Biomedical Engineering and Bioengineering Commons^™

A Wearable Fiber-Free Optical Sensor For Continuous Measurements Of Cerebral Blood Flow And Oxygenation, Xuhui Liu

Theses and Dissertations--Biomedical Engineering

Wearable technologies for continuous monitoring of cerebral hemodynamics in freely behaving subjects not only advance our understanding of cognitive processing and adaptive behavior, but also provide vital information for diagnosis and therapeutic assessment of cerebral diseases associated with hypoxia/ischemia. Wearable near-infrared diffuse optical techniques have been used at the bedside to probe deep cerebral hemodynamics, including near-infrared spectroscopy (NIRS) for cerebral oxygenation measurement and diffuse correlation spectroscopy (DCS) for cerebral blood flow (CBF) measurement, respectively. However, most systems are relatively large and expensive, and use rigid fiber-optic probes that significantly constrain subject’s movement. A novel, wearable, fiber-free diffuse speckle contrast …

Characterizing The Internal Porous Structure Of Equine Proximal Sesamoid Bones Subjected To Race Training Using Fast Fourier Transforms, Joseph Erik Davis

Theses and Dissertations--Biomedical Engineering

The equine racing industry is one of the main proponents in Kentucky’s economic infrastructure. In this industry there has come a need to investigate the nature of the proximal sesamoid bone (PSB). Breakdowns involving the PSBs are the leading cause in racehorse deaths in the industry, with still little known about what causes this bone to fracture. This study seeks to shed insight by investigating the internal structure of the PSB. Using microCT scanning, the internal porous structure was captured. From there, noticeable differences in the pores were noticed and quantified using fast Fourier transform (FFT) analysis.

The dominant peak …

Assessment Of White Matter Hyperintensity, Cerebral Blood Flow, And Cerebral Oxygenation In Older Subjects Stratified By Cerebrovascular Risk, Ahmed A. Bahrani

Theses and Dissertations--Biomedical Engineering

Objective: Cerebrovascular disease (CVD) is the fifth most common cause of mortality in the United States. Diagnosis of CVD at an early stage is critical for optimal intervention designed to prevent ongoing and future brain injury. CVD is commonly associated with abnormalities of the cerebral microvasculature leading to tissue dysfunction, neuronal injury and death, and resultant clinical symptoms, which in turn, further impacts cerebral autoregulation (CA). This series of studies aims to test the hypothesis that white matter hyperintensities (WMH) and cerebral hemodynamics (quantified by magnetic resonance imaging (MRI) and an by innovative hybrid near-infrared diffuse optical instrument) can be …

Noncontact Multiscale Diffuse Optical Imaging Of Deep Tissue Hemodynamics In Animals And Humans, Siavash Mazdeyasna

Theses and Dissertations--Biomedical Engineering

Blood flow (BF) impacts the delivery of oxygen and nutrients to tissues and the removal of metabolic byproducts from tissues. Imaging of BF distributions helps characterize many diseases associated with tissue hypoxia/ischemia. The purpose of this study was to develop and validate a novel, noninvasive, noncontact, high-density camera-based speckle contrast diffuse correlation tomography (scDCT) device for use in both animal and human studies. The scDCT uses a galvo-mirror to remotely deliver the focused point near-infrared light to source positions and a sensitive 2D camera to quantify spatial diffuse speckle fluctuations, resulting from the movement of red blood cells in deep …

Quantification Of Myocardial Mechanics In Left Ventricles Under Inotropic Stimulation And In Healthy Right Ventricles Using 3d Dense Cmr, Zhan-Qiu Liu

Theses and Dissertations--Mechanical Engineering

Statistical data from clinical studies indicate that the death rate caused by heart disease has decreased due to an increased use of evidence-based medical therapies. This includes the use of magnetic resonance imaging (MRI), which is one of the most common non-invasive approaches in evidence-based health care research. In the current work, I present 3D Lagrangian strains and torsion in the left ventricle of healthy and isoproterenol-stimulated rats, which were investigated using Displacement ENcoding with Stimulated Echoes (DENSE) cardiac magnetic resonance (CMR) imaging. With the implementation of the 12-segment model, a detailed profile of regional cardiac mechanics was reconstructed for …

Noninvasive Multimodal Diffuse Optical Imaging Of Vulnerable Tissue Hemodynamics, Mingjun Zhao

