Methods for Reducing Noise in Optical Biological Sensors

Abstract

Optical measurement of physiological parameters with wearable devices often includes measuring signals in the presence of significant noise sources. These noise sources include, but are not limited to, noise associated with: variable optical coupling to skin or tissue, variations in tissue optical properties with time due to changes in humidity, temperature, hydration, variations in tissue optical properties between individuals, variable coupling of ambient light sources into detectors, and instrument and detector noise, including electrical noise, radio frequency or magnetic interference, or noise caused by mechanical movement of the detector or its components. The present disclosure includes devices and methods configured to produce representations of the raw data in which noise, broadly defined, is separated from the data of interest. The disclosed devices and methods may include subtracting or calibrating out these noise sources and other spurious fluctuations in wearable devices with optical sensors.

What is claimed is: 
     
         1 . A method comprising:
 providing, in a wearable medical diagnostic device, a first and a second optical signal transmitted from within a lumen of subsurface vasculature, wherein the first optical signal comprises an unfiltered target signal and a first noise signal and the second optical signal comprises a second noise signal, wherein the first and second noise signals are correlated and wherein a quotient of the unfiltered target signal and the first noise signal comprises an unfiltered signal to noise ratio; and   determining a filtered signal, based at least on the unfiltered target signal, the first noise signal, and the second noise signal, wherein the filtered signal comprises a filtered target signal and a filtered noise signal, and wherein a quotient of the filtered target signal and the filtered noise signal comprises a filtered signal to noise ratio wherein the filtered signal to noise ratio is higher than the unfiltered signal to noise ratio.   
     
     
         2 . The method of  claim 1  wherein the wearable medical diagnostic device comprises a detector and at least a first source and a second source wherein the first and second sources are configured to illuminate an analyte within the lumen substantially at a first wavelength and a second wavelength, respectively, and the method further comprising:
 periodically illuminating the analyte with the first source at a given period and a given duty cycle wherein the duty cycle is less than one; 
 periodically illuminating the analyte with the second source at the given period, wherein the second source illuminates the analyte for at least a portion of the given period while the first source is not illuminating the analyte; 
 detecting the first optical signal with the detector while the analyte is illuminated by the first source; and 
 detecting the second optical signal with the detector while the analyte is illuminated by the second source. 
 
     
     
         3 . The method of  claim 2  wherein the first source is configured to substantially optically excite the analyte and the second source is configured to substantially not optically excite the analyte. 
     
     
         4 . The method of  claim 1  wherein the wearable medical diagnostic device comprises a detector and a source and wherein the lumen comprises a primary contrast agent configured to fluoresce at a first spectral maximum and a normalization contrast agent configured to fluoresce at a second spectral maximum, the method further comprising:
 illuminating the lumen with the source; 
 detecting the first optical signal substantially at the first spectral maximum; and 
 detecting the second optical signal substantially at the second spectral maximum. 
 
     
     
         5 . The method of  claim 4  wherein the normalization contrast agent is configured to provide a calibration reference for an optical coupling factor between the detector and a skin surface. 
     
     
         6 . The method of  claim 1  wherein the lumen comprises at least a first and a second portion and the wearable medical diagnostic device comprises a source configured to illuminate at least the first and second portions at a spectral illumination maximum, the method further comprising:
 illuminating the first and second portions of the lumen with the source so as to cause a first portion emission and a second portion emission; 
 detecting the first optical signal from the first portion emission; and 
 detecting the second optical signal from the second portion emission. 
 
     
     
         7 . The method of  claim 6  wherein the wearable medical diagnostic device further comprises a first and a second detector configured to detect the first and the second optical signals, respectively. 
     
     
         8 . The method of  claim 6  wherein the wearable medical diagnostic device further comprises a detector, wherein illuminating the first and second portions of the lumen comprises illuminating the first and second portions of the lumen at a first time and a second time, respectively, and wherein detecting the first optical signal comprises the detector detecting the first optical signal during the first time and wherein detecting the second optical signal comprises the detector detecting the second optical signal during the second time. 
     
