Prashant Bhadri

Doheny Eye Institute, Los Ángeles, California, United States

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Publications (37)43.44 Total impact

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    ABSTRACT: This study evaluates water and porcine vitreous flow rates and duty cycle using the Millennium Vitrectomy Enhancer (MVE) system (Bausch & Lomb, St. Louis, MO). A precision balance measured mass of water or vitreous removed from a vial within a certain time by 20-, 23-, and 25-gauge MVE cutters at 800, 1,000, 1,500, 2,000, and 2,500 cuts per minute (CPM) with various aspiration levels was studied. Frame-by-frame analysis of high-speed video was used to determine duty cycle. Larger cutter and higher aspiration levels produced greater flow rates. Water flow rate showed a parabolic trend peaking at 1,500 CPM and dropping moderately and vitreous flow rate increased moderately with cut-rate increased. The MVE system maintained a high flow rate and high duty cycle even at high cut-rates. Flow rates for the MVE system are stable and predictable for all cutter gauges, which should aid the surgeon to select the optimal parameters for vitrectomy.
    No preview · Article · Dec 2010 · Ophthalmic Surgery Lasers and Imaging
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    ABSTRACT: To evaluate and compare the performance of several designs of 20-gauge dual port (DP) vitreous cutter tips with a standard 20-gauge single port tip. Custom 20-gauge pneumatic vitreous DP cutter tips with different sizes and port positions were evaluated through porcine vitreous and water flow rates. Five designed and fabricated DP cutter tips were compared with a normal single port control tip and evaluated by the measurement of water and porcine vitreous flow rates, and surgical examination in enucleated porcine eyes. Some DP tips approached a maximum vitreous and water flow rates, removing water and vitreous faster than the normal control tip. With reference to surgical evaluation, some DP tips performed better than the single port tip for bulk vitrectomy, but none shaved the vitreous base more effectively. The DP cutter system has the potential to increase the flow rates depending on the size and position of the extra port. In the future, the DP cutter may allow the surgeon to perform bulk vitrectomy more efficiently.
    No preview · Article · Oct 2010 · Retina (Philadelphia, Pa.)
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    ABSTRACT: To quantify the vitreous traction created by pneumatic (20-, 23-, and 25-gauge) and electric cutters (20- and 25-gauge) during vitrectomy. Experimental study. This is a preclinical study, and no patients were involved. Five separate cutters for each drive mechanism and gauge (20-, 23-, and 25-gauge pneumatic and 20- and 25-gauge electric) were used for each cut speed at predetermined aspiration rates. The retinal layers of fresh porcine eyes were transfixed with a 0.15-mm steel wire and fixed to the load cell of a strain gauge. The cutter to be assessed was introduced into the eye by a micromanipulator at a 45-degree angle adjacent to the retina. The traction force was determined and evaluated at a distance of 3 and 5 mm from the retina with different vacuum and cut rates. Vacuum, cut speed, force (dynes), distance (millimeters), vitreoretinal traction, and gauge. The 20-, 23-, and 25-gauge pneumatic cutters have a range of traction from 2.06 to 37.22 dynes, 3.85 to 15.38 dynes, 5.13 to 27.91 dynes, respectively. The 20- and 25-gauge electric cutters have a range of traction from 3.60 to 41.78 dynes and 5.28 to 27.91 dynes, respectively. All results are related to distance, cut, and aspiration rate. With an increase of 100 mmHg of vacuum/aspiration, the traction increased from 7.89 to 3.14 dynes (e.g., 4.96 for 20-gauge pneumatic). The traction decreased as the cut rate was increased, from 5.71 to 2.51 dynes (e.g., 3.41 for 20-gauge pneumatic). The results indicate that retinal traction increased with increasing aspiration vacuum and proximity to the retina; conversely, retinal traction decreased with increasing cut rate. The present study demonstrates that the effects of aspiration, distance from the retina, and cut rate are crucial factors in the amount of retinal traction created by vitreous cutters. Proprietary or commercial disclosure may be found after the references.
