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Akl TJ, Wilson MA, Ericson MN, Farquhar E, Coté GL. Wireless monitoring of liver hemodynamics in vivo. PLoS One 2014; 9:e102396. [PMID: 25019160 PMCID: PMC4097065 DOI: 10.1371/journal.pone.0102396] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2014] [Accepted: 06/17/2014] [Indexed: 11/19/2022] Open
Abstract
Liver transplants have their highest technical failure rate in the first two weeks following surgery. Currently, there are limited devices for continuous, real-time monitoring of the graft. In this work, a three wavelengths system is presented that combines near-infrared spectroscopy and photoplethysmography with a processing method that can uniquely measure and separate the venous and arterial oxygen contributions. This strategy allows for the quantification of tissue oxygen consumption used to study hepatic metabolic activity and to relate it to tissue stress. The sensor is battery operated and communicates wirelessly with a data acquisition computer which provides the possibility of implantation provided sufficient miniaturization. In two in vivo porcine studies, the sensor tracked perfusion changes in hepatic tissue during vascular occlusions with a root mean square error (RMSE) of 0.135 mL/min/g of tissue. We show the possibility of using the pulsatile wave to measure the arterial oxygen saturation similar to pulse oximetry. The signal is also used to extract the venous oxygen saturation from the direct current (DC) levels. Arterial and venous oxygen saturation changes were measured with an RMSE of 2.19% and 1.39% respectively when no vascular occlusions were induced. This error increased to 2.82% and 3.83% when vascular occlusions were induced during hypoxia. These errors are similar to the resolution of a commercial oximetry catheter used as a reference. This work is the first realization of a wireless optical sensor for continuous monitoring of hepatic hemodynamics.
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Affiliation(s)
- Tony J. Akl
- Department of Biomedical Engineering, Texas A&M University, College Station, Texas, United States of America
- * E-mail:
| | - Mark A. Wilson
- Department of Surgery, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America
- Veterans Affairs Pittsburgh Healthcare System, Pittsburgh, Pennsylvania, United States of America
| | - M. Nance Ericson
- Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States of America
| | - Ethan Farquhar
- Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States of America
| | - Gerard L. Coté
- Department of Biomedical Engineering, Texas A&M University, College Station, Texas, United States of America
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Hu S, Azorin-Peris V, Zheng J. Opto-physiological modeling applied to photoplethysmographic cardiovascular assessment. JOURNAL OF HEALTHCARE ENGINEERING 2014; 4:505-28. [PMID: 24287429 DOI: 10.1260/2040-2295.4.4.505] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
This paper presents opto-physiological (OP) modeling and its application in cardiovascular assessment techniques based on photoplethysmography (PPG). Existing contact point measurement techniques, i.e., pulse oximetry probes, are compared with the next generation non-contact and imaging implementations, i.e., non-contact reflection and camera-based PPG. The further development of effective physiological monitoring techniques relies on novel approaches to OP modeling that can better inform the design and development of sensing hardware and applicable signal processing procedures. With the help of finite-element optical simulation, fundamental research into OP modeling of photoplethysmography is being exploited towards the development of engineering solutions for practical biomedical systems. This paper reviews a body of research comprising two OP models that have led to significant progress in the design of transmission mode pulse oximetry probes, and approaches to 3D blood perfusion mapping for the interpretation of cardiovascular performance.
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Affiliation(s)
- Sijung Hu
- School of Electronic, Electrical and Systems Engineering, Loughborough University, Loughborough Leicestershire LE11 3TU, UK
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Akl TJ, Wilson MA, Ericson MN, Coté GL. Intestinal perfusion monitoring using photoplethysmography. JOURNAL OF BIOMEDICAL OPTICS 2013; 18:87005. [PMID: 23942635 PMCID: PMC3739875 DOI: 10.1117/1.jbo.18.8.087005] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/06/2013] [Revised: 07/15/2013] [Accepted: 07/16/2013] [Indexed: 05/27/2023]
Abstract
In abdominal trauma patients, monitoring intestinal perfusion and oxygen consumption is essential during the resuscitation period. Photoplethysmography is an optical technique potentially capable of monitoring these changes in real time to provide the medical staff with a timely and quantitative measure of the adequacy of resuscitation. The challenges for using optical techniques in monitoring hemodynamics in intestinal tissue are discussed, and the solutions to these challenges are presented using a combination of Monte Carlo modeling and theoretical analysis of light propagation in tissue. In particular, it is shown that by using visible wavelengths (i.e., 470 and 525 nm), the perfusion signal is enhanced and the background contribution is decreased compared with using traditional near-infrared wavelengths leading to an order of magnitude enhancement in the signal-to-background ratio. It was further shown that, using the visible wavelengths, similar sensitivity to oxygenation changes could be obtained (over 50% compared with that of near-infrared wavelengths). This is mainly due to the increased contrast between tissue and blood in that spectral region and the confinement of the photons to the thickness of the small intestine. Moreover, the modeling results show that the source to detector separation should be limited to roughly 6 mm while using traditional near-infrared light, with a few centimeters source to detector separation leads to poor signal-to-background ratio. Finally, a visible wavelength system is tested in an in vivo porcine study, and the possibility of monitoring intestinal perfusion changes is showed.
