Method and apparatus for measuring internal property distribution in scattering medium

• US 6,335,792 B1
• Filed: 11/21/2000
• Issued: 01/01/2002
• Est. Priority Date: 05/26/1998
• Status: Expired due to Term

• Current Assignee: Hamamatsu Photonics KK
• Original Assignee: Hamamatsu Photonics KK
• Inventors: Tsuchiya, Yutaka
• Primary Examiner(s): Pham, Hoa Q.
• Application Number:
  US09/716,264
• Time in Patent Office: 406 Days
• Field of Search: 356/432, 356/433, 356/435, 356/436, 356/441, 356/442, 356/336, 356/338, 356/339, 356/340, 356/343, 356/39, 600/310, 600/316, 600/322, 600/323, 600/328, 600/339, 600/473, 600/476
• US Class Current: 356/432
• CPC Class Codes: G01N 21/4795 spatially resolved investigating of object in scattering medium in vivo A61B

Abstract

A method of measuring an internal property distribution of a scattering medium, comprises a step of injecting rays into a measured medium, a step of detecting rays having passed through the interior of the measured medium, a step of acquiring a measurement value of a predetermined parameter for each of combinations of a light injection position with light detection positions, a step of setting a reference value of an absorption coefficient, a step of acquiring an estimate of the parameter for each of the combinations of the light injection position with the light detection positions, a step of computing a weight function in each voxel, based on the Microscopic Beer-Lambert Law, a step of computing a deviation of the absorption coefficient in each voxel, based on the measurement value and estimate of the parameter, and the weight function, and a step of computing an absolute value of the absorption coefficient in each voxel.

Claims

1. A method of measuring an internal property distribution of a scattering medium, said method comprising:

a light injection step of successively injecting rays from at least one light injection position into a medium to be measured, which is a scattering medium;

a light detection step of detecting rays having passed through the interior of said medium to be measured, at a plurality of light detection positions;

a measurement value acquisition step of acquiring a measurement value of a predetermined parameter of said rays for each of combinations of said light injection position with said light detection positions, based on each ray detected;

a reference value setting step of setting a reference value of an absorption coefficient of said medium to be measured;

an estimate computation step of computing an estimate of said parameter for each of the combinations of said light injection position with said light detection positions, based on said reference value of the absorption coefficient, on the assumption that said medium to be measured has the homogeneous reference value of said absorption coefficient as a whole;

a weight function operation step of obtaining a weight function in each voxel of said medium to be measured, the medium being divided into a plurality of voxels, based on the Microscopic Beer-Lambert Law, using said reference value of the absorption coefficient;

an absorption coefficient deviation computation step of computing a deviation of the absorption coefficient from the reference value of the absorption coefficient in each voxel, based on the measurement value of said parameter, the estimate of said parameter, and said weight function; and

an absorption coefficient absolute value computation step of computing an absolute value of the absorption coefficient in each voxel, based on the reference value of said absorption coefficient and the deviation of said absorption coefficient, to obtain a distribution of absolute values of absorption coefficients in said medium to be measured.

2. The method according to claim 1, wherein said weight function is a function of a mean path length in each voxel and a variance of a distribution of path lengths, on the assumption that said medium to be measured has the homogeneous reference value of said absorption coefficient as a whole.

3. The method according to claim 2, further comprising a mean path length acquisition step of acquiring a mean path length in each voxel, based on the reference value of said absorption coefficient, on the assumption that said medium to be measured has the homogeneous reference value of said absorption coefficient as a whole,

wherein said weight function operation step comprises a step of gaining said weight function, based on the following equation:

4. The method according to claim 1, wherein said weight function is a function of a mean path length in a predetermined time domain in each voxel and a variance of a distribution of path lengths, on the assumption that said medium to be measured has the homogeneous reference value of said absorption coefficient as a whole.

5. The method according to claim 4, further comprising a mean path length acquisition step of acquiring a mean path length in a predetermined time domain in each voxel, based on the reference value of said absorption coefficient, on the assumption that said medium to be measured has the homogeneous reference value of said absorption coefficient as a whole,

wherein said weight function operation step comprises a step of gaining said weight function, based on the following equation:

6. The method according to claim 1, wherein said weight function is a function of a group delay in each voxel and a variance of a distribution thereof, on the assumption that said medium to be measured has the homogeneous reference value of said absorption coefficient as a whole.

