Method and apparatus for measuring the absorption coefficient and the reduced scattering coefficient of a multiple scattering medium

• US 20060033928A1
• Filed: 10/14/2005
• Published: 02/16/2006
• Est. Priority Date: 01/23/2004
• Status: Active Grant

• Current Assignee: Chien Chou
• Original Assignee: Chien Chou
• Inventors: Chou, Chien, Wu, Jheng-Syong, Yu, Li-Ping, Chan, Yi-Shin
• Granted Patent: US 7,333,212 B2
• Time in Patent Office: Days
• US Class Current: 356/484
• CPC Class Codes: A61B 5/0059 using light, e.g. diagnosis by transillumination, diascopy, fluorescence A61B5/0093, A61B5/1455, A61B5/02416 and A61B5/0261 take precedence
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: G01N 2021/4792 Polarisation of scatter light
• CPC Class Codes: G01N 21/4795 spatially resolved investigating of object in scattering medium in vivo A61B

Abstract

In a method for measuring an absorption coefficient and a reduced scattering coefficient of a multiple scattering medium, a source light beam is outputted, and is transformed into a transformed light beam that includes a mutually parallel circularly polarized photon pair. The transformed light beam is split into a signal beam, which is focused and projected into the multiple scattering medium to produce a diffused polarized photon pair density wave, and a reference beam, which is converted into a reference heterodyne interference signal. The diffused polarized photon pair density wave is converted into a test heterodyne interference signal. Amplitude attenuation and phase delay of the signal beam that has propagated through the multiple scattering medium is obtained based on the reference and test heterodyne interference signals, from which the absorption coefficient and the reduced scattering coefficient of the multiple scattering medium are inferred.

Claims

1. A method for measuring an absorption coefficient and a reduced scattering coefficient of a multiple scattering medium, comprising the steps of:

outputting a source light beam using a two-frequency polarized laser, the source light beam including a mutually correlated and mutually orthogonal polarized photon pair;

transforming the source light beam into a transformed light beam that includes a mutually parallel circularly polarized photon pair, the mutually parallel circularly polarized photon pair being one of a pair of R waves and a pair of L waves;

splitting the transformed light beam into a signal beam and a reference beam;

detecting and converting the reference beam into a reference heterodyne interference signal;

focusing the signal beam and projecting the focused signal beam into the multiple scattering medium via an optical signal fiber to produce a diffused polarized photon pair density wave;

detecting the diffused polarized photon pair density wave via an optical detection fiber that is spaced apart from the optical signal fiber;

converting the diffused polarized photon pair density wave into a test heterodyne interference signal;

obtaining amplitude attenuation and phase delay of the signal beam that has propagated through the multiple scattering medium based on the reference and test heterodyne interference signals; and

inferring the absorption coefficient and the reduced scattering coefficient of the multiple scattering medium with reference to the amplitude attenuation and the phase delay thus obtained.

2. The method as claimed in claim 1, wherein the source light beam is outputted using a two-frequency circularly polarized laser, and the mutually correlated and mutually orthogonal polarized photon pair of the source light beam is circularly polarized and includes an R wave and an L wave.

3. The method as claimed in claim 1, wherein the step of transforming the source light beam includes:

converting the mutually correlated and mutually orthogonal polarized photon pair of the source light beam into a mutually correlated and mutually orthogonal linearly polarized photon pair, which includes a P wave and an S wave, using a first λ

/4 wave plate;

converting the mutually correlated and mutually orthogonal linearly polarized photon pair into a mutually parallel linearly polarized photon pair via a polarizer; and

converting the mutually parallel linearly polarized photon pair into the mutually parallel circularly polarized photon pair of the transformed light beam through a second λ

/4 wave plate.

4. The method as claimed in claim 1, wherein:

the source light beam is outputted using a two-frequency linearly polarized laser, and the mutually correlated and mutually orthogonal polarized photon pair of the source light beam is linearly polarized and includes a P wave and an S wave;

the step of transforming the source light beam including

converting the mutually correlated and mutually orthogonal polarized photon pair of the source light beam into a mutually parallel linearly polarized photon pair via a polarizer, and

converting the mutually parallel linearly polarized photon pair into the mutually parallel circularly polarized photon pair of the transformed light beam through a λ

/4 wave plate.

