WO2003042670B1 - Method and system for performing three-dimensional teraherz imaging on an object - Google Patents

Method and system for performing three-dimensional teraherz imaging on an object

Info

Publication number
WO2003042670B1
WO2003042670B1 PCT/US2002/036279 US0236279W WO03042670B1 WO 2003042670 B1 WO2003042670 B1 WO 2003042670B1 US 0236279 W US0236279 W US 0236279W WO 03042670 B1 WO03042670 B1 WO 03042670B1
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WO
WIPO (PCT)
Prior art keywords
pulse
thz
optical
detecting
path
Prior art date
Application number
PCT/US2002/036279
Other languages
French (fr)
Other versions
WO2003042670A1 (en
Inventor
Bradley Ferguson
Shaohong Wang
Xi-Cheng Zhang
Original Assignee
Rensselaer Polytech Inst
Bradley Ferguson
Shaohong Wang
Xi-Cheng Zhang
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 Rensselaer Polytech Inst, Bradley Ferguson, Shaohong Wang, Xi-Cheng Zhang filed Critical Rensselaer Polytech Inst
Publication of WO2003042670A1 publication Critical patent/WO2003042670A1/en
Publication of WO2003042670B1 publication Critical patent/WO2003042670B1/en
Priority to US10/844,105 priority Critical patent/US7119339B2/en
Priority to US10/843,899 priority patent/US7129491B2/en

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Classifications

    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/05—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves 
    • A61B5/0507—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves  using microwaves or terahertz waves
    • 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
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
    • G01N21/3581—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light using far infrared light; using Terahertz radiation
    • 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
    • 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
    • A61B5/0073—Measuring for diagnostic purposes; Identification of persons using light, e.g. diagnosis by transillumination, diascopy, fluorescence by tomography, i.e. reconstruction of 3D images from 2D projections

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  • Health & Medical Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Pathology (AREA)
  • General Health & Medical Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Immunology (AREA)
  • General Physics & Mathematics (AREA)
  • Biochemistry (AREA)
  • Molecular Biology (AREA)
  • Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
  • Animal Behavior & Ethology (AREA)
  • Radiology & Medical Imaging (AREA)
  • Public Health (AREA)
  • Veterinary Medicine (AREA)
  • Optics & Photonics (AREA)
  • Surgery (AREA)
  • Biophysics (AREA)
  • Medical Informatics (AREA)
  • Heart & Thoracic Surgery (AREA)
  • Biomedical Technology (AREA)
  • Toxicology (AREA)
  • Engineering & Computer Science (AREA)
  • Investigating Or Analysing Materials By Optical Means (AREA)

Abstract

A method and a system for obtaining a series of images of a three dimensional object by transmitting pulsed terahertz (Thz) radiation (37) through the entire object (38) from a plurality of angles, optically detecting changes in the transmitted THz radiation using pulsed laser radiation, and constructing a plurality of imaged slices of the three dimensional object (38) using the detected changes in the transmitted THz radiation. The THz radiation may be transmitted through the object (38) as a scanning spot, a scanning line or a two dimensional array of parallel rays. The optical detection may similarly be a single detector or an array of detectors such as a CCD sensor (70).

