Patent Publication Number: US-2020275871-A1

Title: Physiological measurement devices, systems, and methods

Description:
INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS 
     The present application is a continuation of U.S. patent application Ser. No. 16/835,712, filed Mar. 31, 2020, which is a continuation of U.S. patent application Ser. No. 16/791,955, filed Feb. 14, 2020, which is a continuation of U.S. patent application Ser. No. 16/532,061 filed Aug. 5, 2019, which is a continuation of U.S. patent application Ser. No. 15/195,199 filed Jun. 28, 2016, which claims priority benefit under 35 U.S.C. § 119(e) from U.S. Provisional Application No. 62/188,430, filed Jul. 2, 2015, which is incorporated by reference herein. Any and all applications for which a foreign or domestic priority claim is identified in the Application Data Sheet as filed with the present application are hereby incorporated by reference under 37 CFR 1.57. 
    
    
     FIELD OF THE DISCLOSURE 
     The present disclosure relates to the field of non-invasive optical-based physiological monitoring sensors, and more particularly to systems, devices and methods for improving the non-invasive measurement accuracy of oxygen saturation, among other physiological parameters. 
     BACKGROUND 
     Spectroscopy is a common technique for measuring the concentration of organic and some inorganic constituents of a solution. The theoretical basis of this technique is the Beer-Lambert law, which states that the concentration c i  of an absorbent in solution can be determined by the intensity of light transmitted through the solution, knowing the pathlength d λ , the intensity of the incident light I 0,λ , and the extinction coefficient ε i,λ  at a particular wavelength λ. 
     In generalized form, the Beer-Lambert law is expressed as: 
     
       
         
           
             
               
                 
                   
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     where μ α,λ  is the bulk absorption coefficient and represents the probability of absorption per unit length. The minimum number of discrete wavelengths that are required to solve equations 1 and 2 is the number of significant absorbers that are present in the solution. 
     A practical application of this technique is pulse oximetry, which utilizes a noninvasive sensor to measure oxygen saturation and pulse rate, among other physiological parameters. Pulse oximetry relies on a sensor attached externally to the patient to output signals indicative of various physiological parameters, such as a patient&#39;s blood constituents and/or analytes, including for example a percent value for arterial oxygen saturation, among other physiological parameters. The sensor has an emitter that transmits optical radiation of one or more wavelengths into a tissue site and a detector that responds to the intensity of the optical radiation after absorption by pulsatile arterial blood flowing within the tissue site. Based upon this response, a processor determines the relative concentrations of oxygenated hemoglobin (HbO 2 ) and deoxygenated hemoglobin (Hb) in the blood so as to derive oxygen saturation, which can provide early detection of potentially hazardous decreases in a patient&#39;s oxygen supply. 
     A pulse oximetry system generally includes a patient monitor, a communications medium such as a cable, and/or a physiological sensor having one or more light emitters and a detector, such as one or more light-emitting diodes (LEDs) and a photodetector. The sensor is attached to a tissue site, such as a finger, toe, earlobe, nose, hand, foot, or other site having pulsatile blood flow which can be penetrated by light from the one or more emitters. The detector is responsive to the emitted light after attenuation or reflection by pulsatile blood flowing in the tissue site. The detector outputs a detector signal to the monitor over the communication medium. The monitor processes the signal to provide a numerical readout of physiological parameters such as oxygen saturation (SpO2) and/or pulse rate. A pulse oximetry sensor is described in U.S. Pat. No. 6,088,607 entitled Low Noise Optical Probe; pulse oximetry signal processing is described in U.S. Pat. Nos. 6,650,917 and 6,699,194 entitled Signal Processing Apparatus and Signal Processing Apparatus and Method, respectively; a pulse oximeter monitor is described in U.S. Pat. No. 6,584,336 entitled Universal/Upgrading Pulse Oximeter; all of which are assigned to Masimo Corporation, Irvine, Calif., and each is incorporated by reference herein in its entirety. 
     There are many sources of measurement error introduced to pulse oximetry systems. Some such sources of error include the pulse oximetry system&#39;s electronic components, including emitters and detectors, as well as chemical and structural physiological differences between patients. Another source of measurement error is the effect of multiple scattering of photons as the photons pass through the patient&#39;s tissue (arterial blood) and arrive at the sensor&#39;s light detector. 
     SUMMARY 
     This disclosure describes embodiments of non-invasive methods, devices, and systems for measuring blood constituents, analytes, and/or substances such as, by way of non-limiting example, oxygen, carboxyhemoglobin, methemoglobin, total hemoglobin, glucose, proteins, lipids, a percentage thereof (e.g., saturation), pulse rate, perfusion index, oxygen content, total hemoglobin, Oxygen Reserve Index™ (ORI™) or for measuring many other physiologically relevant patient characteristics. These characteristics can relate to, for example, pulse rate, hydration, trending information and analysis, and the like. 
     In an embodiment, an optical physiological measurement system includes an emitter configured to emit light of one or more wavelengths. The system also includes a diffuser configured to receive the emitted light, to spread the received light, and to emit the spread light over a larger tissue area than would otherwise be penetrated by the emitter directly emitting light at a tissue measurement site. The tissue measurement site can include, such as, for example, a finger, a wrist, or the like. The system further includes a concentrator configured to receive the spread light after it has been attenuated by or reflected from the tissue measurement site. The concentrator is also configured to collect and concentrate the received light and to emit the concentrated light to a detector. The detector is configured to detect the concentrated light and to transmit a signal indicative of the detected light. The system also includes a processor configured to receive the transmitted signal indicative of the detected light and to determine, based on an amount of absorption, an analyte of interest, such as, for example, arterial oxygen saturation or other parameter, in the tissue measurement site. 
