Using an optical energy meter to normalize acoustic signals generated by laser pulses of various wavelengths to permit accurate calculation of blood oxygenation
The systems, devices, and methods herein make optoacoustic measurements and correct or normalize them for variations in optical energy level of the different light pulses used. An optical source directs optical pulses to tissue, an optical energy meter measures the optical energy of the different optical pulses, an acoustic detector measures an acoustic response generated by the tissue in response to the optical pulses, and a processor calculates a concentration of an analyte based on the measured acoustic response and as corrected or normalized for the different energy levels among the optical pulses.
1 . A method of measuring a concentration of an analyte, the method comprising:
(a) directing a plurality of optical pulses to tissue;
(b) measuring optical energy levels of the plurality of optical pulses directed to the tissue;
(c) measuring a plurality of acoustic responses of the tissue in response to the plurality of optical pulses directed to the tissue;
(d) normalizing the plurality of measured acoustic responses based on the measured optical energy levels by forming at least one ratio of at least one of the plurality of acoustic responses to at least one corresponding measured optical energy level; and
(e) determining a concentration of an analyte based on the plurality of normalized acoustic responses.
2 . The method of claim 1 , wherein directing the plurality of optical pulses to the tissue comprises directing a first optical pulse at a first wavelength to the tissue and directing a second optical pulse at a second wavelength to the tissue, wherein the first and second wavelengths are different.
3 . The method of claim 1 , wherein the plurality of optical pulses is at one or more wavelengths from 600 nm to 1,300 nm.
4 . The method of claim 1 , wherein the plurality of acoustic responses of the tissue are measured from a same side of the tissue the plurality of optical pulses is directed from.
5 . The method of claim 1 , wherein the plurality of acoustic responses of the tissue are measured from a different side of the tissue the plurality of optical pulses is directed from.
6 . The method of claim 1 , wherein the analyte is one or more of hemoglobin, oxyhemoglobin, and deoxyhemoglobin.
7 . The method of claim 1 , further comprising determining blood oxygenation based on the determined concentration of one or more analytes and the characterized property of the tissue.
8 . The method of claim 1 , wherein the tissue comprises one or more blood vessels and tissue surrounding the one or more blood vessels.
9 . The method of claim 8 , wherein the one or more blood vessels is selected from a superficial vein, a radial artery, a superior sagittal sinus, or an internal jugular vein.
10 . The method of claim 1 , wherein normalizing the plurality of measured acoustic responses comprises forming a ratio for each of the plurality of acoustic responses to a corresponding measured optical energy level.
11 . The method of claim 10 , wherein normalizing the plurality of measured acoustic responses further comprises averaging the ratios of the measured acoustic responses to the corresponding measured optical energy levels.
12 . The method of claim 1 , wherein the plurality of optical pulses are at a first wavelength.
13 . The method of claim 12 , further comprising repeating steps (a) to (d) for a plurality of optical pulses at a second wavelength different from the first wavelength.
14 . The method of claim 13 , wherein (e) determining the concentration of an analyte based on the plurality of normalized responses comprises determining a ratio of (i) the plurality of normalized acoustic responses to the plurality of optical pulses at the first wavelength and (ii) the plurality of normalized acoustic responses to the plurality of optical pulses at the second wavelength.
15 . A system for measuring a concentration of an analyte, the system comprising:
at least one optical source configured to direct a plurality of optical pulses to tissue;
an optical energy meter configured to measure optical energy levels of the plurality of optical pulses directed to the tissue;
an acoustic detector configured to measure a plurality of acoustic responses of the tissue to the plurality of optical pulses; and
a processor configured to normalize the plurality of measured acoustic responses based on the measured optical energy levels by forming at least one ratio of at least one of the plurality of acoustic responses to at least one corresponding measured optical energy level and determine a concentration of an analyte based on the plurality of normalized acoustic responses.
16 . The system of claim 15 , wherein the at least one optical source comprises a first optical source configured to generate a first optical pulse at a first wavelength and a second optical source configured to generate a second optical pulse at a second wavelength, wherein the first and second wavelengths are different.
17 . The system of claim 15 , wherein the plurality of optical pulses is at one or more wavelengths from 600 nm to 1,300 nm.
18 . The system of claim 15 , wherein the at least one optical source comprises a plurality of optical sources, each optical source configured to generate an optical pulse at a different wavelength.
19 . The system of claim 15 , wherein the at least one optical source and the acoustic detector are oriented on a same side as one another with respect to the tissue.
20 . The system of claim 15 , wherein the at least one optical source and the acoustic detector are oriented on different sides of one another with respect to the tissue.
21 . The system of claim 15 , wherein the processor is configured to normalize the plurality of measured acoustic responses by forming a ratio for each of the plurality of acoustic responses to a corresponding measured optical energy level.
22 . The system of claim 21 , wherein the processor is further configured to normalize the plurality of measured acoustic responses by averaging the ratios of the measured acoustic responses to the corresponding measured optical energy levels.