# US 9,433,362 B2 · Analyzing photon density waves in a medical monitor > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,433,362 B2 - Document ID: US9433362B2 - Status: Granted - Kind: B2 - Application number: 13/764,977 - Filed: 2013-02-12 - Published: 2013-07-25 - Granted: 2016-09-06 - Earliest claimed: 2009-09-30 - Assignees: Covidien LP - Applicants: Covidien LP - Inventors: Clark R. Baker, Jr.; Edward M. McKenna - Web page: https://patentgrep.com/patent/US9433362B2 ## CPC - A61B 5/0261: {using optical means, e.g. infrared light} - A61B 5/0059: {using light, e.g. diagnosis by transillumination, diascopy, fluorescence (photoacoustic A61B5/0093; optical measurement of heart rate A61B5/02416; optical measurement of blood flow A61B5/0261; optical measurement of analytes A61B5/1455)} - A61B 5/0295: using plethysmography, i.e. measuring the variations in the volume of a body part as modified by the circulation of blood therethrough, e.g. impedance plethysmography - A61B 5/14551: {for measuring blood gases} - A61B 5/14552: {Details of sensors specially adapted therefor} - A61B 5/7203: {for noise prevention, reduction or removal} - A61B 5/7228: {Signal modulation applied to the input signal sent to patient or subject; Demodulation to recover the physiological signal} - G01N 21/3151: {using two sources of radiation of different wavelengths (G01N21/33 - G01N21/39 take precedence)} - A61B 5/7239: {using differentiation including higher order derivatives} - A61B: DIAGNOSIS; SURGERY; IDENTIFICATION (usefulness limited to only animals A61D) - G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q) ## Abstract A monitoring system that may include an emission feature capable of emitting light into tissue, a modulator portion capable of modulating the emitter at a modulation frequency to generate photon density waves, a detection portion capable of detecting photons of the photon density waves after propagation through the tissue and capable of providing a distribution of detected photons over a time period for the photon density waves, and an analysis portion capable of calculating a skewness of the distribution and making determinations relating to a value of a physiologic parameter of the tissue based at least in part on the skewness of the distribution. ## Claims ### Claim 1 One or more non-transitory computer-readable media having stored thereon program instructions to facilitate the determination of physiological parameters of tissue, wherein the program instructions, when executed by a computing system, direct the computing system to at least: drive a light source to emit light at a modulation frequency to generate photon density waves; receive a signal from a detector, wherein the signal is representative of photons of the photon density waves that have propagated through a tissue; determine a skewness of a distribution of the photons; and determine a physiologic parameter of the tissue based at least in part on the skewness of the distribution. ### Claim 2 (depends on 1) The one or more non-transitory computer-readable media of claim 1, wherein the program instructions further direct the computing system to display the physiological parameter on a display. ### Claim 3 (depends on 1) The one or more non-transitory computer-readable media of claim 1, wherein determining the skewness comprises comparing the distribution of the photons to empirical data stored in a memory. ### Claim 4 (depends on 1) The one or more non-transitory computer-readable media of claim 1, wherein determining the skewness of the distribution comprises computing the skewness of the derivative of the modulated detected waveform. ### Claim 5 (depends on 1) The one or more non-transitory computer-readable media of claim 1, wherein determining the skewness of the distribution comprises determining a characteristic of a decay of the photons. ### Claim 6 (depends on 5) The one or more non-transitory computer-readable media of claim 5, wherein the program instructions further direct the computing system to determine if light shunting is present based on at least the characteristic of the decay. ### Claim 7 (depends on 1) The one or more non-transitory computer-readable media of claim 1, wherein the program instructions further direct the computing system to determine a blood oxygen saturation level based at least in part on an amplitude of the distribution. ### Claim 8 (depends on 1) The one or more non-transitory computer-readable media of claim 1, wherein the program instructions further direct the computing system to calculate an estimated number of scattering particles in the tissue based at least in part on detected phase shifts. ### Claim 9 (depends on 1) The one or more non-transitory computer-readable media of claim 1, wherein the physiological parameter is a measure of blood volume. ### Claim 10 A method of analyzing tissue, comprising: receiving a signal from a detector, wherein the signal is representative of photons of the photon density waves that have propagated through a tissue; determining a skewness of a distribution of the photons; and determining a physiologic parameter of the tissue based at least in part on the skewness of the distribution. ### Claim 11 (depends on 10) The method of claim 10, comprising determining the skewness by comparing the distribution of the photons to empirical data associated with tissue conditions. ### Claim 12 (depends on 10) The method of claim 10, wherein determining the skewness of the distribution of the photons comprises determining a derivative of the signal. ### Claim 13 (depends on 10) The method of claim 10, comprising enhancing a signal-to-noise level of the distribution using at least an ensemble averaging procedure. ### Claim 14 (depends on 10) The method of claim 10, wherein the physiological parameter comprises a blood volume parameter.