Publications (12) View all
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Conference Proceeding: Effects of Cerebrospinal Fluid Motion on DTI in the Cervical Spinal Cord
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ABSTRACT: Purpose: Improve the accuracy of DTI in the cervical spinal cord to provide increased predictive and diagnostic value; investigate methods to segment white matter in the spinal cord accounting for CSF motility effects, including a new directionality measure, normalized axial diffusivity (DAn). Methods: Spinal phase contrast MRI (pcMRI) and DTI scans were performed in four healthy adults. Cord and white matter (WM) segmentation were performed both manually and with automatic algorithms. Results: In white matter, MD, DA, DR and MA 1 had significant mean or variance differences between gated and ungated conditions. Only FA and normalized axial diffusivity (DAn) showed no significant differences. Conclusions: Though careful segmentation of cord imaging can yield useful diffusion parameters from non-gated data, the choice of parameters must be informed by the variable effects of CSF flow.ASFNR, Charleston, SC; 03/2013 -
Article: Photon tracking in a multilayer tissue model.
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ABSTRACT: A multilayer tissue description was employed in a Monte Carlo simulation of light-tissue interaction to study photon travel through skin. Paths of photons returning to the tissue surface at a certain range from the point of entry (emitter-detector spacing) were collected. The simulation demonstrates that highly absorptive discrete layers (e.g., containing melanin or blood) tend to channel photons away. As a result, the dependence of mean depth of photon penetration on wavelength is quite different from the predictions of a homogeneous tissue model. The impact upon our understanding of pulse oximetry is discussed.Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 02/2004; 1:643-6. -
Article: Multilayer modeling of reflectance pulse oximetry.
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ABSTRACT: A multilayer tissue description was employed in Monte Carlo simulations of reflectance pulse oximetry to study the impact of assumptions made in previous studies employing homogeneous tissue models. Simulation results with a discrete layer of arterial pulsatility were similar to previous studies employing homogenous tissue models. However, the relationship of normalized pulse amplitude to emitter-detector spacing reiterates that spacing has a significant impact on pulse oximetry function. The effect of melanin content as a thin, superficial absorber was also simulated, with results supporting the general clinical observation that skin shade need not substantially compromise pulse oximeter accuracy.IEEE Transactions on Biomedical Engineering 03/2005; 52(2):153-9. · 2.28 Impact Factor -
Article: The pulse in reflectance pulse oximetry: modeling and experimental studies.
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ABSTRACT: Reflectance pulse oximetry permits the use of alternative monitoring sites such as the face or torso, and is the approach commonly employed in fetal pulse oximetry systems. The purpose of this study is to investigate the impact of assumptions about the nature of arterial pulsatility on the calibration of such systems. Monte Carlo simulations of reflectance pulse oximetry were run on a six-layer tissue model, varying depth and magnitude of the arterial pulse. SpO2 readings on and off the femoral artery obtained during desaturation studies in newborn piglets were compared to predictions. Results. Monte Carlo simulation results clarified the difference between deep and shallow pulsatility found with photon diffusion models, agreeing with earlier in vivo observations. Significant overestimation of SpO2 <75% and slight underestimation >75% is expected if a sensor is placed on a highly pulsatile site. The on- and off-artery SpO2 readings recorded during desaturation in the newborn piglet follow the model predictions. The sensitivity of reflectance pulse oximetry calibration to the depth and magnitude of arterial pulsatility reinforces the observation that monitoring site selection is of importance in optimizing reflectance pulse oximetry performance, particularly fetal pulse oximetry. Sites with palpable pulsatility should be avoided.Journal of Clinical Monitoring and Computing 08/2004; 18(4):289-99. · 0.89 Impact Factor -
Article: Factors influencing fetal pulse oximetry performance.
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ABSTRACT: Fetal pulse oximetry shares many problems with traditional pulse oximetry, but also poses unique challenges that may compromise accurate SpO2 determination and data availability. The purpose of this review is to characterize the factors that may influence fetal pulse oximetry and their relationship to sensor design. A review of the literature of pulse oximetry identifies the factors that have been shown to influence fetal pulse oximetry performance, as well as other factors from traditional pulse oximetry that may also be expected to have an effect. Sensor design choices, including monitoring site, wavelength, and configuration, are related to the incidence and mitigation of these factors. Sensor designs may be characterized by monitoring site, means of retention, and operating mode (reflectance versus transmission). The factors influencing fetal pulse oximetry may be categorized as follows: fetal physiology, tissue characteristics at the monitoring site, sensor-tissue interface, and external influences. Monitoring site selection is of paramount importance in reducing the impact of interfering factors on fetal pulse oximetry performance. Many factors of importance in traditional pulse oximetry have yet to be characterized as far as their potential for interference in fetal pulse oximetry.Journal of Clinical Monitoring and Computing 03/2004; 18(1):13-24. · 0.89 Impact Factor
