Patent Description:
There are many applications where it is useful to be able to measure changes in concentration of a chromophore in a biological medium. Known apparatus tends to be bulky and uncomfortable for the subject. 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. It is also difficult or laborious to image the concentration of a chromophore in a biological medium using known devices and apparatus.

<CIT> discloses an optical sensor for providing information about a subject. The optical sensor is placed in proximity to the subject and includes optical sources and optical detectors. The optical sources irradiate the subject with optical signals and the optical detectors detect signals from the subject. Analysis of the detected signals can yield information about the subject.

<CIT> discloses a tissue-monitoring device for selecting, administering or adjusting a treatment based on information obtained by monitoring the tissue. The device includes a substrate for applying to the tissue; a light source supported by the substrate, the light source emitting light of a first frequency for directing the emitted light onto a surface of the tissue; a photodetector carried by the substrate spaced from the light source for detecting scattered light; and a controller.

<CIT> discloses a patient-monitoring system which includes a platform and one or more monitoring modules. A platform and one or more monitoring modules may be coupled to form a communications bus, allowing communication between any of the plurality of coupled devices.

According to an aspect disclosed herein, there is provided a measuring apparatus for fitting to an animal body for measuring changes in concentration of a chromophore in the animal body, the measuring apparatus comprising:.

The apparatus is convenient for both technicians using the apparatus and the subject to which the apparatus is fitted in use. Examples of the apparatus enable rapid gathering of data from the animal body and facilitate imaging of the region being studied. Having a device controller provided on the devices facilitates modularity of the apparatus as in some examples the devices can more easily be connected to and removed from different locations of the apparatus, and therefore repositioned, as may be required or useful.

The light emerging from said animal body may be for example reflected light or transmitted light, etc., in each case ultimately deriving from the light emitted by the light source at or into the animal body. In general, the "light" may be visible or non-visible light.

In an example, the light sources of the devices are arranged to emit near-infrared light. This may be in the range of for example <NUM> to <NUM>.

In an example, each of the devices comprises at least two light sources wherein a first light source is arranged to emit light of a first wavelength and a second light source is arranged to emit light of a second wavelength which is different from the first wavelength. In some examples, the use of multiple wavelengths enables signals from different chromophores to be more easily distinguished. By way of a specific example in a specific application, the use of multiple wavelengths enables signals due to the less dominant chromophores to be more easily distinguished from those due to haemoglobin (which is the most dominant chromophore in mammalian tissue), and thus for example provide more complete and accurate information about tissue oxygenation, haemodynamics and metabolism.

In an example, the distance between the at least two light sources is no more than <NUM>% of the distance between each of the at least two light sources and the light detector. The light sources may be provided as components of a light source unit. It is desirable that the light sources are co-located as closely as possible, particularly in the case that the light sources emit different wavelengths, as it can then be assumed or at least approximated with a high degree of accuracy that the measurements sample the same volume of tissue.

In an example, the bus is a shared bus in the form of a single cable having plural connector ports to which the device controllers of at least some of the devices are respectively connected. The shared bus may be for example a shared serial communication bus. In an example, at least one of the devices has a connector for removably connecting the device to the shared bus.

In an example, at least one of the devices is connected to the shared bus by flexible conductors.

In an example, the connection arrangement is provided at least in part by a wiring scheme in which the plurality of devices are connected in sequence.

In an example, the connection arrangement is provided at least in part by a wireless connection between at least some of the devices.

In an example, the apparatus comprises a plurality of docks each for removably receiving a respective device. At least some of the docks may comprise an electrical connector for making a connection between the bus and the device controller of a device received in the dock.

In an example, the devices comprise a Faraday cage which encloses at least the light detector of the device. Where amplifiers are provided for the light detectors, the Faraday cage of the devices may also enclose the amplifiers.

In an example, each of the devices comprises:
a charge-to-digital converter for the light detector, the charge-to-digital converter having a plurality of amplifiers and an analogue-to-digital converter, wherein:.

