Systems and methods for real-time laser doppler imaging
Disclosed methods and systems may be operable to obtain non-contact diagnostic information about movements of scattering objects such as fluids in subsurface vasculature in tissue. As an example, a method may include causing a light source to illuminate the tissue with at least a first portion of the emitted light and illuminate an optical modulator with at least a second portion of the emitted light. The second portion of the emitted light may be modulated by the optical modulator. An offset source is configured to provide an offset frequency signal. An image sensor may receive optical information from the sample. A heterodyne signal based on the reference frequency signal and the offset frequency signal may be used as a gain input of each detector element of the image sensor. Based on the received information, a movement of a portion of the sample may be determined.
1. A method comprising:
causing a light source to emit light so as to illuminate a sample with at least a first portion of the emitted light and illuminate an optical modulator with at least a second portion of the emitted light, wherein the optical modulator is configured to controllably modulate at least the second portion of the emitted light based on a reference frequency signal so as to provide modulated light;
adjusting an offset source, wherein the offset source is configured to provide an offset frequency signal, wherein adjusting the offset source comprises varying the offset frequency signal within a predetermined range of offset frequencies;
while adjusting the offset source, receiving information from an image sensor, wherein the image sensor is optically coupled to the sample and the optical modulator, such that the modulated light illuminates the image sensor, wherein the image sensor comprises a plurality of detector elements, wherein each detector element of the plurality of detector elements has a gain input, wherein the gain input is coupled to a mixer, wherein the mixer is configured to provide a heterodyne signal based on the reference frequency signal and the offset frequency signal, and wherein the gain input of each detector element is modulated based on the heterodyne signal; and
determining a movement of a portion of the sample based on the received information.
2. The method of claim 1 , wherein the optical modulator comprises at least one of: an acousto-optic modulator or an electro-optic modulator.
3. The method of claim 1 , wherein the light source comprises a single mode laser.
4. The method of claim 1 , wherein the light source comprises a plurality of lasers.
5. The method of claim 1 , wherein the image sensor comprises a gain-modulated image sensor.
6. The method of claim 1 , wherein the image sensor comprises an avalanche photodiode (APD).
7. The method of claim 1 , wherein determining the movement of the portion of the sample based on the received information comprises determining a fluid flow in the portion of the sample.
8. The method of claim 7 , wherein determining the fluid flow in the portion of the sample comprises determining a flow rate of the fluid flow in the portion of the sample.
9. The method of claim 8 , further comprising determining a flow map for the sample, wherein the flow map includes a respective flow rate for each of a plurality of portions of the sample.
10. The method of claim 1 , wherein the reference frequency signal is between 1 and 100 MHz, and wherein the offset frequency signal is between 0 to 5 MHz.
11. The method of claim 1 , wherein the received information comprises information indicative of scattering interactions between the first portion of the emitted light and the portion of the sample.
12. The method of claim 1 , wherein the first portion of the emitted light that illuminates the sample is unmodulated.
13. The method of claim 1 , wherein the image sensor comprises a photomultiplier tube (PMT).
14. The method of claim 1 , wherein the image sensor comprises a complementary metal oxide semiconductor (CMOS) detector.
15. The method of claim 1 , wherein the image sensor comprises a charge-coupled device (CCD).