Controllable masking for optical tissue sensing

Abstract

An example system includes a light source configured to emit light towards a tissue of a patient, a detector configured to detect the light emitted by the light source after the light passes through the tissue of the patient, and a controllable mask disposed between the detector and the tissue of the patient. The controllable mask is configured to block a first portion of the light passing through a first portion of the tissue and transmit a second portion of the light passing through a second portion of the tissue. The system also includes processing circuitry configured to determine a physiological characteristic of the patient based on the second portion of the light.

Description

CONTROLLABLE MASKING FOR OPTICAL TISSUE SENSING

[0001] This application claims the benefit of U.S. Provisional Patent Application Serial No. 63 / 639,154, filed April 26, 2024, the entire content of which is incorporated herein by reference.TECHNICAL FIELD

[0002] This disclosure generally relates to determining and / or predicting a physiological characteristic of a patient via an implantable medical device.BACKGROUND

[0003] Various implantable medical devices (IMDs) have been clinically implanted or proposed for therapeutically treating or monitoring one or more conditions of a patient. Such devices may be adapted to monitor or treat conditions or functions relating to heart, muscle, nerve, brain, stomach, endocrine organs or other organs and their related functions. Advances in design and manufacture of miniaturized electronic and sensing devices have enabled development of implantable devices capable of therapeutic as well as diagnostic functions such as pacemakers, cardioverters, defibrillators, biochemical sensors, implantable loop recorders, and pressure sensors, among others. Such devices may be associated with leads that position electrodes or sensors at a desired location or may be leadless with electrodes integrated into the device housing or sensors using other sensing techniques, such as optical sensors. These devices may have the ability to wirelessly transmit data either to another device implanted in the patient or to another instrument located externally of the patient, or both.SUMMARY

[0004] In general, this disclosure is directed to systems, devices, and techniques for measuring and / or determining a physiological characteristic of a patient based on an optical signal of an optical sensor. In particular, methods and devices disclosed herein are directed to controllably (e.g., dynamically) masking an optical receiver / detector and / or an optical source of an optical sensor of an IMD such that the sensor may sample specific portions of tissue of a patient, e.g., specific portions of the local sampling volume of thefield of view of the sensor. Dynamic and controlled masking of one or both of the light source and detector of the optical sensor may enable the optical sensor to determine a masking configuration for which light interacting with specific tissue structure(s) yields the highest signal fidelity while rejecting light from tissues that does not contribute to signal fidelity, which may improve the overall signal-to-noise ratio (SNR) for sensing optical parameters and / or physiological characteristic of the specific tissue structure(s).

[0005] In one example, this disclosure describes a system including: a light source configured to emit light towards a tissue of a patient; a detector configured to detect the light emitted by the light source after the light passes through the tissue of the patient; a controllable mask disposed between the detector and the tissue of the patient, wherein the controllable mask is configured to block a first portion of the light passing through a first portion of the tissue and transmit a second portion of the light passing through a second portion of the tissue; and processing circuitry configured to determine a physiological characteristic of the patient based on the second portion of the light.

[0006] In another example, this disclosure describes a method of determining a physiological characteristic of a patient, the method including: emitting light, by a light source, towards a tissue of the patient; controlling, by processing circuitry, a controllable mask to block a first portion of the light passing through a first portion of the tissue; controlling, by the processing circuitry, the controllable mask to substantially transmit a second portion of the light passing through a second portion of the tissue; detecting, by a detector, the second portion of the light; and determining, by the processing circuitry and based on the detected second portion of the light, the physiological characteristic of the patient.

[0007] In another example, this disclosure describes an implantable medical device (IMD) including: a light source configured to emit light towards a tissue of a patient; a detector configured to detect the light emitted by the light source after the light passes through the tissue of the patient; a controllable mask disposed between the detector and the tissue of the patient, wherein the controllable mask is configured to block a first portion of the light passing through a first portion of the tissue and transmit a second portion of the light passing through a second portion of the tissue; and processing circuitry configured to determine a physiological characteristic of the patient based on the second portion of the light.

[0008] This summary is intended to provide an overview of the subject matter described in this disclosure. It is not intended to provide an exclusive or exhaustive explanation of the apparatus and methods described in detail within the accompanying drawings and description below. The details of one or more aspects of the disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description, drawings, and claims.BRIEF DESCRIPTION OF DRAWINGS

[0009] FIG. l is a conceptual drawing illustrating an example medical system in conjunction with a patient, according to various examples described in this disclosure.

[0010] FIG. 2 is a functional schematic diagram of an example implantable medical device (IMD), according to various examples described in this disclosure.

[0011] FIG. 3 is a conceptual perspective schematic diagram of the example IMD of FIG. 2, according to various examples described in this disclosure.

[0012] FIG. 4 is a block diagram illustrating the example IMD of FIGS. 1-3.

[0013] FIG. 5 is a conceptual cross-sectional side-view of the example IMD of FIGS. 1-4 including a controllable mask in a first configuration, according to various examples described in this disclosure.

[0014] FIG. 6 is a conceptual cross-sectional side-view of the example IMD of FIGS. 1-4 including a controllable mask in a second configuration, according to various examples described in this disclosure.

[0015] FIG. 7 is a conceptual cross-sectional side-view of the example IMD of FIGS. 1-4 including a controllable mask in a third configuration, according to various examples described in this disclosure.

[0016] FIG. 8 is a conceptual cross-sectional side-view of the example IMD of FIGS. 1-4 including a controllable mask in a fourth configuration , according to various examples described in this disclosure.

[0017] FIG. 9 is a flow diagram of an example method of determining a physiological characteristic of a patient, according to various examples described in this disclosure.

[0018] In the figures, use of a same reference number or a same reference number with a letter extension may be used to indicate a same or corresponding device or element when used in a same drawing or in different drawings. In addition, unless otherwise indicated,devices and / or other objects such as a patient, an implantable medical device, or an electrical device such as an electrical coil, are not necessarily illustrated to scale relative to each other and / or relative to an actual example of the item being illustrated. In particular, various drawings provided with this disclosure illustrate a “patient” represented by a human-shaped outline and are not to be considered drawn to scale relative to an actual human patient or with respect to other objects illustrated in the same figure unless otherwise specifically indicated in the figure for example by dimensional indicators, or for example as otherwise described in the text of the disclosureDETAILED DESCRIPTION

[0019] A variety of types of medical devices sense physiological signals or parameters of a patient. An implantable medical device (IMD) may include an optical sensor configured to sense optical signals from which processing circuitry of a system including the IMD may determine physiological signal values or parameter values. The optical sensor may be integrated with a housing of the IMD. Example IMDs that may be configured to sense optical signals that may be used to monitor physiological signals or parameters include pacemakers and implantable cardioverter-defibrillators, which may be coupled to intravascular or extravascular leads, as well as pacemakers with housings configured for implantation within the patient, which may be leadless. An example of pacemaker configured for intracardiac implantation is the Micra™ Transcatheter Pacing System, available from Medtronic, Inc. Some IMDs that do not provide therapy, e.g., implantable patient monitors, may be configured to sense optical signals that may be used to monitor physiological signals or parameters. One example of such an IMD is the Reveal LINQ™ and LINQ II™ Insertable Cardiac Monitors (ICMs), available from Medtronic, pic, which may be inserted subcutaneously. Such IMDs may facilitate relatively longer-term monitoring of patients during normal daily activities, and may periodically transmit collected data to a network service, such as the Medtronic Carelink™ Network.

