Patent Application
20250176874
The present disclosure relates to a light guide module for use with apparatus for measuring an optical property of a medium and to an apparatus for measuring an optical property of a medium.
There are many applications in which it is useful to be able to measure an optical property of a medium. A particular example of the optical property is changes in concentration of a chromophore in a biological medium. Other examples include the absorption coefficient and the decorrelation rate. Known apparatus tends to be bulky and uncomfortable for the subject in the case the medium is a biological one. Known apparatus is also subject to low levels of signal-to-noise, particularly because the signal strength is often very low whilst noise levels can be very high, which can mask the signals that are to be obtained.
This is a problem in apparatus that uses transmission of light to and from the subject, and is a particular problem in the case that the apparatus is being used to transmit light into the head of a (human) subject and detect light that is diffusely reflected back out.
In our WO2018/033751A1, the entire content of which is hereby incorporated by reference, there is disclosed a measuring apparatus for fitting to an animal body for measuring changes in concentration of a chromophore in the animal body. The measuring apparatus has a plurality of devices, which may be referred to colloquially as “tiles”. Each device or tile has at least one light source for emitting light towards an animal body and at least one light detector for detecting light returning from the animal body. A device controller in the tile receives signals from and sends signals to a main controller via a connection arrangement, which may be or include a shared bus. Light guides, in the form of optical fibres, are provided to help channel the light from the light source(s) to the tissue under investigation and back from the tissue to the light detector(s).
According to a first aspect disclosed herein, there is provided a light guide module for use with an apparatus which fits to an animal body for measuring an optical property of a medium in the animal body, the light guide module comprising:
In some examples, the hollow light guide is the fixed light guide. In other examples, the hollow light guide is the movable light guide. In some examples, one of the light guides is a hollow tube (which is fixed or movable in different examples) and the other light guide is a solid light guide (which is movable or fixed in different examples). In other examples, both the first light guide and the second light guide are hollow tubes, with one of them being fixed and the other being movable. In any case, as the movable light guide moves back and forth, there is a telescopic like action between the light guides which accommodates movement of the movable light guide.
When provided in an apparatus for measuring an optical property of a medium in the animal body, the movable light guide can move in and out as the apparatus is fitted to and moved over the animal body so that a good contact is made between the first end of the movable light guide and the adjacent part of the animal body. This ensures efficient transfer of light from the movable light guide to the animal body and/or from the animal body into the movable light guide. The telescopic arrangement of the two light guides and the reflective interior of the hollow tube light guide accommodates the movement whilst maintaining a good transfer of light between the light guides. The use of coaxial, telescopic light guides means that the overall cross-sectional area or “footprint” of the light transmission parts is small.
In an example, the fit between the hollow interior of said hollow tube light guide which receives the other light guide and the other light guide is a clearance fit.
This helps reduce light losses whilst still allowing the light guides to move relative to each other. The clearance fit may in particular be a sliding fit.
In an example, said hollow tube light guide is the fixed light guide and is fixed to and supported by the support member or integral with the support member so as to be fixed against movement relative to the support member.
In an example, said hollow tube light guide is the movable light guide.
In an example, one of the light guides is said hollow tube light guide and the other light guide is a solid optical fibre or bundle of solid optical fibres.
In an example, both the first light guide and the second light guide are hollow tube light guides each having a reflective interior, wherein one of the hollow light guides is the movable light guide which is movable in and out of the hollow interior of the other, fixed, light guide.
In an example, the light guide module comprises a biasing arrangement to bias the movable light guide in a direction away from the fixed light guide.
In use, the biasing arrangement biases the movable light guide in a direction towards the subject animal body, which helps to maintain a good contact between the end of the movable light guide and the surface of the subject.
In an example, the biasing arrangement comprises a spring arranged to bias the movable light guide in a direction away from the fixed light guide.
In an example, the biasing arrangement comprises a first magnet fixed in relation to the movable light guide and a second magnet fixed in relation to the fixed light guide, the magnets being arranged to repel each other so as to bias the movable light guide in a direction away from the fixed light guide.
