EP3375254A1 - Apparatus and method for projecting light through a light dispersive medium - Google Patents

Apparatus and method for projecting light through a light dispersive medium

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Publication number
EP3375254A1
EP3375254A1 EP16797624.0A EP16797624A EP3375254A1 EP 3375254 A1 EP3375254 A1 EP 3375254A1 EP 16797624 A EP16797624 A EP 16797624A EP 3375254 A1 EP3375254 A1 EP 3375254A1
Authority
EP
European Patent Office
Prior art keywords
light
incident light
medium
backscattered
modifier
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP16797624.0A
Other languages
German (de)
French (fr)
Inventor
Robert James Young
Vincent Reid
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Lancaster University Business Enterprises Ltd
Original Assignee
Lancaster University Business Enterprises Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Lancaster University Business Enterprises Ltd filed Critical Lancaster University Business Enterprises Ltd
Publication of EP3375254A1 publication Critical patent/EP3375254A1/en
Withdrawn legal-status Critical Current

Links

Classifications

    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/43—Detecting, measuring or recording for evaluating the reproductive systems
    • A61B5/4306—Detecting, measuring or recording for evaluating the reproductive systems for evaluating the female reproductive systems, e.g. gynaecological evaluations
    • A61B5/4343—Pregnancy and labour monitoring, e.g. for labour onset detection
    • A61B5/4362—Assessing foetal parameters
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
    • G05D25/00—Control of light, e.g. intensity, colour or phase
    • G05D25/02—Control of light, e.g. intensity, colour or phase characterised by the use of electric means
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/0059—Measuring for diagnostic purposes; Identification of persons using light, e.g. diagnosis by transillumination, diascopy, fluorescence
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/103—Detecting, measuring or recording devices for testing the shape, pattern, colour, size or movement of the body or parts thereof, for diagnostic purposes
    • A61B5/11—Measuring movement of the entire body or parts thereof, e.g. head or hand tremor, mobility of a limb
    • A61B5/1104—Measuring movement of the entire body or parts thereof, e.g. head or hand tremor, mobility of a limb induced by stimuli or drugs
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B8/00—Diagnosis using ultrasonic, sonic or infrasonic waves
    • A61B8/08—Detecting organic movements or changes, e.g. tumours, cysts, swellings
    • A61B8/0866—Detecting organic movements or changes, e.g. tumours, cysts, swellings involving foetal diagnosis; pre-natal or peri-natal diagnosis of the baby
    • 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
    • G01N21/47—Scattering, i.e. diffuse reflection
    • 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
    • G01N21/47—Scattering, i.e. diffuse reflection
    • G01N21/4795—Scattering, i.e. diffuse reflection spatially resolved investigating of object in scattering medium
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
    • G02B26/06—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the phase of light
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B8/00—Diagnosis using ultrasonic, sonic or infrasonic waves
    • A61B8/48—Diagnostic techniques
    • A61B8/483—Diagnostic techniques involving the acquisition of a 3D volume of data
    • 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
    • G01N21/47—Scattering, i.e. diffuse reflection
    • G01N2021/4704—Angular selective
    • G01N2021/4709—Backscatter
    • 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
    • G01N21/47—Scattering, i.e. diffuse reflection
    • G01N21/49—Scattering, i.e. diffuse reflection within a body or fluid
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
    • G02B26/08—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light
    • G02B26/0816—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light by means of one or more reflecting elements
    • G02B26/0833—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light by means of one or more reflecting elements the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD

Definitions

  • the present invention relates to light dispersive media, and in particular to an apparatus and a method for projecting light, such as a two dimensional pattern or image, through such media.
  • the term "light dispersive" is used to refer to the spatial dispersion of light caused by scattering of light by a medium. This is distinct from chromatic dispersion where the phase velocity of light (and its angle of refraction) is dependent on its frequency.
  • dispersion can be considered independently for each beam, as it takes a unique path through the material and has its phase relationship with respect to the other beams modified. As a beam travels through the material it scatters randomly, changing the phase and direction of the beam.
  • the light field exiting the material can be considered as an array of individual beams with an amplitude and phase relation that differs from how the input field would have evolved through free space (to Af(xf,yt)) by a time-varying dispersion factor (to give a final field in the form A(xf,yf).D(x,y,t)).
  • the pattern or image may become blurred and difficult to see. As the depth of the light dispersive medium is increased, this blurring effect becomes more pronounced, and the ability to discern the original image is rapidly diminished.
  • apparatus for use in the projection of incident light through a medium, the apparatus comprising a light modifier for modifying at least one characteristic of the incident light, before interaction between the incident light and the medium, a controller for the light modifier, and a detector for detecting an intensity of light backscattered by the medium, wherein the detector is configured to provide a feedback signal to the controller for the light modifier that is dependent on the intensity of backscattered light detected, and the controller is configured to determine the modification of at least one characteristic of the incident light that is applied by the light modifier, in use, using an optimisation algorithm having the feedback signal as a parameter.
  • the apparatus according to the invention is advantageous principally as the detector is configured to provide a feedback signal to the controller for the light modifier that is dependent on the intensity of backscattered light detected, and the controller is configured to determine the modification of at least one characteristic of incident light that is applied by the light modifier, in use, using an optimisation algorithm having the feedback signal as a parameter.
  • the apparatus may provide compensation for any scattering, or spatial dispersion, effects caused by the medium, by modifying at least one characteristic of incident light, in order to reduce the optical dispersive effect of the medium.
  • the apparatus may enable the size, ie cross-sectional or transverse size, of the projected beam or image to be reduced relative to non-modified incident light, and relative to prior art apparatus and methods.
  • the intensity of the projected beam or image may therefore be increased relative to non-modified incident light, and relative to prior art apparatus and methods.
  • the visible spot or image may be better defined, with reduced blurring.
  • the apparatus according to the invention may find particular utility in medical applications, for example in monitoring fetal response to light in utero, or in optical activation of a drug by focussing light through living tissue.
  • the incident light may comprise a two dimensional pattern or image of light.
  • the image may be a complex shape or picture.
  • the apparatus may comprise apparatus for use in the projection of a two dimensional pattern or image of incident light through a medium.
  • backscattered light is meant light that is scattered, or diffusely reflected, upon interaction with a medium, such that the light returns in substantially the opposite direction relative to the direction of the incident light.
  • the backscattered light may be scattered, or diffusely reflected, by any scattering mechanism, for example, Mie scattering, Brillouin scattering, Raman scattering, Rutherford backscattering, Bragg diffraction, or Compton scattering.
  • the backscattered light may arise from an interaction between the incident light and the medium.
  • the backscattered light may arise solely from an interaction between the incident light and the medium.
  • the backscattered light may arise from an interaction between the incident light and the medium, with no interaction with any external applied fields.
  • the medium may be a light dispersive medium, for example a medium which causes the spatial dispersion of light by scattering.
  • the medium may be any medium capable of causing diffuse reflection, for example a medium capable of causing scattering or reflection of light such that an incident ray of light is scattered or reflected at more than one angle.
  • the medium may be living tissue, eg human or animal tissue, which may, for example, comprise any of skin, blood, fat, muscle, or the like.
  • the intensity of backscattered light on which the feedback signal is dependent may exclude any reflection from a first surface, eg the incident surface, of the medium. This may be achieved by either arranging the apparatus to reduce the proportion of this reflected light that is detected (eg via use of Brewster's angle and polarised light), or configuring the controller to remove or lessen the
  • the at least one characteristic of incident light that is modified by the light modifier may be the phase of the incident light, and may be the instantaneous phase of the incident light.
  • the light modifier may therefore be configured to apply a phase shift to incident light.
  • the light modifier may be configured to apply a spatially dependent phase shift to incident light.
  • the phase shift applied may vary across a transverse plane of a field of incident light.
  • the phase shift applied may vary according to the existing phase of the incident light.
  • the phase shift applied to the incident light may at least partially compensate for a phase shift gained by incident light as a result of interaction with a medium, for example a phase shift gained by scattering in the medium.
  • the phase shift applied to incident light may be opposite in value to a phase shift gained by incident light as a result of interaction with the medium. For example, where incident light is phase shifted by a factor of ⁇ /2 as a result of interaction with a medium, the incident light may be phase shifted by a factor of - ⁇ /2 by the light modifier.
  • the phase shift applied to incident light may at least partially cancel out a phase shift gained by incident light as a result of interaction with a medium.
  • the at least one characteristic of the incident light that is modified by the light modifier may affect the intensity of backscattered light detected by the detector.