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Affiliation(s)
- Tony J Akl
- Texas A&M University, Department of Biomedical Engineering, 5045 Emerging Technologies Building, 3120 TAMU, College Station, Texas 77843-3120, USA.
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Akl TJ, King TJ, Long R, McShane MJ, Nance Ericson M, Wilson MA, Coté GL. Performance assessment of an opto-fluidic phantom mimicking porcine liver parenchyma. JOURNAL OF BIOMEDICAL OPTICS 2012; 17:077008. [PMID: 22894521 PMCID: PMC3394684 DOI: 10.1117/1.jbo.17.7.077008] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/20/2011] [Revised: 06/06/2012] [Accepted: 06/14/2012] [Indexed: 06/01/2023]
Abstract
An implantable, optical oxygenation and perfusion sensor to monitor liver transplants during the two-week period following the transplant procedure is currently being developed. In order to minimize the number of animal experiments required for this research, a phantom that mimics the optical, anatomical, and physiologic flow properties of liver parenchyma is being developed as well. In this work, the suitability of this phantom for liver parenchyma perfusion research was evaluated by direct comparison of phantom perfusion data with data collected from in vivo porcine studies, both using the same prototype perfusion sensor. In vitro perfusion and occlusion experiments were performed on a single-layer and on a three-layer phantom perfused with a dye solution possessing the absorption properties of oxygenated hemoglobin. While both phantoms exhibited response patterns similar to the liver parenchyma, the signal measured from the multilayer phantom was three times higher than the single layer phantom and approximately 21 percent more sensitive to in vitro changes in perfusion. Although the multilayer phantom replicated the in vivo flow patterns more closely, the data suggests that both phantoms can be used in vitro to facilitate sensor design.
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Affiliation(s)
- Tony J. Akl
- Texas A&M University, Department of Biomedical Engineering, 5045 Emerging Technologies Building, 3120 TAMU, College Station, Texas 77843-3120
| | - Travis J. King
- Texas A&M University, Department of Biomedical Engineering, 5045 Emerging Technologies Building, 3120 TAMU, College Station, Texas 77843-3120
| | - Ruiqi Long
- Texas A&M University, Department of Biomedical Engineering, 5045 Emerging Technologies Building, 3120 TAMU, College Station, Texas 77843-3120
| | - Michael J. McShane
- Texas A&M University, Department of Biomedical Engineering, 5045 Emerging Technologies Building, 3120 TAMU, College Station, Texas 77843-3120
| | - M. Nance Ericson
- Oak Ridge National Laboratory, P.O. Box 2008, MS 6006, Oak Ridge, Tennessee 37831-6006
| | - Mark A. Wilson
- University of Pittsburgh, Department of Surgery, 200 Lothrop Street, Pittsburgh, Pennsylvania 15213
- University Dr. C-1w142, Veterans Affairs Healthcare System, Pittsburgh, Pennsylvania 15240
| | - Gerard L. Coté
- Texas A&M University, Department of Biomedical Engineering, 5045 Emerging Technologies Building, 3120 TAMU, College Station, Texas 77843-3120
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Akl TJ, Long R, McShane MJ, Ericson MN, Wilson MA, Coté GL. Optimizing probe design for an implantable perfusion and oxygenation sensor. BIOMEDICAL OPTICS EXPRESS 2011; 2:2096-109. [PMID: 21833350 PMCID: PMC3149511 DOI: 10.1364/boe.2.2096] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Subscribe] [Scholar Register] [Received: 05/12/2011] [Revised: 06/27/2011] [Accepted: 06/28/2011] [Indexed: 05/29/2023]
Abstract
In an effort to develop an implantable optical perfusion and oxygenation sensor, based on multiwavelength reflectance pulse oximetry, we investigate the effect of source-detector separation and other source-detector characteristics to optimize the sensor's signal to background ratio using Monte Carlo (MC) based simulations and in vitro phantom studies. Separations in the range 0.45 to 1.25 mm were found to be optimal in the case of a point source. The numerical aperture (NA) of the source had no effect on the collected signal while the widening of the source spatial profile caused a shift in the optimal source-detector separation. Specifically, for a 4.5 mm flat beam and a 2.4 mm × 2.5 mm photodetector, the optimal performance was found to be when the source and detector are adjacent to each other. These modeling results were confirmed by data collected from in vitro experiments on a liver phantom perfused with dye solutions mimicking the absorption properties of hemoglobin for different oxygenation states.
