Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
  • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
  • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/145—Measuring characteristics of blood in vivo, e.g. gas concentration, pH value; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid, cerebral tissue
  • A61B5/1455—Measuring characteristics of blood in vivo, e.g. gas concentration, pH value; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid, cerebral tissue using optical sensors, e.g. spectral photometrical oximeters
  • A61B5/14551—Measuring characteristics of blood in vivo, e.g. gas concentration, pH value; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid, cerebral tissue using optical sensors, e.g. spectral photometrical oximeters for measuring blood gases
  • A61B5/14552—Details of sensors specially adapted therefor
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
  • G01J3/02—Details
  • G01J3/0205—Optical elements not provided otherwise, e.g. optical manifolds, diffusers, windows
  • G01J3/0232—Optical elements not provided otherwise, e.g. optical manifolds, diffusers, windows using shutters

Definitions

• Spectrophotomet ⁇ c-type instruments are known and used in a variety of applications
• An instrument of this type is, for example, disclosed in the Anderson et al U S Patent 5,879,294 There remains, however, a continuing need for instruments capable of providing measurement to a higher degree of accuracy with relatively low levels of output signal drift
• FIG. 1 is block diagram of an instrument useful in the practice of the present invention, along with a probe connector and optical probe connected by optical fibers and a calibration device
• FIG. 2 is a detailed view of the probe connector shown in Figure 1
• Figure 3 is an isometric view of one embodiment of a shutter and path shifting optics useful in the practice of the present invention
• Figure 4 is an illustration of a detector for use in the practice of the present invention
• Figure 5 is a set of graphs representing the characteristic drift for each channel for conventional (prior art) instrument
• Figure 6 is a set of graphs illustrating signal drift trends for an instrument according to the present invention
• Figure 7 is a pair of graphs illustrating uncompensated and compensated St0 2 signal drift over the same time conditions of the graphs of Figure 6
• Figure 8 is a view of an alternative embodiment of the probe connector of Figure 2
• Figure 9 is a view of a first alternative reflector plate for probe tip optical fibers useful in the practice of the present invention
• igure is an exp o e view o t e em o iment o igure s owing a through hole fiber fixture, along with a second alternative embodiment for a reflector plate and side groove fiber fixture
• Figure 1 1 is a simplified section view of the first alternative embodiment reflector plate and fiber fixture
• the instrument 10 includes an optical probe 12 which is releasably connected to an electronics package 14 via optical fibers 16
• the electronics package 14 includes a connector 18, a detector 20, a processor/controller 22, and a display 24
• the probe 12 is positioned on the tissue to be measured or analyzed
• the probe 12 is interfaced to the instrument electronics through the optical fibers 16 and a probe connector 26
• the probe connector 26 includes light emitting diodes (LEDs) or other light sources 30, 32, 34, 36, and 38 for generating light at a number of different wavelengths (e g , 800, 760, 720, 680, and 530 nm, respectively)
• the light used to measure the characteristics of the tissue is coupled to the probe by send optical fibers 40, 42, 44, and 46 After being transmitted from the tissue- engaging surface of the probe 12 into the tissue being measured, the light will travel through the tissue before being collected at the end of the receive optical fibers 40, 42, 44, and 46 After being transmitted from the tissue- engaging surface of the probe 12 into the
• the collected measurement light signals and reference light signals received by the electronics package 14 are transmitted to the detector 20 which produces electrical signals representative of these light signals at each wavelength of interest
• the processor/controller 22 then processes these signals to generate data representative of the measured tissue parameter (e g , saturated oxygen level (StO 2 ))
• the measurement reading can be visually displayed on the display 24
• Algorithms used to compute the tissue parameter data are generally known and described in the Anderson et al U S Patent 5,879,294
• the calibration can, for example, be performed by placing the probe 12 on a calibration device 50 such as that shown in Figure 1