[0020] The fidelity of optical sensing in tissue may depend on the anatomy present in the sampling volume local to the optical receiver. Arterial structures such as arterioles have relatively high dynamic optical absorbance through the cardiac cycle, thus their presence in this sampling volume yields highly dynamic received signal amplitude.Optical sensors are statically coupled with sampling tissue volume containing heterogeneously distributed structures which may or may not contain enough dynamic absorption to yield the signal amplitudes necessary for the target physiological measurement. In some examples, optical sensing may sense static optical absorbance, e.g., of non-moving tissue to determine a tissue oxygen saturation (StO2) or oxygen saturation (SpO2), and there may be instances where the optical sensor is adjacent to structures, such as bone, such that it may be desirable to sample different tissue volumes for a static optical absorbance measurement.

[0021] In some examples, methods disclosed herein allow an optical sensing device to controllably and / or dynamically mask the light entering its optical receiver, e.g., detector, such that it can sample specific portions of the local sampling volume. Controlled masking may allow the optical sensor to seek, e.g., actively search for, light interacting with specific tissue structure(s) that yield the highest signal fidelity while rejecting light from tissue that does not contribute to signal fidelity.

[0022] In examples disclosed herein, the controllable mask my comprise an electronically controllable polarization array, such as liquid crystal stack or a liquid crystal (LC) array. The LC array may be located between the detector and the tissue being sampled, e.g., the local sampling volume. In some examples, the LC array may be bonded to a sapphire cover of the IMD. The LC array may function as an array of pixelated “windows” where each window is configured to block, transmit, or attenuate light passing through the pixel. For example, the LC array may allow the device to dynamically activate certain polarization cells / pixels thus masking the light trying to enter the device from the tissue behind the activated cell / pixel. This controllable, dynamic activation may allow the optical sensor and / or IMD to map the anatomy of the tissue in the local sampling volume and develop a pattern of clear / opaque pixels that yields the most desired received signal properties, such as amplitude, AC / DC ratio, signal to noise, or the like.

[0023] Static masking of the optical sensors may not allow the optical sensor and / or IMD to adapt to the anatomical structure(s) present within the local sampling volume, and does not provide control of the signal fidelity, e.g., to search for masking patterns that allow detection of transmitter-to arterial blood structures-to-emitter optical vector or paths and blocks vectors or paths not including arterial blood structures. A controllable mask may enable the optical sensor and / or IMD to search for, and focus on, arterial bloodstructures specific to its sampling volume at implant and / or over time, e.g., should the position of the IMD (or arterial structures) change over time due to factors such as encapsulations. Additionally, a controllable mask may provide masking of ambient light, e.g., external light sources contributing to measurement noise as the patient's environment changes, which may improve signal fidelity of the optical sensor across a wider range of ambient environments.

[0024] FIG. 1 is a conceptual drawing illustrating an example medical system 10 in conjunction with a patient 12, according to various examples described in this disclosure. The systems, devices, and methods described in this disclosure may include example optical sensors included with IMD 14, as illustrated and described with respect to FIG. 1. For purposes of this description, knowledge of cardiovascular anatomy and functionality is presumed, and details are omitted except to the extent necessary or desirable to explain the context of the techniques of this disclosure. System 10 includes IMD 14 including optical sensor 62, implanted at or near the site of a heart 18 of a patient 12 and an external computing device 24. The systems, devices, and methods described herein may provide controllable masking of a detector and / or light source of optical sensor 62 to improve signal fidelity and / or SNR.

[0025] Example techniques disclosed herein may be used with IMD 14, which may be in wireless communication with at least one of external device 24 and other devices not pictured in FIG. 1. In some examples, IMD 14 is implanted outside of a thoracic cavity of patient 12 (e.g., subcutaneously in the pectoral location illustrated in FIG. 1). IMD 14 may be positioned near the sternum near or just below the level of the heart of patient 12, e.g., at least partially within the cardiac silhouette. IMD 14 includes a plurality of electrodes 48 (FIGS. 2-7) and is configured to sense a cardiac electrogram (EGM) via the plurality of electrodes, as well as other physiological signals and / or parameters via optical sensor 62. In some examples, IMD 14 takes the form of the LINQ™ or LINQ II™ ICM, or another ICM similar to, e.g., a version or modification of, the LINQ™ or LINQ II™ ICM. Although described primarily in the context of examples in which IMD 14 is an ICM, in various examples, IMD 14 may represent a cardiac monitor, a defibrillator, a cardiac resynchronization pacer / defibrillator, a pacemaker, an implantable pressure sensor, a neurostimulator, or any other implantable or external medical device.

[0026] In some examples, IMD 14 is defined by a length L, a width W and thickness or depth D and is in the form of an elongated rectangular prism wherein the length L is much larger than the width W, which in turn is larger than the depth D, as illustrated in FIG. 3 below. In one example, the geometry of the IMD 14 - in particular a width W greater than the depth D - is selected to allow IMD 14 to be inserted under the skin of the patient using a minimally invasive procedure and to remain in the desired orientation during insert. For example, IMD 14 may include a radial asymmetry (notably, a rectangular shape) along the longitudinal axis that maintains the device in the proper orientation following insertion. For example, in one example the spacing between electrode 48 A and electrode 48B may range from 30 millimeters (mm) to 55mm, 35mm to 55mm, and from 40mm to 55mm and may be any range or individual spacing from 25mm to 60mm. In another example the spacing between electrode 48A and electrode 48B may range from 15mm to 30mm, 17mm to 28mm, and from 20mm to 28mm and may be any range or individual spacing from 12mm to 30mm. In addition, IMD 14 may have a length L that ranges from 30mm to about 70mm. In other embodiments, the length L may range from 40mm to 60mm, 45mm to 60mm and may be any length or range of lengths between about 30mm and about 70mm. In some examples, IMD 14 may have a length L that ranges from 15mm to about 35mm, or from 20mm to 30mm, 22mm to 30mm and may be any length or range of lengths between about 15mm and about 35mm. In addition, the width W of a major surface of IMD 14, e.g., insulative cover 76 in the example shown, may range from 3mm to 10mm and may be any single or range of widths between 3mm and 10mm, or may range from 1.5mm to 5mm and may be any single or range of width between 1.5mm and 5mm. The thickness of depth D of IMD 14 may range from 2mm to 9mm, or from 1.5mm to 4.5mm. In other embodiments, the depth D of IMD 14 may range from 2mm to 5mm and may be any single or range of depths from 2mm to 9mm, or may range from 1mm to 2.5mm and may be any single or range of depts from 1mm to 4.5mm. In addition, IMD 14 according to an example of the present invention has a geometry and size designed for ease of implant and patient comfort. Examples of IMD 14 described in this disclosure may have a volume of 3 cubic centimeters (cm) or less, 1.5 cubic cm or less or any volume between 3 and 1.5 cubic centimeters, or may have a volume of 1.5 cubic centimeters (cm) or less, 0.75 cubic cm or less or any volume between 1.5 and 0.75 cubic centimeters.

