Photon Measurement Method and Apparatus
A system and method for measuring photons utilizing a low-power light source modulated with a code sequence to interrogate a sample of interest. Preferably a portion of the scattered light from the sample is detected by a photo-detector. A correlation of the photo-detector signal and the code sequence produces an estimate of the distribution of flight times for photons traveling from the source to the detector.
1 . A cost-effective and accurate photon measurement system for human tissue comprising:
a memory device configured to store a plurality of values corresponding to a plurality of pseudorandom binary code patterns wherein said plurality of values is located by a plurality of cell addresses;
a code selector configured to select a pseudorandom binary code pattern from said plurality of pseudorandom binary code patterns during operation of said photon measurement system;
an address sequencer coupled to said memory device and said code selector configured to provide a cell address from said plurality of cell addresses corresponding to said selected pseudorandom binary code pattern;
a pseudorandom binary code signal generator coupled to the code selector configured to generate a pseudorandom binary code output in accordance with said selected pseudorandom binary code pattern;
a continuous wave light source coupled to the pseudorandom binary code signal generator configured to generate a pseudorandom binary modulated optical wave modulated in accordance with said pseudorandom binary code output from the pseudorandom binary code signal generator;
delivery optics coupled to the continuous wave light source to direct the pseudorandom binary modulated optical wave at a human tissue translucent material;
an optical splitter coupled to the delivery optics between the delivery optics and the translucent material; the optical splitter coupled to an optical detector configured to direct the pseudorandom binary modulated optical wave to the optical detector; the optical detector configured to generate a pseudorandom binary optical reference signal; the optical detector coupled to a signal detector such that when the pseudorandom binary optical reference signal is generated it is communicated to the signal detector;
a corresponding detector configured to detect scattered optical waves from the translucent material; the corresponding detector having as an output a signal indicative of a characteristic of the detected scattered optical wave; the corresponding detector output signal communicated to the signal detector;
the signal detector configured to generate and provide an output indicative of a characteristic of the translucent material, based in part on the pseudorandom binary optical reference signal;
a correlator coupled to the signal detector configured to generate a correlation of said signal indicative of said characteristic of the detected scattered optical wave with said pseudorandom binary optical reference signal; and
a processor coupled to said correlator configured to calculate photon time-of-flight information of said scattered optical wave based on said correlation.
2 . The system of claim 1 further comprising:
an acquisition synchronizer coupled to the corresponding detector to control acquisition of said signal indicative of said characteristic of the detected scattered optical wave; and
a synchronization clock coupled to said acquisition synchronizer to control phase of said acquisition synchronizer and wherein the optical splitter is positioned between the continuous wave light source and the delivery optics.
3 . The system of claim 1 wherein a first analog to digital converter is positioned between the optical detector and the signal detector to convert the optical reference signal into a digital signal;
a second analog to digital converter is positioned between the corresponding detector and the signal detector to convert the corresponding detector output signal into a digital detector signal; and
the signal detector configured to use digital processing techniques to generate the output indicative of the characteristic of the translucent material, based in part on the digitized optical reference signal.
4 . The system of claim 1 wherein the signal detector is configured to employ temporal over-sampling to generate and provide the output indicative of the characteristic of the translucent material.
5 . The system of claim 1 wherein the pseudorandom binary code pattern represents a single code pattern.
6 . The system of claim 1 wherein the pseudorandom binary code pattern represents multiple repeats of a same pattern.
7 . The system of claim 1 wherein the pseudorandom binary code pattern is a Gold code pattern.
8 . The system of claim 1 wherein the pseudorandom binary code pattern is a Kasami code pattern.
9 . The system of claim 1 wherein the pseudorandom binary code pattern is a Walsh code pattern.
10 . The system of claim 1 wherein said characteristic of the translucent material is an absorption coefficient.
11 . The system of claim 1 wherein said characteristic of the translucent material is a scattering coefficient.
12 . The system of claim 1 wherein said characteristic of the translucent material is an absorption coefficient and a scattering coefficient.
13 . The system of claim 1 wherein said pseudorandom binary code signal generator comprises a linear feedback shift register.
14 . The system of claim 13 wherein said pseudorandom binary code signal generator comprises a gain code input.
15 . The system of claim 14 wherein said pseudorandom binary code signal generator comprises a gain code memory.
16 . The system of claim 1 further comprising:
a linear feedback shift register coupled to said memory device.
17 . The system of claim 16 further comprising:
a gain code input coupled to said linear feedback shift register.
18 . The system of claim 17 further comprising:
a gain code memory coupled to said gain code input.
19 . The system of claim 1 further comprising:
a state machine coupled to said memory device.
20 . The system of claim 1 wherein said pseudorandom binary code signal generator comprises a state machine.