FIELD

The present disclosure relates to a physiological sensor for a near-infrared spectroscopy, as well as to a near-infrared spectroscopy system comprising such a physiological sensor.

BACKGROUND

The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

In vivo monitoring and/or imagery applications for use in the field of near-infrared spectroscopy for medical diagnosis applications and/or for physiological parameters monitoring include:

vascular volumes or blood volumes, and in particular subcutaneous vascular or blood volumes, such as a cortical or tissue blood volume or others;

volumes and concentrations of hemoglobins, and in particular oxyhemoglobin (HbO2) and deoxyhemoglobin (Hb);

reperfusion tests;

hemodynamic parameters such as tissue oxygen saturation (StO2), regional cerebral oxygen saturation (RScO2), cerebral autoregulation plateau;

volumes and concentrations of metabolites.

Near-infrared spectroscopy is a conventional technology in the medical field, which essentially consists in implementing, on the one hand, at least one emitter emitting a light beam in the near-infrared, with a length comprised between 650 and 1000 nanometers, which passes through the organic tissues (unlike visible light and ultraviolet) and, on the other hand, at least one photosensitive receiver which measures the absorption and scattering of the photons that have passed through the organic tissues.

In this specific spectrum of the near-infrared, it is possible to detect the electronic transitions of chromophores that are oxyhemoglobin and deoxyhemoglobin. Indeed, these molecules present in the blood have their absorption spectrum change in the near-infrared depending on their interaction with oxygen, because they absorb the near-infrared spectrum in a differential manner according to their concentration and their interaction with oxygen.

The wavelengths used by the emitter are selected in order to be sensitive to these biological molecules (generally between 650 and 1000 nanometers), the oxyhemoglobin absorbing more the wavelengths between 800 and 1000 nanometers while the deoxyhemoglobin absorbs more the wavelengths between 650 and 800 nanometers. The absorption of near-infrared light waves by oxyhemoglobin and deoxyhemoglobin is used in particular as a basis for calculating the oxygen saturation in application of the Beer-Lambert law, which stipulates that the concentration of a substance can be measured according to its light absorption degree.

The beam of photons emitted by an emitter and received by a receiver takes the shape of a diffuse light arc which passes through the organic tissues, wherein the penetration depth of the beam between the emitter and the receiver corresponds to about one third of the distance between the emitter and the receiver.

Thus, the distance between the emitter and the receiver has a considerable impact on the penetration depth of the beam into the organic tissues. The more distant is a receiver from the emitter, the more the beam collect thereby would have crossed a large distance (or depth) in the organic tissues, thus probing deeper layers. A distance between the emitter and the receiver that is large enough is therefore necessary to provide sufficient penetration that allows providing a measurement on deep layers and not on surface layers. However, increasing this emitter—receiver distance will lead to an increased diffusion/absorption of the emitted signal having the consequence of decreasing the spatial resolution of the measurement and attenuating the received signal. Indeed, the spatial resolution of near-infrared spectroscopy does not exceed 0.5 millimeters immediately beneath the skin, and degrades as the depth increases.

A known medical application of infrared spectroscopy is the measurement of cerebral activity or cerebral oximetry, by following the curves of oxyhemoglobin and deoxyhemoglobin concentrations at a given intracranial depth.

For this application, it is known, in particular from documents WO 2015/109005 and EP 2 434 942, to use a physiological sensor comprising a flexible strip on which are mounted a near-infrared beam emitter and at least two near-infrared photosensitive receivers, including a proximal receiver separated from the emitter by a proximal distance and a distal receiver separated from the emitter by a distal distance which is larger than the proximal distance. Thus, the signal acquired by the proximal receiver comes from a more superficial (less deep) source and the signal acquired by the distal receiver includes this superficial area but also a deeper component. By subtracting the proximal signal from the distal signal, it is possible to obtain a value of a distal signal free of surface components.