Claims

AMENDED CLAIMS
[received by the International Bureau on 11 June 2003 (11.06.03); original claims 1-39 replaced by new claims 1-37 (6 pages)]
We claim: 1. A method for obtaining a compositional image of an object comprising obtaining a series of images of said object by transmitting pulsed electromagnetic radiation in a frequency range between about 100 GHz to 10 THz through the entire object from a plurality of angles, detecting changes in the electromagnetic radiation following transmission through said object for each of said plurality of angles using an optical probe beam comprising a chirped laser pulse, and constructing a plurality of imaged slices of the three dimensional object using the detected changes in the transmitted THz radiation.
2. The method according to claim 1 wherein the step of detecting comprises optically detecting said changes in said electromagnetic radiation.
3. The method according to claim 1 wherein said detecting changes in the electromagnetic radiation comprises receiving both transmitted and scattered electromagnetic radiation pulses following transmitting said electromagnetic pulse through said object for each of said plurality of angles.
4. The method according to claim 1 wherein said detecting changes in the electromagnetic radiation following transmission through said object for each of said plurality of angles comprises detecting spectroscopic dielectric information.
5. The method according to claim 4 further comprising using said spectroscopic dielectric information to identify specific materials in said objects.
6. The method according to claim 1 wherein said object is a biological tissue.
7. A method for performing T-ray computed tomography on an object, the method comprising the steps of: (a) emitting a THz pulse and a chirped laser optical probe pulse; (b) transmitting the THz pulse in a first path through the object and transmitting the optical probe pulse in a second path not through the object; (c) modulating the optical probe pulse with the transmitted THz pulse in an electro- optic crystal to create a modulated optical pulse; (d) detecting the modulated optical pulse with a two-dimensional CCD imaging system and storing information corresponding thereto; (e) repeating steps (a)-(d) for a plurality of delay times between the THz pulse and the optical pulse sufficient to characterize a full waveform of the THz pulse; (f) repeating steps (a)-(e) for a plurality of projection angles relative to the object. ; (g) constructing at least one image of the object using data collected during steps (a)-(f).
8. The method according to claim 7 wherein the step of constructing at least one image of the object comprises constructing said at least one image representing a cross sectional slice of said object.
9. The method according to claim 7 wherein in step (g) the image constructed is a 3D representation of the object.
10. The method of claim 9 comprising using a filtered backprojection algorithm in step (g) to construct the three-dimensional image.
11. The method of claim 7 wherein step (g) comprises measuring a phase and amplitude of the transmitted THz pulses and reconstructing the complex refractive index of the object using said measured phase and amplitude as the input to an algorithm which inverts the Radon transform to reconstruct the complex refractive index of the object.
12. The method of claim 11 wherein there are transmitted a plurality of THz pulses and wherein the phase measurement comprises a phase delay and is estimated by interpolating the transmitted THz pulses and interpolating a reference THz pulse, cross-correlating the interpolated reference pulse with the transmitted pulses and using a timing of a peak of the cross correlation as the estimated phase delay.
13. The method of claim 11 where the amplitude and phase are estimated at a plurality of frequencies by Fourier transforming the time domain THz pulses and calculating a phase and amplitude of the complex Fourier coefficients at each given frequency.
14. The method of claim 7 comprising detecting the modulated optical pulse using a spectrometer and a CCD camera.
15. The method of claim 9 wherein said three-dimensional image comprises voxels and wherein a Fourier frequency-dependent refractive index and absorption coefficient for each voxel in the three-dimensional image is constructed using a Fourier transform of the information.
16. The method of claim 7, wherein the THz pulse comprises an expanded THz pulse, the optical probe pulse comprises an expanded optical probe pulse, and detecting the modulated optical probe pulse comprises using a two-dimensional charge coupled device (CCD) camera and the information corresponding thereto includes diffraction information.
17. The method of claim 16, wherein step (e) comprises repeating steps (a)-(d) for a plurality of delay times between the THz pulse and the optical pulse sufficient to characterize a full wavelength of the THz pulse. 22
18. The method of claim 17, wherein step (g) comprises constructing the three-dimensional image using a mathematical algorithm selected from the group consisting of: an algorithm based on a linearization of the wave equation, an algorithm that inverts the non-linear wave equation using iterative finite difference techniques, an iterative algorithm based on the contrast source inversion algorithm, or an algorithm based upon reconstruction of 2D profiles of the object using Fresnel Diffraction.
19. The method of claim 18, wherein the linearization algorithm comprises a Born or Rytov approximation.
20. The method of claim 18, wherein the iterative finite difference technique comprises a propagation-back propagation (PBP) algorithm.
21. The method of claim 7, further comprising using a dynamic subtraction technique to increase the signal to noise ratio.
22. A system for performing T-ray tomography, the system comprising: means for providing a THz pulse and an optical pulse; means for directing the THz pulse in a first path through an object; means for directing the optical pulse through a second path not through the object; an electro-optic crystal at a point of conversion of the first path and second path, for modulating the optical pulse with the THz pulse to create a modulated optical pulse; means for detecting the modulated optical pulse; means for storing information including diffraction information relating to the detected modulated optical pulse; means for obtaining the stored information for the temporal profile of the THz pulse for a plurality of pixels along an x-axis of the object and a y-axis of the object for a plurality of projection angles; means for rotating the object relative to the THz pulse along a z-axis to obtain the plurality of projecting angles; means for constructing a three-dimensional image of the object using the information obtained for the plurality of pixels for the plurality of projection angles.
23. The system of claim 22 wherein the means for obtaining the stored information for a THz pulse comprises means for providing a chirped optical pulse.
24. The system of claim 22 wherein the means for detecting the modulated optical pulse comprises a spectrometer and a CCD camera.
