Method and apparatus for optical Doppler tomographic imaging of fluid flow velocity in highly scattering media

A method for tomographic imaging of a fluid flow in a highly scattering medium comprising:

• providing a source of at least partially coherent radiation through an interferometer;
• phase modulating said radiation in said interferometer at a modulation frequency;
• scanning a fluid flow sample with said source of at least partially coherent radiation through said interferometer;
• detecting interference fringes of said radiation backscattered from said sample into said interferometer;
• and
• data processing Doppler frequency changes of said detected backscattered interference fringes with respect to said modulation frequency at each pixel of a scanned image to form a tomographic image of said scanned fluid flow sample,
• wherein said interferometer has a sample and a reference beam and wherein said reference beam is attenuated to reduce photon bunching noise and increase signal-to-noise ratio of interference fringes between said reference and a backscattered sample beam within said interferometer.

A method for tomographic imaging of a fluid flow in a highly scattering medium comprising:

• providing a source of at least partially coherent radiation through an interferometer;
• phase modulating said radiation in said interferometer at a modulation frequency;
• scanning a fluid flow sample with said source of at least partially coherent radiation through said interferometer;
• detecting interference fringes of said radiation backscattered from said sample into said interferometer;
• and
• data processing Doppler frequency changes of said detected backscattered interference fringes with respect to said modulation frequency at each pixel of a scanned image to form a tomographic image of said scanned fluid flow sample,
• wherein said interferometer has a sample optical path and a reference optical path with a reference mirror disposed in said reference optical path, said radiation having a beam waist in said sample path which includes said fluid flow sample, said method further comprising dynamically maintaining a zero optical path length difference between said beam waist in said fluid flow sample and said reference mirror notwithstanding axial movement of said beam waist in said fluid flow sample by means of compensating axial movement of said reference mirror in said reference optical path as said fluid flow sample is scanned.

An apparatus for optical Doppler tomographic imaging of fluid flow velocity in highly scattering medium comprising:

• a source of at least partially coherent radiation;
• an interferometer coupled to said source of radiation, said interferometer having a reference arm for a reference beam and a sample arm for a sample beam;
• a modulator coupled to said interferometer for modulating optical path length difference in said reference and sample arms of said interferometer at a predetermined phase modulation frequency;
• a scanner coupled to said interferometer for scanning a fluid flow sample with said sample beam of said interferometer;
• a sensor coupled to said interferometer for detecting backscattered radiation received by said interferometer from said scanner to detect interference fringes within said interferometer;
• and
• a data processor coupled to said sensor for processing signals from said sensor corresponding to said interference fringes established by said backscattered radiation in said interferometer and for controlling said scanner to generate tomographic images, wherein said data processor generates a power spectrum of interference fringe intensity at each pixel defined within said scan, and wherein said data processor simultaneously generates a tomographic structural image and a tomographic flow velocity image from said power spectrum at each pixel in said image.

An apparatus for optical Doppler tomographic imaging of fluid flow velocity in highly scattering medium comprising:

• a source of at least partially coherent radiation;
• an interferometer coupled to said source of radiation, said interferometer having a reference arm for a reference beam and a sample arm for a sample beam;
• a modulator coupled to said interferometer for modulating optical path length difference in said reference and sample arms of said interferometer at a predetermined phase modulation frequency;
• a scanner coupled to said interferometer for scanning a fluid flow sample with said sample beam of said interferometer;
• a sensor coupled to said interferometer for detecting backscattered radiation received by said interferometer from said scanner to detect interference fringes within said interferometer;
• and
• a data processor coupled to said sensor for processing signals from said sensor corresponding to said interference fringes established by said backscattered radiation in said interferometer and for controlling said scanner to generate tomographic images,
• where said reference arm of said interferometer includes a reference mirror, and where said sample beam has a beam waist, said apparatus further comprising means for maintaining a zero optical path length difference between said sample and reference beams as said beam waist of said sample beam is axially moved in said sample by compensating axial movement of said reference mirror.

An apparatus for optical Doppler tomographic imaging of fluid flow velocity in highly scattering medium comprising:

• a source of at least partially coherent radiation;
• an interferometer coupled to said source of radiation, said interferometer having a reference arm for a reference beam and a sample arm for a sample beam;
• a modulator coupled to said interferometer for modulating optical path length difference in said reference and sample arms of said interferometer at a predetermined phase modulation frequency;
• a scanner coupled to said interferometer for scanning a fluid flow sample with said sample beam of said interferometer;
• a sensor coupled to said interferometer for detecting backscattered radiation received by said interferometer from said scanner to detect interference fringes within said interferometer;
• and
• a data processor coupled to said sensor for processing signals from said sensor corresponding to said interference fringes established by said backscattered radiation in said interferometer and for controlling said scanner to generate tomographic images,
• wherein said data processor generates a power spectrum of interference fringe intensity at each pixel defined within said scan, and
• wherein said data processor simultaneously generates a tomographic structural image and a tomographic flow velocity image from said power spectrum at each pixel in said image.

A method for tomographic imaging of a fluid flow in a highly scattering medium comprising:

• scanning a fluid flow sample with a source of at least partially coherent radiation through an interferometer to generate backscattered radiation in said interferometer;
• phase modulating said radiation in said interferometer at a modulation frequency;
• measuring spectral periods and phase change rates of modulation of an interference spectral density of said backscattered radiation in said interferometer;
• and
• generating a tomographic image of said scanned fluid flow sample from said spectral periods and phase change rates to simultaneously obtain positions and velocities of objects moving within said fluid flow sample.

An apparatus for optical Doppler tomographic imaging of fluid flow velocity in highly scattering medium comprising:

• a source of at least partially coherent radiation;
• an interferometer coupled to said source of radiation, said interferometer having a reference arm for a reference beam and a sample arm for a sample beam, and an output;
• a modulator coupled to said interferometer for modulating optical path lengths in said reference and sample arms of said interferometer at a predetermined phase modulation frequency;
• a probe coupled to said interferometer for exposing a fluid flow sample with said sample beam of said interferometer;
• an optical spectrum analyzer coupled to said output of said interferometer for detecting backscattered radiation received by said interferometer from said probe to detect and analyze a plurality of modulated optical spectral interference densities produced by said interferometer;
• and
• a data processor coupled to said optical spectrum analyzer for processing signals from said probe for spectral scanning said fluid flow sample corresponding to said plurality of modulated optical spectral interference densities established by said backscattered radiation in said interferometer to generate tomographic images from said plurality of interference spectral densities.

An apparatus for optical Doppler tomographic imaging of fluid flow velocity in highly scattering medium comprising:

• a source of at least partially coherent radiation;
• an interferometer coupled to said source of radiation, said interferometer having a reference arm for a reference beam and a sample arm for a sample beam, and an output;
• a modulator coupled to said interferometer for modulating optical path lengths in said reference and sample arms of said interferometer at a predetermined phase modulation frequency;
• a probe coupled to said interferometer for exposing a fluid flow sample with said sample beam of said interferometer;
• an optical spectrum analyzer coupled to said output of said interferometer for detecting backscattered radiation received by said interferometer from said probe to detect and analyze modulated spectral interference densities produced by said interferometer;
• and
• a data processor coupled to said optical spectrum analyzer for processing signals from said probe corresponding to said interference spectral densities established by said backscattered radiation in said interferometer to generate tomographic images,
• wherein said optical spectrum analyzer measures spectral periods and phase change rates of said modulation of said interference spectral densities of said radiation in said interferometer.