In an example, each of the devices comprises:
a current-to-digital converter for the light detector, the current-to-digital converter having a transimpedance amplifier and an analogue-to-digital converter, wherein:.

In an example, each of the devices comprises a substrate in which the light source, the light detector and device controller are arranged. The substrate may be transparent to light emitted by the light source.

In an example, each of the devices comprises a plurality of light guides, wherein:.

In an example, the first light guide is generally cylindrical and arranged around the light source.

In an example, the second light guide is generally cylindrical and arranged around the light detector.

The first and second light guides may be provided as part of a separate component which can be removably placed over the light source and light detector. This enables the light guides to be easily removed for cleaning or replacement (for example, before use on a different subject or biological medium).

In an example, the device controller of each device is a microcontroller, and each device comprises a local memory for storing data received from at least one of a main controller and the light detector. The local memory may be part of the microcontroller and/or provided separately of the microcontroller.

In an example, the device controller is arranged to send signals to the light source in accordance with signals received from a main controller and is arranged to send signals to a main controller in accordance with signals received from the light detector.

In an example, the signals include at least one of light source intensity instructions, clock signals and data signals.

In an example, at least one device comprises an electrode arranged to measure electrical signals produced in a medium to non-invasively monitor electrical activity in the medium. The device may be used to obtain for example simultaneous electroencephalography (EEG) measurements.

There is also described herein a device for use with measuring apparatus as described above for measuring changes in concentration of a chromophore in a biological medium, the device comprising:.

Such a device is in effect a self-contained unit, at least to a large extent. Having a device controller provided on the device facilitates modularity of the apparatus with which plural such devices may be used in practice.

In an example, the light source is arranged to emit near-infrared light. This may be in the range of for example <NUM> to <NUM>.

In an example, the device comprises at least two light sources wherein a first light source is arranged to emit light of a first wavelength and a second light source is arranged to emit light of a second wavelength which is different from the first wavelength.

In an example, the device has a connector for removably connecting the device to a bus. The bus may be for example a serial communication bus.

In an example, the device has a wireless transceiver for wirelessly connecting the device to another device as described above. In an example of this, the device may have its own power source, such as a battery, which may be a rechargeable battery or a non-rechargeable battery, in effect enabling the device to be a self-contained measuring device.

As mentioned above, there are many applications where it is useful to be able to measure changes in concentration of a chromophore in 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..

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.

Known fNIRS systems typically involve coupling large arrays of optical fibres or fibre bundles to the scalp. Imaging over an entire scalp typically requires around <NUM> discrete source positions and a similar number of detector positions, which often results in an array that is bulky and heavy, and that severely restricts movement. More recently, portable systems have been developed which employ sources and detectors in direct contact with the scalp, with the analogue signal being transferred via long electrical cables to a controller module. One problem with this approach is that long analogue cables can introduce noise into the measurement. It is also difficult or laborious to image the concentration of the chromophores with known fNIRS systems. Patients or other people or animals who are subject to such studies are, inevitably, often reluctant to be subjected to extended periods of study, or are even incapable of being studied for an extended period.

Examples of apparatus <NUM> described herein may be used to measure changes in concentration of a chromophore in a biological medium. In turn, this may enable changes in concentration of a chromophore in a biological medium to be monitored, over time. Furthermore, examples of apparatus <NUM> described herein may be used to enable images of concentration of a chromophore in a biological medium to be produced, and to be produced in real time, which is of significant value to practitioners.

Referring to <FIG>, there is shown a schematic view of an example of an apparatus <NUM> for measuring changes in chromophore concentration in the body. The apparatus <NUM> in this example has at least one device <NUM> and a bus <NUM>, which in use is in communication with a base unit <NUM> which in turn is in communication with a data recorder such as a computer <NUM>. The base unit <NUM> may act as a "hub" or master or main controller for the apparatus <NUM>.

