Quantitative analyses of biological tissue using phase modulation spectroscopy

A spectroscopic system for examining biological tissue, comprising:

• an oscillator constructed to generate a first carrier waveform of a first frequency on the order of 108 Hz;
• a light source, operatively coupled to said oscillator, constructed to generate electromagnetic radiation of a selected wavelength modulated by said carrier waveform, said wavelength being sensitive to concentration of said absorptive pigment present in the tissue;
• an input port constructed to introduce said radiation into the tissue;
• a detection port, located several centimeters apart from said input port, constructed to acquire photons of the radiation that has migrated from said input port over migration paths in a portion of the tissue, said portion of the tissue depending on locations of said input and detection ports;
• a detector, optically connected to said detection port, constructed to detect the radiation;
• a phase detector constructed to compare the detected radiation with the introduced radiation and determine therefrom the phase shift of said detected radiation;
• and
• a processor constructed to receive said phase shift and a scattering property of said portion of the tissue, processor being arranged to use a recursive procedure to calculate a value of the absorption coefficient, at said wavelength, using the following equation:
• θ ⁡ ( ρ , f ) = - ψ ⁢ ⁢ sin ⁢ ⁢ Θ 2 - tan - 1 ⁢ ⁢ - ψ ⁢ ⁢ sin ⁢ ⁢ Θ 2 1 + ψ ⁢ ⁢ cos ⁢ ⁢ Θ 2 wherein ψ = 3 ⁢ ( 1 - g ) ⁢ μ s ⁢ p 2 ⁢ { ( μ a ⁢ c ) 2 + ( 2 ⁢ ⁢ π ⁢ ⁢ f ) 2 } 1 / 2 ⁢ c - 1 , ψ ∞ = ψ ⁡ ( f = 0 ) Θ = tan - 1 ⁢ ⁢ { 2 ⁢ ⁢ π ⁢ ⁢ f μ a ⁢ c } .

An in vivo spectroscopic method for examining biological tissue, comprising:

• positioning an input port at a selected location relative to the biological tissue;
• positioning a detection port at another location spaced at a selected distance of several centimeters from said input port;
• generating a first carrier waveform at a selected frequency on the order of 108 Hz;
• introducing into the tissue at said input port electromagnetic radiation of a selected wavelength modulated by said carrier waveform, said wavelength being sensitive to concentration of said absorptive pigment present in the tissue;
• detecting at said detection port the radiation that has migrated over migration paths in a portion of the tissue from said input port, said portion of the tissue depending on said locations of said input and detection ports;
• creating a first and a second reference phase signals of predefined substantially different phases;
• comparing the detected radiation with said first and said second reference signals and determining therefrom a real output signal and an imaginary output signal, respectively;
• providing said scattering property of said portion of the tissue;
• calculating a value of the phase shift (θ) of said detected radiation as the inverse tangent of the ratio of said imaginary output signal and said real output signal;
• using a recursive procedure to calculate a value of the absorption coefficient, at said wavelength, using the following equation:
• θ ⁡ ( ρ , f ) = - ψ ⁢ ⁢ sin ⁢ ⁢ Θ 2 - tan - 1 ⁢ ⁢ - ψ ⁢ ⁢ sin ⁢ ⁢ Θ 2 1 + ψ ⁢ ⁢ cos ⁢ ⁢ Θ 2 wherein ψ = 3 ⁢ ( 1 - g ) ⁢ μ s ⁢ p 2 ⁢ { ( μ a ⁢ c ) 2 + ( 2 ⁢ ⁢ π ⁢ ⁢ f ) 2 } 1 / 2 ⁢ c - 1 , ψ ∞ = ψ ⁡ ( f = 0 ) Θ = tan - 1 ⁢ ⁢ { 2 ⁢ ⁢ π ⁢ ⁢ f μ a ⁢ c }
• and
• examining said tissue portion by using said calculated value of the absorption coefficient.

A spectroscopic system for examining biological tissue, comprising:

• an oscillator constructed to generate a first carrier waveform at a selected frequency on the order of 108 Hz;
• a light source, operatively coupled to said first oscillator, constructed to generate electromagnetic radiation of a selected wavelength modulated by said carrier waveform, said wavelength being sensitive to concentration of said absorptive pigment present in the tissue;
• an input port constructed to introduce photons of electromagnetic radiation into the examined biological tissue;
• a detection port, spaced several centimeters apart from said input port, constructed to acquire photons that have migrated over migration paths in an examined portion of the tissue from said input port, said portion of the tissue depending on locations of said input and detection ports;
• a detector constructed to detect, at said detection port, the radiation that has migrated over migration paths in the examined portion of the tissue;
• a phase splitter constructed to receive said carrier waveform and produce first and second reference phase signals of predefined substantially different phases;
• first and second double balanced mixers connected to receive from said phase splitter said first and second reference phase signals, respectively, and connected to receive from said detector said detector signal, and constructed to produce therefrom a real output signal and an imaginary output signal, respectively;
• and
• a processor constructed to receive a scattering property of said portion of the tissue and arranged to calculate a phase shift (θ) of said detected radiation as the inverse tangent of the ratio of said imaginary output signal and said real output signal, said processor being further arranged to use a recursive procedure to calculate a value of the absorption coefficient, at said wavelength, using the following equation:
• θ ⁡ ( ρ , f ) = - ψ ⁢ ⁢ sin ⁢ ⁢ Θ 2 - tan - 1 ⁢ ⁢ - ψ ⁢ ⁢ sin ⁢ ⁢ Θ 2 1 + ψ ⁢ ⁢ cos ⁢ ⁢ Θ 2 wherein ψ = 3 ⁢ ( 1 - g ) ⁢ μ s ⁢ p 2 ⁢ { ( μ a ⁢ c ) 2 + ( 2 ⁢ ⁢ π ⁢ ⁢ f ) 2 } 1 / 2 ⁢ c - 1 , ψ ∞ = ψ ⁡ ( f = 0 ) Θ = tan - 1 ⁢ ⁢ { 2 ⁢ ⁢ π ⁢ ⁢ f μ a ⁢ c } .