  • the intensity of the backscattered light may be indicative of the intensity of the projected light, such that increase of the intensity of the backscattered light may increase the intensity of the projected light.
  • backscattered light may be indicative of the size, ie cross-sectional or transverse size, of the projected beam or image, such that increase of the intensity of the backscattered light may reduce the size, ie cross-sectional or transverse size, of the projected beam or image.
  • the at least one characteristic of incident light may therefore be modified, in use, to increase or maximise the intensity of
  • the light modifier may be configured to modify at least one characteristic of incident light continuously during a period of projection.
  • the detector may be configured to provide the feedback signal to the controller either at regular intervals or continuously during a period of projection, and the controller may be configured to use the optimisation algorithm either at regular intervals or
  • the optimisation algorithm may comprise the application of iterative changes to the modification of at least one characteristic of the incident light that is applied by the light modifier, until an optimal or satisfactory feedback signal is obtained.
  • the light modifier may be configured to modify at least one characteristic of the incident light at a rate that is faster than the rate at which the dispersion by the medium varies.
  • the controller may be configured to determine the modification of at least one characteristic of the incident light that is applied by the light modifier, in use, without user intervention.
  • the controller may comprise a microprocessor.
  • the light modifier may comprise at least one phase modulator, for example at least one device capable of modifying the instantaneous phase of the incident light.
  • the at least one phase modulator may comprise an array or grid or matrix of independent phase modulator devices, each connected separately to the controller, for example a two-dimensional (2D) array of phase modulators. Each phase modulator in the array of phase modulators may be configured to modify the instantaneous phase of the incident light.
  • the light modifier may comprise a phase modulator device having an array of operative pixels for receiving the incident light, and the operative pixels may be configured to independently modify the instantaneous phase of the incident light transmitted through the operative pixels.
  • the phase modulator device having an array of operative pixels may include the controller, as an integral component of the device, or may be connectable to an external controller.
  • the light modifier may comprise a microelectromechanical system (MEMS), and may, for example, comprise a micromirror array.
  • MEMS microelectromechanical system
  • An example of a suitable micromirror array is the Digital Light Processing (DLP®) technology available from Texas Instruments.
  • the light modifier may comprise an array of independent phase modulators, for example an array comprising independent phase modulators such as those available from Thor Labs (for example part number LN65S-FC,).
  • the light modifier may have any desired resolution, and may, for example, have a resolution of at least 16 pixels, at least 64 pixels, or at least 256 pixels.
  • the light modifier may be configured to transmit the incident light through a window of the light modifier, eg through only some operative pixels. Furthermore, the light modifier may be configured to change the position of the window, and hence provide a moving light beam or image, without any need for movement of the apparatus. Alternatively, a moving light beam or image may be achieved by a variable optical diversion arrangement, or by moving the apparatus relative to the medium.
  • the detector for detecting the backscattered light may be any detector suitable for detecting light intensity.
  • the detector may comprise a point detector or a 2D detector, and may, for example, comprise a CCD detector, a CMOS detector or the like.
  • the detector may include a lens or other optics for directing the
  • backscattered light onto the detector for example to focus the backscattered light onto a point detector.
  • the feedback signal provided to the controller for the light modifier may be representative of the intensity of backscattered light detected by the detector.
  • the feedback signal may be dependent on the size and shape, eg an image, of the intensity of the backscattered light detected by the detector.
  • the feedback signal provided to the controller may be continuous or pulsed.
  • the feedback signal provided to the controller may be provided at a rate that is faster than the rate at which the dispersion by the medium varies.
  • the apparatus may include a light source for directing incident light towards the medium.
  • the light source may be a spatially coherent light source, and, for example, may be a laser light source.
  • the light source may output incident light at a pre-determined wavelength.
  • the pre-determined wavelength may be chosen dependent on the medium through which it is desired to project light.
  • the predetermined wavelength may be in the region of 100nm to 1500nm, in the region of 200nm to 1400nm, in the region of 400nm to 1200nm, or in the region of 400nm to 700 nm, or in the region of 600-700nm.
  • the pre-determined wavelength may be a wavelength in the visible region of the electromagnetic spectrum.
  • the light source may output incident light at a pre-determined power and/or intensity.
  • the predetermined power and/or intensity may be chosen dependent on the medium through which it is desired to project light.
  • the pre-determined power may be less than 1 mW, less than 10 mW, or less than 100mW.
  • the apparatus may comprise a light focussing device for focussing incident and/or backscattered light, and may, for example, comprise a light focussing device for focussing incident and/or backscattered light either prior to, or after, incident and/or backscattered light has interacted with the medium.
  • the apparatus may comprise at least one lens for focussing incident and/or backscattered light.
  • the apparatus may comprise at least one filter for filtering the incident and/or the backscattered light, and may, for example, comprise at least one filter for filtering the incident and/or the backscattered light either prior to, or after, the incident and/or the backscattered light has interacted with a medium.
  • the apparatus may comprise at least one filter for filtering the backscattered light prior to the backscattered light being detected by the detector.
  • the at least one filter may be configured to allow the passage of only certain wavelengths, or certain ranges of wavelengths, of light.
  • the at least one filter may comprise any, or any combination of, the following: a notch filter; a band-pass filter; a long-pass filter; or a short-pass filter.
  • the at least one filter for filtering the backscattered light prior to the backscattered light being detected by the detector may be configured to transmit backscattered light in a range of wavelengths that corresponds to light that is generated by a specific scattering process.
  • the range of transmitted wavelengths may correspond to light that is generated by a non-linear process. This may improve the sensitivity of the apparatus.
  • Suitable non-linear processes may comprise frequency doubling, four-wave mixing, Raman scattering, or the like.
  • the backscattered light may comprise light having a frequency which is equal to, or a multiple of, the frequency of the incident light, for example light having a frequency which is an integer multiple of the frequency of the incident light.
  • the backscattered light may comprise light having a frequency which is equal to, or a harmonic of, the frequency of the incident light.
  • the at least one filter for filtering the backscattered light prior to the backscattered light being detected by the detector may be configured to transmit backscattered light having a frequency which is equal to, or an integer multiple of, the frequency of the incident light.
  • the detector may be configured to detect backscattered light having a frequency which is equal to, or an integer multiple of, the frequency of the incident light.
  • the apparatus may comprise a power monitor for monitoring the power of the light source.
  • the power monitor for monitoring the power of the light source may comprise an optical intensity monitor which monitors the optical intensity, ie the power transferred per unit area, of the light source.
  • the power monitor may comprise a photodiode or the like.
  • the power monitor may be configured to provide a feedback signal to a controller for the power source, and may, for example, be configured to provide a feedback signal dependent on the monitored optical intensity.
  • the controller for the power source may be configured to increase and/or decrease the power output of the power source, dependent on the feedback of monitored optical intensity, eg to maintain a consistent optical intensity.
  • the apparatus may comprise a first light diverter for diverting at least a portion of incident light to the power monitor, and/or may comprise a second light diverter for diverting at least a portion of backscattered light to the detector for detecting intensity of backscattered light.
  • the first light diverter and the second light diverter may comprise a single component.
  • the first light diverter and/or the second light diverter may comprise a beam-splitter.
  • the apparatus may be enclosed within a housing, such that the apparatus forms a self-contained device.
  • the device may be handheld, ie may be held in the hand of a user, in use, and may be manipulated by a user's hand, in use.
  • the device may be portable.
  • the device may be mains-powered, or battery-powered.
  • a method of projecting incident light through a medium comprising the steps of:
  • the method may utilise the apparatus defined above, such that the light source directs the incident light through the medium, the detector detects an intensity of light backscattered by the medium, the controller for the light modifier determines a modification of at least one characteristic of the incident light that is to be applied, in use, before interaction between the incident light and the medium, using an optimisation algorithm having the intensity of light backscattered by the medium as a parameter, and the light modifier applies the determined modification to the incident light, before interaction between the incident light and the medium.
  • the method may comprise directing incident light through a light dispersive medium, for example a medium which causes the spatial dispersion of light by scattering.
  • the medium may be any medium capable of causing diffuse reflection, for example a medium capable of causing scattering or reflection of light such that an incident ray of light is scattered or reflected at more than one angle.
  • the medium may be living tissue, eg human or animal tissue, which may, for example, comprise any of skin, blood, fat, muscle, or the like.
  • the method may comprise modifying the phase, eg the instantaneous phase, of the incident light.
  • the modification of the phase of the light may be spatially dependent.
  • the phase shift applied may vary across a transverse plane of a field of incident light.
  • the phase shift applied may vary according to the existing phase of the incident light.