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Affiliation(s)
- Tony J. Akl
- Department of Biomedical Engineering, Texas A&M University, 337 Zachry Engineering Center, 3120 TAMU, College Station, TX 77843-3120, USA
| | - Ruiqi Long
- Department of Biomedical Engineering, Texas A&M University, 337 Zachry Engineering Center, 3120 TAMU, College Station, TX 77843-3120, USA
| | - Michael J. McShane
- Department of Biomedical Engineering, Texas A&M University, 337 Zachry Engineering Center, 3120 TAMU, College Station, TX 77843-3120, USA
| | - M. Nance Ericson
- Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831-6006, USA
| | - Mark A. Wilson
- Department of Surgery, University of Pittsburgh, 200 Lothrop Street, Pittsburgh, PA 15213, USA
- Veterans Affairs Healthcare System, University Dr. C-1w142, Pittsburgh, PA 15240, USA
| | - Gerard L. Coté
- Department of Biomedical Engineering, Texas A&M University, 337 Zachry Engineering Center, 3120 TAMU, College Station, TX 77843-3120, USA
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Long R, King T, Akl T, Ericson MN, Wilson M, Coté GL, McShane MJ. Optofluidic phantom mimicking optical properties of porcine livers. BIOMEDICAL OPTICS EXPRESS 2011; 2:1877-92. [PMID: 21750766 PMCID: PMC3130575 DOI: 10.1364/boe.2.001877] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/10/2011] [Revised: 06/03/2011] [Accepted: 06/04/2011] [Indexed: 05/19/2023]
Abstract
One strategy for assessing efficacy of a liver transplant is to monitor perfusion and oxygenation after transplantation. An implantable optical sensor is being developed to overcome inadequacies of current monitoring approaches. To facilitate sensor design while minimizing animal use, a polydimethylsiloxane (PDMS)-based liver phantom was developed to mimic the optical properties of porcine liver in the 630-1000 nm wavelength range and the anatomical geometry of liver parenchyma. Using soft lithography to construct microfluidic channels in pigmented elastomer enabled the 2D approximation of hexagonal liver lobules with 15mm sinusoidal channels, which will allow perfusion with blood-mimicking fluids to facilitate the development of the liver perfusion and oxygenation monitoring system.
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Affiliation(s)
- Ruiqi Long
- Department of Biomedical Engineering, Texas A&M University, 337 Zachry Engineering Center, 3120 TAMU, College Station, TX 77843-3120, USA
| | - Travis King
- Department of Biomedical Engineering, Texas A&M University, 337 Zachry Engineering Center, 3120 TAMU, College Station, TX 77843-3120, USA
| | - Tony Akl
- Department of Biomedical Engineering, Texas A&M University, 337 Zachry Engineering Center, 3120 TAMU, College Station, TX 77843-3120, USA
| | | | - Mark Wilson
- Department of Surgery, University of Pittsburgh, Pittsburgh, PA 15213, USA
- Pittsburgh VA Healthcare System, Pittsburgh, PA 15240, USA
| | - Gerard L. Coté
- Department of Biomedical Engineering, Texas A&M University, 337 Zachry Engineering Center, 3120 TAMU, College Station, TX 77843-3120, USA
| | - Michael J. McShane
- Department of Biomedical Engineering, Texas A&M University, 337 Zachry Engineering Center, 3120 TAMU, College Station, TX 77843-3120, USA
- Materials Science and Engineering Program, Texas A&M University, College Station, TX 77843, USA
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Baba JS, Letzen BS, Ericson MN, Cote GL, Xu W, Wilson MA. Development of a multispectral tissue characterization system for optimization of an implantable perfusion status monitor for transplanted liver. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2009; 2009:6565-6568. [PMID: 19964906 DOI: 10.1109/iembs.2009.5334499] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Optimizing wavelength selection for monitoring perfusion during liver transplant requires an in-depth characterization of liver optical properties. With these, the impact of liver absorption and scattering properties can be investigated to select optimal wavelengths for perfusion monitoring. To accomplish this, we are developing a single integrating-sphere-based technique using a unique spatially resolved diffuse reflectance system for multispectral optical properties determination for thick samples. We report early results using a monochromatic source to measure the optical properties of well characterized tissue phantoms made from polystyrene spheres and Trypan blue. The presented results demonstrate the feasibility of using this unique system to measure optical properties of tissue phantoms. We are currently in the process of implementing an automated Levenberg-Marquardt diffuse-reflectance-profile fitting algorithm to enable near realtime robust computation of sample optical properties. Future work will focus on the incorporation of multispectral capability to provide needed data to facilitate development of more realistic liver tissue phantoms.
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Affiliation(s)
- J S Baba
- Measurement Science & Systems Engineering Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
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