    No preview · Article · Feb 2010 · Ophthalmology
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    ABSTRACT: The purpose of this study was to use a novel method to quantify the traction applied to the retina during vitrectomy. Five 20-gauge electric cutters were used. Fresh porcine eyes were positioned in a specially developed holder and transfixed to the retinal layers with a microwire, and the other end was fixed to the load cell of a strain gauge. The cutter to be assessed was introduced into the eye by a micromanipulator at a 45 degrees angle adjacent to the retina. The traction force was evaluated when the cutter was at 3 and 5 mm from the retina. As control, the experiment was repeated in eyes filled with water, and the results were compared to those when the eyes had vitreous gel. Results from the eyes with vitreous gel indicate that retinal traction increased with increasing aspiration vacuum (7.90 dyn for each 100 mm Hg increased; P < 0.05) and proximity to the retina (2.17 dyn; P < 0.05) and decreased with increasing cut rate (2.51 dyn for each 500 cuts per minute increased; P < 0.05). In all eyes filled with water, traction was not observed. The present study establishes a new reproducible technique to quantify vitreoretinal traction during vitrectomy and demonstrates that the effects of aspiration, distance from the retina, and cut rate are crucial factors in the amount of retinal traction created by vitreous cutters.
    No preview · Article · Feb 2010 · Investigative ophthalmology & visual science
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    ABSTRACT: Purpose: To evaluate the duty cycle of different vitrectomy cutters and classify their blade movement. Methods: A precise weighing (0.01 g) high speed (2 samples/s) balance was used to study the 20-gauge and 25-gauge Bausch & Lomb Lightning-Millenium (St. Louis, MO), the 20-gauge (1500 cpm) and the 25-gauge Alcon Accurus (Fort Worth, TX), the 20-gauge Alcon Innovit, and the 23-gauge DORC (Netherlands) cutters. The weight of balanced saline solution (BSS) was recorded in real time using LabView software and then translated into a graph of volume removed versus time. Variable cut rates and vacuum pressures were analyzed in vitreous and BSS. A high-speed (400 frames/s) camera was used to record cutting for each condition. Results: Three types of duty cycle were investigated: parabolic incomplete (pneumatic), sinusoid (electric), and trapezoid (double pneumatic). The parabolic incomplete and trapezoid had a decreased duty cycle at 1500 cuts per minute when it was compared to 600 cuts per minute. The sinusoid had no statistical difference between cut rates. Conclusions: Systems showed different performances of duty cycle. This new classification will be useful for improved understanding of vitrectomy in these different systems.
    No preview · Article · Dec 2008 · Retinal Cases & Brief Reports
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    ABSTRACT: 25-gauge instrumentation has reduced the surgical incision size. This reduction in size has made vitreoretinal procedures not only sutureless but, more importantly, made the procedures less invasive and potentially safer. The sutureless 25-gauge pars plana vitrectomy reduces the postoperative inflammation at sclerotomy sites, thus reducing patient discomfort after surgery and hastening postoperative recovery. The majority of experienced vitreoretinal surgeons have now been exposed at some level to 25-gauge instrumentation, and many use it on a routine basis. However, only a few surgeons have experience with the engineering development challenges and tradeoffs associated with small-diameter instrumentation. This chapter will explore some of the key areas of the design and functioning of small-diameter instruments, so that surgeons may better understand their performance.
    Preview · Chapter · Nov 2008
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    ABSTRACT: To determine the influence of port geometry on water and vitreous flow rates and test novel vitreous cutter tips in specific surgical situations. Custom 20-gauge and 25-gauge vitreous cutter tips with different sized ports were evaluated through porcine vitreous and water flow rates. Five cutter tips were designed and fabricated for specific surgical functionalities. Tips were compared with a normal control tip and evaluated by water and porcine vitreous flow rates, vacuum level required to cut porcine retina, time required to cut and aspirate a porcine lens, and surgical evaluation in enucleated porcine eyes. Both vitreous and water flow asymptotically approached a maximum flow as the port diameter increased. Some tips removed water faster than the normal control tip, but none removed vitreous or lens faster. Several tips required higher vacuum levels to cut retina than the normal tip. Increasing the port diameter of a vitreous cutter to increase flow becomes less effective as the port becomes larger. Furthermore, modifying the port geometry of a vitreous cutter affects its surgical interactions with tissue. In the future, combinational instruments or surgery specific instruments may allow the surgeon to use an optimal port for a specific surgical task.