In an example, the biasing arrangement is provided by a volute spring having a plurality of coils, at least one of the first light guide and the second light guide being provided by at least one coil of the volute spring. In an example, the first light guide and the second light guide are provided by respective coils of the volute spring.
In an example, the light guide module comprises:
In an example, each of the movable light guides is movable back and forth relative to the support member independently of the other movable light guides.
According to a second aspect disclosed herein, there is provided an apparatus for fitting to an animal body for measuring an optical property of a medium in the animal body, the apparatus comprising:
In an example, the fit between the hollow interior of said hollow tube light guide which receives the other light guide and the other light guide is a clearance fit.
In an example, the apparatus comprises a biasing arrangement to bias the movable light guide in a direction away from the fixed light guide.
In an example, the biasing arrangement is provided by a volute spring having a plurality of coils, at least one of the first light guide and the second light guide being provided by at least one coil of the volute spring.
In an example, said hollow tube light guide is the fixed light guide and is fixed to and supported by the support member or integral with the support member so as to be fixed against movement relative to the support member.
In an example, said hollow tube light guide is the movable light guide.
In an example, one of the light guides is said hollow tube light guide and the other light guide is a solid optical fibre or bundle of solid optical fibres.
In an example, both the first light guide and the second light guide are hollow tube light guides each having a reflective interior, wherein one of the hollow light guides is the movable light guide which is movable in and out of the hollow interior of the other, fixed, light guide.
In an example, the apparatus comprises plural sets of fixed and movable light guides, wherein each set of fixed and movable light guides is associated with a respective one of the light source(s) and the light detector(s).
In an example, each of the movable light guides is movable back and forth relative to the support member independently of the other movable light guides.
To assist understanding of the present disclosure and to show how embodiments may be put into effect, reference is made by way of example to the accompanying drawings in which:
As mentioned above, there are many applications in which it is useful to be able to measure an optical property of a biological medium. For example, it can be useful to measure changes in concentration of a chromophore in an animal body, including in particular a human body, where chromophores may be found, for example, in blood flowing through the brain, or heart, or skeletal muscle, etc., etc. Other example properties include absorption coefficient and decorrelation rate.
As one particular example, apparatus for performing functional neuroimaging which aim to measure regional brain activity are known. Functional near-infrared spectroscopy (fNIRS) is a known non-invasive technique for providing information on the vascular and metabolic response to brain activity. The chromophores may be or include for example oxy-haemoglobin, deoxy-haemoglobin and oxidised cytochrome c oxidase. Oxy-haemoglobin and deoxy-haemoglobin are found in the blood. Oxidised cytochrome c oxidase can be found in tissue. Measurement of the changes in concentration of these chromophores may offer insight into, for example, regions of activity in the brain.
In such apparatus, light, which is infrared in the case of fNIRS, is emitted at the subject by one or more light sources and light reflected or transmitted back from the subject is detected by one or more light detectors. Light guides may be provided, typically one light guide for each light source and each light detector, in order to maximise the coupling of light from the light sources to the subject and from the subject to the light detectors, and thereby improve the signal-to-noise ratio. The light guides may be in the form of or provided by optical fibres.
A specific arrangement for such apparatus is disclosed in our WO2018/033751A1, the entire content of which is hereby incorporated by reference.
One or more light sources and one or more light detectors are mounted in the device 10. The dock 12 removably receives a device 10 and acts as a mechanical support and retainer for the device 10. The dock 12 and the device 10 may be a friction fit or a snap fit, with ridges and recesses, etc. to secure the device 10 in the dock 12. The dock 12 in this example also provides power and data in and data out connections for the device 10.
The dock 12 has plural through holes 18, for example, one through hole 18 for each light source and for each light detector, so that light can pass through the dock 12 between the subject and the light source(s) and the light detector(s) respectively.