Thus, it is provided to implement several emitters and/or several receivers, and to proceed with a spatial subtraction of signals acquired in the near-infrared spectroscopy at different depths in order to increase the selectivity in some medical applications, including the measurement of cerebral activity or cerebral oximetry. However, such physiological sensors known from documents WO 2015/109005 and EP 2 434 942 still have a limited selectivity.

This technique, consisting in implementing a spatial subtraction of signals acquired in the near-infrared spectroscopy at different depths, is also implemented for other applications, such as the monitoring of hemodynamic parameters or the imagery of vascular or blood volumes, as described in documents US 2016/0022223, US 2013/0150726 and WO 2015/070162.

The document US 2016/0022223 for a hemodynamic parameters monitoring application and the document US 2013/0150726 for an application for detecting a subcranial hematoma type blood volume, each proposes placing emitters and receivers on a flexible support strip for adapting the support strip to the portions of the body of a patient, such as the skull or a limb. However, the flexibility of the support strip brings an uncontrolled uncertainty on the relative positions between emitters and receivers, thus impairing the accuracy during spatial the subtraction operations and therefore, ultimately, a great inaccuracy in the results.

The document WO 2015/070162, in an application for imaging a subcutaneous blood volume, proposes in turn a physiological sensor comprising emitters and receivers mounted on a rigid support tray, whether flat or curved. However, the rigidity of the support tray contributes in limiting the resolution. For example, in the case of a flat support, all emitters and receivers are in the same plane, so that some of them will not be pressed against the concerned portion of the body of the patient, in particular if this portion is curved like a limb or a skull. Thus, such a sensor is functionally limited in its applications by its own dimensions as to the explorable tissue depth, as to its resolution and as to the cutaneous or tissue surface on which it is applied. This sensor is, for example, unsuitable for monitoring cerebral activity or cerebral oximetry over frontal hemispheres of a large panel of patients with variable cranial morphologies, since this sensor cannot be functionally applied over the roundness of the frontal hemispheres surface. Indeed, an air interface layer would appear between the cutaneous surface and the sensor, which would represent a source of diffusion parasitizing the near-infrared beams, thus raising a problem of graphical modeling of the signal and the accuracy of the measurements.

The state of the art can also be illustrated by the teaching of document US 2014/0275891 which discloses a physiological sensor for a near-infrared spectroscopy at different depths, which comprises three modules each provided with a support (segments) on which at least one optoelectronic component is disposed, wherein each support of a module is connected to the support of at least one adjacent module by means of an articulation hinge.

SUMMARY

The present disclosure proposes solving the aforementioned drawbacks by proposing a solution to be able to perform a near-infrared spectroscopy at different depths with increased resolution and reliability in the measurements.

The present disclosure provides a physiological sensor which allows performing three-dimensional imagery with an improved spatial resolution, and this for all portions of the body and in particular the curved parts such as an internal organ (e.g., heart, liver), a limb (e.g., arm, leg) or a skull.

The present disclosure provides a physiological sensor which is portable and can be easily manipulated by medical personnel.

to the present disclosure enables a near-infrared spectroscopy at different depths, which compensates for the variation of the optical paths in the traversed tissues due to the variation of the roundness of the examined surfaces, and this by means of the same physiological sensor, in particular in order to perform a three-dimensional imagery with an improved spatial resolution.

To this end, it proposes a physiological sensor for near-infrared spectroscopy at different depths, said physiological sensor integrating optoelectronic components comprising emitters of near-infrared beams and near-infrared photosensitive receivers, said physiological sensor comprising elementary modules each provided with at least one optoelectronic component,

wherein each elementary module is connected to at least one adjacent elementary module by means of an articulation configured for a relative movement between the elementary modules according to several angles of inclination,

wherein the elementary modules are assembled at least by means of the articulations and form an optoelectronic spread configurable between:

a planar configuration according to a main plane in which each articulation has a zero angle of inclination, and

a set of curved conformations in which at least one of the articulations has a non-zero angle of inclination.

and wherein each articulation between two elementary modules is coupled to an angle sensor configured for a measurement of the angle of inclination between the two elementary modules.

