. Consequently there are gaps in our understanding of the pathophysiological changes that occur at times when the neonate is at risk of neurological harm. Fractional Moving Blood Volume (FMBV), which is an index generated from the quantification of the power Doppler ultrasound signal in an area, is a technique to evaluate regional perfusion that has been validated in the human fetus. The quantified power Doppler signal in a selected area has been shown to correlate with the amount of blood flow in that region. This thesis investigates the application of FMBV to the neonatal brain and its value as a tool to evaluate perfusion.
Initial studies contained within this thesis focused on the repeatability of FMBV when applied to power Doppler images in the neonate. I established a neonatal reference range for FMBV in the basal ganglia across a range of gestations. This involved a rigorous interrogation of the image acquisition and analysis sequence and the development of an application to analyse images. I also assessed temporal variation during the transitional period through the first 48 hours of life. Following on from this, I investigated the feasibility of using novel impedance indices to evaluate tissue resistance as a complementary tool in the evaluation of tissue perfusion.
The results of these studies show that FMBV is a reproducible technique that can be applied to neonatal images. A reference range for basal ganglia FMBV has been defined for all neonates. In addition, serial assessment during transition demonstrated anticipated interval increases in FMBV. Finally, the generation of tissue impedance indices, as a potential adjunct to perfusion assessment, was feasible and reproducible.
FMBV is applicable to the neonatal brain and an optimised program is now available that uses ultrasound data from neonatal images to calculate FMBV. There are now opportunities for assessment of FMBV in settings where direct evaluation of regional perfusion may provide insights into the pathogenesis of cerebral injury. In the future, the development of an application that calculates FMBV from three dimensional images offers the exciting possibility of evaluating perfusion by quantifying the signal from a volume of tissue rather than a two dimensional area.