In typical implementations, the apparatus <NUM> has plural devices <NUM>, which are identical or at least have substantially the same functionality, and the bus <NUM> is a shared bus <NUM> to which all of the devices <NUM> are connected. In the figure, only a portion of the apparatus <NUM> and four devices <NUM> are shown. In practice, there will typically be say around <NUM> to <NUM> or more such devices <NUM>. The devices <NUM> are connected to each other by the shared bus <NUM>, which also connects to the base unit <NUM>. In the example shown, the base unit <NUM> is connected to the computer <NUM> by a wireless link <NUM>. The base unit <NUM> may have its own power source, such as a battery, which may be a rechargeable battery or a non-rechargeable battery. The power source of the base unit <NUM> may power the components of the base unit <NUM> and optionally also the devices <NUM> (though the devices <NUM> in some examples may have their own power source, such as a rechargeable battery or a non-rechargeable battery). A wireless link <NUM> between the base unit <NUM> and the computer <NUM>, and providing the base unit <NUM> and devices <NUM> with their own power source(s), is more convenient as it means that the combination of the devices <NUM> and the base unit <NUM> (which itself may be relatively small and lightweight) can be effectively untethered and therefore made both wearable and portable. This is convenient for both technicians using the system and the person or other subject under study, who is able to move around relatively freely if desired. Nevertheless, a wired connection to the computer <NUM> and/or providing some external power supply for powering the base unit <NUM> and/or the devices <NUM> may be used instead in other implementations. The devices <NUM> may be in the form of blocks or "tiles", which facilitates the modularity of the apparatus <NUM> as individual devices <NUM> can be added or removed as desired or necessary.

Referring additionally to <FIG>, there are shown schematic views of an example of a device <NUM>. In this example, the device <NUM> is generally cuboid, having a rectangular or square cross-sectional shape. The device <NUM> has at least one light source unit <NUM> and at least one light detector unit <NUM>. In the specific example shown in these figures the device <NUM> has two light source units <NUM> and four light detector units <NUM>. Each light source unit <NUM> has or contains at least one light source <NUM> for emitting light. In an example a light source unit <NUM> has a plurality of light sources <NUM>. In a specific example, each light source unit <NUM> has two light sources <NUM>. Each light source <NUM> may emit light having a wavelength in the range of for example around <NUM> to <NUM>. The light sources <NUM> may emit light having different wavelengths. In an example, each light source unit <NUM> has a first light source <NUM> which can emit light at a first wavelength and a second light source <NUM> which can emit light at a second wavelength. The light sources <NUM> may be for example light-emitting diodes (LEDs). The light detector units <NUM> are arranged to detect light having a wavelength that is emitted by the light sources <NUM>. In the example shown, the light source units <NUM> and light detector units <NUM> are mounted in or supported by a substrate <NUM> which provides the bulk of the body of the device <NUM>. The substrate <NUM> may be for example black pigmented silicone.

In use, the light sources <NUM> emit light towards a medium in which a chromophore is present. In a specific example, the medium may be a human head, but may also be other body parts of a human or other animal. As mentioned above, the light sources <NUM> may emit at a number of different discrete wavelengths. In the specific example of fNIRS, it has been found to be useful to use light of wavelengths around <NUM> and <NUM> to monitor changes in oxyhemoglobin and deoxyhemoglobin concentrations respectively, though different wavelengths may be used. More generally and by way of further example, the shorter wavelength may be in the range of around <NUM> to <NUM> and the longer wavelength may be in the range of around <NUM> to <NUM>.