• the calibration device 50 includes a housing which is filled with light scattering material
• the light scattering material is generally spectrally flat (1 e , reflects all light to the same degree) to provide a reference spectrum White polyethylene foam such as Plastazote LD45 available from Zotefoams pic can be used for this purpose
• One configuration of a spectrophotomet ⁇ c instrument of the type described above includes, for each wavelength of interest, a photomultip er tube (PMT) for detecting the measurement light signal, and a photodiode for detecting the calibration recognition signal (or ambient light)
• PMT photomultip er tube
• Photodiode for detecting the calibration recognition signal (or ambient light)
• Thermal electric coolers can be included in the electronics package to help maintain temperature control of the optical bench to which the PMTs and photodiodes are mounted, and thereby reduce output signal drift
• the present invention is an optical bench configuration, measurement and reference signal acquisition system and measurement and reference signal processing algorithm which provide relatively low levels of output signal drift
• the probe connector 26 used in connection with this invention is illustrated in Figure 2, which shows an embodiment having a reference signal generated within the connector
• the probe connector 26 includes 4 LED's 30, 32, 34, and 36 for generating the measurement light signals at 800, 760, 720 and 680 nm
• Light signals from each of these LEDs are coupled to the probe 12 by a separate measurement signal send fiber 40, 42, 44, 46
• the measurement light signal is coupled back to the probe connector by a measurement signal receive fiber 48
• the end of the measurement signal receive fiber 48 terminates in the probe connector 26 at a sample ferrule 52 which is adapted to mate with a socket in the connector 18 of the electronics package 14
• a reference light signal is also provided by the probe connector 26
• the reference light signal includes a portion of the light from each of the LEDs, and has not been transmitted from the probe before being collected
• the reference light signal is collected by reference light signal send optical fibers 54, 56, 58 and 60, which extend respectively from each measurement light signal source LED 30, 32, 34, 36 to a light mixer/attenuator 62 formed by scattering material attached to a reference fiber fixtu ⁇ ng ferrule 64
• the reference signal send fibers 54, 56, 58, 60 are collected in the fixtu ⁇ ng ferrule 64 at the scattering material along with a reference signal receive fiber 66
• the reference light received from each LED is mixed at the mixer 62 and transmitted through the reference signal receive fiber 66
• the end of the reference signal receive fiber 66 terminates in the probe connector 26 at a reference ferrule 68 which is adapted to mate with a socket in the connector 18 of the electronics package 14 Since it is significantly attenuated when it is transmitted through the tissue, the intensity of the
• the reference light signal and measurement light signal (also referred to as a sample light signal) received at the connector at spatially separated paths are collimated by lenses or other optics and directed to a shutter and path- shifting optics 80 ( Figure 3)
• the shutter and path-shifting optics 80 selectively and alternately direct or fold the signals into a common path to the detector (optical bench)
• a 30 degree stepper motor 82 drives opaque vane 84 and is controlled by the processor/controller 22, as indicated by arrow 86
• the stepper motor 82 positions the vane 84 to selectively block one of the reference light signal and measurement light signal, and to transmit the other of signals to the path shifting optics
• Arrow 88 indicates a collimated LED reference light path
• arrow 90 indicates a collimated measurement/sample light path (from the probe 12)
• the path shifting optics includes a 45° combining (beam splitting) mirror 92 in the measurement light path 94
• This combining mirror allows a significant portion (e g , 98-99%) of the measurement light signal to pass through the mirror to the detector 20 as indicated by arrow 96, with the remaining amount (e g , 1 -2%) being reflected away from the detector (I e , trapped, as indicated by arrow 98)
• a 45° reflecting mirror 100 in the reference light path 102 reflects the reference light signal onto the side of the combining mirror opposite the side to which the measurement light signal is initially directed
• a significant portion of the reference light signal will then pass through the combining mirror, while a smaller amount (e g , 1-2%) will be reflected to the detector along the same optical path 96 as the measurement light signal