  • the method may comprise applying a phase shift to the incident light.
  • the method may comprise applying a spatially dependent phase shift to incident light.
  • the phase shift applied may vary across a transverse plane of a field of incident light.
  • the phase shift applied to the incident light may at least partially compensate for a phase shift gained by incident light as a result of interaction with a medium, for example a phase shift gained by scattering in the medium.
  • the method may comprise applying a phase shift to the incident light which is opposite in value to a phase shift gained by the incident light as a result of interaction with a medium. For example, where the incident light is phase shifted by a factor of ⁇ /2 as a result of interaction with a medium, the method may comprise phase shifting incident light by a factor of - ⁇ /2.
  • the phase shift applied to incident light may at least partially cancel out a phase shift gained by incident light as a result of interaction with a medium.
  • the at least one characteristic of the incident light that is modified by the light modifier may affect the intensity of backscattered light detected by the detector.
  • the intensity of the backscattered light may be indicative of the intensity of the projected light, such that increase of the intensity of the backscattered light may increase the intensity of the projected light.
  • backscattered light may be indicative of the size, ie cross-sectional or transverse size, of the projected beam or image, such that increase of the intensity of the backscattered light may reduce the size, ie cross-sectional or transverse size, of the projected beam or image.
  • the at least one characteristic of incident light may therefore be modified, in use, to increase or maximise the intensity of
  • the method may comprise modifying at least one characteristic of incident light continuously during a period of projection.
  • the method may comprise determining the modification to be applied either at regular intervals or continuously during a period of projection, and the optimisation algorithm may be utilised either at regular intervals or continuously to determine the modification of at least one characteristic of the incident light that is applied. This optimisation enables the apparatus to improve the projection of light through media with time-varying optical properties, such as living tissues.
  • the optimisation algorithm may comprise the application of iterative changes to the modification of at least one characteristic of the incident light that is applied by the light modifier, until an optimal or satisfactory feedback signal is obtained.
  • the method may comprise modifying at least one characteristic of incident light on a timescale that is faster than the rate at which the dispersion by the medium varies.
  • the method may comprise determining the modification of at least one characteristic of the incident light that is applied by the light modifier, in use, without user intervention.
  • the method may comprise focussing incident and/or backscattered light, and may, for example, comprise focussing incident and/or backscattered light either prior to, or after, incident and/or backscattered light has interacted with a medium.
  • the method may comprise filtering incident and/or backscattered light, and may, for example, comprise filtering incident and/or backscattered light either prior to, or after, the incident and/or backscattered light has interacted with a medium.
  • the method may comprise filtering backscattered light prior to backscattered light being detected by the detector.
  • the method may comprise detecting certain wavelengths, or certain ranges of wavelengths, of backscattered light.
  • the method may comprise detecting a range of wavelengths that corresponds to light that is generated by a specific scattering process.
  • the range of transmitted wavelengths may correspond to light that is generated by a non-linear process. This may improve the sensitivity of the method.
  • Suitable non-linear processes may comprise frequency doubling, four-wave mixing, Raman scattering, or the like.
  • a method of monitoring fetal response to a light stimulus in utero comprising the steps of:
  • the method according to this aspect of the present invention may be any method according to this aspect of the present invention.
  • the method of projecting light through a medium that has previously been defined may allow for light to be projected through the uterus with substantially no dispersion, such that a focussed light beam is formed within the uterus.
  • This may allow fetal response to a light stimulus to be more accurately monitored than, for example, fetal response to a diffuse light source.
  • the method according to this aspect of the present invention may also be advantageous in that it may allow fetal vision to be examined in utero, for example by ascertaining fetal head movement in response to light stimulus provided in utero. This may thereby provide an early indicator for failure of vision to develop, and may, for example provide an early indication of retinal formation or
  • the method according to this aspect of the present invention may also be advantageous in that it may provide an early indicator of infantile muscular atrophy (Werdnig-Hoffmann disease), for example by repeated failure of a fetus to orient to the light stimulus provided in the uterus.
  • Werdnig-Hoffmann disease early indicator of infantile muscular atrophy
  • the method may comprise a step of ascertaining fetal orientation, which may be undertaken prior to, or during, projection of light into the uterus of a patient.
  • the fetal orientation may be ascertained using any conventional means, including for example, an ultrasound imaging device.
  • the fetal response to light may be monitored using any conventional means, including, for example, an ultrasound imaging device.
  • the method may comprise monitoring fetal movement in response to a light stimulus, and the light stimulus may comprise the light that is projected into the uterus of the patient.
  • the method may comprise monitoring fetal head movement in response to a light stimulus.
  • the method may comprise monitoring duration of fetal fixation on a light stimulus and the light stimulus may comprise the light that is projected into the uterus of the patient.
  • apparatus for monitoring fetal response to a light stimulus, in utero comprising apparatus as defined above, and an imaging device for providing a real-time image of a fetus, in utero.
  • the imaging device may comprise any conventional imaging device, and may, for example, comprise an ultrasound imaging device.
  • the ultrasound imaging device may provide a 2D scan (ie a 2 dimensional image), a 3D scan (ie a 3 dimensional image), or so-called 4D scan (ie a succession of 3 dimensional images, eg in the form of a video).
  • the method according to this aspect of the present invention is advantageous particularly as the method comprises projecting light into the body of the patient in the region in which the active substance is located by means of the method of projecting incident light through a medium that is defined above.
  • the focussed light beam produced may ensure maximum exposure to the target location, without exposure to nearby tissue. This is in contrast to current photodynamic therapies, which introduce drugs to non-target regions of internal tissue as intense light cannot be accurately focussed on target locations.
  • apparatus for use in the projection of a two-dimensional pattern or image of incident light through a medium, the apparatus comprising a light modifier for modifying at least one characteristic of the incident light, before interaction between the incident light and the medium, a controller for the light modifier, and a detector for detecting an intensity of light backscattered by the medium, the backscattered light arising solely from an interaction between the incident light and the medium, the backscattered light comprising light having a frequency which is equal to, or a harmonic of, a frequency of the incident light, wherein the detector is configured to provide a feedback signal to the controller for the light modifier that is dependent on the intensity of backscattered light detected, and the controller is configured to determine the modification of at least one characteristic of the incident light that is applied by the light modifier, in use, using an optimisation algorithm having the feedback signal as a parameter.
  • Figure 1 is a schematic view of a first embodiment of apparatus according to the present invention
  • Figure 2 is a flow diagram illustrating a method of use of the apparatus of Figure 1 ;
  • Figure 3(a) is a schematic view of light projected where no light dispersive medium is present;
  • Figure 3(b) is a schematic view of light projected through a light dispersive medium without use of the apparatus and method of the present invention
  • Figure 3(c) is a schematic view of light projected through a light dispersive medium when the apparatus and method of the present invention are used.
  • Figure 4 is a schematic view of a second embodiment of apparatus according to the present invention.
  • Apparatus according to the present invention is shown schematically in Figure 1 .
  • the apparatus 10 is depicted here as separate components, it will be recognised that the components of the apparatus 10 can be housed in a common housing, so as to facilitate use of the apparatus 10 as a device, for example a hand-held device.
  • the apparatus 10 comprises a light source 12, a phase modulator array 14 beam-splitter 16, a photo-diode 18, a lens 20, a filter 22, and a detector 24.
  • the light source 12 is a laser (ie a spatially coherent) light source, which has a wavelength chosen dependent on both the media through which it is desired to project light, and the intended application of the projected light. Where light is intended to be projected through human tissue, and is intended to be detected by a human eye, for example, a wavelength of 660nm may be appropriate.
  • the light source 12 is an optional feature of the present invention, and embodiments where the apparatus 10 is used with a separate light source are envisaged. Thus the apparatus 10 may be used in combination with existing light sources.
  • the phase modulator array 14 may be an array of individual phase modulator elements, where incident light 26 has been expanded to a beam of sufficient diameter to illuminate each of the individual phase modulator elements.
  • Suitable individual phase modulator elements are part numbers EO-PM-NR-C1
  • phase modulator array 14 may be a single device comprising an array of phase control elements, such as a micromirror array.
  • phase control elements such as a micromirror array.
  • An example of a suitable micromirror array is the DLP® chip available from Texas Instruments
  • the phase modulator array 14 is located intermediate the light source 12 and the beam splitter 16.
  • the beam splitter 16 is in turn located intermediate the phase modulator array 14 and the lens 20.
