Estimation of source-detector separation in an optical measurement system
An optical measurement system includes a first light source configured to emit a first light pulse toward a target, a second light source configured to emit a second light pulse toward the target, a first detector, a second detector, and a processing unit. The processing unit is configured to determine a plurality of temporal distributions of photons included in the first light pulse and the second light pulse and detected by the first detector and the second detector after the photons are scattered by the target. The processing unit is further configured to determine, based on the plurality of temporal distributions, a distance between the first light source and the second detector.
1. An optical measurement system comprising:
a first light source configured to emit a first light pulse toward a target;
a second light source configured to emit a second light pulse toward the target;
a first detector;
a second detector; and
a processing unit configured to:
determine a plurality of temporal distributions of photons included in the first light pulse and the second light pulse and detected by the first detector and the second detector after the photons are scattered by the target, and
determine, based on the plurality of temporal distributions, a source-detector distance between the first light source and the second detector.
2. The optical measurement system of claim 1 , wherein the processing unit is further configured to determine, based on the plurality of temporal distributions, a source-detector distance between the second light source and the first detector.
3. The optical measurement system of claim 1 , wherein the plurality of temporal distributions comprises:
a first temporal distribution of a first set of photons included in the first light pulse and detected by the first detector after the first set of photons are scattered by the target in a first region;
a second temporal distribution of a second set of photons included in the first light pulse and detected by the second detector after the second set of photons are scattered by the target in the first region and a third region located between the first region and a second region;
a third temporal distribution of a third set of photons included in the second light pulse and detected by the second detector after the third set of photons are scattered by the target in the second region; and
a fourth temporal distribution of a fourth set of photons included in the second light pulse and detected by the first detector after the fourth set of photons are scattered by the target in the second region and the third region.
4. The optical measurement system of claim 3 , wherein:
the first detector is separated from the first light source by a first source-detector distance;
the second detector is separated from the second light source by a second source-detector distance; and
the processing unit is configured to determine the source-detector distance between the first light source and the second detector further based on the first source-detector distance and the second source-detector distance.
5. The optical measurement system of claim 4 , wherein the first source-detector distance and the second source-detector distance are fixed.
6. The optical measurement system of claim 4 , wherein the processing unit is configured to determine the source-detector distance between the first light source and the second detector by:
determining, based on the first temporal distribution and the first source-detector distance, a first reduced scattering coefficient μ′s 1 of the target within the first region;
determining, based on the third temporal distribution and the second source-detector distance, a second reduced scattering coefficient μ′s 2 of the target within the second region; and
determining, based on the second temporal distribution and the fourth temporal distribution, a third reduced scattering coefficient μ′s 3 of the target within the third region and a distance between the first detector and the second detector.
7. The optical measurement system of claim 1 , wherein:
the first light source is further configured to emit a third light pulse toward the target;
the second light source is further configured to emit a fourth light pulse toward the target;
the first light pulse and the second light pulse have a first wavelength;
the third light pulse and the fourth light pulse have a second wavelength different from the first wavelength; and
the processing unit is further configured to:
determine a plurality of additional temporal distributions of additional photons included in the third light pulse and the fourth light pulse and detected by the first detector and the second detector after the additional photons are scattered by the target, and
determine, based on the plurality of additional temporal distributions, the source-detector distance between the first light source and the second detector.
8. The optical measurement system of claim 1 , wherein the processing unit is further configured to:
direct the first light source to emit the first light pulse; and
direct the second light source to emit the second light pulse after the first light source emits the first light pulse.
9. The optical measurement system of claim 1 , wherein the first detector and the second detector are positioned inline with the first light source and the second light source.
10. The optical measurement system of claim 1 , wherein the first detector and the second detector each comprises a plurality of single-photon avalanche diode (SPAD) circuits.
11. The optical measurement system of claim 1 , further comprising:
a first wearable module comprising a first housing and the first light source and the first detector housed within the first housing; and
a second wearable module comprising a second housing and the second light source and the second detector housed within the second housing.