• the measurement light signal and reference light signal are thereby directed or folded onto the same path 96 and directed to a common detector
• the stepper motor 82 will position the opaque vane 84 to block
• FIG 4 is an illustration of a detector 20 for use in the instrument 10 or electronics package 14 shown in Figure 1 and described above
• An approximate 5mm diameter collimated light beam indicated by arrow 104 (either from the reference or sample (measurement) light signal) is transmitted to the front surface of an 800 nm dichroic mirror 106 which is positioned 30° from the optical axis 108 Approximately 90%) of the light having a wavelength greater than 780nm is reflected to the first photomultipher tube (PMT) sensor 110 which has a 800nm bandpass filter (+/- lOnm FWHM) positioned in front of the PMT sensor 110 Approximately 80% of the light having a wavelength shorter than 780nm is transmitted through the 800nm dichroic mirror 106 to the front surface of a 760 nm dichroic mirror 112 which is positioned 25° from the optical axis 108 Approximately 90% of the light having a wavelength greater than 740nm is reflected to the second PMT sensor 114 which has a 760nm
• the processor/controller 22 calculates for each PMT a corrected sample (measurement) signal
• the corrected sample signal is calculated as a function of the current sample (measurement) signal, the baseline reference signal and the current reference signal (taken at substantially the same time as the current sample signal) using the following formula
• Corrected Sample Current Sample x Baseline Reference / Current Reference n one em o iment t e urrent amp e is a point running average o the live sampled PMT intensity values, the Baseline Reference is a 20 point block average of the LED signals just after a warm-up period, and the Current Reference is a 20 point running average of the live LED reference signals
• the processor/controller 22 calculates the tissue absorbance measurement as a function of the Baseline Sample and the Corrected Sample using the following formula
• the Baseline Sample is a 20 point block average of the PMT intensity values just after the warm-up period (I e , when the probe 12 is placed on the calibration device 50)
• the optical bench configuration, measurement and reference signal acquisition system and measurement and reference signal processing algorithm described above compensate for and greatly reduce the drift of measurement readings made by the instrument
• the instrument continuously switches the light detector between the measurement signal and the reference signal
• the measurement signal traverses a complex electrical and optical path through the instrument and tissue being analyzed
• the reference signal traverses substantially the same path with the exception of the tissue Since many if not most of the signal distortion-causing factors such as thermal drift, aging and certain kinds of noise are common to both the measurement and reference signal paths, the processing system described herein causes these factors to cancel themselves
• a relatively clean and undistorted signal from the tissue can be acquired without the requirement of temperature control, component aging correction, noise reduction or other compensation approaches
• Graph 1 ( Figure 5) is provided for purposes of comparison and represents the characteristic drift for each channel (l e , set of LED reference signal photodiode (PD) and photomultipher (PMT) measurement signal) for a spectrophotomet ⁇ c instrument (unlike the preferred embodiment described above) in which LED coupled photodiode detectors are used to measure and compensate for LED output intensity drift
• PD photodiode
• PMT photomultipher
• the LED feedback signal does not correlate with the PMT signal drift This characteristic invalidates the use of the photodiode signals as a useful approach for correcting for overall signal drift
• the drift on each PMT channel is an additive combination of both the LED output signal and PMT sensitivity (gam) drift
• the plot of calculated and simulated saturated oxygen (1 e , StO 2 , a parameter measured by the instrument) shows that the instrument drifted -4% units over the first 25 hours
• Graph 2 ( Figure 6) illustrates signal drift trends for the preferred embodiment instrument described above every three seconds the measurement was segregated into an actual LED reference signal having approximately 8 times more intensity than the actual probe sample signal
• Plot 160 shows the 680 nm signal drift for both reference and sample with % drift in counts on the ordinate and time in minutes on the abscissa