Thus, because of the articulations with known angulations (thanks to the angle sensors) between the elementary modules, the elementary modules—and therefore the emitters and the receivers—can be positioned on the concerned portion of the body of the patient to be analyzed (for example a limb or an internal organ in an aseptic environment) in an accurate, known and controlled manner, thus contributing in adapting the shape of the physiological sensor the closest to the concerned portion of the body of the patient, while having an accurate control of the relative positionings and spacings between the emitters and the receivers; such a knowledge of these positionings and spacings can then be injected into an accurate and reliable calculation of spatial subtraction of signals acquired at different depths. This calculation can also take into account the angle of inclination of each articulation to compensate for the distribution of light in the biological tissues.

Such a physiological sensor thus forms an optoelectronic spread or a spread of optoelectronic components (namely the emitters and the receivers) that can conform to the cutaneous surface of any portion of the body of the patient, thanks to the articulations, as well as to the morphology of the underlying organ, or the organ of the patient, and enables an implementation of a near-infrared spectroscopy for in vivo detection of hemoglobins, circulating by nature only in the vascular network.

The articulations between the elementary modules enable continuous or almost-continuous contact of the optoelectronic components with the examination surface, without creating an intermediate air layer which would be a source of light diffusion.

Moreover, the angle of inclination of each articulation (or angle of inclination between two elementary modules) is known directly and in real-time thanks to the angle sensors, enabling an accurate and effective treatment to establish the spatial coordinates of the emitters and receivers of the different elementary modules.

Such a physiological sensor thus provides an answer to the problem of the normalization of the processed signals, and of the necessary compensation of the variation of the optical paths, induced by the variation of roundness from one examination surface to another, for the purpose of a three-dimensional pictorial representation, in particular by using the angle sensors that will actually contribute to achieving enhanced and reliable spatial resolution.

In a first variation, at least one articulation between two elementary modules is a flexible articulation comprising a flexible strip configured for a relative movement between the elementary modules by bending of the flexible strip.

Thus, the relative movement between two elementary modules at several angles of inclination is obtained by a bending (in the manner of folding/unfolding) of the flexible strip forming the flexible articulation connecting the two elementary modules. The optoelectronic spread, composed of the assembly of the elementary modules and articulations, therefore forms a spread at least partially flexible or flexible and adjustable to the morphology of the surface to be analyzed thanks to the bendings of the various flexible strips.

An articulation with a flexible strip is thus called flexible or flexible articulation, in the sense that it is adjustable in a continuous or non-discrete manner by bending of the flexible strip, thus providing a multiplicity of angles of inclination.

According to one possibility, each articulation between two elementary modules is a flexible articulation comprising a flexible strip configured for a relative movement between the elementary modules by bending of the flexible strip. In other words, all articulations are flexible articulations that bend to adapt to the morphology of the surface to be analyzed.

According to one feature, each elementary module comprises a rigid or flexible support on which at least one optoelectronic component is disposed, and the flexible strip of the flexible articulation between two elementary modules is connected between the supports of said two elementary modules.

In a form of this first variation, the physiological sensor comprises a flexible membrane on which the optoelectronic components are disposed and distributed into islets delimiting the elementary modules, and wherein the flexible strip of the flexible articulation between two elementary modules is formed by a portion of the flexible membrane extending between the islets delimiting said two elementary modules.

According to another feature, the flexible membrane comprises at least one elastomeric polymer layer in which the optoelectronic components are embedded at least partially.

According to another feature, for a flexible articulation comprising a flexible strip, this flexible articulation is coupled to an angle sensor comprising a flexible resistive sensor outputting an angle datum reflecting a variation of resistance as a function of the bending of the flexible strip.