     In certain embodiments of the present disclosure, the diffuser comprises glass, ground glass, glass beads, opal glass, or a microlens-based, band-limited, engineered diffuser that can deliver efficient and uniform illumination. In some embodiments the diffuser is further configured to define a surface area shape by which the emitted spread light is distributed onto a surface of the tissue measurement site. The defined surface area shape can include, by way of non-limiting example, a shape that is substantially rectangular, square, circular, oval, or annular, among others. 
     According to some embodiments, the optical physiological measurement system includes an optical filter having a light-absorbing surface that faces the tissue measurement site. The optical filter also has an opening that is configured to allow the spread light, after being attenuated by the tissue measurement site, to be received by the concentrator. In an embodiment, the opening has dimensions, wherein the dimensions of the opening are similar to the defined surface area shape by which the emitted spread light is distributed onto the surface of the tissue measurement site. In an embodiment, the opening has dimensions that are larger than the defined surface area shape by which the emitted spread light is distributed onto the surface of the tissue measurement site. In other embodiments, the dimensions of the opening in the optical filter are not the same as the diffuser opening, but the dimensions are larger than the detector package. 
     In other embodiments of the present disclosure, the concentrator comprises glass, ground glass, glass beads, opal glass, or a compound parabolic concentrator. In some embodiments the concentrator comprises a cylindrical structure having a truncated circular conical structure on top. The truncated section is adjacent the detector. The light concentrator is structured to receive the emitted optical radiation, after reflection by the tissue measurement site, and to direct the reflected light to the detector. 
     In accordance with certain embodiments of the present disclosure, the processor is configured to determine an average level of the light detected by the detector. The average level of light is used to determine a physiological parameter in the tissue measurement site. 
     According to another embodiment, a method to determine a constituent or analyte in a patient&#39;s blood is disclosed. The method includes emitting, from an emitter, light of at least one wavelength; spreading, with a diffuser, the emitted light and emitting the spread light from the diffuser to a tissue measurement site; receiving, by a concentrator, the spread light after the spread light has been attenuated by the tissue measurement site; concentrating, by the concentrator, the received light and emitting the concentrated light from the concentrator to a detector; detecting, with the detector, the emitted concentrated light; transmitting, from the detector, a signal responsive to the detected light; receiving, by a processor, the transmitted signal responsive to the detected light; and processing, by the processor, the received signal responsive to the detected light to determine a physiological parameter. 
     In some embodiments, the method to determine a constituent or analyte in a patient&#39;s blood includes filtering, with a light-absorbing detector filter, scattered portions of the emitted spread light. According to an embodiment, the light-absorbing detector filter is substantially rectangular in shape and has outer dimensions in the range of approximately 1-5 cm in width and approximately 2-8 cm in length, and has an opening through which emitted light may pass, the opening having dimensions in the range of approximately 0.25-3 cm in width and approximately 1-7 cm in length. In another embodiment, the light-absorbing detector filter is substantially square in shape and has outer dimensions in the range of approximately 0.25-10 cm 2 , and has an opening through which emitted light may pass, the opening having dimensions in the range of approximately 0.1-8cm 2 . In yet another embodiment, the light-absorbing detector filter is substantially rectangular in shape and has outer dimensions of approximately 3 cm in width and approximately 6 cm in length, and has an opening through which emitted light may pass, the opening having dimensions of approximately 1.5 cm in width and approximately 4 cm in length. 
     In still other embodiments of the method to determine a constituent or analyte in a patient&#39;s blood, spreading, with a diffuser, the emitted light and emitting the spread light from the diffuser to a tissue measurement site is performed by at least one of a glass diffuser, a ground glass diffuser, a glass bead diffuser, an opal glass diffuser, and an engineered diffuser. In some embodiments the emitted spread light is emitted with a substantially uniform intensity profile. And in some embodiments, emitting the spread light from the diffuser to the tissue measurement site includes spreading the emitted light so as to define a surface area shape by which the emitted spread light is distributed onto a surface of the tissue measurement site. 
     According to yet another embodiment, a pulse oximeter is disclosed. The pulse oximeter includes an emitter configured to emit light at one or more wavelengths. The pulse oximeter also includes a diffuser configured to receive the emitted light, to spread the received light, and to emit the spread light directed at a tissue measurement sight. The pulse oximeter also includes a detector configured to detect the emitted spread light after being attenuated by or reflected from the tissue measurement site and to transmit a signal indicative of the detected light. The pulse oximeter also includes a processor configured to receive the transmitted signal and to process the received signal to determine an average absorbance of a blood constituent or analyte in the tissue measurement site over a larger measurement site area than can be performed with a point light source or point detector. In some embodiments, the diffuser is further configured to define a surface area shape by which the emitted spread light is distributed onto a surface of the tissue measurement site, and the detector is further configured to have a detection area corresponding to the defined surface area shape by which the emitted spread light is distributed onto the surface of the tissue measurement site. According to some embodiments, the detector comprises an array of detectors configured to cover the detection area. In still other embodiments, the processor is further configured to determine an average of the detected light. 