    No preview · Article · Nov 2008 · Retina (Philadelphia, Pa.)
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    ABSTRACT: A cerebral aneurysm is defined as a weakened portion of an artery in the brain. Rupture of a cerebral aneurysm leads to subarachnoid hemorrhage (SAH). A significant number of patients with SAH are initially misdiagnosed and subjected to the risks associated with aneurysm re-rupture. Traditional detection methods recommended by physicians include computed tomography (CT) scan, lumbar puncture and angiography. Unfortunately, the CT scan is ineffective after 12 h, and angiography is best suited for those cases of finding the aneurysm before surgery. Physicians may therefore rely on lumbar puncture to develop a quick and objective evaluation by assessing xanthochromia. Bilirubin in the cerebrospinal fluid, resulting from the chemical decomposition of whole blood, is an indicator of hemorrhage. This metabolite can be detected after lumbar puncture, by differentiating its optical signature in the spinal fluid. In cases of traumatic spinal tap, bilirubin needs to be distinguished from whole blood. We introduce a diagnostic system based on visible spectroscopy to quickly and objectively assess low blood-volume SAH. The system integrates innovative hardware and a powerful software interface. We explore an algorithm that accounts for the noise and distortion from blood in the cerebrospinal fluid. We introduce a portable, user-friendly hardware platform composed of specific components designed for their sensitivity and specificity.
    No preview · Article · Aug 2008 · Analog Integrated Circuits and Signal Processing
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    ABSTRACT: To evaluate porcine vitreous flow and balanced saline solution (BSS) flow rates in different vitrectomy systems. Porcine vitreous was obtained within 24 hours of slaughter. A high-speed (2 samples/s) balance, precise to 0.01 g, was used. Variable cut rates and vacuum pressures were analyzed in vitreous and BSS. The vitreous was labeled with glass microspheres and triamcinolone acetonide. A high-speed (400 frames/s) camera was used to record cutting for each condition. For all cutters, there was no vitreous flow at zero cut rates (off). In 25-gauge cutters, at 500 mmHg of vacuum, the electric cutter produced higher average flow rates at high cut rates (600 cpm, 0.004 mL/s, and 1500 cpm, 0.013 mL/s) than pneumatic, which demonstrated a decreased flow at speeds higher than 1000 cpm (1000 cpm, 0.015 mL/s, and 1500 cpm, 0.006 mL/s). The percentage of vitreous flow rate/BSS flow rate in different aspiration and cut rates showed an ascending curve. This demonstrates evidence of flow obstruction in 25- (all cut rates), 23- (all cut rates), and 20-gauge (all cut rates). Flow obstruction and surge movements were seen in the high-speed videos. The vitrectomy systems each illustrate different performances of vitreous removal. The physical characteristics of vitreous resulted in nonuniform flow in all vitreous cutters.
    No preview · Article · Mar 2008 · Retina
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    ABSTRACT: To evaluate the effectiveness of a prototype stereoscopic camera-based viewing system (Digital Microsurgical Workstation, three-dimensional (3D) Vision Systems, Irvine, California, USA) for anterior and posterior segment ophthalmic surgery. Institutional-based prospective study. Anterior and posterior segment surgeons performed designated standardized tasks on porcine eyes after training on prosthetic plastic eyes. Both anterior and posterior segment surgeons were able to complete tasks requiring minimal or moderate stereoscopic viewing. The results indicate that the system provides improved ergonomics. Improvements in key viewing performance areas would further enhance the value over a conventional operating microscope. The performance of the prototype system is not at par with the planned commercial system. With continued development of this technology, the three- dimensional system may be a novel viewing system in ophthalmic surgery with improved ergonomics with respect to traditional microscopic viewing.