To accurately interpret data with the apparatus <NUM>, it is desirable to assume that the measurements sample the same volume of tissue. It is therefore preferred that the sources of the discrete wavelengths are co-located as closely as possible. The separation between the light sources <NUM> in the light source units <NUM> is therefore preferably small or even negligible compared to the distance between the light source units <NUM> and the light detector units <NUM>. In an example, the distance between the light sources <NUM> of a light source unit <NUM> is not more than <NUM>% of the distance between the light source unit <NUM> and the light detector unit(s) <NUM>. In one example, the distance between the light sources <NUM> of a light source unit <NUM> is not more than <NUM>% of the distance between the light source unit <NUM> and the light detector unit(s) <NUM>. In another example, the distance between the light sources <NUM> of a light source unit <NUM> is not more than <NUM>% of the distance between the light source unit <NUM> and the light detector unit(s) <NUM>. In an example, the distance between the light sources <NUM> in a light source unit <NUM> may be less than a few millimetres whereas the distance between the light source unit <NUM> and the light detector unit(s) <NUM> may be up to a few centimetres. In a specific example, the distance between the light sources <NUM> in a light source unit <NUM> of a device <NUM> may be between around <NUM> to <NUM>, such as around <NUM> whereas the distance between the light source unit <NUM> and the light detector unit <NUM> of a device <NUM> may be around <NUM>, or at least may be a minimum of around <NUM>. (Where there are plural devices <NUM>, the minimum distance between a light source unit <NUM> of a device <NUM> and a light detector unit <NUM> of an adjacent device <NUM> may be for example around <NUM> to <NUM>.

For some applications, the arrangement of the light source units <NUM> and light detector units <NUM> may be chosen so that the (shortest) distance between a light source unit <NUM> and a light detector unit <NUM> is small, such as a few millimetres, such as around <NUM> or less. A light source unit <NUM> and a light detector unit <NUM> may be closely located and may in some cases be practically co-located.

The light sources <NUM> in the light source units <NUM> may be driven by for example a multiplexed voltage-controlled current source (VCCS). This enables accurate control of the current flowing through the light source <NUM>, which is closely related to its optical intensity. An analogue multiplexer is used instead of discrete transistors to switch between light sources <NUM>. The multiplexing VCCS scheme is more compact and flexible than traditional resistor/op-amp combinations.

Each light detector unit <NUM> has at least one light detector <NUM>, which may be for example a photodiode, for detecting light. In the example shown, each light detector unit <NUM> has a single light detector <NUM>. In a specific example, the four photodiode detectors <NUM> of the light detector units <NUM> of the device <NUM> are coupled to respective channels of a four-channel charge-to-digital converter which includes two charge integrators per channel and at least one analogue-to-digital converter (ADC) and which may be provided on the device <NUM>. In a specific example, the device <NUM> has two ADCs. The charge integrators (also known as charge amplifiers or charge integration amplifiers) integrate the photodiode current generated by the incident light to output a voltage. The use of two parallel charge integrators per channel enables one charge integrator to integrate the generated photodiode current while the output of the other charge integrator is being digitized by an ADC. This facilitates continuous operation of the device <NUM> without any dead time. Moreover, because the analogue signals are digitized early in the signal path (that is, effectively as a first step as the analogue signals are output by the light detector units <NUM>), the signal-to-noise ratio is improved.

In a specific example, the charge integrators are provided as part of an analog-to-digital converter, which may be for example the DDC114 of the Texas Instruments DDC family. In another example, the charge integrators are part of the DDC118 of the Texas Instruments DDC family. The light detectors <NUM> are directly connected to the high impedance analogue inputs of the DDC114/DDC118. Providing the pairs of charge integrators and their associated ADC within one integrated circuit leads to a superior signal-to-noise ratio as compared with the use of discrete elements.

As an alternative to or in addition to the use of charge integrators, current-to-voltage converters can be used for photodiode signal amplification, in the form of transimpedance amplifiers. In a specific example, a Texas Instruments OPA380 may be used. In a specific example a transimpedance amplifier may then be connected to its own ADC. In another example, more than one transimpedance amplifier may be multiplexed to a single ADC that has multiple input channels.