  • the beam-splitter 16 is either an angled glass slide, or a pellicle beam-splitter. Suitable pellicle beam-splitters are available from Thorlabs
  • the beamsplitter 16 is preferably not a 50:50 beam-splitter, and is configured to send a majority of incident light to a medium, and as much backscattered light to the detector 24, as possible.
  • the photo-diode 18 is any device capable of outputting a signal that is correlated to the intensity of light incident on the device, and needs to be a device which is sensitive to the wavelength of the light source 12.
  • a suitable photo-diode 18 may be part number DET10A/M
  • the lens 20 is a conventional lens, the size and numerical aperture of which is chosen dependent on the physical size of the apparatus as a whole. It is envisaged that plastic lenses will be suitable for most applications.
  • the filter 22 is a conventional optical filter, and may be a band-pass filter.
  • the detector 24 is a 2D arrayed light detector which is sensitive to the wavelength of the light to be monitored, for example a silicon CCD or CMOS detector for visible or near infra-red signals.
  • a suitable detector 24 may be any of the CCD cameras available from Thorlabs The operation of the apparatus 10 will now be described with reference to Figures 1 and 2.
  • the light source 12 directs incident light 26 towards a medium 28.
  • the incident light 26 passes through the phase modulator array 14, and is phase-shifted to give phase-engineered light 30.
  • the phase engineered light 30 passes through the beam-splitter 16, such that a first portion 32 of the phase engineered light 30 is directed toward the medium 28, whilst a second portion 34 of the phase engineered light 30 is directed toward the photo-diode 18.
  • the photo-diode 18 monitors the intensity of the second portion 34 of the phase engineered light 30, and provides feedback to the light source 12.
  • the light source 12 may modify its light output dependent on the feedback provided by the photo-diode 18.
  • the first portion 32 of the phase engineered light 30 passes through the lens 20, and focussed light 36 passes through the medium 28.
  • Backscattered light 40 passes through the lens 20 and hits the beam-splitter 16, such that the backscattered light 40 is directed toward the detector 24.
  • the backscattered light 40 passes through the filter 22, and is detected by the detector 18.
  • the detector 24 provides feedback of the intensity 106 to the phase modulator array 14.
  • the optimal correction parameters for the phase modulator array 14 have been found, and the light dispersion of the medium 28 is partially or fully compensated.
  • FIGs 3(a)-3(c) The effects of the apparatus 10 are shown in Figures 3(a)-3(c).
  • incident light 108 is projected directly toward a focal plane 1 10, in the absence of any light dispersive medium.
  • the incident light 108 is projected onto the focal plane 1 10 without any dispersive effects.
  • incident light 1 12 is projected through a medium 1 14, with a focal plane 1 16 located within or beyond the medium 1 14, without use of the apparatus 10.
  • the incident light 1 12 passes through the medium 1 14, the light 1 12 is dispersed, ie scattered, by the medium 1 14, such that the field of light at the focal plane 1 16 is diffuse and has a low power density.
  • incident light 1 18 is projected through a medium 120, with an focal plane 122 located within or beyond the medium 120, with use of the apparatus 10.
  • the light 1 18 is not dispersed, ie scattered, by the medium 120, and is instead focussed such that the field of light at the focal plane 122 is focussed and has a high power density.
  • a second embodiment of apparatus according to the present invention, generally designated 10, is shown schematically in Figure 2, and like reference numerals are used for like components.
  • the second embodiment of apparatus 10 is substantially the same as the first embodiment of apparatus 10, and differs only in the location of the phase modulator array 14.
  • the phase modulator array 14 in the second embodiment of the apparatus 10 is located intermediate the beam splitter 16 and the lens 20.
  • Backscattered light 40 from the focal plane 38 now passes through the phase modulator array 14 prior to being directed toward the detector 24 by the beamsplitter 22. This allows a real image of the field intensity on the focal plane 38 to be detected by the detector 24, and feedback of this real image can be used to optimise the modification applied by the phase modulator array 14.
  • Apparatus 10 may find particular use as apparatus for monitoring fetal vision in utero, and an example of such use will now be described.
  • the orientation of the fetus is ascertained via an initial 2d ultrasound scan.
  • an initial ultrasound is used to determine the amount of maternal tissue between the light source and the fetal face.
  • the light source 12 can be modified to account for the impedance and diffusion measures related to the depth of maternal tissue. This will ensure that the correct amount of light is released.
  • the levels of light presented to the fetus will be of an intensity to produce the desired percept but at the lower end of the normal spectrum in order to avoid discomfort or signs that the fetus finds the light to be aversive. At this point in time the apparatus 10 can be used.
  • an initial orienting response is required.
  • the stimuli will be small in size but with a lumens intensity that will allow for the percept of a stimulus to be observed by the fetus. Via this means fetal fixation time towards the light stimulus can be measured. Head rotation towards stimuli when the stimuli are moved away from an initial fixation presentation location can also be measured.
  • Continual feedback via the apparatus 10 can provide refined focus as a function of change in maternal tissue depth during fetal movement.
  • the apparatus 10 can be synchronised so that the sonographer can determine the appropriate application of the apparatus 10 as a function of fetal orientation and behavioural state.

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Abstract

Apparatus is disclosed for use in the projection of incident light (26), such as a two-dimensional pattern or image, through a medium (28). The apparatus comprises a light modifier (14) for modifying at least one characteristic of the incident light (26), before interaction between the incident light and the medium (28), a controller for the light modifier (14), and a detector (24) for detecting an intensity of light backscattered (40) by the medium (28). The backscattered light (40) arises from an interaction between the incident light (26) and the medium (28), and may comprise light having a frequency which is equal to, or a harmonic of, a frequency of the incident light (26). The detector (24) is configured to provide a feedback signal to the controller for the light modifier (14) that is dependent on the intensity of backscattered light (40) detected, and the controller is configured to determine the modification of at least one characteristic of the incident light (26) that is applied by the light modifier (14), in use, using an optimisation algorithm having the feedback signal as a parameter.

Description

Title - Apparatus and Method for Projecting Light through a Light Dispersive
Medium
The present invention relates to light dispersive media, and in particular to an apparatus and a method for projecting light, such as a two dimensional pattern or image, through such media.
As used herein, the term "light dispersive" is used to refer to the spatial dispersion of light caused by scattering of light by a medium. This is distinct from chromatic dispersion where the phase velocity of light (and its angle of refraction) is dependent on its frequency.
When light passes through a light dispersive medium, it will typically exit the medium with a wider and more diffuse field than that with which it entered the medium. In particular, If the input field is considered as an array of individual beams (with a position-dependent amplitude and phase described by Ai(xi,yi)), then dispersion can be considered independently for each beam, as it takes a unique path through the material and has its phase relationship with respect to the other beams modified. As a beam travels through the material it scatters randomly, changing the phase and direction of the beam. The light field exiting the material, or at some arbitrary image plane within it, can be considered as an array of individual beams with an amplitude and phase relation that differs from how the input field would have evolved through free space (to Af(xf,yt)) by a time-varying dispersion factor (to give a final field in the form A(xf,yf).D(x,y,t)).
If the input field carries a pattern or image then, on exiting the medium, the pattern or image may become blurred and difficult to see. As the depth of the light dispersive medium is increased, this blurring effect becomes more pronounced, and the ability to discern the original image is rapidly diminished.
Whilst such an effect may be desirable for some known uses, for example in frosted glass, the effect is generally viewed as undesirable for most applications, and in particular is undesirable for most imaging applications. There has now been devised apparatus for projecting light through a medium, and a method of projecting light through a medium, which overcome or substantially mitigate the aforementioned and/or other disadvantages associated with the prior art.
According to a first aspect of the present invention there is provided apparatus for use in the projection of incident light through a medium, the apparatus comprising a light modifier for modifying at least one characteristic of the incident light, before interaction between the incident light and the medium, a controller for the light modifier, and a detector for detecting an intensity of light backscattered by the medium, wherein the detector is configured to provide a feedback signal to the controller for the light modifier that is dependent on the intensity of backscattered light detected, and the controller is configured to determine the modification of at least one characteristic of the incident light that is applied by the light modifier, in use, using an optimisation algorithm having the feedback signal as a parameter.
The apparatus according to the invention is advantageous principally as the detector is configured to provide a feedback signal to the controller for the light modifier that is dependent on the intensity of backscattered light detected, and the controller is configured to determine the modification of at least one characteristic of incident light that is applied by the light modifier, in use, using an optimisation algorithm having the feedback signal as a parameter. In particular, the apparatus may provide compensation for any scattering, or spatial dispersion, effects caused by the medium, by modifying at least one characteristic of incident light, in order to reduce the optical dispersive effect of the medium.