Referring particularly to
The use of such light guides 20 is of particular advantage when it is the subject's head, and particular the brain, that is being subject to study, particularly in the case of fNIRS which uses infrared light. This is because hair is a strong absorber of light, and particularly a strong absorber of near-infrared light, and is often a major factor in preventing a measurement with a good signal-to-noise ratio being obtained. The light guides 20 comb through the user's hair, i.e. pass between the hair strands, which means that the light to and from the light sources and light detectors is less likely to be absorbed by the hair as the light passes through the light guides 20 instead. This improves the quality of the detected signal.
Ideally, the distal ends of each of the light guides 20 (i.e. the end that is remote from the light source or light detector respectively) are in contact with the subject's scalp or other body part that is being studied in order to minimise the light losses and therefore maximise the signal-to-noise ratio. A problem with light guides that are static is that they cannot conform well to the shape of the subject's scalp or other body part that is being studied. Ridges or bumps or depressions in the scalp or other body part often mean that whilst some light guides are making good contact, others of the light guides are held away from the scalp or other body part. This is a particular problem in the case that there are many light guides per unit area, which is required for a high density study and high resolution imaging, such as is often desired in the case of fNIRS.
A known solution to this is to allow one or more or all of the light guides to move back and forth, and particularly to move back and forth independently of the others. Examples of this are disclosed in WO2011/083563A1, US2015/0038811A1 and US2021/0259632A1. Each of these documents discloses apparatus for optical study and imaging, including for fNIRS of the brain, in which light guides are used to convey light to and from the subject and in which the light guides are movable. The movement of the light guides allows the light guides to conform to the shape of the body part better, which helps to make a good contact between the light guides and the subject's body. In each of these documents, the movable light guides are spring-loaded so as to be biased towards contact with the subject's body to assist in ensuring a good contact with the subject's body.
However, with movable light guides, particularly in the case of arrangements like those disclosed in US2021/0259632A1 in which the light guides move relative to the light sources or light detectors respectively, there remains a problem in ensuring efficient transmission of light out of the light sources into the light guides and out of the light guides into the light detectors over the whole movement range of the light guides. In particular, when the light guide has been moved away from the light source or light detector respectively, light can be lost between the light guide and the light source or light detector respectively. The device disclosed in US2021/0259632A1 attempts to solve this on the light source side by the use of a prism and lens plate, located between the end of the light guide and the light source, for directing and focussing the light onto the end of the light guide. The device disclosed in US2021/0259632A1 attempts to solve this on the light detector side by the use of first and second lenses, located between the end of the light guide and the light detector, for collimating and focussing the light on to the light detector.
In examples described herein, there is provided a light guide module for use with an apparatus which fits to an animal body for measuring an optical property of a medium in the animal body. Examples of and applications of such apparatus are described further above. In one example, the light guide module has a support member, a first light guide and a second light guide supported in the support member. One of the light guides is a fixed light guide and the other light guide is a movable light guide which is movable back and forth relative to the support member between an extended position and a retracted position. The light guides are arranged coaxially. At least one of the fixed light guide and the movable light guide is a hollow tube light guide having a hollow interior which receives the other light guide. The interior of the hollow tube light guide is reflective. As such, when the movable light guide is in the extended position, at least one of: (I) light entering an end of said hollow tube light guide can be internally reflected by the interior of said hollow tube light guide into an end of the other light guide that is facing said end of said hollow tube light guide, and (ii) light exiting said end of the other light guide can be internally reflected by the interior of said hollow tube light guide towards said end of said hollow tube light guide.
This ensures efficient transfer of light from the light source to the animal body and/or from the animal body to the light detector. The hollow tube light guide (which in some examples is the fixed light guide and in other examples is the movable light guide) having a reflective interior accommodates movement of the movable light guide whilst maintaining a good transfer of light.
