Bill Rogers

Fractional anisotropy of cerebral white matter and thickness of cortical gray matter across the lifespan

We examined age trajectories of fractional anisotropy (FA) of cerebral white matter (WM) and thickness of cortical gray matter (GM) in 1031 healthy human subjects (aged 11-90 years). Whole-brain FA and GM thickness values followed quadratic trajectories with age but the relationship between them was linear, indicating that a putative biological mechanism may explain the non-linearity of their age trajectories. Inclusion of the FA values into the quadratic model of the whole-brain and regional GM thickness changes with age made the effect of the age(2) term no longer significant for the whole-brain GM thickness and greatly reduced its significance for regional GM thickness measurements. The phylogenetic order of cerebral myelination helped to further explain the intersubject variability in GM thickness. FA values for the early maturing WM were significantly better (p=10(-6)) at explaining variability in GM thickness in maturing (aged 11-20) subjects than FA values for the late maturing WM. The opposite trend was observed for aging subjects (aged 40-90) where FA values for the late maturing WM were better (p=10(-16)) at explaining the variability in GM thickness. We concluded that the non-linearity of the age trajectory for GM thickness, measured from T1-weighted MRI, was partially explained by the heterogeneity and the heterochronicity of the age-related changes in the microintegrity of cerebral WM. We consider these findings as the evidence that the measurements of age-related changes in GM thickness and FA are driven, in part, by a common biological mechanism, presumed to be related to changes in cerebral myelination.

Understanding the neural mechanisms involved in sensory control of voice production

Auditory feedback is important for the control of voice fundamental frequency (F0). In the present study we used neuroimaging to identify regions of the brain responsible for sensory control of the voice. We used a pitch-shift paradigm where subjects respond to an alteration, or shift, of voice pitch auditory feedback with a reflexive change in F0. To determine the neural substrates involved in these audio-vocal responses, subjects underwent fMRI scanning while vocalizing with or without pitch-shifted feedback. The comparison of shifted and unshifted vocalization revealed activation bilaterally in the superior temporal gyrus (STG) in response to the pitch shifted feedback. We hypothesize that the STG activity is related to error detection by auditory error cells located in the superior temporal cortex and efference copy mechanisms whereby this region is responsible for the coding of a mismatch between actual and predicted voice F0.

Advanced Trans-Tibial Socket Fabrication Using Selective Laser Sintering

There have been a variety of efforts demonstrating the use of solid freeform fabrication (SFF) for prosthetic socket fabrication though there has been little effort in leveraging the strengths of the technology. SFF encompasses a class of technologies that can create three dimensional objects directly from a geometric database without specific tooling or human intervention. A real strength of SFF is that cost of fabrication is related to the volume of the part, not the parts complexity. For prosthetic socket fabrication this means that a sophisticated socket can be fabricated at essentially the same cost as a simple socket. Adding new features to a socket design becomes a function of software. The work at The University of Texas Health Science Center at San Antonio (UTHSCSA) and University of Texas at Austin (UTA) has concentrated on developing advanced sockets that incorporate structural features to increase comfort as well as built in fixtures to accommodate industry standard hardware. Selective laser sintering (SLS) was chosen as the SFF technology to use for socket fabrication as it was capable of fabricating sockets using materials appropriate for prosthetics. This paper details the development of SLS prosthetic socket fabrication techniques at UTHSCSA/UTA over a six-year period.

Case Report: Variably Compliant Transtibial Prosthetic Socket Fabricated Using Solid Freeform Fabrication

Achieving and maintaining a comfortable fit in a lower-limb prosthetic socket is an important goal to help ensure a successful rehabilitation. The purpose of this case study was to assess the performance of sockets with compliant features integrated into the socket wall to relieve in-socket pressure during transtibial amputee gait. Two sockets incorporating variably compliant areas over the fibula head and distal tibia were fabricated for a transtibial amputee. The two sockets were designed with different levels of compliance and were compared with a third more conventional socket without compliant areas. All three sockets were otherwise geometrically identical and were aligned identically to eliminate in-socket pressure differences due to alignment. The three sockets were fabricated using selective laser sintering, a form of solid freeform fabrication. The in-socket pressure measurements were acquired during normal walking. Tekscan F-Socket pressure sensors were attached to the amputees residual limb rather than to the socket wall, which made it possible to measure pressures in the same location on the residual limb upon change of socket. A Vicon motion capture system was used to match in-socket pressures to the subjects gait cycle. The pressure measurements showed that the compliant socket peak pressures over the distal tibia and fibula head were similar for the two compliance levels and nearly 50% and 30% lower than the conventional socket pressures, respectively. This case study showed that selective laser sintering manufactured sockets with variably compliant regions holds great promise for reducing contact pressure in sensitive regions of the residual limb.