     For purposes of summarizing, certain aspects, advantages and novel features of the disclosure have been described herein. It is to be understood that not necessarily all such advantages can be achieved in accordance with any particular embodiment of the systems, devices and/or methods disclosed herein. Thus, the subject matter of the disclosure herein can be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other advantages as can be taught or suggested herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Throughout the drawings, reference numbers can be re-used to indicate correspondence between referenced elements. The drawings are provided to illustrate embodiments of the disclosure described herein and not to limit the scope thereof. 
         FIG. 1  illustrates a conventional approach to 2D pulse oximetry in which the emitter is configured to emit optical radiation as a point optical source. 
         FIG. 2  illustrates the disclosed 3D approach to pulse oximetry in which the emitted light irradiates a substantially larger volume of tissue as compared to the point source approach described with respect to  FIG. 2A . 
         FIG. 3  illustrates schematically a side view of a 3D pulse oximetry sensor according to an embodiment of the present disclosure. 
         FIG. 4A  is a top view of a portion of a 3D pulse oximetry sensor according to an embodiment of the present disclosure. 
         FIG. 4B  illustrates the top view of a portion of the 3D pulse oximetry sensor shown in  FIG. 4A , with the addition of a tissue measurement site in operational position. 
         FIG. 5  illustrates a top view of a 3D pulse oximetry sensor according to an embodiment of the present disclosure. 
         FIG. 6  illustrates a conventional 2D approach to reflective pulse oximetry in which the emitter is configured to emit optical radiation as a point optical source. 
         FIG. 7A  is a simplified schematic side view illustration of a reflective 3D pulse oximetry sensor according to an embodiment of the present disclosure. 
         FIG. 7B  is a simplified schematic top view illustration of the 3D reflective pulse oximetry sensor of  FIG. 7A . 
         FIG. 8  illustrates a block diagram of an example pulse oximetry system capable of noninvasively measuring one or more blood analytes in a monitored patient, according to an embodiment of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates schematically a conventional pulse oximetry sensor having a two-dimensional (2D) approach to pulse oximetry. As illustrated, the emitter  104  is configured to emit optical radiation as a point optical source, i.e., an optical radiation source that has negligible dimensions such that it may be considered as a point. This approach is referred to herein as “two-dimensional” pulse oximetry because it applies a two-dimensional analytical model to the three-dimensional space of the tissue measurement site  102  of the patient. Point optical sources feature a defined, freely selectable, and homogeneous light beam area. Light beams emitted from LED point sources often exhibit a strong focus which can produce a usually sharply-defined and evenly-lit illuminated spot often with high intensity dynamics. Illustratively, when looking at the surface of the tissue measurement site  102  (or “sample tissue”), which in this example is a finger, a small point-like surface area of tissue  204  is irradiated by a point optical source. In some embodiments, the irradiated circular area of the point optical source is in the range between 8 and 150 microns. Illustratively, the emitted point optical source of light enters the tissue measurement site  102  as a point of light. As the light penetrates the depth of the tissue  102 , it does so as a line or vector, representing a two-dimensional construct within a three-dimensional structure, namely the patient&#39;s tissue  102 . 
     Use of a point optical source is believed to reduce variability in light pathlength which would lead to more accurate oximetry measurements. However, in practice, photons do not travel in straight paths. Instead, the light particles scatter, bouncing around between various irregular objects (such as, for example, red blood cells) in the patient&#39;s blood. Accordingly, photon pathlengths vary depending on, among other things, their particular journeys through and around the tissue at the measurement site  102 . This phenomenon is referred to as “multiple scattering.” In a study, the effects of multiple scattering were examined by comparing the results of photon diffusion analysis with those obtained using an analysis based on the Beer-Lambert law, which neglects multiple scattering in the determination of light pathlength. The study found that that the difference between the average lengths of the paths traveled by red and infrared photons makes the oximeter&#39;s calibration curve (based on measurements obtained from normal subjects) sensitive to the total attenuation coefficients of the tissue in the two wavelength bands used for pulse oximetry, as well as to absorption by the pulsating arterial blood. 
       FIG. 2  illustrates schematically the disclosed systems, devices, and methods to implement three-dimensional (3D) pulse oximetry in which the emitted light irradiates a larger volume of tissue at the measurement site  102  as compared to the 2D point optical source approach described with respect to  FIG. 1 . In an embodiment, again looking at the surface of the tissue measurement site  102 , the irradiated surface area  206  of the measurement site  102  is substantially rectangular in shape with dimensions in the range of approximately 0.25-3 cm in width and approximately 1-6 cm in length. In another embodiment, the irradiated surface area  206  of the measurement site  102  is substantially rectangular in shape and has dimensions of approximately 1.5 cm in width and approximately 2 cm in length. In another embodiment, the irradiated surface area  206  of the measurement site  102  is substantially rectangular in shape and has dimensions of approximately 0.5 cm in width and approximately 1 cm in length. In another embodiment, the irradiated surface area  206  of the measurement site  102  is substantially rectangular in shape has dimensions of approximately 1 cm in width and approximately 1.5 cm in length. In yet another embodiment, the irradiated surface area  206  of the measurement site  102  is substantially square in shape and has dimensions in a range of approximately 0.25-9 cm 2 . In certain embodiments, the irradiated surface area  206  of the measurement site  102  is within a range of approximately 0.5-2 cm in width, and approximately 1-4 cm in length. Of course a skilled artisan will appreciate that many other shapes and dimensions of irradiated surface area  206  can be used. Advantageously, by irradiating the tissue measurement site  102  with a surface area  206 , the presently disclosed systems, devices, and methods apply a three-dimensional analytical model to the three-dimensional structure being measured, namely, the patient&#39;s sample tissue  102 . 