Theses and Dissertations--Biomedical Engineering

Measurement of tissue hemodynamics provides vital information for the assessment of tissue viability. This thesis reports three noninvasive near-infrared diffuse optical systems for spectroscopic measurements and tomographic imaging of tissue hemodynamics in vulnerable tissues with the goal of disease diagnosis and treatment monitoring. A hybrid near-infrared spectroscopy/diffuse correlation spectroscopy (NIRS/DCS) instrument with a contact fiber-optic probe was developed and utilized for simultaneous and continuous monitoring of blood flow (BF), blood oxygenation, and oxidative metabolism in exercising gastrocnemius. Results measured by the hybrid NIRS/DCS instrument in 37 subjects (mean age: 67 ± 6) indicated that vitamin D supplement plus aerobic training …

Calibrated Short Tr Recovery Mri For Rapid Measurement Of Brain-Blood Partition Coefficient And Correction Of Quantitative Cerebral Blood Flow, Scott William Thalman

Theses and Dissertations--Biomedical Engineering

The high prevalence and mortality of cerebrovascular disease has led to the development of several methods to measure cerebral blood flow (CBF) in vivo. One of these, arterial spin labeling (ASL), is a quantitative magnetic resonance imaging (MRI) technique with the advantage that it is completely non-invasive. The quantification of CBF using ASL requires correction for a tissue specific parameter called the brain-blood partition coefficient (BBPC). Despite regional and inter-subject variability in BBPC, the current recommended implementation of ASL uses a constant assumed value of 0.9 mL/g for all regions of the brain, all subjects, and even all species.

The …

Multimodal Noncontact Diffuse Optical Reflectance Imaging Of Blood Flow And Fluorescence Contrasts, Daniel Irwin

Theses and Dissertations--Biomedical Engineering

In this study we design a succession of three increasingly adept diffuse optical devices towards the simultaneous 3D imaging of blood flow and fluorescence contrasts in relatively deep tissues. These metrics together can provide future insights into the relationship between blood flow distributions and fluorescent or fluorescently tagged agents. A noncontact diffuse correlation tomography (ncDCT) device was firstly developed to recover flow by mechanically scanning a lens-based apparatus across the sample. The novel flow reconstruction technique and measuring boundary curvature were advanced in tandem. The establishment of CCD camera detection with a high sampling density and flow recovery by speckle …

Validation, Optimization, And Image Processing Of Spiral Cine Dense Magnetic Resonance Imaging For The Quantification Of Left And Right Ventricular Mechanics, Gregory J. Wehner

Theses and Dissertations--Biomedical Engineering

Recent evidence suggests that cardiac mechanics (e.g. cardiac strains) are better measures of heart function compared to common clinical metrics like ejection fraction. However, commonly-used parameters of cardiac mechanics remain limited to just a few measurements averaged over the whole left ventricle. We hypothesized that recent advances in cardiac magnetic resonance imaging (MRI) could be extended to provide measures of cardiac mechanics throughout the left and right ventricles (LV and RV, respectively).

Displacement Encoding with Stimulated Echoes (DENSE) is a cardiac MRI technique that has been validated for measuring LV mechanics at a magnetic field strength of 1.5 T but …

Biventricular Finite Element Modeling And Quantification Of 3d Langragian Strains And Torsion Using Dense Mri, Zhanqiu Liu

Theses and Dissertations--Mechanical Engineering

Statistical data suggests that increased use of evidence-based medical therapies has largely contributed to the decrease in American death rate caused by heart disease. And my studies are about two applications of magnetic resonance imaging (MRI) as a non-invasive approach in evidence-based health care research. In my first study, the achievement of a pulmonary valve replacement surgery was assessed on a patient with tetralogy of Fallot (TOF). In order to evaluate the remodeling of right ventricle, two biventricular finite element models were built up for pre-surgical images and post-surgical images. In my second study, 3D Lagrangian strains and torsion in …

Diffuse Optical Measurements Of Head And Neck Tumor Hemodynamics For Early Prediction Of Chemo-Radiation Therapy Outcomes, Lixin Dong

Theses and Dissertations--Biomedical Engineering

Chemo-radiation therapy is a principal modality for the treatment of head and neck cancers, and its efficacy depends on the interaction of tumor oxygen with free radicals. In this study, we adopted a novel hybrid diffuse optical instrument combining a commercial frequency-domain tissue oximeter (Imagent) and a custom-made diffuse correlation spectroscopy (DCS) flowmeter, which allowed for simultaneous measurements of tumor blood flow and blood oxygenation. Using this hybrid instrument we continually measured tumor hemodynamic responses to chemo-radiation therapy over the treatment period of 7 weeks. We also explored monitoring dynamic tumor hemodynamic changes during radiation delivery. Blood flow data analysis …