Double-wall, transtibial prosthetic socket fabricated using selective laser sintering: A case study

The primary goal of this study was to test the feasibility of using selective laser sintering (SLS) to fabricate a functional transtibial prosthetic socket. Prosthetic socket computer-assisted design and computer-assisted manufacturing techniques were combined with SLS technology to produce a sophisticated, monolithic, transtibial prosthetic socket. The socket combined a rigid outer shell with a variably compliant inner shell and incorporated a fitting for a pylon directly into it. The socket was manufactured for a 65-year-old transtibial amputee using a socket shape identical to his current definitive socket. A prosthesis was then assembled using the same foot as the subjects definitive prosthesis. A comparison of socket performance suggested improved comfort, greater step symmetry, and similar lower extremity joint function.

Computerized manufacturing of transparent face masks for the treatment of facial scarring.

In this work an integrated system of computer-aided design and computer-aided manufacturing specifically designed to fabricate affordable transparent face masks is discussed. FaceScan, a custom-designed software system, integrates shape capture, mask design, and pattern fabrication. The software controls a linear scan noncontact laser imager for facial topography acquisition and a milling machine for pattern fabrication. Compared with conventional methods of mask fabrication, this system is faster, more accurate, and less stressful for the patient and allows for greater control of the finished product. Masks for two subjects have been successfully fabricated using this system.

fMRI of Deep Brain Stimulation at the Rat Ventral Posteromedial Thalamus

BACKGROUND Functional magnetic resonance imaging (fMRI) of deep brain stimulation (DBS) has potentials to reveal neuroanatomical connectivity of a specific brain region in vivo. OBJECTIVE This study aimed to demonstrate frequency and amplitude tunings of the thalamocortical tract using DBS fMRI at the rat ventral posteromedial thalamus. METHODS Blood oxygenation level dependent (BOLD) fMRI data were acquired in a total of twelve rats at a high-field 11.7 T MRI scanner with modulation of nine stimulus frequencies (1-40 Hz) and seven stimulus amplitudes (0.2-3.6 mA). RESULTS BOLD response in the barrel cortex peaked at 25 Hz. The response increased with stimulus amplitude and reached a plateau at 1 mA. Cortical spreading depolarization (CSD) was observed occasionally after DBS that carries >10% BOLD waves spanning the entire ipsilateral cortex. CONCLUSION fMRI is sensitive to the frequency effect of DBS and has potential to investigate the function of a particular neuroanatomical pathway.

Three-Dimensional laser imaging system for measuring wound geometry

Background and Objective: A low cost laser imager was designed and fabricated for measurement of wound geometry.

Locating anatomical landmarks for prosthetics design using ensemble neural networks

Computer aided design of a prosthesis for a below-the-knee (trans-tibial) amputee begins with a digitized representation of the shape of the residual limb. Certain anatomical landmarks must be located on this shape to identify optimal areas for load and pressure relief. A method of locating the midpoint of the patellar tendon, the distal end of the tibia and the head of the fibula is presented. The method involves training ensembles of neural networks on shapes for which the markers have been located manually; the neural networks are then used to find the landmarks for arbitrary shapes. Experimental results show that the method is at least as accurate as a trained prosthetist.

Force sensing system for automated assessment of motor performance during fMRI

Finger tapping sequences are a commonly used measure of motor learning in functional imaging studies. Subjects repeat a defined sequence of finger taps as fast as possible for a set period of time. The number of sequences completed per unit time is the measure of performance. Assessment of speed and accuracy is generally accomplished by video recording the session then replaying in slow motion to assess rate and accuracy. This is a time consuming and error prone process. Keyboards and instrumented gloves have also been used for task assessment though they are relatively expensive and not usually compatible in a magnetic resonance imaging (MRI) scanner. To address these problems, we developed a low cost system using MRI compatible force sensitive resistors (FSR) to assess the performance during a finger sequence task. This system additionally provides information on finger coordination including time between sequences, intervals between taps, and tap duration. The method was validated by comparing the FSR system results with results obtained by video analysis during the same session.