     According to the Beer-Lambert law, the amount of light absorbed by a substance is proportional to the concentration of the light-absorbing substance in the irradiated solution (i.e., arterial blood). Advantageously, by irradiating a larger volume of tissue  102 , a larger sample size of light attenuated (or reflected) by the tissue  102  is measured. The larger, 3D sample provides a data set that is more representative of the complete interaction of the emitted light as it passes through the patient&#39;s blood as compared to the 2D point source approach described above with respect to  FIG. 1 . By taking an average of the detected light, as detected over a surface area substantially larger than a single point, the disclosed pulse oximetry systems, devices, and methods will yield a more accurate measurement of the emitted light absorbed by the tissue, which will lead to a more accurate oxygen saturation measurement. 
       FIG. 3  illustrates schematically a side view of a pulse oximetry 3D sensor  300  according to an embodiment of the present disclosure. In the illustrated embodiment, the 3D sensor  300  irradiates the tissue measurement site  102  and detects the emitted light, after being attenuated by the tissue measurement site  102 . In other embodiments, for example, as describe below with respect to  FIGS. 7A and 7B , the 3D sensor  300  can be arranged to detect light that is reflected by the tissue measurement site  102 . The 3D sensor  300  includes an emitter  302 , a light diffuser  304 , a light-absorbing detector filter  306 , a light concentrator  308 , and a detector  310 . In some optional embodiments, the 3D sensor  300  further includes a reflector  305 . The reflector  305  can be a metallic reflector or other type of reflector. Reflector  305  can be a coating, film, layer or other type of reflector. The reflector  305  can serve as a reflector to prevent emitted light from emitting out of a top portion of the light diffuser  304  such that light from the emitter  302  is directed in the tissue rather than escaping out of a side or top of the light diffuser  304 . Additionally, the reflector  305  can prevent ambient light from entering the diffuser  304  which might ultimately cause errors within the detected light. The reflector  305  also prevent light piping that might occur if light from the detector  302  is able to escape from the light diffuser  304  and be pipped around a sensor securement mechanism to detector  310  without passing through the patient&#39;s tissue  102 . 
     The emitter  302  can serve as the source of optical radiation transmitted towards the tissue measurement site  102 . The emitter  302  can include one or more sources of optical radiation, such as LEDs, laser diodes, incandescent bulbs with appropriate frequency-selective filters, combinations of the same, or the like. In an embodiment, the emitter  302  includes sets of optical sources that are capable of emitting visible and near-infrared optical radiation. In some embodiments, the emitter  302  transmits optical radiation of red and infrared wavelengths, at approximately  650  nm and approximately  940  nm, respectively. In some embodiments, the emitter  302  includes a single source optical radiation. 
     The light diffuser  304  receives the optical radiation emitted from the emitter  302  and spreads the optical radiation over an area, such as the area  206  depicted in  FIG. 2 . In some embodiments, the light diffuser  304  is a beam shaper that can homogenize the input light beam from the emitter  302 , shape the output intensity profile of the received light, and define the way (e.g., the shape or pattern) the emitted light is distributed to the tissue measurement site  102 . Examples of materials that can be used to realize the light diffuser  304  include, without limitation, a white surface, glass, ground glass, glass beads, polytetrafluoroethylene (also known as Teflon®, opal glass, and greyed glass, to name a few. Additionally, engineered diffusers can be used to realize the diffuser  304  by providing customized light shaping with respect to intensity and distribution. Such diffusers can, for example, deliver substantially uniform illumination over a specified target area (such as, for example, irradiated surface area  206 ) in an energy-efficient manner. Examples of engineered diffusers can include molded plastics with specific shapes, patterns or textures designed to diffuse the emitter light across the entirety of the patient&#39;s tissue surface. 
     Advantageously, the diffuser  304  can receive emitted light in the form of a point optical source and spread the light to fit a desired surface area on a plane defined by the surface of the tissue measurement site  102 . In an embodiment, the diffuser  304  is made of ground glass which spreads the emitted light with a Gausian intensity profile. In another embodiment the diffuser  304  includes glass beads. In some embodiments, the diffuser  304  is constructed so as to diffuse the emitted light in a Lambertian pattern. A Lambertian pattern is one in which the radiation intensity is substantially constant throughout the area of dispersion. One such diffuser  304  is made from opal glass. Opal glass is similar to ground glass, but has one surface coated with a milky white coating to diffuse light evenly. In an embodiment, the diffuser  304  is capable of distributing the emitted light on the surface of a plane (e.g., the surface of the tissue measurement site  102 ) in a predefined geometry (e.g., a rectangle, square, or circle), and with a substantially uniform intensity profile and energy distribution. In some embodiments, the efficiency, or the amount of light transmitted by the diffuser  304 , is greater than 70% of the light emitted by the emitter  302 . In some embodiments, the efficiency is greater than 90% of the emitted light. Other optical elements known in the art may be used for the diffuser  304 . 