12. The optical measurement system of claim 11 , wherein the second wearable module is movable relative to the first wearable module.
13. The optical measurement system of claim 11 , wherein the second wearable module is positioned adjacent to the first wearable module.
14. The optical measurement system of claim 11 , wherein the first wearable module and the second wearable module are included in a head-mountable component configured to be worn on a head of a user.
15. The optical measurement system of claim 11 , wherein the processing unit is housed in one or more of the first housing or the second housing.
16. The optical measurement system of claim 11 , further comprising a third housing separate from the first housing and the second housing,
wherein the processing unit is housed in the third housing and communicatively coupled with the first detector and the second detector by way of one or more wired or wireless communication links.
17. The optical measurement system of claim 16 , wherein the third housing is wearable by a user.
18. The optical measurement system of claim 1 , wherein the target comprises a brain of a user.
19. A method comprising:
directing, by an optical measurement system, a first light source to emit a first light pulse toward a target;
directing, by the optical measurement system, a second light source to emit a second light pulse toward the target;
determining, by the optical measurement system, a plurality of temporal distributions of photons included in the first light pulse and the second light pulse and detected by a first detector and a second detector after the photons are scattered by the target; and
determining, by the optical measurement system based on the plurality of temporal distributions, a source-detector distance between the first light source and the second detector.
20. The method of claim 19 , further comprising determining, by the optical measurement system based on the plurality of temporal distributions, a source-detector distance between the second light source and the first detector.
21. The method of claim 19 , wherein the plurality of temporal distributions comprises:
a first temporal distribution of a first set of photons included in the first light pulse and detected by the first detector after the first set of photons are scattered by the target in a first region;
a second temporal distribution of a second set of photons included in the first light pulse and detected by the second detector after the second set of photons are scattered by the target in the first region and a third region located between the first region and a second region;
a third temporal distribution of a third set of photons included in the second light pulse and detected by the second detector after the third set of photons are scattered by the target in the second region; and
a fourth temporal distribution of a fourth set of photons included in the second light pulse and detected by the first detector after the fourth set of photons are scattered by the target in the second region and the third region.
22. The method of claim 21 , wherein:
the first detector is separated from the first light source by a first source-detector distance;
the second detector is separated from the second light source by a second source-detector distance; and
the source-detector distance between the first light source and the second detector is determined further based on the first source-detector distance and the second source-detector distance.
23. The method of claim 22 , wherein the first source-detector distance and the second source-detector distance are fixed.
24. The method of claim 22 , wherein the determining of the source-detector distance between the first light source and the second detector comprises:
determining, based on the first temporal distribution and the first source-detector distance, a first reduced scattering coefficient μ′s 1 of the target within the first region;
determining, based on the third temporal distribution and the second source-detector distance, a second reduced scattering coefficient μ′s 2 of the target within the second region; and
determining, based on the second temporal distribution and the fourth temporal distribution, a third reduced scattering coefficient μ′s 3 of the target within the third region and a distance between the first detector and the second detector.
25. The method of claim 19 , further comprising:
directing, by the optical measurement system, the first light source to emit a third light pulse toward the target;
directing, by the optical measurement system, the second light source to emit a fourth light pulse toward the target;
determining, by the optical measurement system, a plurality of additional temporal distributions of additional photons included in the third light pulse and the fourth light pulse and detected by the first detector and the second detector after the additional photons are scattered by the target; and
determining, by the optical measurement system based on the plurality of additional temporal distributions, the source-detector distance between the first light source and the second detector,
wherein the first light pulse and the second light pulse have a first wavelength and the third light pulse and the fourth light pulse have a second wavelength different from the first wavelength.
26. The method of claim 19 , wherein the second light pulse is emitted after the first light pulse.
27. The method of claim 19 , wherein the target comprises a brain of a user.