5. A method for measuring an absorption coefficient and a reduced scattering coefficient of a multiple scattering medium, comprising the steps of:

outputting a source light beam using a two-frequency circularly polarized laser, the source light beam including a mutually correlated and mutually orthogonal circularly polarized photon pair, the mutually correlated and mutually orthogonal circularly polarized photon pair including an R wave and an L wave;

splitting the source light beam into a signal beam and a reference beam;

converting the reference beam into a mutually parallel polarized photon pair via a polarizer;

detecting and further converting the reference beam with the mutually parallel polarized photon pair into a reference heterodyne interference signal;

focusing the signal beam and projecting the focused signal beam into the multiple scattering medium via an optical signal fiber to produce a diffused polarized photon pair density wave;

detecting the diffused polarized photon pair density wave via an optical detection fiber that is spaced apart from the optical signal fiber;

converting the detected diffused polarized photon pair density wave into a mutually parallel polarized photon pair;

further converting the mutually parallel polarized photon pair converted from the detected diffused polarized photon pair density wave into a test heterodyne interference signal;

obtaining amplitude attenuation and phase delay of the signal beam that has propagated through the multiple scattering medium based on the reference and test heterodyne interference signals; and

inferring the absorption coefficient and the reduced scattering coefficient of the multiple scattering medium with reference to the amplitude attenuation and the phase delay thus obtained.

6. A method for measuring an absorption coefficient and a reduced scattering coefficient of a multiple scattering medium, comprising the steps of:

outputting source light beams from a set of two-frequency circularly polarized lasers, the source light beams having distinct center frequencies and different beat frqeuencies, each of the source light beams including a mutually correlated and mutually orthogonal circularly polarized photon pair, the mutually correlated and mutually orthogonal circularly polarized photon pair of each of the source light beams including an R wave and an L wave;

transforming each of the source light beams into a corresponding transformed light beam that includes a mutually parallel circularly polarized photon pair, the mutually parallel circularly polarized photon pair of each of the transformed light beams being one of a pair of R waves and a pair of L waves;

splitting the transformed light beams into a signal beam and a reference beam;

detecting and converting the reference beam into a set of filtered reference heterodyne interference signals;

focusing the signal beam and projecting the focused signal beam into the multiple scattering medium via an optical signal fiber to produce a diffused polarized photon pair density wave;

detecting the diffused polarized photon pair density wave via an optical detection fiber that is spaced apart from the optical signal fiber;

converting the diffused polarized photon pair density wave into a set of filtered test heterodyne interference signals;

obtaining amplitude attenuation and phase delay of the signal beam that has propagated through the multiple scattering medium based on the filtered reference and test heterodyne interference signals; and

inferring the absorption coefficient and the reduced scattering coefficient of the multiple scattering medium with reference to the amplitude attenuation and the phase delay thus obtained.

7. The method as claimed in claim 6, wherein detection and conversion of the reference beam is conducted using a set of photo detectors and a set of band-pass filters coupled respectively to the photo detectors, the band-pass filters having distinct pass-band frequency ranges.

8. A spectrometer apparatus adapted for measuring an absorption coefficient and a reduced scattering coefficient of a multiple scattering medium, said spectrometer apparatus comprising:

a set of two-frequency circularly polarized lasers for outputting a set of source light beams, the source light beams having distinct center frequencies and different beat frequencies, each of the source light beams including a mutually correlated and mutually orthogonal circularly polarized photon pair, the mutually correlated and mutually orthogonal circularly polarized photon pair of each of the source light beams including an R wave and an L wave;

a set of beam-transforming units, each including a first λ

/4 wave plate, a polarizer, and a second λ

/4 wave plate arranged in sequence at an output side of a respective one of said lasers, each of said beam-transforming units transforming a respective one of the source light beams into a transformed light beam that includes a mutually parallel circularly polarized photon pair, the mutually parallel circularly polarized photon pair of each of the transformed light beams being one of a pair of R waves and a pair of L waves;

a beam splitter for splitting the transformed light beams from said beam-transforming units into a signal beam and a reference beam;

a set of first photo detectors for detecting the reference beam from said beam splitter, and a set of reference band-pass filters coupled respectively to said first photo detectors, said reference band-pass filters having distinct pass-band frequency ranges, and converting the reference beam detected by said first photo detectors into a set of filtered reference heterodyne interference signals;

an object lens for focusing the signal beam from said beam splitter;

an optical signal fiber adapted for projecting the focused signal beam from said object lens into the multiple scattering medium to produce a diffused polarized photon pair density wave;

an optical detection fiber spaced apart from said optical signal fiber and adapted for detecting the diffused polarized photon pair density wave;

a set of second photo detectors for receiving the diffused polarized photon pair density wave detected by said second photo detectors, and a set of test band-pass filters coupled respectively to said second photo detectors, said test band-pass filters having distinct pass-band frequency ranges, and converting the diffused polarized photon pair density wave processed by said second photo detectors into a set of filtered test heterodyne interference signals;

a set of signal processors, each of which is coupled to a respective one of said reference band-pass filters and a respective one of said test band-pass filters, each of said signal processors obtaining amplitude attenuation and phase delay of the signal beam that has propagated through the multiple scattering medium based on the filtered reference and test heterodyne interference signals received thereby, and inferring the absorption coefficient and the reduced scattering coefficient of the multiple scattering medium with reference to the amplitude attenuation and the phase delay obtained thereby.