This may, for example, allow incident light to be focussed through the medium with little or substantially no spatial dispersion, thereby providing a light beam or an image at a focal plane within or beyond the medium. In particular, the apparatus may enable the size, ie cross-sectional or transverse size, of the projected beam or image to be reduced relative to non-modified incident light, and relative to prior art apparatus and methods. The intensity of the projected beam or image may therefore be increased relative to non-modified incident light, and relative to prior art apparatus and methods. Furthermore, the visible spot or image may be better defined, with reduced blurring. The apparatus according to the invention may find particular utility in medical applications, for example in monitoring fetal response to light in utero, or in optical activation of a drug by focussing light through living tissue. These applications and methods of use are discussed in more detail below. The incident light may comprise a two dimensional pattern or image of light. For example, the image may be a complex shape or picture. Thus the apparatus may comprise apparatus for use in the projection of a two dimensional pattern or image of incident light through a medium. By "backscattered" light is meant light that is scattered, or diffusely reflected, upon interaction with a medium, such that the light returns in substantially the opposite direction relative to the direction of the incident light. The backscattered light may be scattered, or diffusely reflected, by any scattering mechanism, for example, Mie scattering, Brillouin scattering, Raman scattering, Rutherford backscattering, Bragg diffraction, or Compton scattering. The backscattered light may arise from an interaction between the incident light and the medium. The backscattered light may arise solely from an interaction between the incident light and the medium. For example, the backscattered light may arise from an interaction between the incident light and the medium, with no interaction with any external applied fields.
The medium may be a light dispersive medium, for example a medium which causes the spatial dispersion of light by scattering. The medium may be any medium capable of causing diffuse reflection, for example a medium capable of causing scattering or reflection of light such that an incident ray of light is scattered or reflected at more than one angle. The medium may be living tissue, eg human or animal tissue, which may, for example, comprise any of skin, blood, fat, muscle, or the like. The intensity of backscattered light on which the feedback signal is dependent may exclude any reflection from a first surface, eg the incident surface, of the medium. This may be achieved by either arranging the apparatus to reduce the proportion of this reflected light that is detected (eg via use of Brewster's angle and polarised light), or configuring the controller to remove or lessen the
dependence of the feedback signal to the intensity of this reflected light.
The at least one characteristic of incident light that is modified by the light modifier may be the phase of the incident light, and may be the instantaneous phase of the incident light. The light modifier may therefore be configured to apply a phase shift to incident light. The light modifier may be configured to apply a spatially dependent phase shift to incident light. For example, the phase shift applied may vary across a transverse plane of a field of incident light. The phase shift applied may vary according to the existing phase of the incident light.
The phase shift applied to the incident light may at least partially compensate for a phase shift gained by incident light as a result of interaction with a medium, for example a phase shift gained by scattering in the medium. The phase shift applied to incident light may be opposite in value to a phase shift gained by incident light as a result of interaction with the medium. For example, where incident light is phase shifted by a factor of ττ/2 as a result of interaction with a medium, the incident light may be phase shifted by a factor of -ττ/2 by the light modifier. The phase shift applied to incident light may at least partially cancel out a phase shift gained by incident light as a result of interaction with a medium.
The at least one characteristic of the incident light that is modified by the light modifier may affect the intensity of backscattered light detected by the detector. The intensity of the backscattered light may be indicative of the intensity of the projected light, such that increase of the intensity of the backscattered light may increase the intensity of the projected light. Similarly, the intensity of the
backscattered light may be indicative of the size, ie cross-sectional or transverse size, of the projected beam or image, such that increase of the intensity of the backscattered light may reduce the size, ie cross-sectional or transverse size, of the projected beam or image. The at least one characteristic of incident light may therefore be modified, in use, to increase or maximise the intensity of
backscattered light detected by the detector. The light modifier may be configured to modify at least one characteristic of incident light continuously during a period of projection. The detector may be configured to provide the feedback signal to the controller either at regular intervals or continuously during a period of projection, and the controller may be configured to use the optimisation algorithm either at regular intervals or
continuously to determine the modification of at least one characteristic of the incident light that is applied by the light modifier. This optimisation enables the apparatus to improve the projection of light through media with time-varying optical properties, such as living tissues. The optimisation algorithm may comprise the application of iterative changes to the modification of at least one characteristic of the incident light that is applied by the light modifier, until an optimal or satisfactory feedback signal is obtained.
The light modifier may be configured to modify at least one characteristic of the incident light at a rate that is faster than the rate at which the dispersion by the medium varies. The controller may be configured to determine the modification of at least one characteristic of the incident light that is applied by the light modifier, in use, without user intervention. The controller may comprise a microprocessor. The light modifier may comprise at least one phase modulator, for example at least one device capable of modifying the instantaneous phase of the incident light. The at least one phase modulator may comprise an array or grid or matrix of independent phase modulator devices, each connected separately to the controller, for example a two-dimensional (2D) array of phase modulators. Each phase modulator in the array of phase modulators may be configured to modify the instantaneous phase of the incident light. Alternatively, the light modifier may comprise a phase modulator device having an array of operative pixels for receiving the incident light, and the operative pixels may be configured to independently modify the instantaneous phase of the incident light transmitted through the operative pixels. The phase modulator device having an array of operative pixels may include the controller, as an integral component of the device, or may be connectable to an external controller.
The light modifier may comprise a microelectromechanical system (MEMS), and may, for example, comprise a micromirror array. An example of a suitable micromirror array is the Digital Light Processing (DLP®) technology available from Texas Instruments. Alternatively, the light modifier may comprise an array of independent phase modulators, for example an array comprising independent phase modulators such as those available from Thor Labs (for example part number LN65S-FC,). The light modifier may have any desired resolution, and may, for example, have a resolution of at least 16 pixels, at least 64 pixels, or at least 256 pixels.
For some applications, the light modifier may be configured to transmit the incident light through a window of the light modifier, eg through only some operative pixels. Furthermore, the light modifier may be configured to change the position of the window, and hence provide a moving light beam or image, without any need for movement of the apparatus. Alternatively, a moving light beam or image may be achieved by a variable optical diversion arrangement, or by moving the apparatus relative to the medium.
The detector for detecting the backscattered light may be any detector suitable for detecting light intensity. The detector may comprise a point detector or a 2D detector, and may, for example, comprise a CCD detector, a CMOS detector or the like. The detector may include a lens or other optics for directing the
backscattered light onto the detector, for example to focus the backscattered light onto a point detector.
The feedback signal provided to the controller for the light modifier may be representative of the intensity of backscattered light detected by the detector. In addition, the feedback signal may be dependent on the size and shape, eg an image, of the intensity of the backscattered light detected by the detector. The feedback signal provided to the controller may be continuous or pulsed. The feedback signal provided to the controller may be provided at a rate that is faster than the rate at which the dispersion by the medium varies.
The apparatus may include a light source for directing incident light towards the medium. The light source may be a spatially coherent light source, and, for example, may be a laser light source. The light source may output incident light at a pre-determined wavelength. The pre-determined wavelength may be chosen dependent on the medium through which it is desired to project light. The predetermined wavelength may be in the region of 100nm to 1500nm, in the region of 200nm to 1400nm, in the region of 400nm to 1200nm, or in the region of 400nm to 700 nm, or in the region of 600-700nm. The pre-determined wavelength may be a wavelength in the visible region of the electromagnetic spectrum. The light source may output incident light at a pre-determined power and/or intensity. The predetermined power and/or intensity may be chosen dependent on the medium through which it is desired to project light. The pre-determined power may be less than 1 mW, less than 10 mW, or less than 100mW. The apparatus may comprise a light focussing device for focussing incident and/or backscattered light, and may, for example, comprise a light focussing device for focussing incident and/or backscattered light either prior to, or after, incident and/or backscattered light has interacted with the medium. The apparatus may comprise at least one lens for focussing incident and/or backscattered light.
The apparatus may comprise at least one filter for filtering the incident and/or the backscattered light, and may, for example, comprise at least one filter for filtering the incident and/or the backscattered light either prior to, or after, the incident and/or the backscattered light has interacted with a medium. The apparatus may comprise at least one filter for filtering the backscattered light prior to the backscattered light being detected by the detector. The at least one filter may be configured to allow the passage of only certain wavelengths, or certain ranges of wavelengths, of light. The at least one filter may comprise any, or any combination of, the following: a notch filter; a band-pass filter; a long-pass filter; or a short-pass filter.