The device <NUM> has a device controller <NUM>. The device controller <NUM> in an example is a microcontroller. The device controller <NUM> is arranged to send signals originating in the light detector units <NUM> to the base unit <NUM> via the bus <NUM>. The device controller <NUM> is arranged to receive signals from the base unit <NUM> via the bus <NUM>. As mentioned, the base unit <NUM> is in communication with the computer <NUM>. In this way the computer <NUM> may communicate with the device <NUM>. The base unit <NUM> may send signals to the device <NUM> which include at least one of light source intensity instructions, clock signals and data signals. In the case that the light sources <NUM> are LEDs, the light source intensity instructions may be for example LED status commands which control switching the LEDs on and off as well as controlling the intensity of their illumination. The clock signals enable the base unit <NUM> to synchronise one or more components of the apparatus <NUM>.

In a specific example the device <NUM> has a local memory store for the device controller <NUM>. The local memory store may be a part of the device controller <NUM>, particularly in the case that the device controller <NUM> is a microcontroller. Additionally or alternatively the local memory store may be provided as separate memory. In the specific example wherein the local memory store is provided as a separate memory, the device controller <NUM> is in communication with the local memory store. Either way, the device controller <NUM> may store in the local memory information received or obtained from the light detector units <NUM>. The device controller <NUM> may additionally or alternatively store instructions for the light source units <NUM> in the memory store. The information and instructions may be stored locally to the device <NUM>.

Referring specifically now to <FIG>, in this example the device <NUM> shown has a connector <NUM> for removably connecting the device <NUM> to the bus <NUM>. The connector <NUM> in this example is provided internally of a lip <NUM> in the substrate <NUM> of the device <NUM>. The connector <NUM> can receive a portion of the shared bus <NUM> to connect the device <NUM> to the bus <NUM>. In the example shown the connector <NUM> is on the opposite face of the device <NUM> to the light source units <NUM> and light detector units <NUM>. This helps prevent the shared bus <NUM> from physically interfering with the operation of the light source units <NUM> and light detector units <NUM>.

The device <NUM> may have a flexible or a so-called "rigid-flex" printed circuit board. A rigid-flex circuit is a hybrid construction of a circuit on rigid and flexible substrates which are laminated together to form a single structure. In this example, the rigid-flex printed circuit board has flexible conductors which may connect the device <NUM> to, for example, the base unit <NUM>. In this example, the device <NUM> therefore does not need a connector <NUM> of the type described above. The flexible conductors of the rigid-flex printed circuit board may alternatively or additionally be used to connect one device <NUM> to another device <NUM>. In an example, the entire printed circuit board of the device <NUM> is enclosed within a Faraday cage, which reduces or eliminates the susceptibility of the device <NUM> to external electromagnetic noise. A specific example of an arrangement for a Faraday cage will be discussed further below.

In an example the light source unit(s) <NUM> and light detector unit(s) <NUM> of the device <NUM> are each encapsulated in a protective polymer, such as for example optically transparent silicone or UV-curing epoxy resin. In an example the protective polymer is transparent to light emitted by the light sources <NUM>.

In an example, the one or more light sources <NUM>, such as LEDs, within a light source unit <NUM> may be encapsulated in a protective polymer, such as optically transparent silicone or UV-curing epoxy resin. This may be carried out as follows. A silicone rubber mask may be made to create a cavity for dispensing the liquid epoxy. As silicone rubber is inherently hydrophobic, a chemical bond to the epoxy resin is prevented and the mask is easily removed when the epoxy is fully cured. The mask may be produced using an open cast mould made out of <NUM> thick laser-cut acrylonitrile butadiene styrene (ABS). The mould may be lightly sprayed with a releasing agent before platinum cure silicone polymer is poured in. The one or more light sources <NUM>, such as LED dies, for each light source unit <NUM> may then be positioned in the silicone, which is then cured. Alternatively, a Perspex (TM) mask may be used to form the silicone mask. In a specific example, the Perspex mask is around <NUM> thick. The silicone mask is cured and then pushed against the LEDs. The window within the silicone mask may then be filled with UV-curing epoxy.