• Plot 162 shows the 720 nm signal drift for both reference and sample with % drift in counts on the ordinate and time in minutes on the abscissa
• Plot 164 shows the 760 nm signal drift for both reference and sample with % drift in counts on the ordinate and time in minutes on the abscissa
• Plot 166 shows the 800 nm signal drift for both reference and sample with %> drift in counts on the ordinate and time in minutes on the abscissa
• Plot 168 shows optical bench temperature obtained during both reference and sample signal measurements with temperature in degrees C on the ordinate and time in minutes on the abscissa
• Graph 3 ( Figure 7) illustrates how the compensated and uncompensated St0 2 signals drifted during the same time conditions of the intensity drift trends shown in the second graph ( Figure 6)
• Plot 170 shows % St0 2 drift with no drift compensation with % StO2 drift on the ordinate and time in minutes on the abscissa
• Plot 172 shows % St0 2 drift with drift compensation with % StO2 drift on the ordinate and time in minutes on the abscissa
• the drift corrected St0 2 signal in plot 172 of Graph 3 ( Figure 7) is calculated from 3 second PMT intensity values compensated in accordance with the formulas described above Within the calculation the LED reference signal is time averaged longer than the sample signal in order to minimize the influence of noise on the reference signal measurement It has been determined from tests of the optical bench temperature oscillations (period of approximately 3 minutes) that pulse width modulation control of the thermal electric coolers induced excessive noise within the compensated StO 2 signal As long as the reference and sample signal track accurately it appears reasonable to let the PMT temperature float with ambient temperature in order to avoid excessive oscillation of the intensity values It is evident from Graph 3 ( Figure 7) that the compensated StO 2 signal (with the thermal electric coolers removed) is more stable than the uncompensated signal and that the mean compensated StO 2 signal did not significantly drift when the live PMT signal intensities were forced to drift nearly 20% from the baseline values
• Figures 8-1 1 illustrate an alternative optical approach for obtaining the reference light signal Rather than collecting the reference light signal from within the probe connector (I e , there is no reference light from within the probe connector), a portion of the measurement light signal in the send fibers 40-46 (before it reaches the probe tip), is reflected back to (I e , is intercepted by) a reference receive fiber 248 by a reflector Several reflector options are shown
• Figures 9, 10 and 11 show a first option for a reflector plate for probe tip optical fibers
• a second option for the reflector plate is shown in Figure 10
• a retaining sleeve 174 surrounds a through hole fiber fixture 176 (in the first option) or a side groove fiber fixture 178 (in the second option)
• Reflector plate 180 is used in the first option, while reflector plate 182 is used in the second option
• the 800 nm signal fiber 40, the 760 nm signal fiber 42, the 720 nm signal fiber 44, and the 680 nm signal fiber 46 surround the reference receive fiber 248
• Reflector plate 180 has a concave surface in front of the reference fiber 248, as may be seen most clearly in Figure 1 1
• the reflector plate 180 acts as a one way light collector Light backscattered from a measurement surface cannot enter the reference receive fiber 248 as illustrated by arrow 184 indicating light backscattered from the sample
• the concave inside surface 186 reflects a portion of the e
• the invention offers important advantages
• the LED feedback photodiodes and associated hardware of conventional prior art instruments can be removed LED output drift is measured in combination with PMT drift with the dual optical path shutter configuration
• there is no need for thermal electric coolers and associated hardware for maintaining precise temperature control of the optical bench Since there is no need for thermal electric coolers, the instrument power supply can be downsized to better match the monitor power consumption
• Dual axial muffin fans can be used to provide an even forced air convection around the PMTs and optical bench to maintain the temperature of these components near ambient

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• 2000
  • 2000-06-01 WO PCT/US2000/015157 patent/WO2000075638A1/en not_active Application Discontinuation
  • 2000-06-01 EP EP00936460A patent/EP1183522A1/en not_active Ceased
  • 2000-06-01 JP JP2001501864A patent/JP2003501652A/ja active Pending
  • 2000-06-01 AU AU51775/00A patent/AU5177500A/en not_active Abandoned

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