25. The system of claim 23 wherein the means for obtaining the stored information for a full wavelength comprises a delay stage for providing a plurality of delays between the THz pulse and the optical probe pulse and the means for detecting the modulated optical pulse comprises one of a two-dimensional CCD imaging system or single photo-detector.
26. The system of claim 25, wherein the means for providing a THz pulse and an optical pulse comprises means for providing an expanded THz pulse and an expanded optical pulse, the means for obtaining the stored information for the temporal profile comprises a delay stage for providing a plurality of delays between the THz pulse and the optical probe pulse, and the means for detecting the modulated optical pulse comprises a two-dimensional CCD imaging system.
27. The system according to claim 22 further comprising an optical system placed in said first path at a point between said object and said point of conversion, said optical system comprising at least a focusing lens and a limiting aperture means at a focal point of the focusing lens to attenuate scattered radiation components of said expanded THz pulse.
28. A system for performing T-ray tomography, the system comprising: means for simultaneously providing a THz pulse and an optical pulse; means for directing the THz pulse in a first path through an object; means for directing the optical pulse through a second path not through the object; a conversion point for said first and said second paths a photoconductive antenna at said point of conversion of the first path and second path for generating a photocurrent proportional to the instantaneous THz field; means for detecting the generated photocurrent; means for storing information relating to the generated photocurrent; means for obtaining the stored information for the temporal profile of the THz pulse for a plurality of pixels along an x-axis of the object and a y-axis of the object for a plurality of projection angles; means for rotating the object relative to the THz pulse along a z-axis to obtain the plurality of projecting angles; means for constructing a three-dimensional image of the object using the information obtained for the plurality of pixels for the plurality of projection angles.
29. A method for performing T-ray imaging on an object, the method comprising the steps of: (a) emitting a THz pulse and an optical probe pulse; (b) transmitting the THz pulse in a first path through the object and transmitting the optical probe pulse in a second path not through the object; (c) modulating the optical probe pulse with the transmitted THz pulse in an electro-optic crystal to create a modulated optical pulse; (d) detecting the modulated optical pulse and storing information corresponding thereto using a spectrometer and a CCD camera.; (e) repeating steps (a)-(d) from a plurality of locations relative to the object sufficient to characterize the object; (f) constructing a three-dimensional image of the object using the information collected during steps (a)-(e).
30. The method of claim 29 comprising using a filtered backprojection algorithm in step (f) to construct the three-dimensional image.
31. The method of claim 29 wherein said three dimensional image comprises voxels the method further comprising using a Fourier transform of the information to construct a frequency-dependent refractive index and absorption coefficient for each voxel in the three-dimensional image.
32. The method of claim 31 further comprising means for performing a dynamic subtraction technique to improve signal-to-noise ratio in the detected information relating to the modulated expanded optical pulse.
33. A method for providing a two-dimensional profile image of an object, the method comprising the steps of: (a) emitting an expanded THz pulse and an expanded optical probe pulse; (b) transmitting the expanded THz pulse in a first path through the object and transmitting the expanded optical probe pulse in a second path not through the object; (c) modulating the expanded optical probe pulse with the transmitted expanded THz pulse in an electro-optic crystal to create a modulated expanded optical pulse; (d) detecting the modulated expanded optical pulse with a charge coupled device (CCD) camera and storing information corresponding thereto, including diffraction information; (e) constructing a two-dimensional profile image of the object using a mathematical algorithm based upon the time-reversal of the Huygen-Fresnel Diffraction integral.
34. A method for obtaining a compositional image of an object comprising obtaining a series of images of said object by transmitting pulsed electromagnetic radiation in a frequency range between about 100 GHz to 10 THz through the entire object from a plurality of angles, detecting changes in the electromagnetic radiation following transmission through said object for each of said plurality of angles using an optical probe beam, and constructing a three dimensional image of the three dimensional object using the detected changes in the transmitted THz radiation wherein said constructing of said three dimensional image comprises assuming a linearized propagation model and applying a filtered backprojection algorithm.
35. The method of claim 34 wherein the filtered backprojection algorithm is used to perform an inverse Radon equation to construct the three dimensional image.
36. The method of claim 34 wherein the linearized propagation model comprises an approximation relating the transmitted electromagnetic radiation and the detected changes in the electromagnetic radiation following transmission through said object by a line integral.
37. The method of claim 36 wherein the line integral has the form:
r- iω n{r)
Pd (ω,θ, l) = Pi(ω) ex ■dr
L(θ,l) where: Pd is the Fourier transform of the detected THz radiation at frequency ω, a projection angle θ, and a horizontal offset from the axis of rotation /, Pt is the Fourier component of the transmitted THz radiation at the same frequency, L is a straight line between the source and detector, c is the speed of light, and n(τ) = n(r) + ik(r) is the unknown complex refractive index of the sample.
PCT/US2002/036279 2001-11-13 2002-11-13 Method and system for performing three-dimensional teraherz imaging on an object WO2003042670A1 (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
US10/844,105 US7119339B2 (en) 2002-11-13 2004-05-12 Transmission mode terahertz computed tomography
US10/843,899 US7129491B2 (en) 2002-11-13 2004-05-12 Diffraction mode terahertz tomography

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
US34889601P 2001-11-13 2001-11-13
US60/348,896 2001-11-13
US38054002P 2002-05-14 2002-05-14
US60/380,540 2002-05-14

Related Child Applications (2)

Application Number Title Priority Date Filing Date
US10/843,899 Continuation-In-Part US7129491B2 (en) 2002-11-13 2004-05-12 Diffraction mode terahertz tomography
US10/844,105 Continuation-In-Part US7119339B2 (en) 2002-11-13 2004-05-12 Transmission mode terahertz computed tomography

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WO2003042670A1 WO2003042670A1 (en) 2003-05-22
WO2003042670B1 true WO2003042670B1 (en) 2003-12-11

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