[0027] External device 24 may be a computing device with a display viewable by the user and an interface for providing input to external device 24 (i.e., a user input mechanism). In some examples, external device 24 may be a notebook computer, tablet computer, workstation, one or more servers, cellular phone, personal digital assistant, or another computing device that may run an application that enables the computing device to interact with IMD 14. External device 24 is configured to communicate with IMD 14 and, optionally, another computing device (not illustrated in FIG. 1), via wireless communication. External device 24, for example, may communicate via near-field communication technologies (e.g., inductive coupling, NFC or other communication technologies operable at ranges less than 10-20 cm) and far-field communication technologies (e.g., RF telemetry according to the 802.11 or Bluetooth® specification sets, or other communication technologies operable at ranges greater than near-field communication technologies).

[0028] External device 24 may be used to configure operational parameters for IMD 14. External device 24 may be used to retrieve data from IMD 14. The retrieved data may include values of physiological parameters measured by IMD 14, indications of episodes of arrhythmia or other maladies detected by IMD 14, and physiological signals recorded by IMD 14, e.g., from optical sensor 62. For example, external device 24 may retrieve cardiac EGM segments recorded by IMD 14, e.g., due to IMD 14 determining that an episode of arrhythmia or another malady occurred during the segment, or in response to a request to record the segment from patient 12 or another user. In some examples, one or more remote computing devices may interact with IMD 14 in a manner similar to external device 24, e.g., to program IMD 14 and / or retrieve data from IMD 14, via a network.

[0029] In various examples, IMD 14 may include one or more additional sensor circuits configured to sense a particular physiological or neurological parameter associated with patient 12, or may comprise a plurality of sensor circuits, which may be located at various and / or different positions relative to patient 12 and / or relative to each other and may be configured to sense one or more physiological parameters associated with patient 12.

[0030] For example, IMD 14 may include a sensor operable to sense a body temperature of patient 12 in a location of the IMD 14, or at the location of the patient where a temperature sensor coupled by a lead to IMD 14 is located. In another example,IMD 14 may include a sensor configured to sense motion, such as steps taken by patient 12 and / or a position or a change of posture of patient 12. In various examples, IMD 14 may include a sensor that is configured to detect breaths taken by patient 12. In various examples, IMD 14 may include a sensor configured to detect heartbeats of patient 12.

[0031] In various examples, IMD 14 includes optical sensor 62 that is configured to measure systemic blood pressure of patient 12, an oxygenation of blood of patient 12, blood movement within tissue and / or vasculature of patient 12 which may be indicative of pulse pressure waveforms. In some examples, the optical sensor 62 of IMD 14 includes a light source 63 configured to emit light towards tissue of patient 12, e.g., a photo emitter such as a light emitting diode (LED), a laser such as a vertical cavity surface emitting laser (VCSEL), or any suitable light source. Optical sensor 62 also includes a detector configured to detect the light emitted by the light source after the light passes through the tissue of the patient. Although optical sensor 62 as shown in the examples of FIGS. 2-8 include light source 63, in other examples, light source 63 may be external to optical sensor 62 and / or IMD 14, e.g., a separate device may include light source 63.

[0032] Optical sensor 62 also includes a controllable mask disposed between the detector and the tissue of the patient. The controllable mask may be configured to block a first portion of the light passing through a first portion of the tissue and transmit a second portion of the light passing through a second portion of the tissue. For example, the controllable mask maybe configured to transmit a portion of the light passing through a portion of the tissue including vasculature and is indicative, upon detection by the detector, of blood movement (e.g., at a constant rate, accelerating, or decelerating) and / or blood volume change within the vasculature, and the controllable mask maybe configured to block a different portion of light from a different portion of the tissue that does not include vasculature (or does not include vasculature of substantial size or interest) and is not indicative of blood movement and / or blood volume change through vasculature but would still otherwise be detected by the detector and contribute to noise or reducing the effective dynamic range of the detector (e.g., by effectively being ambient light). In some examples, the controllable mask may be configured to block ambient light, e.g., light from a different light source external to optical sensor 62 that would be detected by the detector (if not blocked) and contribute to noise or reducing the effective dynamic range of the detector. Processing circuitry of IMD 14 or external device 24 may be configured todetermine a physiological characteristic (e.g., a physiological signal or parameter) of patient 12 based on the second portion of the light, e.g., the transmitted portion of the light.

[0033] In some examples, one or more of the sensors comprising IMD 14 may be implanted within patient 12, that is, implanted below at least the skin level of the patient. In various examples, IMD 14 may be configured to sense one or more physiological parameters associated with patient 12, and to transmit data corresponding to the sensed physiological parameter or parameters to the external device 24, as represented by the lightning bolt coupling IMD 14 to the external device 24.

[0034] Transmission of data from IMD 14 to external device 24 in various examples may be performed via wireless transmission, using for example any of the formats for wireless communication described above. In various examples, IMD 14 may communicate wirelessly to an external device (e.g., an instrument or instruments) other than or in addition to external device 24, such as a transceiver or an access point that provides a wireless communication link between IMD 14 and a network. Examples of communication techniques used by any of the devices described above with respect to FIG. 1 may include radiofrequency (RF) telemetry, which may be an RF link established via Bluetooth®, Wi-Fi, or medical implant communication service (MICS).

[0035] In some examples, system 10 may include more or fewer components than depicted in FIG. 1. For example, in some examples, system 10 may include multiple additional IMDs, such as implantable pacemaker devices or other IMDs, implanted within patient 12. In these examples, IMD 14 may function as a hub device for the other IMDs. For example, the additional IMDs may be configured to communicate with the IMD 14, which would then communicate to the external device 24, such as a user’s smartphone, via a low-energy telemetry protocol. IMD 14 may provide a theoretically infinite energy capacity, in that IMD 14 may not need to be replaced or otherwise removed. Accordingly, IMD 14 may provide the ability to more-frequently telemeter information, as well as more-active titration of therapies.

[0036] For the remainder of the disclosure, a general reference to a medical device system may refer collectively to include any examples of medical device system 10, a general reference to IMD 14 may refer collectively to include any examples of IMD 14, a general reference to sensor circuits may refer collectively to include any examples ofsensor circuits of IMD 14, and a general reference to an external device may refer collectively to any examples of external device 24.

[0037] FIG. 2 is a functional schematic diagram of IMD 14, and FIG. 3 is a conceptual perspective schematic diagram of IMD 14, according to various examples described in this disclosure. IMD 14 may be a leadless, subcutaneously implantable monitoring device including proximal electrode 48B located at proximal end 222, distal electrode 48A located at distal end 220 (collectively “electrodes 48”), optical sensor(s) 62, integrated antenna 226, electrical circuitry 200 and power source 202. In particular, electrical circuitry 200 is coupled to proximal electrode 48B and distal electrode 48A to sense cardiac signals and monitor events. Electrical circuitry 200 may also connected to transmit and receive communications via integrated antenna 226. Power source 202 provides power to electrical circuitry 200, as well as to any other components that require power. Power source 202 may include one or more energy storage devices, such as one or more rechargeable or non-rechargeable batteries. In some examples, electrical circuitry 200 includes processing circuitry 50 and storage device 56, such as a memory, as shown in FIG. 4, the memory 56 being operatively coupled to the processing circuitry 50 and configured to store data and / or instructions.