Noncontact Diffuse Correlation Tomography Of Breast Tumor, Lian He

Theses and Dissertations--Biomedical Engineering

Since aggressive cancers are frequently hypermetabolic with angiogenic vessels, quantification of blood flow (BF) can be vital for cancer diagnosis. Our laboratory has developed a noncontact diffuse correlation tomography (ncDCT) system for 3-D imaging of BF distribution in deep tissues (up to centimeters). The ncDCT system employs two sets of optical lenses to project source and detector fibers respectively onto the tissue surface, and applies finite element framework to model light transportation in complex tissue geometries. This thesis reports our first step to adapt the ncDCT system for 3-D imaging of BF contrasts in human breast tumors. A commercial 3-D …

Stabilization Of Extended Diffuse Optical Spectroscopy Measurements On In Vivo Human Skeletal Muscle During Dynamic Exercise, Brad A. Henry

Theses and Dissertations--Biomedical Engineering

This research investigates various applications of diffuse correlation spectroscopy (DCS) on in-vivo human muscle tissue, both at rest and during dynamic exercise. Previously suspected muscle tissue relative blood flow (rBF) baseline shift during extended measurement with DCS and DCS-Near infrared spectroscopy (NIRS) hybrid optical systems are verified, quantified, and resolved by redesign of optical probe and alteration in optical probe attachment methodology during 40 minute supine bed rest baseline measurements. We then translate previously developed occlusion techniques, whereby rBF and relative oxygen consumption rV̇O₂ are calibrated to initial resting absolute values by use of a venous occlusion (VO) and …

Noninvasive Near-Infrared Diffuse Optical Monitoring Of Cerebral Hemodynamics And Autoregulation, Ran Cheng

Theses and Dissertations--Biomedical Engineering

Many cerebral diseases are associated with abnormal cerebral hemodynamics and impaired cerebral autoregulation (CA). CA is a mechanism to maintain cerebral blood flow (CBF) stable when mean arterial pressure (MAP) fluctuates. Evaluating these abnormalities requires direct measurements of cerebral hemodynamics and MAP. Several near-infrared diffuse optical instruments have been developed in our laboratory for hemodynamic measurements including near-infrared spectroscopy (NIRS), diffuse correlation spectroscopy (DCS), hybrid NIRS/DCS, and dual-wavelength DCS flow-oximeter. We utilized these noninvasive technologies to quantify CBF and cerebral oxygenation in different populations under different physiological conditions/manipulations. A commercial finger plethysmograph was used to continuously monitor MAP. For investigating …

Recovering Local Neural Tract Directions And Reconstructing Neural Pathways In High Angular Resolution Diffusion Mri, Ning Cao

Theses and Dissertations--Computer Science

Magnetic resonance imaging (MRI) is an imaging technique to visualize internal structures of the body. Diffusion MRI is an MRI modality that measures overall diffusion effect of molecules in vivo and non-invasively. Diffusion tensor imaging (DTI) is an extended technique of diffusion MRI. The major application of DTI is to measure the location, orientation and anisotropy of fiber tracts in white matter. It enables non-invasive investigation of major neural pathways of human brain, namely tractography. As spatial resolution of MRI is limited, it is possible that there are multiple fiber bundles within the same voxel. However, diffusion tensor model is …

Use Of Hybrid Diffuse Optical Spectroscopies In Continuous Monitoring Of Blood Flow, Blood Oxygenation, And Oxygen Consumption Rate In Exercising Skeletal Muscle, Katelyn Gurley

Theses and Dissertations--Biomedical Engineering

This study combines noninvasive hybrid diffuse optical spectroscopies [near-infrared spectroscopy (NIRS) and diffuse correlation spectroscopy (DCS)] with occlusive calibration for continuous measurement of absolute blood flow (BF), tissue blood oxygenation (S_tO₂), and oxygen consumption rate (VO₂) in exercising skeletal muscle. Subjects performed rhythmic dynamic handgrip exercise, while an optical probe connected to a hybrid NIRS/DCS flow-oximeter directly monitored oxy-, deoxy-, and total hemoglobin concentrations ([HbO₂], [Hb], and [tHb]), S_tO₂, relative BF (rBF), and relative VO₂ (rVO₂) in the forearm flexor muscles. Absolute baseline BF and …