NONINVASIVE ABSOLUTE CEREBRAL OXIMETRY WITH FREQUENCY-DOMAIN NEAR-INFRARED SPECTROSCOPY.
Near-infrared spectroscopy (NIRS) measurements of absolute concentrations of
oxy-hemoglobin and deoxy-hemoglobin in the human brain can provide critical information
about cerebral physiology in terms of cerebral blood volume, blood flow, oxygen
delivery, and metabolic rate of oxygen. We developed several frequency domain NIRS data
acquisition and analysis methods aimed at absolute m... read moreeasurements of hemoglobin
concentration and saturation in cerebral tissue of adult human subjects. Extensive
experimental investigations were carried out in various homogenous and two-layered
tissue-mimicking phantoms, and biological tissues. The advantages and limitations of
commonly used homogenous models and inversion strategies were thoroughly investigated.
Prior to human subjects, extensive studies were carried out in in vivo animal models. In
rabbits, absolute hemoglobin oxygen desaturation was shown to depend strongly on
surgically induced testicular torsion. Methods developed in this study were then adapted
for measurements in the rat brain. Absolute values were demonstrated to discern
cerebrovascular impairment in a rat model of diet-induced vascular cognitive impairment.
These results facilitated the development of clinically useful optical measures of
cerebrovascular health. In a large group of human subjects, employing a homogeneous
model for absolute measurements was shown to be reliable and robust. However, it was
also shown to be limited due to the relatively thick extracerebral tissue. The procedure
we develop in this work and the thesis thereof performs a nonlinear inversion procedure
with six unknown parameters with no other prior knowledge for the retrieval of the
optical coefficients and top layer thickness with high accuracy on two-layered media.
Our absolute measurements of cerebral hemoglobin concentration and saturation are based
on the discrimination of extracerebral and cerebral tissue layers, and they can enhance
the impact of NIRS for cerebral hemodynamics and oxygenation assessment both in the
research arena and clinical practice.
Thesis (Ph.D.)--Tufts University, 2013.
Submitted to the Dept. of Biomedical Engineering.
Advisor: Sergio Fantini.
Committee: Aron Troen, Fiorenzo Omenetto, and Robin Kanarek.
Keywords: Optics, Biomedical engineering, and Medical imaging and radiology.read less