The at least one filter for filtering the backscattered light prior to the backscattered light being detected by the detector may be configured to transmit backscattered light in a range of wavelengths that corresponds to light that is generated by a specific scattering process. For example, the range of transmitted wavelengths may correspond to light that is generated by a non-linear process. This may improve the sensitivity of the apparatus. Suitable non-linear processes may comprise frequency doubling, four-wave mixing, Raman scattering, or the like.
The backscattered light may comprise light having a frequency which is equal to, or a multiple of, the frequency of the incident light, for example light having a frequency which is an integer multiple of the frequency of the incident light. The backscattered light may comprise light having a frequency which is equal to, or a harmonic of, the frequency of the incident light. The at least one filter for filtering the backscattered light prior to the backscattered light being detected by the detector may be configured to transmit backscattered light having a frequency which is equal to, or an integer multiple of, the frequency of the incident light. The detector may be configured to detect backscattered light having a frequency which is equal to, or an integer multiple of, the frequency of the incident light. The apparatus may comprise a power monitor for monitoring the power of the light source. The power monitor for monitoring the power of the light source may comprise an optical intensity monitor which monitors the optical intensity, ie the power transferred per unit area, of the light source. The power monitor may comprise a photodiode or the like. The power monitor may be configured to provide a feedback signal to a controller for the power source, and may, for example, be configured to provide a feedback signal dependent on the monitored optical intensity. The controller for the power source may be configured to increase and/or decrease the power output of the power source, dependent on the feedback of monitored optical intensity, eg to maintain a consistent optical intensity.
The apparatus may comprise a first light diverter for diverting at least a portion of incident light to the power monitor, and/or may comprise a second light diverter for diverting at least a portion of backscattered light to the detector for detecting intensity of backscattered light. The first light diverter and the second light diverter may comprise a single component. The first light diverter and/or the second light diverter may comprise a beam-splitter.
The apparatus may be enclosed within a housing, such that the apparatus forms a self-contained device. The device may be handheld, ie may be held in the hand of a user, in use, and may be manipulated by a user's hand, in use. The device may be portable. The device may be mains-powered, or battery-powered.
According to a further aspect of the present invention there is provided a method of projecting incident light through a medium, the method comprising the steps of:
(a) directing the incident light through the medium,
(b) detecting an intensity of light backscattered by the medium,
(c) determining a modification of at least one characteristic of the incident light that is to be applied, in use, before interaction between the incident light and the medium, using an optimisation algorithm having the intensity of light backscattered by the medium as a parameter, and
(d) applying the determined modification to the incident light, before interaction between the incident light and the medium.
The method may utilise the apparatus defined above, such that the light source directs the incident light through the medium, the detector detects an intensity of light backscattered by the medium, the controller for the light modifier determines a modification of at least one characteristic of the incident light that is to be applied, in use, before interaction between the incident light and the medium, using an optimisation algorithm having the intensity of light backscattered by the medium as a parameter, and the light modifier applies the determined modification to the incident light, before interaction between the incident light and the medium.
The method may comprise directing incident light through a light dispersive medium, for example a medium which causes the spatial dispersion of light by scattering. The medium may be any medium capable of causing diffuse reflection, for example a medium capable of causing scattering or reflection of light such that an incident ray of light is scattered or reflected at more than one angle. The medium may be living tissue, eg human or animal tissue, which may, for example, comprise any of skin, blood, fat, muscle, or the like.
The method may comprise modifying the phase, eg the instantaneous phase, of the incident light. The modification of the phase of the light may be spatially dependent. For example, the phase shift applied may vary across a transverse plane of a field of incident light. The phase shift applied may vary according to the existing phase of the incident light.
Where the method comprises modifying the phase of incident light, the method may comprise applying a phase shift to the incident light. The method may comprise applying a spatially dependent phase shift to incident light. For example, the phase shift applied may vary across a transverse plane of a field of incident light.
The phase shift applied to the incident light may at least partially compensate for a phase shift gained by incident light as a result of interaction with a medium, for example a phase shift gained by scattering in the medium. The method may comprise applying a phase shift to the incident light which is opposite in value to a phase shift gained by the incident light as a result of interaction with a medium. For example, where the incident light is phase shifted by a factor of ττ/2 as a result of interaction with a medium, the method may comprise phase shifting incident light by a factor of -ττ/2. The phase shift applied to incident light may at least partially cancel out a phase shift gained by incident light as a result of interaction with a medium. The at least one characteristic of the incident light that is modified by the light modifier may affect the intensity of backscattered light detected by the detector. The intensity of the backscattered light may be indicative of the intensity of the projected light, such that increase of the intensity of the backscattered light may increase the intensity of the projected light. Similarly, the intensity of the
backscattered light may be indicative of the size, ie cross-sectional or transverse size, of the projected beam or image, such that increase of the intensity of the backscattered light may reduce the size, ie cross-sectional or transverse size, of the projected beam or image. The at least one characteristic of incident light may therefore be modified, in use, to increase or maximise the intensity of
backscattered light detected by the detector.
The method may comprise modifying at least one characteristic of incident light continuously during a period of projection. The method may comprise determining the modification to be applied either at regular intervals or continuously during a period of projection, and the optimisation algorithm may be utilised either at regular intervals or continuously to determine the modification of at least one characteristic of the incident light that is applied. This optimisation enables the apparatus to improve the projection of light through media with time-varying optical properties, such as living tissues.
The optimisation algorithm may comprise the application of iterative changes to the modification of at least one characteristic of the incident light that is applied by the light modifier, until an optimal or satisfactory feedback signal is obtained.
The method may comprise modifying at least one characteristic of incident light on a timescale that is faster than the rate at which the dispersion by the medium varies. The method may comprise determining the modification of at least one characteristic of the incident light that is applied by the light modifier, in use, without user intervention. The method may comprise focussing incident and/or backscattered light, and may, for example, comprise focussing incident and/or backscattered light either prior to, or after, incident and/or backscattered light has interacted with a medium. The method may comprise filtering incident and/or backscattered light, and may, for example, comprise filtering incident and/or backscattered light either prior to, or after, the incident and/or backscattered light has interacted with a medium. The method may comprise filtering backscattered light prior to backscattered light being detected by the detector.
The method may comprise detecting certain wavelengths, or certain ranges of wavelengths, of backscattered light. The method may comprise detecting a range of wavelengths that corresponds to light that is generated by a specific scattering process. For example, the range of transmitted wavelengths may correspond to light that is generated by a non-linear process. This may improve the sensitivity of the method. Suitable non-linear processes may comprise frequency doubling, four-wave mixing, Raman scattering, or the like.
According to a further aspect of the present invention there is provided a method of monitoring fetal response to a light stimulus in utero, the method comprising the steps of:
(a) projecting light into the uterus of a patient by means of the method of projecting incident light through a medium that is defined above, and
(b) monitoring fetal response to the light that is projected into the uterus.
The method according to this aspect of the present invention may be
advantageous in that it monitors fetal response to light that is projected into the uterus, whilst utilising the method of projecting incident light through a medium previously defined. In particular, the method of projecting light through a medium that has previously been defined may allow for light to be projected through the uterus with substantially no dispersion, such that a focussed light beam is formed within the uterus. This may allow fetal response to a light stimulus to be more accurately monitored than, for example, fetal response to a diffuse light source. The method according to this aspect of the present invention may also be advantageous in that it may allow fetal vision to be examined in utero, for example by ascertaining fetal head movement in response to light stimulus provided in utero. This may thereby provide an early indicator for failure of vision to develop, and may, for example provide an early indication of retinal formation or
maladaptive rod/cone development for peripheral vision reorientations.
Furthermore, the method according to this aspect of the present invention may also be advantageous in that it may provide an early indicator of infantile muscular atrophy (Werdnig-Hoffmann disease), for example by repeated failure of a fetus to orient to the light stimulus provided in the uterus.
The method may comprise a step of ascertaining fetal orientation, which may be undertaken prior to, or during, projection of light into the uterus of a patient. The fetal orientation may be ascertained using any conventional means, including for example, an ultrasound imaging device.
The fetal response to light may be monitored using any conventional means, including, for example, an ultrasound imaging device. The method may comprise monitoring fetal movement in response to a light stimulus, and the light stimulus may comprise the light that is projected into the uterus of the patient. The method may comprise monitoring fetal head movement in response to a light stimulus. The method may comprise monitoring duration of fetal fixation on a light stimulus and the light stimulus may comprise the light that is projected into the uterus of the patient.