    No preview · Article · Jun 2007 · American Journal of Ophthalmology
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    ABSTRACT: Annually, approximately 30,000 people suffer from aneurysmal subarachnoid hemorrhage (SAH) in the United States. In an estimated 5% of these patients, the hemorrhage is difficult to diagnose using conventional methods. Clinicians must rely upon a combination of clinical history, Computerized Tomography (CT) scan evidence and lumbar puncture results to diagnose and differentiate SAH from a traumatic spinal tap (blood in the spinal fluid due to the procedure). Here we describe an algorithm based development of an analytic methodology using visible spectroscopy to reliably quantify bilirubin in hemorrhagic spinal fluid. The analysis, which may be useful for diagnoses concerning hemorrhagic stroke, is based on the detection of bilirubin, and concomitant blood products produced within the Cerebral Spinal Fluid (CSF) following SAH. The algorithm quantifies bilirubin (0.3 to 10 mg/dL) from the resultant absorption spectrum. A model is developed from standard visible spectroscopic absorption curves of bilirubin and hemoglobin by applying traditional Beer's Law principles. The model is coupled to a modified partial least square analysis and control theory concept where the bilirubin is the "signal" and is masked by hemoglobin "noise." This paper describes the computational methods, sensitivity and utility of a system to quantify bilirubin in CSF like solutions containing hemoglobin and bilirubin over 0.5 g/dL-10 g/dL of hemoglobin concentrations.
    Full-text · Article · Feb 2007 · Medicinal Chemistry
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    A. Das · P. Bhadri · F.R. Beyette · Am Jang · P. Bishop · W. Timmons
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    ABSTRACT: The need to monitor the conditions prevailing in the external environment in order to control environmental pollution is one of the prime necessities of the modern age. This paper introduces a robust, self-contained, inexpensive integrated potentiometric sensor that can be used for in situ environmental monitoring. The primary focus is to design, implement and integrate a potentiometric CMOS circuit with the sensor device to measure the potential developed across a working probe (microelectrode sensor) and the reference probe. The magnitude of the output voltage signal is dependent on the characteristics (pH) of the solution being evaluated by the system. A Printed Circuit Board has been built to integrate the microelectrode sensor device and the sensor chip with the aim of producing a fully integrated system. The microelectrode sensor device may be replaced by a NEMS based sensor device in areas that require further miniaturization like biomedical applications.
    Full-text · Conference Paper · Jul 2006
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    A. Das · P. Bhadri · F.R. Beyette · Am Jang · P. Bishop · W. Timmons
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    ABSTRACT: In the modern era, some of the most serious causes for public health problems can be attributed to environmental pollution. Proper monitoring of environmental conditions helps us to control the pollution in an effective manner. This paper introduces a robust, self-contained, inexpensive integrated amperiometric microelectrode sensor that can be used for in situ environmental monitoring. The work primarily focuses on the design, implementation and integration of an amperiometric CMOS sensor chip with a microelectrode sensor device in order to measure the current flowing through the working probe (microelectrode sensor) and the reference probe, when they are immersed in the test solution. The magnitude of the current signal, of the order of nanoamperes, is shown to be dependent on the characteristics (oxygen content) of the solution being evaluated by the system. The integration of the microelectrode sensor with the sensor chip is done with the help of a Printed Circuit Board. The microelectrode sensor device may be replaced by a NEMS based sensor device for applications requiring further miniaturization, like that in the biomedical field where the solution under test may be a biofilm.
    Full-text · Conference Paper · Jul 2006
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    ABSTRACT: There is a clear need for in situ monitoring of oxidation–reduction potential (ORP) in many environmental applications, particularly those involving water quality monitoring and wastewater treatment. This paper describes fabrication of microelectrode sensor arrays for measurements of ORP in situ in the environment, such as at Superfund sites. The four-probe microelectrode arrays were fabricated from glass using a two-step, HF-based meniscus etching process. The tip size of individual microelectrodes was approximately 200 nm. The electrochemical performance of these ORP electrodes was fully characterized by measuring redox potentials of standard and reference solutions. When compared with commercial milli-electrodes, the microelectrode arrays exhibited very fast response time (from a few milliseconds to 30 s) and proved to be extraordinarily stable (variability on the order of 2 mV over a 4-day test period). This successful development of microelectrode arrays for ORP measurements will enable in situ measurement of redox potentials in the environment, such as contaminated soils, biofilm or sediments at Superfund sites.