     In an embodiment, the diffuser  304  has a substantially rectangular shape having dimensions within a range of approximately 0.5-2 cm in width and approximately 1-4 centimeters in length. In another embodiment, the substantially rectangular shape of the diffuser  304  has dimensions of approximately 0.5 cm in width and approximately 1 cm in length. In another embodiment, the diffuser&#39;s  304  substantially rectangular shape has dimensions of approximately 1 cm in width and approximately 1.5 cm in length. In yet another embodiment, the diffuser  304  has a substantially square shape with dimensions in the range of approximately 0.25-10 cm 2 . 
     The light-absorbing detector filter  306 , which is also depicted in  FIG. 4A  in a top view, is a planar surface having an opening  402  through which the emitted light may pass after being attenuated by the tissue measurement site  102 . In the depicted embodiment, the opening  402  is rectangular-shaped, with dimensions substantially similar to the irradiated surface area  206 . According to an embodiment, the light-absorbing detector filter is substantially rectangular in shape and has outer dimensions of 4 cm in width and 8 cm in length, and has an opening through which emitted light may pass, the opening having dimensions of 2 cm in width and 5 cm in length. In another embodiment, the light-absorbing detector filter is substantially rectangular in shape and has outer dimensions in the range of 1-3 cm in width and 2-8 cm in length, and has an opening through which emitted light may pass, the opening having dimensions in the range of 0.25-2 cm in width and 1-4 cm in length. In yet another embodiment, the light-absorbing detector filter is substantially rectangular in shape and has outer dimensions of 3 cm in width and 6 cm in length, and has an opening through which emitted light may pass, the opening having dimensions of 1.5 cm in width and 4 cm in length. 
     The top surface of the light-absorbing filter  306  (facing the tissue measurement site  102  and the emitter  302 ) is coated with a material that absorbs light, such as, for example, black pigment. Many other types of light-absorbing materials are well known in the art and can be used with the detector filter  306 . During operation, light emitted from the emitter  302  can reflect off of the tissue measurement site  102  (or other structures within the 3D sensor  300 ) to neighboring portions of the 3D sensor  300 . If those neighboring portions of the 3D sensor  300  possess reflective surfaces, then the light can reflect back to the tissue measurement site  102 , progress through the tissue and arrive at the detector  310 . Such multiple scattering can result in detecting photons whose pathlengths are considerably longer than most of the light that is detected, thereby introducing variations in pathlength which will affect the accuracy of the measurements of the pulse oximetry 3D sensor  300 . Advantageously, the light-absorbing filter  306  reduces or eliminates the amount of emitted light that is reflected in this manner because it absorbs such reflected light, thereby stopping the chain of scattering events. In certain embodiments, the sensor-facing surfaces of other portions of the 3D sensor  300  are covered in light-absorbing material to further decrease the effect of reflective multiple scattering. 
     The light concentrator  308  is a structure to receive the emitted optical radiation, after attenuation by the tissue measurement site  102 , to collect and concentrate the dispersed optical radiation, and to direct the collected and concentrated optical radiation to the detector  310 . In an embodiment, the light concentrator  308  is made of ground glass or glass beads. In some embodiments, the light concentrator  308  includes a compound parabolic concentrator. 
     As described above with respect to  FIG. 1 , the detector  310  captures and measures light from the tissue measurement site  102 . For example, the detector  310  can capture and measure light transmitted from the emitter  302  that has been attenuated by the tissue in the measurement site  102 . The detector  310  can output a detector signal responsive to the light captured or measured. The detector  310  can be implemented using one or more photodiodes, phototransistors, or the like. In addition, a plurality of detectors  310  can be arranged in an array with a spatial configuration corresponding to the irradiated surface area  206  to capture the attenuated or reflected light from the tissue measurement site. 
     Referring to  FIG. 4A , a top view of a portion of the 3D sensor  300  is provided. The light-absorbing detector filter  306  is illustrated having a top surface coated with a light-absorbing material. The light-absorbing material can be a black opaque material or coating or any other dark color or coating configured to absorb light. Additionally, a rectangular opening  402  is positioned relative to the light concentrator  308  (shown in phantom) and the detector  310  such that light may pass through the rectangular opening  402 , into the light concentrator  308 , and to the detector  310 .  FIG. 4B  illustrates the top view of a portion of the 3D sensor  300  as in  FIG. 4A , with the addition of the tissue measurement site  102  in operational position. Accordingly, the rectangular opening  402 , the light concentrator  308  and the detector  310  are shown in phantom as being under the tissue measurement site  102 . In  FIGS. 4A and 4B , the light concentrator  308  is shown to have dimensions significantly larger than the dimensions of the rectangular opening  402 . In other embodiments, the dimensions of the light concentrator  308 , the rectangular opening  402 , and the irradiated surface area  206  are substantially similar. 
       FIG. 5  illustrates a top view of a 3D pulse oximetry sensor  500  according to an embodiment of the present disclosure. The 3D sensor  500  is configured to be worn on a patient&#39;s finger  102 . The 3D sensor  500  includes an adhesive substrate  502  having front flaps  504  and rear flaps  506  extending outward from a center portion  508  of the 3D sensor  500 . The center portion  508  includes components of the 3D pulse oximetry sensor  300  described with respect to  FIGS. 3, 4A and 4B . On the front side of the adhesive substrate  502  the emitter  302  and the light diffuser  304  are positioned. On the rear side of the adhesive substrate  502  the light-absorbent detector filter  306 , the light concentrator  308  and the detector  310  are positioned. In use, the patient&#39;s finger serving as the tissue measurement site  102  is positioned over the rectangular opening  402  such that when the front portion of the adhesive substrate is folded over on top of the patient&#39;s finger  102 , the emitter  302  and the light diffuser  304  are aligned with the measurement site  102 , the filter  306 , the light concentrator  308  and the detector  310 . Once alignment is established, the front and rear flaps  504 ,  506  can be wrapped around the finger measurement site  102  such that the adhesive substrate  502  provides a secure contact between the patient&#39;s skin and the 3D sensor  500 .  FIG. 5  also illustrates an example of a sensor connector cable  510  which is used to connect the 3D sensor  500  to a monitor  809 , as described with respect to  FIG. 8 . 