This arrangement maximises the coupling of light from the light sources to the subject and from the subject to the light detectors, even though the movable light guide has moved away from the light source or light detector respectively. This therefore reduces losses of the light passing from the light sources to the subject and/or from the subject to the light detector. Furthermore, the hollow tube light guide can also prevent ambient light from entering the system, which can otherwise worsen the signal-to-noise ratio. Moreover, the use of a hollow tube light guide for accommodating movement of the movable light guide means that collimating and focussing lenses and the like used in some known apparatus to direct light into and out of a movable light guide can be avoided. This in turn means that the overall cross-sectional area or “footprint” of the light transmission parts is small. This allows a higher density (i.e. number per unit area) of light sources and light detectors to be provided, in turn enabling higher quality and resolution to be obtained. Alternatively or additionally, this means that the spacing between adjacent light guides can be relatively large, making it easier to comb the light guides through a subject's hair when fitting the apparatus to the subject's head and moving the apparatus and light guides over the head. In addition, reducing the light losses means that the light guides themselves can have a smaller diameter, which again makes it easer to comb the light guides through a subject's hair when fitting and locating the apparatus to the subject's head. Finally, avoiding the use of collimating and focussing lenses and the like also means that the number of interfaces through which the light must pass between the light sources and subject and the light detector can be minimised (indeed, can be unchanged from the arrangement as disclosed in our WO2018/033751A1 in some examples). This keeps down any reflective losses that can occur when light passes through an interface between materials having different refractive indices, again improving the signal-to-noise ratio.
Some specific examples of the present disclosure will now be described with reference to
Referring first to
In this example, the device 100 can be removably located in the dock 120. The dock 120 removably receives the device 100 and acts as a mechanical support and retainer for the device 100. The dock 120 and the device 100 may be a friction fit or a snap fit, with ridges and recesses, etc. to secure the device 100 in the dock 120. The dock 120 in an example also provides power and data connections for the device 100. In an example, plural such docks 120 with associated light guide modules 140 may be permanently fixed to a carrier such as for example a cap or other headgear as mentioned above (see also
As an alternative, the device(s) 100 and the light guide module(s) 140 may be “permanently” fixed to or be part of a carrier such as for example a cap or other headgear, and not to be easily removed and relocated, and docks for allowing the devices 100 to be removably attached are not provided.
One or more light sources and one or more light detectors are mounted in the device 100. Referring to
Each light source unit 162 has or contains at least one light source 163 for emitting light. In an example a light source unit 162 has a plurality of light sources 163. In the specific example shown, each light source unit 162 has three light sources 163. Each light source 163 may emit light having a wavelength in the range of for example around 600 nm to 1000 nm. The light sources 163 may emit light having different wavelengths. That is, in an example, each light source unit 162 has a first light source 163 which can emit light at a first wavelength, a second light source 163 which can emit light at a second wavelength, and a third light source 163 which can emit light at a third wavelength, each wavelength being different. In an example, the three wavelengths might be 735 nanometres, 810 nanometres and 850 nanometres. The light sources 163 may be for example light-emitting diodes (LEDs). In use in an example, each of the light sources 163 is powered in turn such that, at least within a particular light source unit 162, only one light source 163 is emitting light at a time.
Each light detector unit 164 has at least one light detector 165, which may be for example a photodiode, for detecting light. In the example shown, each light detector unit 164 has a single light detector 165. The light detectors 165 are arranged to detect light having a wavelength that is emitted by the light sources 163. In use in an example, each light detector 165 is continually able to detect light.
The board 160 may be a printed circuit board (PCB). In the example shown, the light source units 162 and light detector units 164, and specifically the light sources 163 and light detectors 165 contained therein, are mounted directly on the board 160. An advantage of mounting the light source units 162 and light detector units 164, and specifically the light sources 163 and light detectors 165 contained therein, directly on the PCB 160 is that it avoids (relatively) long connecting wires from the PCB to the light sources 163 and light detectors 165, which therefore reduces noise and interference. The light detector units 164 are arranged on the PCB 160 close to respective amplifier and other circuits (not shown), which again helps to reduce noise arising in the device 100.
Returning to the dock 120 briefly, in this example, this has seven through holes 122, one for each of the light source units 162 and light detector units 164 of the device 100, for light to pass through. When the dock 120 and light guide module 140 are assembled, parts of the light guide module 140 project through the through holes 122 of the dock 120 to transmit the light, as will be discussed further below.