According to a further aspect of the present invention there is provided apparatus for monitoring fetal response to a light stimulus, in utero, the apparatus comprising apparatus as defined above, and an imaging device for providing a real-time image of a fetus, in utero. The imaging device may comprise any conventional imaging device, and may, for example, comprise an ultrasound imaging device. The ultrasound imaging device may provide a 2D scan (ie a 2 dimensional image), a 3D scan (ie a 3 dimensional image), or so-called 4D scan (ie a succession of 3 dimensional images, eg in the form of a video).
According to a further aspect of the present invention there is provided a method of optical activation of an active substance, in vivo, the method comprising the steps of:
(a) providing an active substance to a patient such that the active substance is located with the body of the patient; and
(b) projecting light into the body of the patient in the region in which the active substance is located by means of the method of projecting incident light through a medium that is defined above.
The method according to this aspect of the present invention is advantageous particularly as the method comprises projecting light into the body of the patient in the region in which the active substance is located by means of the method of projecting incident light through a medium that is defined above. In particular, by using the method of projecting incident light through a medium that is defined above, the focussed light beam produced may ensure maximum exposure to the target location, without exposure to nearby tissue. This is in contrast to current photodynamic therapies, which introduce drugs to non-target regions of internal tissue as intense light cannot be accurately focussed on target locations.
According to a further aspect of the present invention there is provided apparatus for use in the projection of a two-dimensional pattern or image of incident light through a medium, the apparatus comprising a light modifier for modifying at least one characteristic of the incident light, before interaction between the incident light and the medium, a controller for the light modifier, and a detector for detecting an intensity of light backscattered by the medium, the backscattered light arising solely from an interaction between the incident light and the medium, the backscattered light comprising light having a frequency which is equal to, or a harmonic of, a frequency of the incident light, wherein the detector is configured to provide a feedback signal to the controller for the light modifier that is dependent on the intensity of backscattered light detected, and the controller is configured to determine the modification of at least one characteristic of the incident light that is applied by the light modifier, in use, using an optimisation algorithm having the feedback signal as a parameter.
It will be recognised that preferential features of the aspects of the present invention may be equally applied to other aspects of the present invention, where appropriate.
Practicable embodiments of the invention will now be described in further detail, with reference to the accompanying drawings, of which: Figure 1 is a schematic view of a first embodiment of apparatus according to the present invention;
Figure 2 is a flow diagram illustrating a method of use of the apparatus of Figure 1 ; Figure 3(a) is a schematic view of light projected where no light dispersive medium is present;
Figure 3(b) is a schematic view of light projected through a light dispersive medium without use of the apparatus and method of the present invention;
Figure 3(c) is a schematic view of light projected through a light dispersive medium when the apparatus and method of the present invention are used; and
Figure 4 is a schematic view of a second embodiment of apparatus according to the present invention.
Apparatus according to the present invention, generally designated 10, is shown schematically in Figure 1 . Although the apparatus 10 is depicted here as separate components, it will be recognised that the components of the apparatus 10 can be housed in a common housing, so as to facilitate use of the apparatus 10 as a device, for example a hand-held device.
The apparatus 10 comprises a light source 12, a phase modulator array 14 beam-splitter 16, a photo-diode 18, a lens 20, a filter 22, and a detector 24.
The light source 12 is a laser (ie a spatially coherent) light source, which has a wavelength chosen dependent on both the media through which it is desired to project light, and the intended application of the projected light. Where light is intended to be projected through human tissue, and is intended to be detected by a human eye, for example, a wavelength of 660nm may be appropriate. An example of a suitable light source 12 is part number HL6545MG available from Thorlabs (hltp://www jhoria s de/i o= producl cfni?parlnu ber:=Hl6545MG). The light source 12 is an optional feature of the present invention, and embodiments where the apparatus 10 is used with a separate light source are envisaged. Thus the apparatus 10 may be used in combination with existing light sources.
The phase modulator array 14 may be an array of individual phase modulator elements, where incident light 26 has been expanded to a beam of sufficient diameter to illuminate each of the individual phase modulator elements. Suitable individual phase modulator elements are part numbers EO-PM-NR-C1
(hitp://w w ihorla s de/l o= prod;.;ci clTn?parinurrU)ei ; :0- P -- F^--Ci ) and LN65S- FC
(http://www.thorlabs.de/newgrouppage9.cfm7objeGtgroup id=3918&pn=LN85S- FC) available from Thorlabs.
Alternatively, the phase modulator array 14 may be a single device comprising an array of phase control elements, such as a micromirror array. An example of a suitable micromirror array is the DLP® chip available from Texas Instruments
(htlp.//www i.∞m^
works.page). The phase modulator array 14 is located intermediate the light source 12 and the beam splitter 16. The beam splitter 16 is in turn located intermediate the phase modulator array 14 and the lens 20. The beam-splitter 16 is either an angled glass slide, or a pellicle beam-splitter. Suitable pellicle beam-splitters are available from Thorlabs
(■httff //www.thor The beamsplitter 16 is preferably not a 50:50 beam-splitter, and is configured to send a majority of incident light to a medium, and as much backscattered light to the detector 24, as possible.
The photo-diode 18 is any device capable of outputting a signal that is correlated to the intensity of light incident on the device, and needs to be a device which is sensitive to the wavelength of the light source 12. A suitable photo-diode 18 may be part number DET10A/M
(http:/ywww.thorlabs.de/thorproduct.cfm?partnumber^DET10A/ ) available from Thorlabs.
The lens 20 is a conventional lens, the size and numerical aperture of which is chosen dependent on the physical size of the apparatus as a whole. It is envisaged that plastic lenses will be suitable for most applications.
The filter 22 is a conventional optical filter, and may be a band-pass filter. A suitable filter 22 may be any of the band-pass filters available from Thorlabs (http://www.thorlabs.de/newgrouppage9.cfm7objeGtgroup id=1001 ).
The detector 24 is a 2D arrayed light detector which is sensitive to the wavelength of the light to be monitored, for example a silicon CCD or CMOS detector for visible or near infra-red signals. A suitable detector 24 may be any of the CCD cameras available from Thorlabs The operation of the apparatus 10 will now be described with reference to Figures 1 and 2.
As an initia step 100, the light source 12 directs incident light 26 towards a medium 28. The incident light 26 passes through the phase modulator array 14, and is phase-shifted to give phase-engineered light 30. The phase engineered light 30 passes through the beam-splitter 16, such that a first portion 32 of the phase engineered light 30 is directed toward the medium 28, whilst a second portion 34 of the phase engineered light 30 is directed toward the photo-diode 18. The photo-diode 18 monitors the intensity of the second portion 34 of the phase engineered light 30, and provides feedback to the light source 12. The light source 12 may modify its light output dependent on the feedback provided by the photo-diode 18. The first portion 32 of the phase engineered light 30 passes through the lens 20, and focussed light 36 passes through the medium 28. As the focussed light 36 passes through the medium 28, some of the light is backscattered by the medium 28. Backscattered light 40 passes through the lens 20 and hits the beam-splitter 16, such that the backscattered light 40 is directed toward the detector 24. The backscattered light 40 passes through the filter 22, and is detected by the detector 18.
The detector 24 provides feedback of the intensity 106 to the phase modulator array 14. When the intensity of the first portion 42 of the backscattered light 40 maximized, the optimal correction parameters for the phase modulator array 14 have been found, and the light dispersion of the medium 28 is partially or fully compensated.
The effects of the apparatus 10 are shown in Figures 3(a)-3(c). In Figure 3(a), incident light 108 is projected directly toward a focal plane 1 10, in the absence of any light dispersive medium. As can be seen, the incident light 108 is projected onto the focal plane 1 10 without any dispersive effects. In Figure 3(b), incident light 1 12 is projected through a medium 1 14, with a focal plane 1 16 located within or beyond the medium 1 14, without use of the apparatus 10. As the incident light 1 12 passes through the medium 1 14, the light 1 12 is dispersed, ie scattered, by the medium 1 14, such that the field of light at the focal plane 1 16 is diffuse and has a low power density. In Figure 3(c), incident light 1 18 is projected through a medium 120, with an focal plane 122 located within or beyond the medium 120, with use of the apparatus 10. As the incident light 1 18 passes through the medium 120, due to the corrective factors applied by the apparatus 10, the light 1 18 is not dispersed, ie scattered, by the medium 120, and is instead focussed such that the field of light at the focal plane 122 is focussed and has a high power density.