[0038] In the example shown in FIG. 2, electrical circuitry 200 may receive raw EGM signals monitored by proximal electrode 48B and distal electrode 48A and raw optical signals monitored by optical sensor(s) 62. Electrical circuitry 200 may include components / modules for converting the raw EGM signal to a processed EGM signal that can be analyzed to detect sense events and for converting the raw optical signals to calibrated processed optical signal(s) that can be analyzed to detect sense events. Although not shown, electrical circuitry 200 may include any discrete and / or integrated electronic circuit components that implement analog and / or digital circuits capable of producing the functions described for analyzing optical signal(s) to determine a health condition status of a patient. For example, the electrical circuitry 200 may include analog circuits, e.g., preamplification circuits, filtering circuits, and / or other analog signal conditioning circuits. The modules may also include digital circuits, e.g., digital filters, combinational or sequential logic circuits, state machines, integrated circuits, a processor (shared, dedicated, or group) that executes one or more software or firmware programs, memory devices, orany other suitable components or combination thereof that provide the described functionality.

[0039] In one example, electrical circuitry 200 includes a sensing unit for monitoring the EGM signal detected by the respective proximal and distal electrodes 48A and 48B and light signals received by the optical sensor(s) 62, respectively. In one example, electrical circuitry 200 includes processing circuitry 50 that is utilized to receive information regarding sensed events and implements one or more algorithms for determining a health condition status of a patient. In addition, the analog voltage signals received from electrodes 48A and 48B may be passed to analog-to-digital (A / D) converters included in the electrical circuitry 200 and stored in a memory unit (not shown) included as part of electrical circuitry 200 for subsequent analysis with firmware executed by the processor included as part of electrical circuitry 200.

[0040] In the examples shown in FIGS. 2-3, IMD 10 may include container 15 and an insulative cover 76. Electrode 48A and electrode 48B may be formed or placed on an outer surface of cover 76. Electrical circuitry 200 may be formed or placed on an inner surface of cover 76, or within container 15. In some examples, antenna 226 is formed or placed on the inner surface of cover 76. In other examples, antenna 236 is formed or placed on the outer surface of cover 76, and in other examples, antenna 236 may be formed or placed at least partially on the inner surface and partially on the outer surface of cover 76. In some examples, insulative cover 76 may be positioned over an open container 15 such that container 15 and cover 76 form housing 20 and enclose electrical circuitry 200 (and in some cases antenna 226) and protect the circuitries from fluids such as body fluids. For example, housing 20 may be a hermetically-sealed housing configured for subcutaneous implantation within the patient, wherein at least the power source 202, memory, and processing circuitry 50 are within the hermetically-sealed case, and in some examples, optical sensor(s) 62 are within the hermetically-sealed case.

[0041] Electrical circuitry 200 may be formed on the inner side of insulative cover 76, such as by using flip-chip technology. Insulative cover 76 may be flipped onto a container 15. When flipped and placed onto container 15, the components of IMD 10 formed on the inner side of insulative cover 76 may be positioned in a gap defined by container 15. Electrodes 48 and antenna 226 (when placed or formed on the outer surface of cover 76) may be electrically connected to sensing circuitry 52 and communication circuitry 54(FIG. 4), respectively, e.g., through one or more vias formed through insulative cover 76. Insulative cover 76 may be formed of sapphire (i.e., corundum), glass, and / or any other suitable insulating material. Container 15 may be formed from any suitable material configured to house electrical circuitry 200, support and mate with cover 76 to isolate electrical circuitry 200 from contact with tissue and / or fluids of patient 12, and to be implantable within patient 12. In some examples, container 15 may house power source 202 (e.g., a battery). In some examples, container 15 may also be electrically conductive. For example, container 15 may be formed from titanium or any other suitable material (e.g., a biocompatible material). Electrodes 48 may be formed from any of stainless steel, titanium, platinum, iridium, or alloys thereof. In addition, electrodes 48 may be coated with a material such as titanium nitride or fractal titanium nitride, although other suitable materials and coatings for such electrodes may be used.

[0042] FIG. 4 is a block diagram illustrating an example of IMD 14 of FIGS. 1-3. FIG. 4 is described with reference to FIGS. 5-8. FIG. 5 is a conceptual cross-sectional side-view of an example IMD 14 including a controllable mask 66 in a first configuration, FIG. 6 is a conceptual cross-sectional side-view of the example IMD 14 including the controllable mask 66 in a second configuration, FIG. 7 is a conceptual cross-sectional side-view of the example IMD 14 including the controllable mask 66 in a third configuration, and FIG. 8 is a conceptual cross-sectional side-view of the example IMD 14 including the controllable mask 66 in a fourth configuration, e.g., over both a detector and a light source.

[0043] As shown in FIG. 4, IMD 14 includes processing circuitry 50, memory 56, one or more sensor(s) 61, which may include one or more optical sensor(s) 62, sensing circuitry 52 coupled to sensors 61 and electrodes 48 (e.g., electrodes 48 A and 48B), power source 202, and communication circuitry 54. Power source 202 provides operational power for processing circuitry 50, sensing circuitry 52, sensor(s) 61, communication circuitry 54, and memory 56. As used herein, “sensors” may refer to any sensors described herein, including electrodes 48 and optical sensor 62.

[0044] Processing circuitry 50 may include fixed function circuitry and / or programmable processing circuitry. Processing circuitry 50 may include any one or more of a microprocessor, a controller, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or equivalent discreteor analog logic circuitry. In some examples, processing circuitry 50 may include multiple components, such as any combination of one or more microprocessors, one or more controllers, one or more DSPs, one or more ASICs, or one or more FPGAs, as well as other discrete or integrated logic circuitry. The functions attributed to processing circuitry 50 herein may be embodied as software, firmware, hardware or any combination thereof.

[0045] Sensing circuitry 52 may be coupled to electrodes 48 to sense electrical signals of the heart of patient 12, for example by selecting electrodes 48 and polarity, used to sense an ECG as controlled by processing circuitry 50. Sensing circuitry 52 may sense the ECG from electrodes 48 in order to facilitate monitoring the electrical activity of the heart. In some examples, electrodes 48 may be configured to sense other electrogram signals of patient 12, and / or impedance of tissue fluid proximate the electrodes 48. Sensing circuitry 52 also may monitor signals from sensors 61, which may include one or more accelerometers (e.g., 3-axis accelerometers), pressure sensors, temperature sensors, heart sound sensors (e.g., microphones or accelerometers), optical sensors 62, or other sensors.

[0046] In some examples, sensing circuitry 52 may include one or more filters and amplifiers for filtering and amplifying signals received from electrodes 48 and / or sensors 61. In some examples, sensing circuitry 52 may sense or detect physiological parameters, such as heart rate, blood pressure, respiration, and other physiological parameters associated with a patient. Sensing circuitry 52 and processing circuitry 50 may store ECG data in memory 56.

[0047] Communication circuitry 54 may include any suitable hardware, firmware, software or any combination thereof for communicating with another device, such as external device 24 (FIG. 1), another networked computing device, or another IMD or sensor. Under the control of processing circuitry 50, communication circuitry 54 may receive downlink telemetry from, as well as send uplink telemetry to external device 24 or another device with the aid of an internal or external antenna, e.g., antenna 226. In addition, processing circuitry 50 may communicate with a networked computing device via external device 24 and a computer network, such as the Medtronic CareLink® Network. Antenna 226 and communication circuitry 54 may be configured to transmit and / or receive signals via inductive coupling, electromagnetic coupling, Near Field Communication (NFC), Radio Frequency (RF) communication, Bluetooth®, Wi-Fi, orother proprietary or non-proprietary wireless communication schemes. Communication antenna 226 may telemeter data at a high frequency, such as around 2.4 gigahertz (GHz).