       FIG. 6  is a simplified schematic illustration of a conventional, 2D approach to reflective pulse oximetry in which the emitter is configured to emit optical radiation as a point optical source. Reflective pulse oximetry is a method by which the emitter and detector are located on the same side of the tissue measurement site  102 . Light is emitted into a tissue measurement site  102  and attenuated. The emitted light passes into the tissue  102  and is then reflected back to the same side of the tissue measurement site  102  as the emitter. As illustrated in  FIG. 6 , a depicted reflective 2D pulse oximetry sensor  600  includes an emitter  602 , a light block  606 , and a detector  610 . The light block  606  is necessary because the emitter  602  and the detector  610  are located on the same side of the tissue measurement site  102 . Accordingly, the light block  606  prevents incident emitter light, which did not enter the tissue measurement site  102 , from arriving at the detector  610 . The depicted 2D pulse oximetry sensor  600  is configured to emit light as a point source. As depicted in  FIG. 6 , a simplified illustration of the light path  620  of the emitted light from the emitter  602 , through the tissue measurement site  102 , and to the detector  610  is provided. Notably, a point source of light is emitted, and a point source of light is detected. As discussed above with respect to  FIG. 1 , use of a point optical source can result in substantial measurement error due to pathlength variability resulting from the multiple scatter phenomenon. The sample space provided by a 2D point optical emitter source is not large enough to account for pathlength variability, which will skew measurement results. 
       FIGS. 7A and 7B  are simplified schematic side and top views, respectively, of a 3D reflective pulse oximetry sensor  700  according to an embodiment of the present disclosure. In the illustrated embodiment, the 3D sensor  700  irradiates the tissue measurement site  102  and detects the emitted light that is reflected by the tissue measurement site  102 . The 3D sensor  700  can be placed on a portion of the patient&#39;s body that has relatively flat surface, such as, for example a wrist, because the emitter  702  and detector  710  are on located the same side of the tissue measurement site  102 . The 3D sensor  700  includes an emitter  702 , a light diffuser  704 , a light block  706 , a light concentrator  708 , and a detector  710 . 
     As previously described, the emitter  702  can serve as the source of optical radiation transmitted towards the tissue measurement site  102 . The emitter  702  can include one or more sources of optical radiation. Such sources of optical radiation can include LEDs, laser diodes, incandescent bulbs with appropriate frequency-selective filters, combinations of the same, or the like. In an embodiment, the emitter  702  includes sets of optical sources that are capable of emitting visible and near-infrared optical radiation. In some embodiments, the emitter  702  transmits optical radiation of red and infrared wavelengths, at approximately 650 nm and approximately 940 nm, respectively. In some embodiments, the emitter  702  includes a single source of optical radiation. 
     The light diffuser  704  receives the optical radiation emitted from the emitter  302  and homogenously spreads the optical radiation over a wide, donut-shaped area, such as the area outlined by the light diffuser  704  as depicted in  FIG. 7B . Advantageously, the diffuser  704  can receive emitted light in the form of a 2D point optical source (or any other form) and spread the light to fit the desired surface area on a plane defined by the surface of the tissue measurement site  102 . In an embodiment, the diffuser  704  is made of ground glass or glass beads. A skilled artisan will understand that may other materials can be used to make the light diffuser  704 . 
     The light blocker  706  includes an annular ring having a cover portion  707  sized and shaped to form a light isolation chamber for the light concentrator  708  and the detector  710 . (For purposes of illustration, the light block cover  707  is not illustrated in  FIG. 7B .) The light blocker  706  and the cover  707  can be made of any material that optically isolates the light concentrator  708  and the detector  710 . The light isolation chamber formed by the light blocker  706  and cover  708  ensures that the only light detected by the detector  710  is light that is reflected from the tissue measurement site. 
     The light concentrator  708  is a cylindrical structure with a truncated circular conical structure on top, the truncated section of which of which is adjacent the detector  710 . The light concentrator  708  is structured to receive the emitted optical radiation, after reflection by the tissue measurement site  102 , and to direct the reflected light to the detector  710 . In an embodiment, the light concentrator  708  is made of ground glass or glass beads. In some embodiments, the light concentrator  708  includes a compound parabolic concentrator. 
     As previously described, the detector  710  captures and measures light from the tissue measurement site  102 . For example, the detector  710  can capture and measure light transmitted from the emitter  702  that has been reflected from the tissue in the measurement site  102 . The detector  710  can output a detector signal responsive to the light captured or measured. The detector  710  can be implemented using one or more photodiodes, phototransistors, or the like. In addition, a plurality of detectors  710  can be arranged in an array with a spatial configuration corresponding to the irradiated surface area depicted in  FIG. 7B  by the light concentrator  708  to capture the reflected light from the tissue measurement site. 
