Patent ID: 6795199
Filing Date: 2004-09-21
Classification: A61B,G01B

Abstract:
An apparatus for determining the tomography of a volume of an object bya) illuminating the object with a temporally ultrashort pulse of light having a preselected temporal width, corresponding to a narrow range of wavelengths penetrating said object, and b) determining the spatial coordinates of a voxel, at the surface or within the object, by measuring the time-of-flight from the pulsed source of light to said voxel defined by the cross-section of the impinging pulse of light and the thickness of the voxel defined by the temporal width of the pulse of light, c) measuring the intensity of the interaction between the impinging pulse of light and the matter within said small voxel, by measuring the intensity of the scattered light as a function of the wavelength of the impinging pulse of light and spectrum of the detected pulse of light, within the elapsed time between two consecutive pulses of light and d) determining the position and scattering intensity of all axially adjoining voxels in the direction of the impinging pulse of light, in the Z direction, by sorting all scattered light photons according to their time-of-flight, within the elapsed time between two consecutive pulses of light and e) scanning the desired volume of the object transversally in the X and Y directions by deflecting the light beam from one set of axially adjoined Z voxels in the direction of the impinging pulse of light, to an adjacent set of axially adjoined Z voxels in the direction of the impinging pulse of light, comprising (i) A femtolaser generating a first ultrashort light pulse divided by a beamsplitter or optical coupler in unequal proportions into mutually coherent second and third ultrashort light pulses, directing the second ultrashort light pulse to the small voxel whose distance is to be measured and the third ultrashort light pulse to an AND time-gate, said unequal proportions determined experimentally as the proportion that maximizes the signal-to-noise ratio at the output of the AND time-gate, and (ii) means for monitoring the intensity of each ultrashort pulse illuminating the object (iii) means disposed between the second light pulse and the object, to process and shape said second light pulse geometrically, temporally, spectrally and polarization-wise, before it interacts with matter in said voxel of the object, and (iv) means disposed between the third ultrashort light pulse and the AND time-gate, to process geometrically, spectrally and polarization-wise said ultrashort light beam, before it interacts with said time-gate, and (v) means for collecting the backscattered light following the interactions between said processed second light pulse and the voxels along the cross-section of the object penetrated by said processed second light pulse, as a function of the backscattering angle, and (vi) means for amplifying and processing said collected back-scattered light pulse temporally, spectrally and polarization-wise and directing it to the AND time-gate, collinearly with the said coherent, processed third ultrashort light pulse, (vii) means disposed between said processed third ultrashort light pulse and said AND time-gate for varying the transit time of said third ultrashort light pulse and its pulsewidth, to cause said processed third ultrashort light pulse to temporally and geometrically overlap with selected temporal sections of the collected back-scattered light pulse at said AND time-gate, and (viii) a wavelength filter or grating for spatially separating the spectral components of the light pulse exiting the AND time-gate, and (ix) means for sampling in real-time the temporal intensity of each of the spectral components of the amplified back-scattered light pulse exiting the AND time-gate, each adjacent sample denoting the intensity of the back-scattered light of a specific wavelength, emitted from an adjacent voxel of the object along the path penetrated by the processed second light pulse, and (x) means for sampling in real-time the temporal intensity of each of the spectral components of the amplified back-scattered light pulse exiting the AND time-gate, as a function of the wavelength of the processed second light pulse impinging on the object, each temporally adjacent sample denoting the intensity of the back-scattered light of a specific wavelength emitted from an axially adjacent voxel of the object, along the path penetrated by the processed second light pulse of a specific wavelength, and (xi) Analog-to-Digital Converters for digitizing in parallel the light intensity for each sample in the time domain as a function of the wavelength of the processed second light pulse impinging on the object and the wavelength of the processed back-scattered light pulse, and normalizing said intensity by dividing it by the intensity of the first pulse of light, and (xii) means for deflecting the light beam continuously from one position to another transversal position within the time elapsed between two consecutive light pulses, comprising two acousto-optical deflectors operating orthogonally and placed at a distance from the object so that their small angular apertures cover the desired span of the surface to be scanned and (xiii) means for raster scanning a surface by deflecting the light beam continuously along an arc of a circle or a straight line and then to an adjacent arc of a circle or a straight line and (xiv) means for synchronizing the beam deflectors (xii) and (xiii) with the laser pulse rate, and (xv) multi-dimensional storage means for storing the normalized intensity of the backscattered light from each voxel along the axial and transversal directions as a function of the impinging light's wavelength, the scattered light's wavelength and the backscattered angle.