Method and apparatus for total hemoglobin measurement

Abstract

The present invention pertains to a method and apparatus for total hemoglobin measurement. A modulated optical signal based on a digital code sequence is transmitted to human tissue. A temporal transfer characteristic is determined from the modulated optical signal. Total hemoglobin is determined based on the temporal transfer characteristic.

What is claimed is: 
     
         1 . A total hemoglobin measurement system for measuring total hemoglobin in human tissue comprising:
 a signal generator configured to generate a digital modulation signal representing a code sequence;   an optical illumination source coupled to the signal generator configured to receive the digital modulation signal and transmit a modulated optical signal along an optical transmission path to the human tissue in response to the digital modulation signal;   a detector optically coupled to the human tissue configured to receive the modulated optical signal after transmission through the optical transmission path through the human tissue; and   a processor coupled to the detector configured to determine a temporal transfer characteristic for the optical signal received by the detector and determine the total hemoglobin based on at least the temporal transfer characteristic.   
     
     
         2 . The total hemoglobin measurement system of  claim 1  further comprising:
 a delay component optically coupled to the optical illumination source configured to increase a length of the optical transmission path. 
 
     
     
         3 . The total hemoglobin measurement system of  claim 2  wherein the delay component comprises a reflective surface. 
     
     
         4 . The total hemoglobin measurement system of  claim 1  wherein the code sequence comprises multiple identical code sequences of a single code sequence. 
     
     
         5 . The total hemoglobin measurement system of  claim 1  wherein the code sequence is circular. 
     
     
         6 . The total hemoglobin measurement system of  claim 1  wherein the code sequence is orthogonal. 
     
     
         7 . The total hemoglobin measurement system of  claim 1  wherein the code sequence is unipolar. 
     
     
         8 . The total hemoglobin measurement system of  claim 1  wherein the code sequence is a Galois code. 
     
     
         9 . The total hemoglobin measurement system of  claim 1  wherein the code sequence is a maximal-length sequence. 
     
     
         10 . The total hemoglobin measurement system of  claim 1  further comprising:
 a second signal generator configured to generate a second digital modulation signal representing a second code sequence; 
 a second optical illumination source coupled to the second signal generator configured to receive the second digital modulation signal and transmit a second modulated optical signal to the human tissue in response to the second digital modulation signal. 
 
     
     
         11 . The total hemoglobin measurement system of  claim 10  wherein the second code sequence and the code sequence have the same ordering of code elements and begin at different code elements. 
     
     
         12 . A method for measuring total hemoglobin in a human tissue comprising:
 generating a digital modulation signal associated with a code sequence;   generating a modulated optical signal based at least on the digital modulation signal;   transmitting the modulated optical signal to the human tissue;   receiving a modified version of the modulated optical signal after transmission through the human tissue;   determining a temporal transfer characteristic for the modified version of the modulated optical signal; and   determining the total hemoglobin based on at least the temporal transfer characteristic.   
     
     
         13 . The method of  claim 12  further comprising:
 delaying the modulated optical signal to reduce noise effects. 
 
     
     
         14 . The method of  claim 12  further comprising:
 determining an absorption coefficient of the human tissue from the temporal transfer characteristic. 
 
     
     
         15 . The method of  claim 12  wherein the code sequence is circular. 
     
     
         16 . The method of  claim 12  further comprising:
 determining a first absorption coefficient during systole based on at least the temporal transfer characteristic; and 
 determining a second absorption coefficient during diastole based on at least the temporal transfer characteristic. 
 
     
     
         17 . The method of  claim 12  wherein the code sequence is orthogonal. 
     
     
         18 . The method of  claim 12  further comprising:
 generating a second digital modulation signal associated with a second code sequence; 
 generating a second modulated optical signal based on at least the second digital modulation signal; 
 transmitting the second modulated optical signal to the human tissue; 
 receiving a second modified version of the second modulated optical signal after transmission through the human tissue; and 
 determining a second temporal transfer characteristic for the second modified version of the second modulated optical signal. 
 
     
     
         19 . The method of  claim 12  further comprising:
 delaying the code sequence to generate a second code sequence; 
 generating a second digital modulation signal associated with the second code sequence; 
 generating a second modulated optical signal based on at least the second digital modulation signal; 
 transmitting the second modulated optical signal to the human tissue; 
 receiving a second modified version of the second modulated optical signal after transmission through the human tissue; and 
 determining a second temporal transfer characteristic for the second modified version of the second modulated optical signal. 
 
     
     
         20 . A total hemoglobin measurement system for measuring total hemoglobin in human tissue comprising:
 means for generating a digital modulation signal associated with a code sequence;   means for generating a modulated optical signal based on at least the digital modulation signal;   means for transmitting the modulated optical signal to the human tissue;   means for receiving a modified version of the modulated optical signal after transmission through the human tissue;   means for determining a temporal transfer characteristic for the modified version of the modulated optical signal; and   means for determining the total hemoglobin based on at least the temporal transfer characteristic.