     Advantageously, the light path  720  illustrated in  FIG. 7A  depicts a substantial sample of reflected light that enter the light isolation chamber formed by the light blocker  706  and cover  707 . As previously discussed, the large sample of reflected light (as compared to the reflected light collected using the 2D point optical source approach) provides the opportunity to take an average of the detected light, to derive a more accurate measurement of the emitted light absorbed by the tissue, which will lead to a more accurate oxygen saturation measurement. 
     Referring now to  FIG. 7B , a top view of the 3D sensor  700  is illustrated with both the emitter  702  and the light blocker cover  707  removed for ease of illustration. The outer ring illustrates the footprint of the light diffuser  704 . As light is emitted from the emitter  702  (not shown in  FIG. 7B ), it is diffused homogenously and directed to the tissue measurement site  102 . The light blocker  706  forms the circular wall of a light isolation chamber to keep incident light from being sensed by the detector  710 . The light blocker cover  707  blocks incidental light from entering the light isolation chamber from above. The light concentrator  710  collects the reflected light from the tissue measurement site  102  and funnels it upward toward the detector  710  at the center of the 3D sensor  700 . 
       FIG. 8  illustrates an example of an optical physiological measurement system  800 , which may also be referred to herein as a pulse oximetry system  800 . In certain embodiments, the pulse oximetry system  800  noninvasively measures a blood analyte, such as oxygen, carboxyhemoglobin, methemoglobin, total hemoglobin, glucose, proteins, lipids, a percentage thereof (e.g., saturation), pulse rate, perfusion index, oxygen content, total hemoglobin, Oxygen Reserve Index™ (ORI™) or many other physiologically relevant patient characteristics. These characteristics can relate to, for example, pulse rate, hydration, trending information and analysis, and the like. The system  800  can also measure additional blood analytes and/or other physiological parameters useful in determining a state or trend of wellness of a patient. 
     The pulse oximetry system  800  can measure analyte concentrations at least in part by detecting optical radiation attenuated by tissue at a measurement site  102 . The measurement site  102  can be any location on a patient&#39;s body, such as a finger, foot, earlobe, wrist, forehead, or the like. 
     The pulse oximetry system  800  can include a sensor  801  (or multiple sensors) that is coupled to a processing device or physiological monitor  809 . In an embodiment, the sensor  801  and the monitor  809  are integrated together into a single unit. In another embodiment, the sensor  801  and the monitor  809  are separate from each other and communicate with one another in any suitable manner, such as via a wired or wireless connection. The sensor  801  and monitor  809  can be attachable and detachable from each other for the convenience of the user or caregiver, for ease of storage, sterility issues, or the like. 
     In the depicted embodiment shown in  FIG. 8 , the sensor  801  includes an emitter  804 , a detector  806 , and a front-end interface  808 . The emitter  804  can serve as the source of optical radiation transmitted towards measurement site  102 . The emitter  804  can include one or more sources of optical radiation, such as light emitting diodes (LEDs), laser diodes, incandescent bulbs with appropriate frequency-selective filters, combinations of the same, or the like. In an embodiment, the emitter  804  includes sets of optical sources that are capable of emitting visible and near-infrared optical radiation. 
     The pulse oximetry system  800  also includes a driver  811  that drives the emitter  804 . The driver  111  can be a circuit or the like that is controlled by the monitor  809 . For example, the driver  811  can provide pulses of current to the emitter  804 . In an embodiment, the driver  811  drives the emitter  804  in a progressive fashion, such as in an alternating manner. The driver  811  can drive the emitter  804  with a series of pulses for some wavelengths that can penetrate tissue relatively well and for other wavelengths that tend to be significantly absorbed in tissue. A wide variety of other driving powers and driving methodologies can be used in various embodiments. The driver  811  can be synchronized with other parts of the sensor  801  to minimize or reduce jitter in the timing of pulses of optical radiation emitted from the emitter  804 . In some embodiments, the driver  811  is capable of driving the emitter  804  to emit optical radiation in a pattern that varies by less than about 10 parts-per-million. 
     The detector  806  captures and measures light from the tissue measurement site  102 . For example, the detector  806  can capture and measure light transmitted from the emitter  804  that has been attenuated or reflected from the tissue at the measurement site  102 . The detector  806  can output a detector signal  107  responsive to the light captured and measured. The detector  806  can be implemented using one or more photodiodes, phototransistors, or the like. In some embodiments, a detector  806  is implemented in detector package to capture and measure light from the tissue measurement site  102  of the patient. The detector package can include a photodiode chip mounted to leads and enclosed in an encapsulant. In some embodiments, the dimensions of the detector package are approximately 2 square centimeters. In other embodiments, the dimensions of the detector package are approximately 1.5 centimeters in width and approximately 2 centimeters in length. 
     The front-end interface  808  provides an interface that adapts the output of the detectors  806 , which is responsive to desired physiological parameters. For example, the front-end interface  808  can adapt the signal  807  received from the detector  806  into a form that can be processed by the monitor  809 , for example, by a signal processor  810  in the monitor  809 . The front-end interface  808  can have its components assembled in the sensor  801 , in the monitor  809 , in a connecting cabling (if used), in combinations of the same, or the like. The location of the front-end interface  808  can be chosen based on various factors including space desired for components, desired noise reductions or limits, desired heat reductions or limits, and the like. 