Discussing now the first example of the light guide module 140 in more detail, a function of this is to be or provide a support member to support one or more light guides 142 which in use are close to and preferably in contact with the animal body, for example the scalp of the subject's head. As noted, the light guide module 140 may be provided as a discrete component or may be part of a larger carrier, such as for example a cap or other headgear, which is fitted to the animal body in use.
The light guides 142 are arranged to be able to move back and forth, i.e. in a reciprocating manner, in and out, relative to the light sources 163 and the light detectors 165 of the device 100. That is, in this example where a separate light guide module 140 is provided to support the light guides 142, the light guides 142 can move back and forth relative to the body of the light guide module 140. This is illustrated in
A problem with allowing the light guides 142 to move back and forth relative to the light sources 163 and the light detectors 165 of the device 100 is that the proximal ends 146 of the light guides 142, that is, the ends of the light guides 142 that are closest to the light sources 163 and the light detectors 165, can become located some distance from the light sources 163 and the light detectors 165. This means that light can be lost between the light guide 142 and the light source 163 or light detector 165 respectively. It also means that ambient light may enter into the transmission path, which can affect both the illumination of the subject and the quality of the returning light signal that is detected.
To address this, and as shown most clearly in the cross-sectional views of
In the example shown in
The fit between the hollow tube light guide and the other light guide that moves within it may be for example a clearance fit, and may particularly be a sliding fit.
In short, providing a second light guide in the form of a hollow tube having a reflective interior and within which the first light guide moves back and forth helps reduce light losses whilst still allowing the first light guide to move to make contact with the subject animal body in use. This therefore maximises the coupling of light from the light sources to the subject and from the subject to the light detectors, even though the movable light guide has moved away from the light source or light detector respectively.
Furthermore, the hollow tube light guide can be opaque, at least to ambient light (including visible light and infrared) which prevents ambient light from entering the system, which can otherwise worsen the signal-to-noise ratio.
In addition, this telescopic arrangement of light guides means that collimating and focussing lenses and the like used in some known apparatus to direct light into and out of a movable light guide can be avoided. This in turn means that the overall cross-sectional area or “footprint” of the light transmission parts is small. This allows a higher density (i.e. number per unit area) of light sources and light detectors to be provided, in turn enabling data of higher quality and resolution to be obtained. Alternatively or additionally, this means that the spacing between adjacent light guides can be relatively large, making it easier to comb the light guides through a subject's hair when fitting the apparatus to the subject's head and moving the apparatus and light guides over the head. In addition, reducing the light losses means that the light guides themselves can have a smaller diameter, which again makes it easer to comb the light guides through a subject's hair when fitting and locating the apparatus to the subject's head. Finally, avoiding the use of collimating and focussing lenses and the like also means that the number of interfaces through which the light must pass between the light sources and subject and the light detectors can be minimised (indeed, can be unchanged from the arrangement as disclosed in our WO2018/033751A1 in some examples). This reduces any reflective losses that can occur when light passes through an interface between materials having different refractive indices, again improving the signal-to-noise ratio.
It may be noted that at one extreme end of its motion, the movable light guide 142 may move entirely out of the hollow tube light guide 150. However, it is preferred that the proximal end 146 of the movable light guide 142, which is closest to the light source 163 or the light detector 165 respectively, always remains within the hollow tube light guide 150 (as indicated in
In this example, there is one set or pair of a movable light guide 142 and a fixed light guide 150 for each of the light source units 162 and light detector units 164 of the device 100. In other examples, not all of the light source units 162 and light detector units 164 of the device 100 have an associated set or pair of a movable light guide 142 and a fixed light guide 150.
The reflective interior surface of the hollow tube light guide 150 may be provided in a number of ways. For example, the whole of the hollow tube light guide 150 may be formed of a reflective material, such as for example a metal, including for example stainless steel. Alternatively or additionally, the interior surface of the hollow tube light guide 150 may be coated with a reflective material. A metallic mirror coating or a dielectric highly reflective coating may be used. Suitable metallic materials include for example aluminium, gold, silver, titanium, etc.