In other words, the flexible articulation is coupled to a flexible resistive sensor or bending sensor. For this purpose, a technology allowing measuring angles accurately is used, based on the exploitation of variations of resistance occurring when a conductive material is curved; the flexible resistive sensor behaving as a passive potentiometer whose resistance varies as a function of the bending.

According to a first possibility, the flexible resistive sensor is integrated into the flexible strip, in other words the flexible strip which forms the flexible articulation between two elementary modules integrates (internally or at the surface) such a flexible resistive sensor, by using a conductive material at least partially embedded in the flexible strip or fastened at the surface on the flexible strip.

Alternatively, the flexible resistive sensor is offset with respect to the flexible strip, that is to say that the flexible resistive sensor is not located on the flexible strip but is shifted with respect to this flexible strip on an offset portion which will bend at the same time as or with the flexible strip. Thus, the flexible resistive sensor will be adapted to indirectly measure the bending of the flexible strip by directly measuring the bending of this offset portion.

With this first possibility, the flexible resistive sensors may thus be integrated into the above-described flexible membrane, in particular by being offset on the sides of the flexible membrane.

According to a second possibility, the flexible resistive sensor is integrated to a flexible blade fastened to the flexible strip, in particular in a detachable manner, so that a bending of the flexible strip results in a bending of the flexible blade.

In other words, the flexible resistive sensor comprises a conductive material at least partially embedded in the flexible blade or fastened at the surface on the flexible blade, and this flexible blade is attached on the flexible strip forming the flexible articulation between two elementary modules. The flexible blade being attached to the flexible strip, the latter bends with the flexible strip so that the measurement performed by the flexible resistive sensor integrated into the flexible blade reflects the bending of the flexible strip and therefore outputs a measurement of the angle of inclination between the two elementary modules.

Thus, the angle sensor function is provided on the flexible blade whereas the articulation function is provided by the flexible strip, thus dissociating the optoelectronic portion (the optoelectronic components connected by the flexible articulations) from the angle measuring portion (the angle sensors on the flexible blades).

In another variation, the physiological sensor comprises a flexible film on which flexible resistive sensors are disposed, wherein this flexible film is superimposed and fastened on the flexible membrane, and wherein this flexible film defines flexible blades superimposed or offset with respect to the flexible strips of the flexible articulations between the elementary modules, said flexible resistive sensors being provided on these flexible blades.

In other words, the flexible resistive sensors are provided on the flexible film which is in turn attached on the flexible membrane receiving the optoelectronic components, thus separating the optoelectronic portion (the flexible membrane) from the angle measuring portion (the flexible film).

According to another feature, the flexible film comprises at least one elastomeric polymer layer in which the flexible resistive sensors are at least partially embedded.

In a second variation, at least one articulation between two elementary modules is a semi-rigid articulation configured for a relative movement between the elementary modules according to several predefined discrete angles of inclination, wherein said semi-rigid articulation is configured to keep a stable inclination between two elementary modules in each of said angles of inclination, and to tilt between two distinct angles of inclination under the effect of a force applied on at least one of the two concerned elementary modules.

Such an articulation is semi-rigid, in the sense that, unlike the previously described flexible strip, this semi-rigid articulation is not adjustable in a continuous and non-stable manner, but rather in a discrete manner with several predefined angles of inclination wherein, for each angle of inclination, the articulation keeps this angle of inclination in a stable manner.

According to one possibility, a semi-rigid articulation is provided with notches for setting the angle of inclination between the two elementary modules according to several predefined values.

In another variation, a semi-rigid articulation is coupled to an angle sensor comprising electrical contactors, wherein each electrical contactor is coupled to a setting notch.

In other words, each setting notch is coupled to a contactor, all these contactors forming the angle sensor capable of establishing the measurement of the angle of inclination, each setting notch being indeed associated with an angle of inclination.

According to another possibility, a semi-rigid articulation is coupled to an angle sensor made in the form of a flexible resistive sensor attached on the articulation and comprising a flexible blade which bends with the articulation, said flexible resistive sensor outputting a measurement data reflecting a variation of resistance as a function of the bending of the flexible blade.