     
         9 . A wearable medical diagnostic device, comprising:
 at least one detector configured to provide an unfiltered target signal, a first noise signal, and a second noise signal, wherein the unfiltered target signal is transmitted substantially from within a lumen of subsurface vasculature, wherein the first and second noise signals are correlated, and wherein a quotient of the unfiltered target signal and the first noise signal comprises an unfiltered signal to noise ratio; and   a computing device configured to determine a filtered signal, based at least on the unfiltered target signal, the first noise signal, and the second noise signal, wherein the filtered signal comprises a filtered target signal and a filtered noise signal and wherein a quotient of the filtered target signal and the filtered noise signal comprises a filtered signal to noise ratio in which the filtered signal to noise ratio is higher than the unfiltered signal to noise ratio.   
     
     
         10 . The wearable medical diagnostic device of  claim 9  further comprising:
 a first source; and 
 a second source, wherein the first and second sources are configured to illuminate an analyte within the lumen substantially at a first and a second wavelength, respectively, and wherein the computing device is further configured to: 
 periodically illuminate the analyte with the first source at a given period and a given duty cycle wherein the duty cycle is less than one; 
 periodically illuminate the analyte with the second source at the given period, wherein the second source illuminates the analyte for at least a portion of the given period while the first source is not illuminating the analyte; 
 detect the unfiltered target signal and the first noise signal with the at least one detector while the analyte is illuminated by the first source; and 
 detect the second noise signal with the at least one detector while the analyte is illuminated by the second source. 
 
     
     
         11 . The wearable medical diagnostic device of  claim 9  further comprising:
 a source, wherein the lumen comprises a primary contrast agent configured to fluoresce at a first spectral maximum and a normalization contrast agent configured to fluoresce at a second spectral maximum, and wherein the computing device is further configured to: 
 illuminate the lumen with the source; 
 detect, with the at least one detector, the unfiltered target signal and the first noise signal substantially at the first spectral maximum; and 
 detect, with the at least one detector, the second noise signal substantially at the second spectral maximum. 
 
     
     
         12 . The wearable medical diagnostic device of  claim 9 , wherein the lumen comprises at least a first and a second portion and the wearable medical diagnostic device further comprises a source configured to illuminate at least the first and second portions, and wherein the computing device is further configured to:
 illuminate the first and second portions of the lumen with the source so as to cause a first portion emission and a second portion emission;   detect, with the at least one detector, the unfiltered target signal and the first noise signal from the first portion emission; and   detect, with the at least one detector, the second noise signal from the second portion emission.   
     
     
         13 . A non-transitory computer readable medium having stored therein instructions executable by a computing device to cause the computing device to perform functions comprising:
 receiving, in a wearable medical diagnostic device, a first and a second optical signal transmitted from within a lumen of subsurface vasculature, wherein the first optical signal comprises an unfiltered target signal and a first noise signal and the second optical signal comprises a second noise signal, wherein the first and second noise signals are correlated and wherein a quotient of the unfiltered target signal and the first noise signal comprises an unfiltered signal to noise ratio; and   determining a filtered signal, based at least on the unfiltered target signal, the first noise signal, and the second noise signal, wherein the filtered signal comprises a filtered target signal and a filtered noise signal, and wherein a quotient of the filtered target signal and the filtered noise signal comprises a filtered signal to noise ratio in which the filtered signal to noise ratio is higher than the unfiltered signal to noise ratio.   
     
     
         14 . The non-transitory computer readable medium of  claim 13 , wherein the wearable medical diagnostic device comprises a detector and at least a first source and a second source wherein the first and second sources are configured to illuminate an analyte within the lumen substantially at a first wavelength and a second wavelength, respectively, and the non-transitory computer readable medium further comprising:
 causing the first source to periodically illuminate the analyte at a given period and a given duty cycle wherein the duty cycle is less than one;   causing the second source to periodically illuminate the analyte at the given period, wherein the second source illuminates the analyte for at least a portion of the given period while the first source is not illuminating the analyte;   receiving the first optical signal from the detector while the analyte is illuminated by the first source; and   receiving the second optical signal from the detector while the analyte is illuminated by the second source.   
     
     
         15 . The non-transitory computer readable medium of  claim 13 , wherein the wearable medical diagnostic device comprises a detector and a source and wherein the lumen comprises a primary contrast agent configured to fluoresce at a first spectral maximum and a normalization contrast agent configured to fluoresce at a second spectral maximum, and the non-transitory computer readable medium further comprising:
 causing the lumen to be illuminated by the source;   receiving the first optical signal substantially at the first spectral maximum; and   receiving the second optical signal substantially at the second spectral maximum.