     The front-end interface  808  can be coupled to the detector  806  and to the signal processor  810  using a bus, wire, electrical or optical cable, flex circuit, or some other form of signal connection. The front-end interface  808  can also be at least partially integrated with various components, such as the detectors  806 . For example, the front-end interface  808  can include one or more integrated circuits that are on the same circuit board as the detector  806 . Other configurations can also be used. 
     As shown in  FIG. 8 , the monitor  909  can include the signal processor  810  and a user interface, such as a display  812 . The monitor  809  can also include optional outputs alone or in combination with the display  812 , such as a storage device  814  and a network interface  816 . In an embodiment, the signal processor  810  includes processing logic that determines measurements for desired analytes based on the signals received from the detector  806 . The signal processor  810  can be implemented using one or more microprocessors or sub-processors (e.g., cores), digital signal processors, application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), combinations of the same, and the like. 
     The signal processor  810  can provide various signals that control the operation of the sensor  801 . For example, the signal processor  810  can provide an emitter control signal to the driver  811 . This control signal can be useful in order to synchronize, minimize, or reduce jitter in the timing of pulses emitted from the emitter  804 . Accordingly, this control signal can be useful in order to cause optical radiation pulses emitted from the emitter  804  to follow a precise timing and consistent pattern. For example, when a transimpedance-based front-end interface  808  is used, the control signal from the signal processor  810  can provide synchronization with an analog-to-digital converter (ADC) in order to avoid aliasing, cross-talk, and the like. As also shown, an optional memory  813  can be included in the front-end interface  808  and/or in the signal processor  810 . This memory  813  can serve as a buffer or storage location for the front-end interface  808  and/or the signal processor  810 , among other uses. 
     The user interface  812  can provide an output, e.g., on a display, for presentation to a user of the pulse oximetry system  800 . The user interface  812  can be implemented as a touch-screen display, a liquid crystal display (LCD), an organic LED display, or the like. In alternative embodiments, the pulse oximetry system  800  can be provided without a user interface  812  and can simply provide an output signal to a separate display or system. 
     The storage device  814  and a network interface  816  represent other optional output connections that can be included in the monitor  809 . The storage device  814  can include any computer-readable medium, such as a memory device, hard disk storage, EEPROM, flash drive, or the like. The various software and/or firmware applications can be stored in the storage device  814 , which can be executed by the signal processor  810  or another processor of the monitor  809 . The network interface  816  can be a serial bus port (RS-232/RS-485), a Universal Serial Bus (USB) port, an Ethernet port, a wireless interface (e.g., WiFi such as any 802.1x interface, including an internal wireless card), or other suitable communication device(s) that allows the monitor  809  to communicate and share data with other devices. The monitor  809  can also include various other components not shown, such as a microprocessor, graphics processor, or controller to output the user interface  812 , to control data communications, to compute data trending, or to perform other operations. 
     Although not shown in the depicted embodiment, the pulse oximetry system  800  can include various other components or can be configured in different ways. For example, the sensor  801  can have both the emitter  804  and detector  806  on the same side of the tissue measurement site  102  and use reflectance to measure analytes. 
     Although the foregoing disclosure has been described in terms of certain preferred embodiments, many other variations than those described herein will be apparent to those of ordinary skill in the art. 
     Conditional language used herein, such as, among others, “can,” “might,” “may,” “e.g.,” and the like, unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements and/or states. Thus, such conditional language is not generally intended to imply that features, elements and/or states are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without author input or prompting, whether these features, elements and/or states are included or are to be performed in any particular embodiment. The terms “comprising,” “including,” “having,” and the like are synonymous and are used inclusively, in an open-ended fashion, and do not exclude additional elements, features, acts, operations, and so forth. Also, the term “or” is used in its inclusive sense (and not in its exclusive sense) so that when used, for example, to connect a list of elements, the term “or” means one, some, or all of the elements in the list. Further, the term “each,” as used herein, in addition to having its ordinary meaning, can mean any subset of a set of elements to which the term “each” is applied. 
     While the above detailed description has shown, described, and pointed out novel features as applied to various embodiments, it will be understood that various omissions, substitutions, and changes in the form and details of the systems, devices or algorithms illustrated can be made without departing from the spirit of the disclosure. As will be recognized, certain embodiments of the disclosure described herein can be embodied within a form that does not provide all of the features and benefits set forth herein, as some features can be used or practiced separately from others. 
     The term “and/or” herein has its broadest, least limiting meaning which is the disclosure includes A alone, B alone, both A and B together, or A or B alternatively, but does not require both A and B or require one of A or one of B. As used herein, the phrase “at least one of” A, B, “and” C should be construed to mean a logical A or B or C, using a non-exclusive logical or. 
     The apparatuses and methods described herein may be implemented by one or more computer programs executed by one or more processors. The computer programs include processor-executable instructions that are stored on a non-transitory tangible computer readable medium. The computer programs may also include stored data. Non-limiting examples of the non-transitory tangible computer readable medium are nonvolatile memory, magnetic storage, and optical storage. Although the foregoing disclosure has been described in terms of certain preferred embodiments, other embodiments will be apparent to those of ordinary skill in the art from the disclosure herein. Additionally, other combinations, omissions, substitutions and modifications will be apparent to the skilled artisan in view of the disclosure herein. Accordingly, the present invention is not intended to be limited by the description of the preferred embodiments, but is to be defined by reference to claims. 
     Additionally, all publications, patents, and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent, or patent application were specifically and individually indicated to be incorporated by reference.