The LEDs may be for example near-infrared AlGaAs pn-junction semiconductors. The LED dies have the n-side (cathode) of the LED facing upwards, while their opposite p-side (anode) is metallized for adhesion to the substrate. All the dies are attached to a square gold-coated substrate with dimensions of <NUM> × <NUM>. This area is used as the common anode, and each die can be individually addressed by passing a current through its cathode. Initially, the substrate is coated with a thin layer of a thermally-curable electrically-conductive paste. The paste creates an electrical connection for the rear surface (anode) of the dies and provides mechanical fixation once it is cured.

As shown in <FIG>, light guides <NUM> are arranged around at least some and preferably each of the light source units <NUM> and the light detector units <NUM>. The light guides <NUM> create an optical interface between the light source units <NUM> and the light detector units <NUM> and the body in which changes in concentration of a chromophore are being monitored. More specifically, the light guides <NUM> provide a medium through which light may travel between the device <NUM> and the body. The light guides <NUM> may bypass hair on, for example, a scalp or chest so that emitted light does not pass through the hair, which could otherwise reduce the signal-to-noise ratio of the acquired signal. The light guides <NUM> may be formed of a semi-flexible material which is comfortable when in contact with a subject. In an example the light guides are generally cylindrical. The cross-sectional shape of the light guides may be for example circular or elliptical or polygonal, such as square or other regular or irregular shape.

Referring now to <FIG>, there is shown a specific example of a light guide <NUM>. The light guide <NUM> has an inner core and at least one coating layer. In the example shown the light guide <NUM> has an inner core <NUM>, an inner coating <NUM> and an outer coating <NUM>.

In an example the inner core <NUM> is a light transmission medium and is transparent to light emitted by the light sources <NUM>. The inner core <NUM> may be made of, for example, optically clear silicone polymer. The inner core <NUM> may be made by for example filling an acrylic (poly(methyl methacrylate) or PMMA) tube of a predetermined diameter with liquid silicone. The filled tube is placed in an oven, or similar curing environment, for the silicone to cure. Once cured, the acrylic tube is broken and the silicone core is removed. In an example, the light guide <NUM> may be formed of glass, for example borosilicate glass.

The inner coating <NUM> is a light reflective medium having a reflective surface to channel rays of light within the light guide <NUM>. The inner coating <NUM> may be formed of transparent silicone mixed with a white, or substantially white, pigment to create a diffusive reflective surface. The white pigment may be a white powder from a metal oxide such as for example titanium dioxide. The silicone and pigment is highly scattering to the light and diffusively reflects light at its surface. The inner coating <NUM> ensures efficient transmission of light from the light sources <NUM> to the medium in which changes in a concentration of a chromophore are being measured and from the medium to the light detector unit <NUM>.

The outer coating <NUM> is an opaque medium to prevent light from outside the light guide <NUM> passing into the light guide <NUM>. The outer coating <NUM> also prevents light transmission from within the light guide <NUM> to the outside of the light guide <NUM>. The outer coating <NUM> may be formed of transparent silicone mixed with a black, or substantially dark, pigment to provide an opaque surface. The black pigment may be for example charcoal powder.

The light guides <NUM> do not need to be polished during production as the light guides <NUM> can be cut with a sharp tool, such as a razor blade. The light guides <NUM> may be made of a material such that the light guides <NUM> do not get easily scratched, snapped or chipped in use, which is important given the intended application of the light guides <NUM>. The silicone in the inner core <NUM>, the inner coating <NUM> and the outer coating <NUM> of the light guide <NUM> may be formed of the same silicone in order to maximize adhesion strength. This facilitates strong bonding between the three parts of the light guide <NUM>.

In the case that the light guide <NUM> is made of a polishable substance, for example glass or PMMA (poly(methyl methacrylate)) or the like, one end of the light guide <NUM> may be polished to achieve a flat surface for improving optical transmission. This will increase the transmission of emitted light into the medium in which changes in a concentration of a chromophore are being monitored. The other end of the light guide <NUM> may be coupled to a light source unit <NUM> or a light detector unit <NUM> using an optical grade UV cured adhesive.

