Ischemia Sensing Smart Organ Retractor _____________________________________________________________

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Ischemia Sensing Smart Organ Retractor___________
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Background Presentation
Optical Properties of Native and Coagulated
Human Liver Tissue and Liver Metastases in the
Near Infrared Range, Germer et. al, Lasers in
Surgery and Medicine, 1998. United States
Patent 6,272,363 B1 Pulse Oximeter and Sensor
Optimized for Low Saturation, Casciani et. al,
2001.

• Presented by
• Sunipa Saha
• Mentors
• Greg Fischer,
• Mark A.Talamini, MD

MISTC Lab, Johns Hopkins Hospital03/17/04
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Smart Organ Retractor

• Intraoperative retraction can produce ischemia in
  the affected tissue
• Force and ischemia sensors on the Smart Organ
  Retractor will allow measurement of the effects
  of retractor force on ischemia in the tissue over
  time
• Focus Pulse Oximetry and Optimization of
  Sensor Readings

Courtesy Greg Fischer
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Background Papers

• Germer et. al, Optical Properties of Native and
  Coagulated Human Liver Tissue and Liver
  Metastases in the Near Infrared Range, Lasers in
  Surgery and Medicine 23194-203, 1998.
• Casciani et. al, United States Patent 6,272,363
  B1 Pulse Oximeter and Sensor Optimized for Low
  Saturation, 2001.

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Objectives

• Gain knowledge about optical parameters in human
  liver tissue to improve laser-induced
  thermotherapy (LITT)
• Compare optical properties of healthy hepatic
  tissue and liver metastases at certain
  wavelengths
• Determine the effect of thermocoagulation on the
  optical properties of liver tissue

www.lambdares.com/products/tracepro/laser.phtml
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Thermocoagulation
Germer et. al, 1998
Germer et. al, 1998
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Liver Optical Properties
Background

• Metastases
• cancerous growth formed by transmission of
  cancerous cells from a primary growth elsewhere
• Liver most common site for transmitted
  colorectal carcinomas
• LITT
• Thermal tissue coagulation changes optical
  parameters with temperature

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Liver Optical Properties
Materials Methods

• Liver Metastatic tissue samples
• Collected by partial liver resection
• Parameters measured
• Macroscopic absorption, scattering, anisotropy,
  penetration depth
• Diffuse remission
• Total transmission
• Collimated transmission
• Wavelengths 850, 980, 1064 nm

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Experimental Setup
Sensor
Warm Water BathThermocoagulation
Measure Optical Parameters
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Experimental Setup
Germer et. al, 1998
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Analysis

• Inverse Monte Carlo simulation
• Initial set of optical properties estimated
• Take into consideration geometric and optical
  properties
• If measured data - calculated values lt error
  threshold, set of optical parameters accepted
• Validation
• Intraindividual samples were checked for
  significant differences

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Results

• Absorption ? as Wavelength ?
• Healthy Absorption, Scattering, Anisotropy
  higher
• Metastatic Optical Penetration higher
• Less hemoglobin, DNA, etc...
• Thermocoagulation
• ? Absorption, ? Scattering, ? Anisotropy
• ? Penetration
• Statistically significant differences between
  tissue types

Germer et. al, 1998
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Conclusions

• Light diffusion affects accuracy of laser
  therapy
• In LITT, parameters must change during therapy
  for optimal results
• Assessment Possible Future Work
• More tissues samples
• Should provide a method for analyzing optical
  parameters during the LITT procedure, without
  having to resect the liver

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Significance

• Necrotic tissue may allow more light through
  because of higher optical penetration
• Diseased tissues display a combination of
  effects, not only lower absorption ratios
• Other parameters, not just oxygenation level, can
  be used to measure health of retracted tissue

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Background Papers

• Germer et. al, Optical Properties of Native and
  Coagulated Human Liver Tissue and Liver
  Metastases in the Near Infrared Range, Lasers in
  Surgery and Medicine 23194-203, 1998.
• Casciani et. al, United States Patent 6,272,363
  B1 Pulse Oximeter and Sensor Optimized for Low
  Saturation, 2001.

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Patents

• Abstract
• References
• Figures
• Background of Invention
• Summary of Invention
• Brief Description of Drawings
• Detailed Description of Preferred Embodiments
• Claims

www.premierpatents.com/us-patent-office-search-la
w.htm
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Objective

• Pulse oximeter sensor optimized for reading low
  oxygen saturation levels
• Minimizing perturbation induced artifact (noise
  and scattering)

• Sensors for monitoring oxygen levels of fetus
  during labor and of cardiac patients

www.wardray-premise.com/engineering_services.htm
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Perturbation Induced Artifacts

• Differences in Tissue Composition
• Fat, bone, skin, muscle, arteries, etc
• Differences in Hemoglobin Concentration
• Differences in Force applied to Tissue

Casciani, 2001.
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Pulse Oximetry

• Measures amount of oxygenated hemoglobin in the
  blood
• Usually gt 90 saturation, except for a fetus
  during labor and certain cardiac patients
• Traditional oximeters Red (660nm) and Infrared
  (880-940nm) Light
• Optimum signal transmission through tissue
• Sensitivity to changes in saturation
• Intensity
• Availability of LEDs at desired wavelengths

www.sunled.com/
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Proposed Theories

• Traditionally for selecting wavelengths
• Greatest difference in absorption by oxygenated
  and deoxygenated hemoglobin

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Pulse Oximetry
Casciani, 2001.
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Proposed Theories

• Traditionally for selecting wavelengths
• Where there is greatest difference in absorption
  by oxygenated and deoxygenated hemoglobin
• Optimum pair of wavelengths should also have
  similar absorption and scattering properties
• More accurate readings
• More resistance to artifacts and noise
• Less sensitivity

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Pulse Oximetry
Casciani, 2001.
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Proposed Theories

• The greater the distance between the sensors, the
  more tissue is penetrated, the greater chance of
  perterbation

Casciani, 2001.
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Preferred Embodiment

• Fetal Pulse Oximeter
• Red (700-790nm) and IR (805-940nm)

Casciani, 2001.
Casciani, 2001.
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Significance

• Importance of similar absorption rates
• Placement of sensors
• Use of lasers and fiber optics instead
  ofbicolor LEDs
• Assesment Future Work
• Should describe procedure for insertion and risk
  of causing damage to both mother and child when
  sensor is being placed on fetus head

Smart Organ Retractor, 03/23/05
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Conclusions

• Different parameters for determining when tissue
  is ischemic, or damaged
• Different programs written for necrotic tissue
  vs. healthy liver tissue
• Find LEDs with optimal wavelengths and similar
  absorption patterns
• Placement of sensors on the retractor sheath

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Experiment Trial
MISTC, Johns Hopkins University, 03/24/05