    Full-text · Article · May 2006 · Sensors and Actuators B Chemical
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    ABSTRACT: Microelectrodes have been developed over the last few years with tip diameters of 1-10 μm, but they are fragile and susceptible to electrical interference. In addition, they are difficult to manufacture and operate, and are often unsuitable for measurement in small volumes of liquid or in soils. This limits their use to specialized laboratories under highly controlled conditions. The paper introduces a robust, self-contained, inexpensive MEMS based microelectrode sensor that can be used in situ environments. It deals with the design, analysis and performance of circuitry for a microelectrode sensor. The primary focus is to design, implement and integrate a CMOS circuit with the MEMS device to process, amplify and transmit the signal from the microelectrode to a measuring instrument. A current sensing circuit is developed for amperometric measurement with the microelectrode array. The magnitude of the output signal is dependent on the characteristics of the liquid being evaluated by the system. A printed circuit board (PCB) has been built to integrate the microelectrode sensor array along with the sensor chip with the aim of producing a fully integrated system.
    Full-text · Conference Paper · Sep 2005
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    ABSTRACT: The need for accurate, robust in situ microscale monitoring of oxidation-reduction potentials (ORP) is required for continuous soil pore water quality monitoring. We are developing a suite of self-contained microelectrodes that can be used in the environment, such as at Superfund sites, to monitor ORP in contaminated soils and sediments. This paper presents details on our development of microelectrode sensor arrays for ORP measurements. The electrochemical performance of these ORP electrodes was fully characterized by measuring redox potentials in standard solutions. It found that the newly developed integrated ORP microelectrodes produced a very stable voltage response (the corresponding rate of the integrated microelectrode potential change was in the range of 0.6-1.1 mV/min), even when the measurement was carried out outside of a Faraday cage where signals from most conventional microelectrodes are usually inhibited by external electrical nose. These new microelectrodes were easier to fabricate and were more robust than conventional microelectrodes. The tip size of the integrated ORP microelectrode was approximately 200 nm square, with a taper angle of approximately 20 degrees and a length of 57 microm. The integrated ORP microelectrode exhibited better signal stability and substantially shorter response times (from less than a few milliseconds to 30 s, depending on the standard solution used) than the commercial millielectrode (a few minutes). Compared with the slope of the commercial millelectrode, the slope of the integrated microelectrode (61.5 mV/pH) was closerto the ideal slope against quinhydrone calibration solutions. Therefore, it is to be expected that the newly developed ORP microelectrode may have wider applications in contaminated soils, biofilms, and sediments.
    Full-text · Article · Sep 2005 · Environmental Science and Technology
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    ABSTRACT: This paper describes a microelectrode array (MEA) sensor system for measurements of oxidation-reduction potentials (ORP) in situ in the environment. The four-probe MEAs were fabricated from glass using a two-step, HF-based meniscus etching process. A CMOS ASIC chip was developed for signal acquisition and processing and packaged with the microelectrode sensors to reduce noise. The electrochemical performance of these ORP MEAs was fully characterized by measuring redox potentials of standard and reference solutions. The MEAs exhibited a substantially faster response time, proved to be extraordinarily stable, and were independent of the microelectrode position within the array.