A second embodiment of apparatus according to the present invention, generally designated 10, is shown schematically in Figure 2, and like reference numerals are used for like components. The second embodiment of apparatus 10 is substantially the same as the first embodiment of apparatus 10, and differs only in the location of the phase modulator array 14. In particular, the phase modulator array 14 in the second embodiment of the apparatus 10 is located intermediate the beam splitter 16 and the lens 20. Backscattered light 40 from the focal plane 38 now passes through the phase modulator array 14 prior to being directed toward the detector 24 by the beamsplitter 22. This allows a real image of the field intensity on the focal plane 38 to be detected by the detector 24, and feedback of this real image can be used to optimise the modification applied by the phase modulator array 14.
Apparatus 10 according to the first and second embodiments of the present invention may find particular use as apparatus for monitoring fetal vision in utero, and an example of such use will now be described. Initially the orientation of the fetus is ascertained via an initial 2d ultrasound scan. Prior to presenting the light stimuli from the light source 12, an initial ultrasound is used to determine the amount of maternal tissue between the light source and the fetal face. The light source 12 can be modified to account for the impedance and diffusion measures related to the depth of maternal tissue. This will ensure that the correct amount of light is released. The levels of light presented to the fetus will be of an intensity to produce the desired percept but at the lower end of the normal spectrum in order to avoid discomfort or signs that the fetus finds the light to be aversive. At this point in time the apparatus 10 can be used.
Importantly, light will not be directly shone into the eyes of the fetus. To determine the state of the fetus (sleep, alert), an initial orienting response is required. The stimuli will be small in size but with a lumens intensity that will allow for the percept of a stimulus to be observed by the fetus. Via this means fetal fixation time towards the light stimulus can be measured. Head rotation towards stimuli when the stimuli are moved away from an initial fixation presentation location can also be measured. Continual feedback via the apparatus 10 can provide refined focus as a function of change in maternal tissue depth during fetal movement. When combined with a so-called 4D ultrasound scan, the apparatus 10 can be synchronised so that the sonographer can determine the appropriate application of the apparatus 10 as a function of fetal orientation and behavioural state.
meter.

Claims

Claims
1 . An apparatus for use in the projection of incident light through a medium, the apparatus comprising a light modifier for modifying at least one characteristic of the incident light, before interaction between the incident light and the medium, a controller for the light modifier, and a detector for detecting an intensity of light backscattered by the medium, wherein the detector is configured to provide a feedback signal to the controller for the light modifier that is dependent on the intensity of backscattered light detected, and the controller is configured to determine the modification of at least one characteristic of the incident light that is applied by the light modifier, in use, using an optimisation algorithm having the feedback signal as a parameter.
2. An apparatus as claimed in Claim 1 , wherein the backscattered light comprises light having a frequency which is equal to, or a harmonic of, the frequency of the incident light.
3. An apparatus as claimed in Claim 1 or Claim 2, wherein the backscattered light arises from an interaction between the incident light and the medium.
4. An apparatus as claimed in any preceding claim, wherein the backscattered light arises from an interaction between the incident light and the medium only.
5. An apparatus as claimed in any preceding claim, wherein the incident light comprises a two dimensional pattern or image of light.
6. An apparatus as claimed in any preceding claim, wherein the at least one characteristic of incident light that is modified by the light modifier is the
instantaneous phase of the incident light.
7. An apparatus as claimed in any preceding claim, wherein the light modifier is configured to apply a phase shift to incident light.
8. An apparatus as claimed in Claim 6 or Claim 7, wherein the phase shift applied to the incident light at least partially compensates for a phase shift gained by incident light as a result of interaction with a medium.
9. An apparatus as claimed in any preceding claim, wherein the controller is configured to modify at least one characteristic of incident light, in use, to increase the intensity of backscattered light detected by the detector.
10. An apparatus as claimed in any preceding claim, wherein the light modifier is configured to modify at least one characteristic of incident light continuously during a period of projection.
1 1 . An apparatus as claimed in any preceding claim, wherein the detector is configured to provide the feedback signal to the controller either at regular intervals or continuously during a period of projection.
12. An apparatus as claimed in any preceding claim, wherein the controller is configured to use the optimisation algorithm either at regular intervals or continuously to determine the modification of at least one characteristic of the incident light that is applied by the light modifier.
13. An apparatus as claimed in any preceding claim, wherein the optimisation algorithm comprises the application of iterative changes to the modification of at least one characteristic of the incident light that is applied by the light modifier, until an optimal or satisfactory feedback signal is obtained.
14. An apparatus as claimed in any preceding claim, wherein the light modifier is configured to modify at least one characteristic of the incident light at a rate that is faster than the rate at which the dispersion by the medium varies.
15. An apparatus as claimed in any preceding claim, wherein the light modifier comprises at least one phase modulator, capable of modifying the instantaneous phase of the incident light.
16. An apparatus as claimed in any preceding claim, wherein the light modifier comprises an array or grid or matrix of independent phase modulator devices, each connected separately to the controller.
17. An apparatus as claimed in any preceding claim, wherein the light modifier comprises a phase modulator device having an array of operative pixels for receiving the incident light, the operative pixels being configured to independently modify the instantaneous phase of the incident light transmitted through the operative pixels.
18. An apparatus as claimed in any preceding claim, wherein the feedback signal provided to the controller for the light modifier is dependent on the size and shape of the intensity of the backscattered light detected by the detector.
19. An apparatus as claimed in any preceding claim, wherein the apparatus includes a light source for directing incident light towards the medium.
20. An apparatus as claimed in Claim 20, wherein the light source outputs incident light at a pre-determined wavelength in the visible region of the electromagnetic spectrum.
21 . An apparatus as claimed in any preceding claim, wherein the apparatus comprises at least one filter for filtering the backscattered light prior to the backscattered light being detected by the detector.
22. An apparatus as claimed in Claim 21 , wherein the at least one filter is configured to transmit backscattered light in a range of wavelengths that corresponds to light that is generated by a specific scattering process.
23. An apparatus as claimed in Claim 22, wherein the range of transmitted wavelengths corresponds to light that is generated by a non-linear process.
24. An apparatus as claimed in any preceding claim, wherein the apparatus is enclosed within a housing, such that the apparatus forms a self-contained device.
25. An apparatus as claimed in Claim 24, wherein the device is a handheld device.
26. A method of projecting incident light through a medium, the method comprising the steps of:
(a) directing the incident light through the medium,
(b) detecting an intensity of light backscattered by the medium,
(c) determining a modification of at least one characteristic of the incident light that is to be applied, in use, before interaction between the incident light and the medium, using an optimisation algorithm having the intensity of light backscattered by the medium as a parameter, and
(d) applying the determined modification to the incident light, before interaction between the incident light and the medium.
27. A method as claimed in Claim 26, wherein the method utilises an apparatus as claimed in any one of Claims 1 to 25, such that a light source directs the incident light through the medium, the detector detects an intensity of light backscattered by the medium, the controller for the light modifier determines a modification of at least one characteristic of the incident light that is to be applied, in use, before interaction between the incident light and the medium, using an optimisation algorithm having the intensity of light backscattered by the medium as a parameter, and the light modifier applies the determined modification to the incident light, before interaction between the incident light and the medium.
28. A method of monitoring fetal response to a light stimulus in utero, the method comprising the steps of:
(a) projecting light into the uterus of a patient by means of the method of projecting incident light through a medium as defined in Claim 26 or Claim 27, and (b) monitoring fetal response to the light that is projected into the uterus.
29. A method as claimed in Claim 28, wherein the method comprises a step of ascertaining fetal orientation, which is undertaken prior to, or during, projection of light into the uterus of a patient.
30. A method as claimed in Claim 28 or Claim 29, wherein the fetal response to light is monitored using an ultrasound imaging device.
31 . A method as claimed in any one of Claims 28 to 30, wherein the method comprises monitoring fetal head movement in response to a light stimulus.
32. A method as claimed in any one of Claims 28 to 30, wherein the method comprises monitoring duration of fetal fixation on a light stimulus.
33. Apparatus for monitoring fetal response to a light stimulus, in utero, the apparatus comprising apparatus as claimed in any one of Claims 1 to 25, and an imaging device for providing a real-time image of a fetus, in utero.
34. Apparatus as claimed in Claim 33, wherein the imaging device comprises an ultrasound imaging device.
35. A method of optical activation of an active substance, in vivo, the method comprising the steps of:
(a) providing an active substance to a patient such that the active substance is located with the body of the patient; and
(b) projecting light into the body of the patient in the region in which the active substance is located by means of the method of projecting incident light through a medium as defined in Claim 26 or Claim 27.
EP16797624.0A 2015-11-13 2016-11-11 Apparatus and method for projecting light through a light dispersive medium Withdrawn EP3375254A1 (en)

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