Method and device for correcting optical signals
Inventors
Kintz, Gregory J. • McMillan, William A. • Wisniewski, Natalie
Assignees
Publication Number
US-11134871-B2
Publication Date
2021-10-05
Expiration Date
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Abstract
An optical device is used to monitor an implant embedded in the tissue of a mammal (e.g., under the skin). The implant receives excitation light from the optical device and emits light that is detected by the optical device, including an analyte-dependent optical signal. Scatter and absorption properties of tissue change over time due to changes in hydration, blood perfusion and oxygenation. The optical device has an arrangement of light sources, filters and detectors to transmit excitation light within excitation wavelength ranges and to measure emitted light within detection wavelengths. Changes in scattering and absorption of light in the tissue, such as diffuse reflectance, are monitored. The light sources, filters and detectors may also be used to monitor autofluorescence in the tissue to correct autofluorescence background.
Core Innovation
The invention provides a method and an optical detection device for correcting at least one analyte-dependent optical signal emitted from an implant embedded in tissue of a mammalian body. The implant is capable of emitting, in response to excitation light within an excitation wavelength range, the analyte-dependent optical signal within an emission wavelength range, and the method comprises transmitting first excitation light within the excitation wavelength range through the tissue to the implant and measuring a first optical signal emitted from the tissue within the emission wavelength range in response to the first excitation light, transmitting second excitation light within the emission wavelength range into the tissue and measuring a second optical signal emitted from the tissue within the emission wavelength range in response to the second excitation light, and calculating at least one corrected signal value in dependence upon the measured signals.
The background identifies that implanted sensors are often difficult to read optically because of low levels of fluorescence in the presence of high scatter due to dynamic changes in skin conditions and that scatter and absorption properties of tissue change over time, e.g., due to changes in hydration, blood perfusion and oxygenation. The invention addresses the need for a compact device and methods that correct primary analyte-dependent signals using reference signals such as diffuse reflectance and autofluorescence so that accurate and consistent analyte values may be determined from measurements of light emitted from an implant located in tissue.
Claims Coverage
Two independent claims were identified and four main inventive features were extracted from those claims.
Transcutaneous excitation and detection of an analyte-dependent optical signal
Sending a first generated light within an excitation wavelength range from a first LED of an optical device disposed on skin through tissue to an implant configured to fluoresce to emit an analyte-dependent optical signal within an emission wavelength range; and receiving, with at least one detector disposed on the skin and in response to the first generated light, a first optical signal emitted from the implant within the emission wavelength range, and calculating an initial value indicative of a concentration of the analyte based on the first optical signal.
Emission-wavelength reference excitation to derive a background correction factor
Sending, from the optical device into the tissue, a second generated light from a second LED pre-configured to emit light within the emission wavelength range; receiving, with the at least one detector and in response to the second generated light, a second optical signal emitted from the tissue within the emission wavelength range; and calculating, with a processor, a correction factor based on the second optical signal indicative of background within the emission wavelength range, and applying the correction factor to the initial value to calculate the concentration of the analyte.
Autofluorescence and laterally spaced reference measurement for correction
Sending a third generated light within the excitation wavelength range and receiving, with a detector, a third optical signal emitted from the tissue in the emission wavelength range where at least a portion of the second light path is spaced laterally from a corresponding portion of the first light path such that the concentration of the analyte is calculated by applying both a first correction factor and a second correction factor associated with autofluorescence of the tissue to the initial value indicative of the concentration of the analyte.
Device-contained source/detector spacing to obtain depth-dependent correction signals
Using multiple light sources and detectors disposed within a case and spaced apart such that different generated lights travel light paths that extend to different depths in the tissue to produce correction signals (including analyte-independent implant signals and diffuse reflectance/autofluorescence signals), and calculating the concentration of the analyte by applying correction factors derived from those measured signals to values indicative of the analyte-dependent excitation.
The independent claims cover methods and a device that perform transcutaneous excitation and detection of implant-emitted analyte-dependent signals, obtain emission-wavelength and excitation-wavelength reference measurements including laterally spaced autofluorescence measurements, and calculate corrected analyte concentrations using processor-applied correction factors derived from those measured reference signals.
Stated Advantages
Corrects the primary analyte-dependent optical signal for diffuse reflectance and/or autofluorescence to account for optical scattering or absorption in tissue, enabling accurate analyte measurements.
Enables accurate and/or consistent glucose values from measurements of light emitted from an implant located relatively deep in the tissue.
Provides measurements of reference optical signals in substantially the same region of tissue and within a few seconds so that dynamic skin or tissue properties are substantially the same for correction signals and the primary signal.
Facilitates continuous and/or automatic monitoring of an analyte and can provide a warning when the analyte level is at or near a threshold level.
Allows implementation in small, compact devices that do not substantially restrict movements and activities of a patient.
Documented Applications
Monitoring an implant embedded in tissue of a mammalian body to measure analytes such as glucose, lactate or oxygen.
Continuous and/or automatic monitoring to provide warnings for current or impending hyperglycemia or hypoglycemia in individuals with diabetes.
Correcting luminescent signals emitted from implants by using diffuse reflectance, autofluorescence, exciter power normalization, and analyte-independent reference signals.
Implementation as cabled or wireless hand-held readers, wireless skin patch readers, bench-top instruments, imaging systems, handheld devices (e.g., cell phones), smartphone attachments and applications.
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