[0048] In some examples, memory 56 includes computer-readable instructions that, when executed by processing circuitry 50, cause IMD 14 and processing circuitry 50 to perform various functions attributed to IMD 14 and processing circuitry 50 herein. Memory 56 may include any volatile, non-volatile, magnetic, optical, or electrical media, such as a random-access memory (RAM), dynamic RAM (DRAM), static RAM (SRAM), read-only memory (ROM), non-volatile RAM (NVRAM), electrically erasable programmable ROM (EEPROM), flash memory, or any other digital media. Memory 56 may store, as examples, programmed values for one or more operational parameters of IMD 14 and / or data collected by IMD 14, e.g., posture, heart rate, activity level, respiration rate, and other parameters, as well as digitized versions of physiological signals sensed by IMD 14, for transmission to another device using communication circuitry 54. In some examples, memory 56 is used to store program instructions for execution by processing circuitry 50. Memory 50 may be used by software or applications running on processing circuitry 50 and / or sensing circuitry 52 to temporarily store information during program execution.

[0049] In the illustrated example, IMD 14 includes processing circuitry 50 and an associated memory 56, sensing circuitry 52, one or more sensors 61, and the communication circuitry 54 coupled to antenna 226 as described above. However, IMD 14 need not include all of these components, or may include additional components.

[0050] Sensing circuitry 52 may additionally be coupled to optical sensor 62 to sense a physiological characteristic, signal, or parameter, of patient 12, e.g., a blood pressure, an oxygenation of arterial blood, perfusion and oxygenation of tissue, a heart rate, a respiration rate, a movement, or any suitable physiological characteristic. Optical sensor 62 may include one or more detector(s) 64 configured to receive and / or detect light, such light originating from one or more light source(s) 63 and reflected and / or scattered from tissue 402 (FIGS. 5-7). Light received and / or detected by detector 64 may be referred to as optical signals. In some examples, optical sensor 62 may be configured to receive light reflected by blood in one or more blood vessels. In some examples, light source 63 may be configured to emit light signals belonging to a particular wavelength spectrum. Some examples of a particular wavelength spectrum may be an amber wavelength spectrum, agreen wavelength spectrum, yellow wavelength spectrum, blue wavelength spectrum, an infrared wavelength spectrum, or any other suitable wavelength spectrum. Detector 64 may be configured to receive optical signals of the corresponding particular wavelength spectrum, e.g., facilitated by filtering and / or or detector material selection.

[0051] Optical sensor 62 may also include one or more controllable mask 66. In some examples, controllable mask 66 comprises a two-dimensional array of a plurality of individually addressable and / or controllable pixels, such as an LC array, with each pixel configured to be controllable to substantially transmit, to attenuate, or to substantially block light independent of the other pixels of the array. In some examples, blocking the light comprises reflecting the light, absorbing the light, or both. In some examples, it may be preferable to absorb the light intended to be blocked, rather than to reflect the light, to prevent that light from being backscattered by tissue 402 towards detector 64. In some examples, controllable mask 66 may also be configured to spectrally filter light, e.g., to transmit, attenuate, or block some wavelengths of light more than others. For example, each pixel of the LC array may comprise three red, green, and blue sub-pixels (RGB), each individually addressable to transmit, attenuate, or block an amount of corresponding RGB spectra of the light independent of the other sub-pixels and independent of other pixels (and RGB sub-pixels) of the LC array. In some examples, the LC array may comprise other spectral filters, e.g., infrared filter(s), visible filter(s), ultraviolet filter(s), or any number of filters configured to transmit, absorb, or reflect any suitable spectral band.

[0052] Sensing circuitry 52 and / or processing circuitry 50 may be configured to control operation of optical sensor 62, e.g., to determine parameters of light source 63 such as brightness level and / or pulsing emission of the light, parameters of detector 64 such as gain, and parameters of controllable mask 66, such as a transmission level of each pixel (or sub-pixel) of the LC array. In some examples, optical sensor 62 may be a photoplethysmography (PPG) sensor, an oxygenation sensor, a blood pressure sensor, a heart rate sensor, or any suitable optical sensor configured to detect a physiological characteristic and / or parameter of patient 14.

[0053] In the examples shown in FIGS. 5-7, IMD 14 is implanted within patent 12 and is in contact with tissue 402. Tissue 402 includes blood vessels, such as arterioles 404 having relatively high dynamic optical absorbance through the cardiac cycle, and tissue structures 406 that do not have relatively high dynamic optical absorbance through thecardiac cycle. In the examples shown, controllable mask is disposed between detector 64 and tissue 402 of patient 12 and is configured to block a first portion of the light from light source 63 passing through a first portion of the tissue 402, e.g., along paths 408 (FIG. 6). As the light from light source 63 passes through tissue 402 along paths 408, it may interact (e.g., be reflected, scattered, transmitted, or absorbed by) tissue structures 406 that do not have relatively high dynamic optical absorbance that changes through the cardiac cycle, and therefore reduce a signal fidelity indicative of the cardiac cycle, e.g., pulsatile blood flow. In the examples shown, controllable mask is also configured to transmit a second portion of the light from light source 63 passing through a second portion of the tissue 402, e.g., along paths 410 (FIG. 6). As the light from light source 63 passes through tissue 402 along paths 410, it may interact (e.g., be reflected, scattered, transmitted, or absorbed by) tissue structures 404 that do have relatively high dynamic optical absorbance through the cardiac cycle, and therefore improve a signal fidelity indicative of the cardiac cycle, e.g., pulsatile blood flow. In some examples, the second portion of tissue along paths 410 include tissue comprising arterial blood (and additionally, in some examples, venous blood, e.g., for sensing oxygenation), and sensor 62 is configured to measure a signal indicative of arterial blood flow (e.g., as a time-series indicating a blood flow waveform, in some examples) from which sensing circuitry 52 and / or processing circuitry 50 may determine a physiological parameter of patient 12. In some examples, controllable mask 62 may be configured to block light passing through tissue 402 along paths 408 by reflecting substantially all of the light, absorbing substantially all of the light, or both, or by reducing a transmission of the light (via reflection and / or absorption), e.g., by a percentage of the amount of light incident on controllable mask 66. In some examples, controllable mask 62 may be configured to block light passing through tissue 402 along paths 408 by reducing a transmission of the light only within a spectral wavelength range, e.g., substantially transmitting light within an IR spectral range and reducing the transmission of shorter wavelengths, e.g., visible and / or ultraviolet (UV) light.

[0054] In some examples, controllable mask 66 may be controlled such that a first portion of the pixels substantially blocks light and a second portion substantially transmits the light in any arbitrary pattern. In the example shown in FIG. 5, controllable mask 66 is in a fully transmissive configuration in which the second portion of the pixels that substantially transmits light comprises all the pixels and the first portion that substantiallyblocks light comprises none of the pixels. In the example shown in FIG. 6, controllable mask 66 is in a different configuration in which the second portion of the pixels that substantially transmits light comprises a plurality of pixels that transmit light along paths 410 that interacts with arterioles 404 having relatively high dynamic optical absorbance through the cardiac cycle, and in which the first portion of the pixels that substantially blocks light comprises a plurality of pixels blocks light along paths 408 that interacts with structures 406 that do not have a relatively high dynamic optical absorbance through the cardiac cycle. In the example shown in FIG. 7, controllable mask 66 is in another different configuration in which the second portion of the pixels that substantially transmits light comprises a plurality of pixels that transmit light along paths 410 that interacts with arterioles 404, and in which the first portion of the pixels that substantially blocks light comprises a plurality of pixels blocks light along paths 408 that interacts with structures 406 and that blocks ambient light along paths 412 that interact with either arterioles 404 or structures 406.