In an example, the movable light guides 142 are biased towards the subject in use, that is away from the light sources 163 and light detectors 165 respectively, namely to the extended configuration. This helps to ensure that the movable light guides 142 make good contact with the subject, or at least bring the distal ends 144 of the movable light guides 142 closer to the subject.
A number of different arrangements for biasing the movable light guides 142 towards the extended configuration are possible. In the example shown in
In more detail, the light guide module 140 has a generally planar base portion 180 and through holes 182 for the first and second light guides 142, 150 to pass through. An elongate tubular collar 184 is located in each through hole 182 to extend therethrough. The upper part of the elongate tubular collar 184 has an external flange 186 around its periphery towards one end. The flange 186 sits in a corresponding recess 188 provided in a facing upper portion of the base portion 180 around the through hole 182 of the base portion 180. The flange 186 may be a snap or press fit in the recess 188 and/or may be fixed in using an adhesive or in some other manner. The fixed light guide 150 is located within the upper part of the elongate tubular collar 184. The fixed light guide 150 may be a snap or press fit in the upper part of the elongate tubular collar 184 and/or may be fixed in using an adhesive or in some other manner. Below the external flange 186 of the elongate tubular collar 184, the elongate tubular collar 184 has an internal flange 190. The elongate tubular collar 184 may be formed of for example black ABS (acrylonitrile butadiene styrene) or some other suitable opaque material.
A second tubular collar 192 is located within the elongate tubular collar 184. The second tubular collar 192 may be formed of for example stainless steel or some other rigid material. The distal end of the movable light guide 142 is fixed within the second tubular collar 192. As the movable light guide 142 moves back and forth relative to the fixed light guide 150, the second tubular collar 192 moves back and forth within the elongate tubular collar 184. In this example, the upper end of the second tubular collar 192 has an external flange 194 around its periphery. The lower part of the module 140 has an internally facing flange 196 towards the lower part of the through hole 182. The external flange 194 of the second tubular collar 192 bears against the internally facing flange 196 at the lower part of the through hole 182 to retain the second tubular collar 192 in the through hole 182 when the movable light guide 142 and the second tubular collar 192 move to the most extended position (downwards in
The external flange 194 of the second tubular collar 192 faces (is opposed to) the internal flange 190 of the elongate tubular collar 184. The spring 170 is located in the cylindrical space between the movable light guide 142 and the lower part of the elongate tubular collar 184, and is trapped between the external flange 194 of the second tubular collar 192 and the internal flange 190 of the elongate tubular collar 184. The spring 170 is partially compressed in its rest state (i.e. when the movable light guide 142 is at its extended configuration shown in
Alternatives to using springs for the biasing arrangement to bias the movable light guide(s) 142 towards the animal body are possible. For example,
In the example of
Whereas the previous example of
In the examples shown in
Another example of a light guide module according to the present disclosure is shown schematically in the cross-sectional views of
Compared to the example of
An advantage of the movable light guide 142 being hollow, in addition to the fixed light guide 150 being hollow, is that this avoids an interface between a solid material and air (as occurs for light passing between the solid movable light guides 142 and the hollow fixed light guides 150 of the examples described above). This reduces loss of light that occurs due to back reflections as light passes between a solid medium and air, again improving the signal-to-noise ratio.
It may be noted that the example of
Another example of a light module according to the present disclosure is shown schematically in the cross-sectional views of
The principal difference of the example of
In the example of
In the example of
In addition, in the example of
In the examples of
Referring to
In the rest state illustrated in
Other examples for the biasing arrangement and the movable and fixed light guides are illustrated schematically in
Referring first to
As known per se, a volute spring is a compression spring having a number of coils. Under compression, the coils slide past each other, thus enabling the spring to be compressed to a very short length, with the resilience of the material of the volute spring biasing the spring to an extended configuration. Volute springs are often in the form of a cone, and may also be referred to as conical springs. In some cases however, a volute coil may have a parabolic profile. In the present examples, the volute spring 500 is typically a right cone (i.e. a cone for which the axis passes through the centre of the base at right angles to its plane) and typically has a circular cross-sectional shape.