    No preview · Conference Paper · Jul 2005
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    ABSTRACT: In North America, approximately 30,000 people annually suffer an aneurismal subarachnoid hemorrhage (SAH). Using computerized tomography (CT), the blood is generally not visible after 12 hours. Currently lumbar puncture (LP) results are equivocal for diagnosing SAH largely because of technical limitations in performing a quick and objective evaluation. Having ruptured once, an aneurysm is statistically more likely to rupture again. Therefore, for those individuals with a sentinel (or warning) hemorrhage, detection within the first 12 hours is paramount. We present a diagnostic technology based on visible spectroscopy to quickly and objectively assess low-blood volume SAH from a diagnostic spinal tap. This technology provides clinicians, with the resources necessary for assessing patients with suspected aneurismal SAH beyond the current 12-hour limitation imposed by CT scans. This aids in the improvement of patient care and results in rapid and appropriate treatment of the patient. To perform this diagnosis, we quantify bilirubin and hemoglobin in human CSF over a range of concentrations. Because the bilirubin and hemoglobin spectra overlap quantification is problematic. To solve this problem, two algorithmic approaches are presented: a statistical or a random stochastic component known as Partial Least Square (PLS) and a control theory based mathematical model. These algorithms account for the noise and distortion from blood in CSF leading to the quantification of bilirubin and methemoglobin spectroscopically. The configurations for a hardware platform is introduced, that is portable and user-friendly composed of specific components designed to have the sensitivity and specificity required. This aids in measuring bilirubin in CSF, hemorrhagic-CSF and CSF-like solutions. The prototype uses purpose built algorithms contained within the platform, such that physicians can use it in the hospital and lab as a point of care diagnostic test.
    No preview · Article · Apr 2005 · Proceedings of SPIE - The International Society for Optical Engineering
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    ABSTRACT: This work presents the mixed mode integrated circuit design. The development of SOC technology, CAD and simulation resources are providing system and chip designers with design tools necessary for successfully completing fully integrated CMOS hardware. The design methodology and new CAD/simulation tools allow the design engineer to focus on the mixed mode integrated circuit design without losing chip functionality or system level performance specifications. Integrated circuits-are designed, prototypes are fabricated, layout implemented and tested with varying degrees of automation. Very large scale integration (VLSI) systems have digital and analog components on the same chip. This shift from purely digital to mixed-signal (MS) systems is due to the high values of operating frequencies in communication circuits and shrinking feature sizes. Hardware description languages and simulators and automatic design software programs (called synthesizers) describe the functionality of each module as a "simulatable" model (also called a virtual prototype) and redesign or modification of the requirements is necessary if model need to meet the functional requirements of the module.
    No preview · Article · Mar 2005 · IEEE Potentials
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    ABSTRACT: Cerebral aneurysm is defined as a weakened portion of an artery in the brain. Its rupture leads to a specific case of bleeding known as a subarachnoid hemorrhage (SAH). Literature indicates that a significant portion of patients suffering from SAH are initially misdiagnosed and subjected to the risks associated with aneurysm re-rupture. Traditional methods of detection that are recommended by the physicians include computer tomography (CT) scan, lumbar puncture (LP) and angiogram. Unfortunately, CT scan is ineffective after 12 hours, and angiogram only applicable in cases of finding the aneurysm before surgery. This paper discusses the invasive technique of lumbar puncture because of the technical limitations in performing a quick and objective evaluation. Bilirubin, resulting from the chemical decomposition of whole blood is a clear indicator a hemorrhage. This metabolite can be detected after a spinal tap, by differentiating its optical signature from that of fresh whole blood. We introduce the development of a diagnostic system that is based on visible spectroscopy to quickly and objectively assess low-blood volume SAH. The system integrates innovative hardware and a powerful software interface. The paper explores algorithms that accounts for the noise and distortion from blood in CSF. Furthermore, a hardware platform is introduced, that is portable and user-friendly composed of specific components designed to have the sensitivity and specificity.
    No preview · Conference Paper · Jan 2005

Publication Stats

201 Citations
43.44 Total Impact Points

Institutions

  • 2010
    • Doheny Eye Institute
      Los Ángeles, California, United States
  • 2007-2010
    • University of Southern California
      • • Doheny Eye Institute
      • • Keck School of Medicine
      Los Ángeles, California, United States
  • 2008
    • University of California, Los Angeles
      • Department of Ophthalmology
      Los Ángeles, California, United States
  • 2001-2006
    • University of Cincinnati
      • Department of Electrical and Computer Engineering and Computer Science
      Cincinnati, OH, United States