7. The method according to claim 6, further comprising a group delay acquisition step of acquiring a group delay in each voxel, based on the reference value of said absorption coefficient, on the assumption that said medium to be measured has the homogeneous reference value of said absorption coefficient as a whole,

wherein said weight function operation step comprises a step of gaining said weight function, based on the following equation:

$\begin{array}{cc}{<br><br>W_i=c<br><br>\text{\hspace{1em}<br><br>}<br><br>\frac{\partial <br><br>{\mathrm{\phi <br><br>}}_i}{\partial <br><br>\mathrm{\omega <br><br>}}<br><br><br><br>}_{{\mathrm{\mu <br><br>}}_{\mathrm{av}}}-\frac{\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\mu <br><br>}}_{\mathrm{ai}}}{2}<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\sigma <br><br>}}_f^2& \left(2\right)\end{array}$

where W_i is the weight function, ${<br><br>\text{\hspace{1em}<br><br>}<br><br>c<br><br>\text{\hspace{1em}<br><br>}<br><br>\frac{\partial <br><br>{\mathrm{\phi <br><br>}}_i}{\partial <br><br>\mathrm{\omega <br><br>}}<br><br><br><br>}_{{\mathrm{\mu <br><br>}}_{\mathrm{av}}}$

is c (speed of light in the medium) times the group delay, Δ

μ

_ai the deviation of the absorption coefficient, and σ

_f² the variance of a distribution.

8. The method according to claim 1, further comprising a concentration computation step of computing a concentration of an absorptive constituent in each voxel by using an absolute value of said absorption coefficient, and thus obtaining a concentration distribution of the absorptive constituent in said medium to be measured.

9. The method according to claim 8, wherein said medium to be measured contains at least two absorptive constituents,

wherein the rays injected into said medium to be measured in said light injection step have at least two wavelengths at which said absorptive constituents demonstrate respective absorption coefficients different from each other,

wherein said light detection step comprises a step of detecting each of the rays having said at least two wavelengths,

wherein said measurement value acquisition step comprises a step of acquiring said measurement value as to each of the rays having said at least two wavelengths,

wherein said reference value setting step comprises a step of setting said reference value as to each of the rays having said at least two wavelengths,

wherein said estimate computation step comprises a step of computing said estimate as to each of the rays having said at least two wavelengths,

wherein said weight function operation step comprises a step of gaining said weight function as to each of the rays having said at least two wavelengths,

wherein said absorption coefficient deviation computation step comprises a step of computing said deviation of the absorption coefficient as to each of the rays having said at least two wavelengths,

wherein said absorption coefficient absolute value computation step comprises a step of computing the absolute value of the absorption coefficient as to each of the rays having said at least two wavelengths, and

wherein said concentration computation step comprises a step of computing concentrations of each said absorptive constituents as to each of the rays having said at least two wavelengths to obtain distributions of concentrations of said respective absorptive constituents in said medium to be measured.

10. The method according to claim 1, further comprising an image display step of displaying an optical CT image to indicate the distribution in said medium to be measured, based on said distribution acquired.

11. An apparatus for measuring an internal property distribution of a scattering medium, said apparatus comprising:

light injection means for successively injecting rays from at least one light injection position into a medium to be measured, which is a scattering medium;

light detection means for detecting rays having passed through the interior of said medium to be measured, at a plurality of light detection positions;

measurement value acquisition means for acquiring a measurement value of a predetermined parameter of said rays for each of combinations of said light injection position with said light detection positions, based on each ray detected;

reference value setting means for setting a reference value of an absorption coefficient of said medium to be measured;

estimate computation means for computing an estimate of said parameter for each of the combinations of said light injection position with said light detection positions, based on said reference value of the absorption coefficient, on the assumption that said medium to be measured has the homogeneous reference value of said absorption coefficient as a whole;

weight function operation means for obtaining a weight function in each voxel of said medium to be measured, the medium being divided into a plurality of voxels, based on the Microscopic Beer-Lambert Law, using said reference value of the absorption coefficient;

absorption coefficient deviation computation means for computing a deviation of the absorption coefficient from the reference value of the absorption coefficient in each voxel, based on the measurement value of said parameter, the estimate of said parameter, and said weight function; and

absorption coefficient absolute value computation means for computing an absolute value of the absorption coefficient in each voxel, based on the reference value of said absorption coefficient and the deviation of said absorption coefficient, to obtain a distribution of absolute values of absorption coefficients in said medium to be measured.