The volute spring 500 is fixed at its proximal end to the main body of the light guide module 140. The proximal end of the volute spring 500 is adjacent to the facing end of the fixed light guide 450. The other, distal, end of the volute spring 500 projects out of the light guide module 140 and can move back and forth. Accordingly, as the light guide module 140 is moved over a subject, the volute spring 500 can compress and extend to accommodate recesses and ridges and the like in the scalp or other body part of the subject.
The volute spring 500 has a reflective interior, by for example being coated with or formed of a reflective material. In this example, the volute spring 500 therefore provides the movable light guide, at the distal end of the light guide module 140, as well as the biasing arrangement.
Referring to
In each of the examples of
In another example shown schematically in
In each of the examples of
On the other hand, in the example of
In any of the examples of the light guide module 140 above, it may be of advantage to provide one or more additional measures to prevent or at least reduce the amount of external or ambient light entering into the transmission path of light from the light source(s) to the subject and/or from the subject to the light detector(s). An example is shown schematically in
In the example of
Whilst in the example of
In each of the examples described above, the distal ends of the light guides that are closest to the subject in use (i.e. the end of those light guides that is remote from the light source or light detector respectively and that is therefore closest to the subject in use) extend a relatively long way from the generally planar base portion 180 of the light guide module 140. This is useful in many applications. However, in some applications, such as when the apparatus and therefore the light guide module 140 is used for study of a baby or infant's brain and is therefore used on a relatively small head, it can be better if the light guide module 140 is more low profile, that is, so that the overall vertical height of the light guide module 140 is less and particularly such that the distal ends of the light guides that are closest to the subject in use do not project far from the generally planar base portion 180 of the light guide module 140.
An example of a low profile light guide module 140 is shown schematically in
Notably, in each of the examples described above, the biasing arrangement if provided is located on the side of the light guide module 140 that is closest to the subject in use. Referring for example to
In contrast, in the low profile light guide module 140 of
This is achieved in this example first by locating the internal flange 190 of the elongate tubular collar 184 of the base portion 180 above the external flange 186 of the elongate tubular collar 184 (that is, on the side of the external flange 186 of the elongate tubular collar 184 that is furthest from the subject in use). In addition, the lower (movable) light guide 142 is relatively shorter and the external flange 194 on the lower (movable) light guide 142 is located relatively further up. In particular, in this example, the external flange 194 on the lower (movable) light guide 142 is generally coplanar with the generally planar base portion 180 of the light guide module 140 in the rest position shown in
As in examples described above, the spring 170 is located in the cylindrical space between the movable light guide 142 and the lower part of the elongate tubular collar 184, and is trapped between the external flange 194 of the movable light guide 142 and the internal flange 190 of the elongate tubular collar 184. But here, the spring 170 is located “above” the main plane of the generally planar base portion 180, allowing the movable light guide 142 to be relatively shorter and the overall vertical height of the light guide module 140 to be small.
It is mentioned again that the same low profile principle, with the biasing arrangement “above” the main plane of the generally planar base portion 180 of the light guide module 140, may be used in one or more of the other examples described herein, which have different arrangements of the light guides and the biasing arrangement.
For completeness, it is noted that the example of
In summary, examples described herein provide sets of two (or more) light guides for one or more of each light source and light detector of the measuring apparatus. At least one of the light guides is a hollow light guide having a reflective interior into which the other light guide relatively moves. This use of a hollow light guide having a reflective interior accommodates relative movement between the light guides whilst maintaining a good transfer of light. This allows the distal light guide to move to come into contact or at least be closer to the subject animal body in use whilst minimising light loss and minimising admission of ambient light.
The examples described herein are to be understood as illustrative examples of embodiments of the invention. Further embodiments and examples are envisaged. Any feature described in relation to any one example or embodiment may be used alone or in combination with other features. In addition, any feature described in relation to any one example or embodiment may also be used in combination with one or more features of any other of the examples or embodiments, or any combination of any other of the examples or embodiments. Furthermore, equivalents and modifications not described herein may also be employed within the scope of the invention, which is defined in the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2204719.5 | Mar 2022 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2023/058290 | 3/30/2023 | WO |