Referring now to <FIG>, there is shown a schematic drawing of the apparatus <NUM> to illustrate the connections to the bus <NUM>. In the example shown, the bus <NUM> is a shared bus <NUM>. In yet another example the bus is a serial communication bus <NUM>. The bus <NUM> variously carries one or more of power, light source intensity instructions, clock signals and data signals to and from the base unit <NUM>, which in this example includes a power supply unit <NUM> (which may be for example a battery, which may be rechargeable or non-rechargeable) and a main controller <NUM>. In a specific example the bus <NUM> is an inter-integrated circuit I<NUM>C shared serial bus. A standard I<NUM>C bus may be used utilising two-way addressable communication. Buses using different protocols for addressing the individual devices <NUM> may be used instead.

In an example the bus <NUM> is a single "highway" connecting each device <NUM> to each other device <NUM> in a linear manner, starting at the base unit <NUM>, passing through each device <NUM> and terminating at the device <NUM> furthest from the base unit <NUM>. In another example the bus <NUM> is in the form of a "two-dimensional" mesh. A mesh configuration may have a more even power distribution among the devices <NUM>. Both the highway and mesh configurations have no upper limit as to the number of devices <NUM> which can be connected to the bus <NUM>. That a large number of devices <NUM> can be connected, and the information from each device <NUM> can be easily processed, enables a large area to be covered and monitored. This, in turn, enables easier investigation of, for example, body parts of animals with large surface areas and enables more rapid gathering of data, which in turn facilitates imaging of the chromophores in the biological medium.

In another example, the bus <NUM> is not a physical, wired bus <NUM> arranged between the devices <NUM> but is instead a wireless connection between the devices <NUM>. Such a wireless connection may be for example via a Bluetooth ™ connection or another suitable wireless network connection. In an example of this, each of the devices <NUM> may have its own power source, such as a battery, which may be a rechargeable battery or a non-rechargeable battery. This in effect enables each device <NUM> to be a self-contained measuring device.

In an example, the devices <NUM> in the apparatus <NUM> may be connected at least in part by a wiring scheme in which the devices <NUM> are connected in sequence or in a ring. In a specific example, the devices <NUM> may be connected by "daisy chaining" the devices <NUM> to each other. In this example the data lines are connected in series rather than in parallel (such as in I<NUM>C). The data is passed from one device <NUM> to another device <NUM> and so the packet of data increases or decreases in size depending on whether the device <NUM> is transmitting or receiving. An advantage of this arrangement is that the data rates are high in comparison with other wiring schemes. This is particularly advantageous if there is a large number of devices <NUM> that are connected. Specific examples of implementations for daisy chaining include the daisy-chained JTAG (Joint Test Action Group) IEEE (Institute of Electrical and Electronics Engineers) Standard <NUM>) and the WS28XX series of RGB LEDs by Shenzhen Worldsemi Technology Co.

A description of an example of the operation of the system now follows. A square electrical waveform is generated by the base unit <NUM>, and the rising and falling edges of the pulses determine the start and end times of the charge integration for each detector channel. This square pulse is the main clock for the system. Each device <NUM> and the base unit <NUM> use a common clock. The frequency of the common clock determines the length of integration time for the controller <NUM> of each device <NUM>. This integration time may be a global parameter for all devices <NUM>. In a specific example, the base unit <NUM> and the device controller <NUM> each use or are a Cypress PSoC (programmable system-on-chip) microcontroller. This enables the use of dedicated logic for clock generation and management which is not possible with traditional microcontrollers.

A square waveform is preferred, but in general the waveform may be other than a square wave and does not need to be symmetrical. For example, an asymmetric pulse with a small duty cycle (e.g. <NUM>% or so) may be used. This enables consecutive short and long integration times. Combining the results from both short and long integrations increases the dynamic range of the measurement system, whilst incurring only a small penalty to the overall sample rate of the system.