12. The apparatus according to claim 11, wherein said weight function is a function of a mean path length in each voxel and a variance of a distribution of path lengths, on the assumption that said medium to be measured has the homogeneous reference value of said absorption coefficient as a whole.

13. The apparatus according to claim 12, further comprising mean path length acquisition means for acquiring a mean path length in each voxel, based on the reference value of said absorption coefficient, on the assumption that said medium to be measured has the homogeneous reference value of said absorption coefficient as a whole,

wherein said weight function operation means performs a step of gaining said weight function, based on the following equation:

14. The apparatus according to claim 11, wherein said weight function is a function of a mean path length in a predetermined time domain in each voxel and a variance of a distribution of path lengths, on the assumption that said medium to be measured has the homogeneous reference value of said absorption coefficient as a whole.

15. The apparatus according to claim 14, further comprising mean path length acquisition means for acquiring a mean path length in a predetermined time domain in each voxel, based on the reference value of said absorption coefficient, on the assumption that said medium to be measured has the homogeneous reference value of said absorption coefficient as a whole,

wherein said weight function operation means performs a step of computing said weight function, based on the following equation:

16. The apparatus according to claim 11, wherein said weight function is a function of a group delay in each voxel and a variance of a distribution thereof, on the assumption that said medium to be measured has the homogeneous reference value of said absorption coefficient as a whole.

17. The apparatus according to claim 16, further comprising group delay acquisition means for acquiring a group delay in each voxel, based on the reference value of said absorption coefficient, on the assumption that said medium to be measured has the homogeneous reference value of said absorption coefficient as a whole,

wherein said weight function operation means performs a step of gaining said weight function, based on the following equation:

$\begin{array}{cc}{<br><br>W_i=c<br><br>\text{\hspace{1em}<br><br>}<br><br>\frac{\partial <br><br>{\mathrm{\phi <br><br>}}_i}{\partial <br><br>\mathrm{\omega <br><br>}}<br><br><br><br>}_{{\mathrm{\mu <br><br>}}_{\mathrm{av}}}-\frac{\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\mu <br><br>}}_{\mathrm{ai}}}{2}<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\sigma <br><br>}}_f^2& \left(2\right)\end{array}$

where W_i is the weight function, ${<br><br>c<br><br>\text{\hspace{1em}<br><br>}<br><br>\frac{\partial <br><br>{\mathrm{\phi <br><br>}}_i}{\partial <br><br>\mathrm{\omega <br><br>}}<br><br><br><br>}_{{\mathrm{\mu <br><br>}}_{\mathrm{av}}}$

is c (speed of light in the medium) times the group delay, Δ

μ

_ai the deviation of the absorption coefficient, and σ

_f² the variance of a distribution.

18. The apparatus according to claim 11, further comprising concentration computation means for computing a concentration of an absorptive constituent in each voxel by using an absolute value of said absorption coefficient, and thus obtaining a concentration distribution of the absorptive constituent in said medium to be measured.

19. The apparatus according to claim 18, wherein said medium to be measured contains at least two absorptive constituents,

wherein the rays injected into said medium to be measured by said light injection means have at least two wavelengths at which said absorptive constituents demonstrate respective absorption coefficients different from each other,

wherein said light detection means performs a step of detecting each of the rays having said at least two wavelengths,

wherein said measurement value acquisition means performs a step of acquiring said measurement value as to each of the rays having said at least two wavelengths,

wherein said reference value setting means performs a step of setting said reference value as to each of the rays having said at least two wavelengths,

wherein said estimate computation means performs a step of computing said estimate as to each of the rays having said at least two wavelengths,

wherein said weight function operation means performs a step of gaining said weight function as to each of the rays having said at least two wavelengths,

wherein said absorption coefficient deviation computation means performs a step of computing said deviation of the absorption coefficient as to each of the rays having said at least two wavelengths,

wherein said absorption coefficient absolute value computation means performs a step of computing the absolute value of the absorption coefficient for each of the rays having said at least two wavelengths, and

wherein said concentration computation means performs a step of computing concentrations of each said absorptive constituents as to each of the rays having said at least two wavelengths to obtain distributions of concentrations of said respective absorptive constituents in said medium to be measured.

20. The apparatus according to claim 11, further comprising image display means for displaying an optical CT image to indicate the distribution in said medium to be measured, based on said distribution acquired.