According to another possibility, each articulation (whether it is a flexible articulation or a semi-rigid articulation) is adjustable between −30 and +30 degrees for the angle of inclination between the two elementary modules.

According to another possibility, each semi-rigid articulation is adjustable according to several predefined angles of inclination separated in pairs by a constant angular step, in particular an angular step comprised between 5 and 15 degrees.

As non-limiting examples, each semi-rigid articulation may have the following angles of inclination, in degrees, [0, 5, 10, 15, 20, 25, 30] or [0, 10, 20, 30] or [0, 15, 30].

In another variation, each semi-rigid articulation comprises several balls cooperating with an elastic thrust element, said balls being movable within a curved rail with a predefined curvature and sliding inside a guide with the same curvature, and further comprises a cursor on the guide adapted to crush the balls according to the sliding of the rail within the guide, wherein the supports linked by the articulation are fastened respectively to one end of the rail and to one end of the guide.

Thus, such a semi-rigid articulation comprises a rail sliding within a guide, with the balls and the elastic thrust element on the rail. The rail and the guide abutting one inside the other represent an angle sector substantially corresponding to half the possible sector of the angle of inclination.

In this variation, the cursor of the guide can establish electrical contact with the crushed ball corresponding to the sliding of the rail within the guide, thus allowing establishing the angle of inclination.

Alternatively, each semi-rigid articulation comprises two full hinge half-faces, of about half the desired maximum sector of the angle of inclination, and having complementary reliefs that fit when said hinge half-faces are pressed against each other. These hinge half-faces are adapted to slide against each other in a controlled manner by applying a suitable force, so that these hinge half-faces slightly deviate to move from a setting notch to the next setting notch. A contactor can allow determining the position of the setting notch.

According to one feature, each elementary module comprises at least one optoelectronic component selected from the emitters and the receivers and disposed according to at least one of the following arrangements:

at least one emitter and at least one receiver;

at least two emitters of signals in distinct lengths in the near-infrared;

at least one emitter disposed at the center of the elementary module and at least one receiver disposed at the periphery of the elementary module;

at least one emitter disposed at the center of the elementary module and several receivers disposed at the periphery around said emitter;

one or several emitter(s) and no receiver;

one or several receiver(s) and no emitter.

According to another feature, in the planar configuration of the optoelectronic spread, the elementary modules are distributed into several rows and into several columns orthogonal to the rows.

Such a distribution into rows and columns is advantageous for the treatment according to a spatial subtraction method.

In another variation, each elementary module comprises a rigid or flexible support, on which at least one optoelectronic component is disposed, and each support comprises two opposite and parallel longitudinal edges, and two opposite and parallel transverse edges, and each articulation links two transverse edges contiguous to two adjacent respective supports, namely two longitudinal edges contiguous to two adjacent respective supports.

According to one feature, in the planar configuration of the optoelectronic spread, each articulation between two elementary modules is an articulation pivoting about an axis of articulation extending in the main plane; this pivoting being obtained by bending (or folding) of the flexible strip of the flexible articulation, or obtained by pivoting between two discrete angles of inclination of the semi-rigid articulation.

The present disclosure also relates to a near-infrared spectroscopy system, comprising a physiological sensor according to the present disclosure, and further comprising a control unit configured to establish the spatial coordinates of each emitter and of each receiver according to the angles of inclination of the articulations, wherein said control unit is connected, on the one hand, to the emitters of the physiological sensor to activate said emitters in an individual and non-concomitant manner, according to a predefined sequence and, on the other hand, to the receivers of the physiological sensor for a recovery and a three-dimensional treatment of the measurements originating from the receivers during said sequence according to the spatial coordinates of the emitters and of the receivers, and wherein the control unit is connected to each angle sensor to establish the spatial coordinates of each emitter and of each receiver according to the measurement data originating from said angle sensors.

