Date of Award

Spring 2007

Degree Type

Thesis - Restricted

Degree Name

Master of Science (MS)

Department

Biomedical Engineering

First Advisor

Audi, Said

Second Advisor

Haworth, Steven

Third Advisor

Clough, Anne

Abstract

Gas exchange between alveolar air and blood, and substrate exchange between tissue and blood are dependent upon the capillary mean transit time and distribution of capillary transit times. The longer the capillary mean transit time, the more time there is available for exchange. Furthermore, it has been mathematically shown that the rate of gas and or/substrate exchange decreases with increase in heterogeneity of the capillary transit time distribution, hc(t) (25). Thus, hc(t) is one measure of lung function in health and disease. This thesis presents a method to estimate hc(t) in rat lung lobes based on an approach developed by Clough et al. (15, 16) to measure hc(t) in dog lung lobes. This method involves imaging the passage of a radiopaque bolus through the rat lung vasculature using microfocal X-ray angiography. The time absorbance curves obtained by positioning a region of interest over an image of the lobar artery and microvascular regions are used to estimate hc(t) with the help of model-based deconvolution. Chapter 1: This chapter states the physiological significance of the capillary transit time distribution and describes previous methods used to estimate hc(t). It also addresses the need for developing a protocol to estimate hc(t) in rat lungs under normal and hyperoxic conditions using X-ray microfocal angiography. Chapter 2: This chapter describes a phantom experiment designed to evaluate the ability of X-ray microfocal angiography to estimate small vascular volumes. Chapter 3: This chapter describes a method for low magnification imaging of isolated perfused rat lungs and subsequently estimating the total vascular mean transit time and dispersion of pulmonary vascular transit times. Chapter 4: This chapter describes a method for imaging the isolated rat lung lobe of normal rats and rats exposed to high levels of oxygen (hyperoxia), and estimating the total lobar vascular mean transit time and the dispersion of the lobar vascular transit times using low magnification images. It also describes a method for estimating the lobar capillary transit time distribution from the high magnification image sequences. Chapter 5: This chapter discusses results obtained by this method and compares them to published results, states the limitations of the method, and draws conclusions.

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