[0055] In some examples, detector 64 may comprise a single detecting element, e.g., a relatively large area photodiode. In some examples, controllable mask 66 is positioned to cover an area that is larger than the area of detector 64 and that corresponds to a position of detector 64 within container 15, and each pixel of controllable mask 66 may cover an area that is smaller than the area of detector 64. Although shown as positioned on an external surface of insulative cover 76, controllable mask 66 may be alternatively positioned. For example, controllable mask 66 may be positioned on an internal surface of insulative cover 76, within insulative cover 76, on a surface of detector 64, or between insulative cover 76 and detector 64.

[0056] In the example shown, detector 64 has an area that is smaller than the area of insulative cover 76, e.g., the at least partially transparent area of insulative cover 76 that does not include electrodes 48 A, 48B. In other examples, detector 64 may have an area that covers all, substantially all, or a large portion of the area of insulative cover 76 that does not include electrodes 48A, 48B and light source 63 (e.g., there may be an area and / or aperture that is clear for light source 63 to emit light out of insulative cover 76), and controllable mask 66 may also cover all, substantially all, or a large portion of the area of insulative cover 76 that does not include electrodes 48A, 48B (but that may cover over light source 63 since controllable mask 66 may be controlled to block, partially block, ortransmit light from light source 63). Controllable mask 66 may then be configured to adjust a sampling volume of light source 63 and detector 64, e.g., adjusting the field of view of one or both of light source 63 and detector 64, by adjusting the location(s) of transmissive and / or blocking pixels of controllable mask 66 such that light to propagates through a longer, shorter, or different transmission path before propagating to detector 64 to be detected / sensed.

[0057] In some examples, detector 64 may comprise a 2D array of a plurality of detectors. For example, detector 64 as a 2D array of pixels, rather than one larger pixel of the same area, may enable control of activation of select detector pixels. Additionally, detector 64 as a 2D array of pixels, rather than one larger pixel of the same area, may have a reduce effective shot or dark noise in the detector circuit, e.g., by reducing active detector area of each pixel in the array relative to a larger pixel, e.g., one large detector may have higher dark noise than a plurality of smaller pixels of the same area.

[0058] In some examples, light source 63 may comprise a plurality of light sources. In other examples, light source 63 may comprise a single light source, e.g., an LED. In some examples, light source 63 may be configured to emit light within a substantially large solid angle, e.g., a Lambertian or substantially Lambertian light source 63. In other examples, light source 63 may be configured to emit light within particular range of angles and in a particular angular direction, e.g., a conical solid angle having an apex angle between 20 degrees and 180 degrees and directed at any suitable angle, e.g., from zero degrees (substantially normal, or perpendicular, to the outer surface of insulative cover 76) to 90 degrees (substantially parallel to the outer surface of insulative cover 76, e.g., a glancing angle along the outer surface of insulative cover 76). In some examples, light source 63 may include, or be used in conjunction with, beam forming and / or shaping optics, such as lenses, diffraction gratings, holographic optical elements, or the like. In some examples, light source 63 may include a coherent light source, e.g., temporally and / or spatially coherent, such as a laser, a VCSEL, or the like, which may have a divergence angle of less than or equal to 20 degrees.

[0059] In some examples, controllable mask 66 may be positioned to be disposed between light source 63 and tissue 402. For example, controllable mask 66 may be shifted to be positioned over light source 63, or preferably extended to cover over both light source 63 and detector 64. In the example shown in FIG. 8, controllable mask 66 isextended to cover both detector 64 and light source 63 and is in a different configuration in which the first portion of the pixels that substantially blocks light comprises a plurality of pixels that block light along paths 407 from light source 63 before interacting with tissue 402 (e.g., light that would otherwise follow paths 408 of FIG. 6) and block light along paths 408 that interacts with structures 406 that do not have a relatively high dynamic optical absorbance through the cardiac cycle, and in which the second portion of the pixels that substantially transmits light comprises a plurality of pixels transmit light along paths 410 that interacts with arterioles 404 having relatively high dynamic optical absorbance through the cardiac cycle.

[0060] Controllable mask 66 may then be controlled to have a pixel pattern in which a first portion of the pixels substantially blocks (or attenuate or reduce a transmission of) light passing through a first portion of tissue 402, e.g., along paths 408, a second portion of the pixels that substantially transmit light passing through a second portion of tissue 402, e.g., along paths 410, a third portion of pixels that substantially blocks (or attenuates or reduces a transmission of) light emitted by light source 63 to a third portion of tissue 402, e.g., blocking light along path 407 before interacting with tissue 402, e.g., which may include tissue 402 along paths 408 (FIG. 6) or along other paths, and a fourth portion of pixels that substantially transmits light emitted by light source 63 to a fourth portion of tissue 402 (not shown), which may include tissue 402 along paths 410 or along other paths, e.g., including other arterioles 404.

[0061] In some examples, IMD 14 may be configured to search for an improved, and / or optimal, signal fidelity using controllable mask 66. For example, sensing circuitry 52 and / or processing circuitry 50 may be configured cause controllable mask 66 to have a first configuration (e.g., pattern of blocking / transmitting pixels) for a first period of time, e.g., blocking light from a first portion of tissue 402 from being detected and passing light from a second portion of tissue 402 to be detected. Sensing circuitry 52 and / or processing circuitry 50 may determine a first signal fidelity useable for determining one or more physiological parameters of patient 12 based on the optical signals collected with controllable mask 66 in the first configuration for the first amount of time. Sensing circuitry 52 and / or processing circuitry 50 may be configured cause controllable mask 66 to have a second configuration (e.g., pattern of blocking / transmitting pixels) for a second period of time, e.g., blocking light from a third portion of tissue 402 from being detectedand passing light from a fourth portion of tissue 402 to be detected, where at least portions of the third and fourth portions of tissued 402 are different from the first and third portions of tissue 402. Sensing circuitry 52 and / or processing circuitry 50 may determine a second signal fidelity useable for determining one or more physiological parameters of patient 12 based on the optical signals collected with controllable mask 66 in the second configuration for the second amount of time. Sensing circuitry 52 and / or processing circuitry 50 may be configured to then determine which of the first or second signal fidelities are greater, and select the first or second configuration of controllable mask 66 based on which signal fidelity is greater. Sensing circuitry 52 and / or processing circuitry 50 may then continue changing the configuration of controllable mask 66 to search for a greater signal fidelity, e.g., until a signal fidelity threshold is reached, and then select the configuration of controllable mask 66 for which the signal fidelity is the greatest and determine the one or more physiological parameters of patient 12 based on the optical signals collected with controllable mask 66 in the configuration for which the signal fidelity is the greatest.

[0062] In some examples, light source 63 may be adjusted along with controllable mask 66. For example, a power level of light source 63 and / or spectral output (e.g., wavelength content) may be adjusted to accommodate first or second configurations of controllable mask 63. In some examples, controlling controllable mask 66 to select a sampling volume of tissue for sensing by detector 64 with a relatively longer path (e.g., optical path) may be used in conjunction with controlling light source 63 to output a greater amount of light (e.g., increasing the power of light source 63) to accommodate for higher static signal attenuation due to absorbance along a relatively longer path. In some examples, light source 63 may change to a shorter or longer wavelength of light, e.g., in conjunction with controlling controllable mask 66 to select a particular sampling volume, e.g., with a shorter or longer path.