Such a spectroscopy system is particularly suitable for all portions of the body, including the limbs and the internal organs (such as the heart) thanks to the conformation of the physiological sensor, and thanks to the control unit which allows activating the emitters according to a predefined sequence and recovering the measurements originating from the receivers. At each activation of an emitter, the control unit will take into consideration some emitters (such as for example pairs of emitters aligned with the activated emitter) and will not take into account some other emitters (in particular those located beyond a predefined threshold distance). Thus, it will be possible to crisscross an examination area at different depths, with a particularly fine resolution. The treatment of the measurements originating from the receivers is called three-dimensional treatment to the extent that it provides a result in depth of the analyzed portion of the body.

As examples of three-dimensional treatment, the control unit is configured for a three-dimensional treatment of the measurements originating from the receivers during the sequence according to a spatial subtraction method, or according to a tomography method with contrasts maps establishment, or according to a point cloud reconstruction method.

The spatial subtraction method implements subtractions between measurements originating from selected receivers.

The tomography method is obtained for example by establishing contrasts maps at different wavelengths.

The point cloud reconstruction method, in turn, implements a consideration of all absorption values by each receiver at each wavelength as constituting a cloud of points. Afterwards, a reconstruction algorithm (such as for example a «machine learning» classification algorithm) will allow identifying a coherence in connection with the different homogeneous absorption volumes, in order to enable a graphical representation, in other words, this reconstruction algorithm will be applied to all points acquired over time so as to better distinguish the areas characterized by the measurement technique. A coefficient of certainty could be assigned to the highly repetitive points, which would allow removing ambiguities on the measurement during an acquisition noised by the movement of the patient for example.

According to one feature, the control unit is configured process according to a three-dimensional treatment (for example, according to a spatial subtraction method, a tomography method, or a point cloud reconstruction method), at each activation of an emitter, only measurements originating from receivers selected according to a relative location with respect to said activated emitter established from their spatial coordinates.

Advantageously, in the planar configuration of the optoelectronic spread, the elementary modules are distributed into several rows and into several columns orthogonal to the rows, and the control unit is configured to process according to a spatial subtraction method, at each activation of an emitter, the measurements originating from receivers disposed in the same row and in the same column as said emitter.

As a complement, it is possible to consider the control unit being configured to process according to a spatial subtraction method, at each activation of an emitter, the measurements originating from receivers also disposed in a row and in a column different from those of said emitter.

The present disclosure also relates to a near-infrared spectroscopy method implementing a spectroscopy system according to the present disclosure, said spectroscopy method comprising the following steps:

collection of the measurement data originating from the angle sensors coupled to each articulation;

establishment of the spatial coordinates of each emitter and of each receiver according to the measurement data originating from the angle sensors (being recalled that these measurement data are dependent of representative of the angles of inclination of the articulations);

activation of the emitters in an individual and non-concomitant manner according to a predefined sequence;

recovery and three-dimensional treatment (for example, according to a spatial subtraction method, a tomography method, or a point cloud reconstruction method) of the measurements originating from the receivers during said sequence according to the spatial coordinates of the emitters and of the receivers.

As previously described, it is possible to consider that the three-dimensional treatment of the measurements originating from the receivers during the sequence implements a spatial subtraction method, or a tomography method with contrasts maps establishment, or a point cloud reconstruction method.

In another variation, the recovery and treatment step is followed by a step of constructing a three-dimensional image representing the underlying tissue strata, and in particular a vascular or blood volume within an analysis volume, said vascular or blood volume being composed of voxels constructed from the three-dimensional treatment of the measurements originating from the receivers during the sequence.

It should be noted that the activation step and the recovery and treatment step are repeated at successive time intervals, in order to enable a dynamic treatment over time to monitor an evolution in real-time.

Advantageously, the spatial coordinates establishment step results in the generation of a three-dimensional and virtual optoelectronic imprint of the physiological sensor in place.

Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