[0063] In some examples, IMD 14 may be configured to search for an improved, and / or optimal, signal fidelity using controllable mask 66 and / or light source 63, according to sorting algorithm. For example, IMD 14 may be configured to search for an improved signal fidelity via changing one or more pixels of controllable mask 66 (e.g., covering over one or both of detector 64 and light source 63) using a selection sort (e.g., an in-place comparison sorting algorithm), an insertion sort (e.g., a simple algorithm building a finalsorted array one pixel at a time via comparison), a quicksort (e.g., a divide-and-conquer algorithm including a “pivot” element), or any suitable sorting algorithm. In some examples, IMD 14 may search for a pixel configuration of controllable mask 66 based on a total static absorbance attenuation (e.g., an attenuation of light via static absorption by tissue), a dynamic absorbance signal amplitude, a dynamic absorbance signal quality, or the like.

[0064] FIG. 9 is a flow diagram of an example method of determining a physiological characteristic of a patient, according to various examples described in this disclosure. Although the example technique of FIG. 1 is described with respect to medical systems 10, IMD 14, and controllable mask 66 of FIGS. 1-7, the example technique of FIG. 9 may be performed using any system including an implantable medical device and a controllable mask described herein.

[0065] Light source 63 may emit light towards a tissue 402 of patient 12 (802). For example, sensing circuitry 52 and / or processing circuitry 50 may cause light source 63 to emit broadband light or light having a specific wavelength band, e.g., IR light.

[0066] Sensing circuitry 52 and / or processing circuitry 50 may control controllable mask 66 to block a first portion of the light passing through a first portion of the tissue 402 (804). For example, sensing circuitry 52 and / or processing circuitry 50 may cause controllable mask to have a first configuration (e.g., pattern) of block / transmit pixels to block light passing through tissue 402 along paths 410 and interacting with tissue structures 406 (as shown in FIG. 6 or FIG. 7), and / or to block ambient light passing through tissue 402 along paths 412 and interacting with tissue structures 406 and / or along paths 408 and interacting with tissue structures 404 (as sown I FIG. 7).

[0067] Sensing circuitry 52 and / or processing circuitry 50 may control controllable mask 66 to transmit a second portion of the light passing through a second portion of the tissue 402 (806). For example, sensing circuitry 52 and / or processing circuitry 50 may cause controllable mask to have the first configuration (e.g., pattern) of block / transmit pixels to transmit light passing through tissue along paths 408 from light source 63 and interacting with tissue structures 404 (as shown in FIG. 6 or FIG. 7).

[0068] Detector 64 may detect the second portion of light (e.g., the transmitted portion) (808). Sensing circuitry 52 and / or processing circuitry 50 may receive a signal indicative of the detected light from detector 64. Sensing circuitry 52 and / or processingcircuitry 50 may determine a physiological characteristic of patient 12 based on the detected second portion of the light (810).

[0069] In some examples, detecting the second portion of the light for the first configuration results in a first signal fidelity of the second portion of the tissue, e.g., sensing circuitry 52 and / or processing circuitry 50 may determine a first signal fidelity for determining the physiological characteristic based on the detected second portion of light. Sensor 62, e.g., sensing circuitry 52 and / or processing circuitry 50 may then search for other configurations of mask 66 to improve the signal fidelity. For example, (802) - (810) may be repeated with a second configuration (pattern) of controllable mask 66 to block a third portion of the light passing through a third portion of tissue 402 and transmitting a fourth portion of the light passing through a fourth portion of the tissue 402. Sensing circuitry 52 and / or processing circuitry 50 may determine a second signal fidelity of the fourth portion of the tissue, and determine the physiological characteristic of patient 12 based on the whichever of the detected second portion of the light or the detected fourth portion of the light resulted in the greater signal fidelity.

[0070] The techniques described in this disclosure may be implemented, at least in part, in hardware, software, firmware or any combination thereof. For example, various aspects of the described techniques may be implemented within one or more processors or processing circuitry, including one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), or any other equivalent integrated or discrete logic circuitry, as well as any combinations of such components. The term “processor” or “processing circuitry” may generally refer to any of the foregoing logic circuitry, alone or in combination with other logic circuitry, or any other equivalent circuitry. A control unit including hardware may also perform one or more of the techniques of this disclosure.

[0071] Such hardware, software, and firmware may be implemented within the same device or within separate devices to support the various operations and functions described in this disclosure. In addition, any of the described units, circuits or components may be implemented together or separately as discrete but interoperable logic devices. Depiction of different features as circuits or units is intended to highlight different functional aspects and does not necessarily imply that such circuits or units must be realized by separate hardware or software components. Rather, functionality associated with one or morecircuits or units may be performed by separate hardware or software components or integrated within common or separate hardware or software components.

[0072] The techniques described in this disclosure may also be embodied or encoded in a computer-readable medium, such as a computer-readable storage medium, containing instructions that may be described as non-transitory media. Instructions embedded or encoded in a computer-readable storage medium may cause a programmable processor, or other processor, to perform the method, e.g., when the instructions are executed. Computer readable storage media may include random access memory (RAM), read only memory (ROM), programmable read only memory (PROM), erasable programmable read only memory (EPROM), electronically erasable programmable read only memory (EEPROM), flash memory, a hard disk, a CD-ROM, a floppy disk, a cassette, magnetic media, optical media, or other computer readable media.

[0073] Various aspects of the techniques may enable the following examples.

[0074] Example 1 : A system including: a light source configured to emit light towards a tissue of a patient; a detector configured to detect the light emitted by the light source after the light passes through the tissue of the patient; a controllable mask disposed between the detector and the tissue of the patient, wherein the controllable mask is configured to block a first portion of the light passing through a first portion of the tissue and transmit a second portion of the light passing through a second portion of the tissue; and processing circuitry configured to determine a physiological characteristic of the patient based on the second portion of the light.

[0075] Example 2: The system of example 1, wherein physiological characteristic comprises at least one of a blood pressure, an oxygenation of arterial blood, perfusion and oxygenation of tissue, a heart rate, a respiration rate, or a movement, wherein the processing circuitry determines the physiological characteristic based on a photoplethysmography (PPG) signal or an absorbance of the second portion of the light by the tissue.

[0076] Example 3: The system of example 1 or example 2, wherein the second portion of the tissue comprises arterial blood.

[0077] Example 4: The system of any one of examples 1-3, wherein the controllable mask is configured to block the first portion of light by reducing a transmission of the first portion of the light.

[0078] Example 5: The system of any one of examples 1-3, wherein the controllable mask is configured to block the first portion of light by reducing a transmission of the first portion of the light only within a spectral wavelength range.

[0079] Example 6: The system of example 5, wherein the controllable mask comprises a plurality of pixels arranged in a two-dimensional array, wherein each pixel of the plurality of pixels is configured to be individually addressable to substantially transmit, block, or attenuate the light independent of the other pixels of the plurality of pixels.

[0080] Example 7: The system of example 6, wherein the controllable mask covers an area that is larger than the area of the detector.

[0081] Example 8: The system of any one of examples 1-7, wherein the detector comprises and single detecting element.

[0082] Example 9: The system of any one of examples 1-8, wherein the light source comprises a single light emitting element.

[0083] Example 10: The system of example 9, wherein the light source comprises a light emitting diode (LED) configured to emit light within a substantially conical solid angle having an apex angle between 20 degrees and 180 degrees.

[0084] Example 11 : The system of any one of examples 1-10, wherein the system is configured to be implantable within the patient.

[0085] Example 12: The system of any one of examples 1-11, wherein the controllable mask is disposed between the light source and the tissue of the patient, wherein the controllable mask is configured to block a third portion of the light emitted towards a third portion of the tissue and transmit a fourth portion of the light emitted towards a fourth portion of the tissue.

[0086] Example 13: A method of determining a physiological characteristic of a patient, the method including: emitting light, by a light source, towards a tissue of the patient; controlling, by processing circuitry, a controllable mask to block a first portion of the light passing through a first portion of the tissue; controlling, by the processing circuitry, the controllable mask to substantially transmit a second portion of the light passing through a second portion of the tissue; detecting, by a detector, the second portion of the light; and determining, by the processing circuitry and based on the detected second portion of the light, the physiological characteristic of the patient.

[0087] Example 14: The method of example 13, wherein the controllable mask comprises a plurality of pixels arranged in a two-dimensional array, wherein each pixel of the plurality of pixels is configured to be individually addressable to substantially transmit, block, or attenuate the light independent of the other pixels of the plurality of pixels, wherein controlling the controllable mask to block a first portion of the light passing through a first portion of the tissue comprises controlling the controllable mask to have a first configuration in which a first portion of the plurality of pixels block the first portion of the light and a second portion of the plurality of pixels substantially transmits the second portion of the light.

[0088] Example 15: The method of example 14, wherein detecting the second portion of the light for the first configuration results in a first signal fidelity of the second portion of the tissue.

[0089] Example 16: The method of example 15, further includes controlling, by the processing circuitry, the controllable mask to have a second configuration in which a third portion of the plurality of pixels block a third portion of the light passing through a third portion of the tissue and a fourth portion of the plurality of pixels substantially transmits a fourth portion of the light passing through a fourth portion of the tissue; and detecting, by the detector, the fourth portion of the light.

[0090] Example 17: The method of example 16, wherein detecting the fourth portion of the light for the second configuration results in a second signal fidelity of the fourth portion of the tissue different from the first signal fidelity of the second portion of the tissue.

[0091] Example 18: The method of example 17, further comprising determining, by the processing circuitry and based on the fourth portion of the light, the physiological characteristic of the patient.

[0092] Example 19: An implantable medical device (IMD) including: a light source configured to emit light towards a tissue of a patient; a detector configured to detect the light emitted by the light source after the light passes through the tissue of the patient; a controllable mask disposed between the detector and the tissue of the patient, wherein the controllable mask is configured to block a first portion of the light passing through a first portion of the tissue and transmit a second portion of the light passing through a secondportion of the tissue; and processing circuitry configured to determine a physiological characteristic of the patient based on the second portion of the light.

[0093] Example 20: The IMD of example 19, wherein the controllable mask comprises a plurality of pixels arranged in a two-dimensional array, wherein each pixel of the plurality of pixels is configured to be individually addressable to substantially transmit, block, or attenuate the light independent of the other pixels of the plurality of pixels, wherein the processing circuitry is further configured to: determine a first configuration of the controllable mask including a first portion of the plurality of pixels configured to block the light and a second portion of the plurality of pixels configured to substantially transmit the light; determine a first signal fidelity based on the first configuration; determine a second configuration of the controllable mask including a third portion of the plurality of pixels configured to block a third portion of the light passing through a third portion of the tissue and a fourth portion of the plurality of pixels configured to substantially transmit a fourth portion of the light passing through a fourth portion of the tissue; determine a second signal fidelity based on the second configuration; and determine, based on the second fidelity being greater than the first fidelity, the physiological characteristic of the patient based on fourth portion of the light.

[0094] Various examples have been described. These and other examples are within the scope of the following claims.

Claims

WHAT IS CLAIMED IS:

1. A system comprising: a light source configured to emit light towards a tissue of a patient; a detector configured to detect the light emitted by the light source after the light passes through the tissue of the patient; a controllable mask disposed between the detector and the tissue of the patient, wherein the controllable mask is configured to block a first portion of the light passing through a first portion of the tissue and transmit a second portion of the light passing through a second portion of the tissue; and processing circuitry configured to determine a physiological characteristic of the patient based on the second portion of the light.

2. The system of claim 1, wherein physiological characteristic comprises at least one of a blood pressure, an oxygenation of arterial blood, perfusion and oxygenation of tissue, a heart rate, a respiration rate, or a movement, wherein the processing circuitry determines the physiological characteristic based on a photoplethysmography (PPG) signal or an absorbance of the second portion of the light by the tissue.

3. The system of claim 1 or claim 2, wherein the second portion of the tissue comprises arterial blood.

4. The system of any one of claims 1-3, wherein the controllable mask is configured to block the first portion of light by reducing a transmission of the first portion of the light.

5. The system of any one of claims 1-3, wherein the controllable mask is configured to block the first portion of light by reducing a transmission of the first portion of the light only within a spectral wavelength range.

6. The system of claim 5, wherein the controllable mask comprises a plurality of pixels arranged in a two-dimensional array, wherein each pixel of the plurality of pixels isconfigured to be individually addressable to substantially transmit, block, or attenuate the light independent of the other pixels of the plurality of pixels.

7. The system of claim 6, wherein the controllable mask covers an area that is larger than the area of the detector.

8. The system of any one of claims 1-7, wherein the detector comprises and single detecting element.

9. The system of any one of claims 1-8, wherein the light source comprises a single light emitting element.

10. The system of claim 9, wherein the light source comprises a light emitting diode (LED) configured to emit light within a substantially conical solid angle having an apex angle between 20 degrees and 180 degrees.

11. The system of any one of claims 1-10, wherein the system is configured to be implantable within the patient.

12. The system of any one of claims 1-11, wherein the controllable mask is disposed between the light source and the tissue of the patient, wherein the controllable mask is configured to block a third portion of the light emitted towards a third portion of the tissue and transmit a fourth portion of the light emitted towards a fourth portion of the tissue.

13. An implantable medical device (IMD) comprising: a light source configured to emit light towards a tissue of a patient; a detector configured to detect the light emitted by the light source after the light passes through the tissue of the patient; a controllable mask disposed between the detector and the tissue of the patient, wherein the controllable mask is configured to block a first portion of the light passing through a first portion of the tissue and transmit a second portion of the light passing through a second portion of the tissue; andprocessing circuitry configured to determine a physiological characteristic of the patient based on the second portion of the light.

14. The IMD of claim 13, wherein the controllable mask comprises a plurality of pixels arranged in a two-dimensional array, wherein each pixel of the plurality of pixels is configured to be individually addressable to substantially transmit, block, or attenuate the light independent of the other pixels of the plurality of pixels, wherein the processing circuitry is further configured to: determine a first configuration of the controllable mask including a first portion of the plurality of pixels configured to block the light and a second portion of the plurality of pixels configured to substantially transmit the light; determine a first signal fidelity based on the first configuration; determine a second configuration of the controllable mask including a third portion of the plurality of pixels configured to block a third portion of the light passing through a third portion of the tissue and a fourth portion of the plurality of pixels configured to substantially transmit a fourth portion of the light passing through a fourth portion of the tissue; determine a second signal fidelity based on the second configuration; and determine, based on the second fidelity being greater than the first fidelity, the physiological characteristic of the patient based on fourth portion of the light.

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