After the integration time has elapsed, the device controller <NUM> receives data signals from the analog-to-digital converter (e.g. the DDC114 mentioned above) and stores them in local memory. Then the device <NUM> waits for the I<NUM>C command packet addressed to the specific device <NUM> from the base unit <NUM>. The command from the base unit <NUM> includes device operational parameters such as light source intensity instructions for the LEDs to be used during the next integration period. The LED intensity instructions, or control signals, determine if the LEDs on the device <NUM> should be ON or OFF during the next integration cycle. Once the command is received by the device <NUM>, the base unit <NUM> sends an I<NUM>C command addressed to the same device <NUM> in order to retrieve data signals stored in the local memory. These packets may include information from the photodiodes of the light detector units <NUM> available on the device <NUM>. In addition, data from peripheral components (e.g. temperature and motion sensors) may be included in the data signals. Once a particular data signal is received by the base unit <NUM>, the address will increment and the next device <NUM> will be targeted. This process is repeated until all the devices <NUM> have been addressed. In an example the bus <NUM> is an electrically shared bus <NUM> which uses I<NUM>C standard bus hardware. The bus <NUM> may also be a single cable (i.e. a bundle of wires carrying clock and data signals, as well as electrical power) and can be shared amongst all the devices <NUM> without any physical preference of the order in which they are attached to the bus <NUM>. This makes the system flexible and modular.

The use of the bus <NUM> and the modularity of the apparatus <NUM> as a whole enable the simultaneous acquisition of data within and across all devices <NUM>, regardless of their physical layout. An intra-device measurement involves a measurement of light from a light source <NUM> by a light detector <NUM> residing on one device <NUM>. An inter-device measurement involves measurement of the light from a light source <NUM> on one device <NUM> by a light detector <NUM> on another device <NUM>. Although examples of the apparatus <NUM> will in general be made up of many devices <NUM>, from the overall system perspective, all the light sources <NUM> and light detectors <NUM> are accessible simultaneously, regardless of on which device <NUM> they reside. In principle and in general, every light detector <NUM> can make measurements of light emitted by every light source <NUM>. Since all photodetection is performed simultaneously, there is no significant scanning rate penalty when the number of light detectors <NUM> is increased; it is only necessary to increase the data throughput rate on the bus <NUM> itself. Therefore, the system provides a significant increase in speed and efficiency over known systems for both data collection and retrieval. The (very) large number of light source-detector pairs that can be obtained with this system provides a great improvement in data quality. This is particularly relevant in imaging applications.

Many existing systems only have a sparse arrangement of light sources <NUM> and light detectors <NUM>, and the light detectors <NUM> communicate with their nearest-neighbour light sources <NUM> only, giving a limited range of light source-detector spacings. With examples of the present system, data with a wide range of spacings and with large numbers of overlapping channels can be collected. The modularity of the present system increases this functionality even further, enabling movement between devices <NUM>, to vary the distribution of light source-detector spacings.

These advantages result in better quality and higher resolution images than are achievable with known wearable systems. The images produced using the apparatus <NUM> can show changes in chromophore concentration in the mediums being monitored.

Furthermore, in some examples, the use of a single cable bus <NUM> leads to a significant reduction in the total amount of cabling required, in comparison with known systems which typically have separate cables for each light detector. This results in the weight of the system being considerably less than known systems. This, in turn, increases the wearability of the apparatus <NUM> and the comfort for a user, and reduces cost on cabling.

During use of some examples of the system, the light sources <NUM>, which in an example are LEDs, are illuminated for the period of the integration time. However, with the introduction of an independent clock for the LED light sources <NUM>, their on-time can be significantly reduced, for example to the order of microseconds. This enables accumulation of less charge on the analog-to-digital integrators, which avoids saturation in situations where attenuation of the transmitted light is low.

Moreover, this implementation may use a combination of a charge integrator and a digital timer-counter simultaneously to measure the light intensity. If the attenuation is high, the charge integrator will not saturate and a readout as described above will be obtained. If the attenuation is low (e.g. because of small source-detector separations) the charge integrator may saturate. However, in that case, the timer-counter may be arranged to stop once the saturation is observed. The time-to-saturation is then proportional to the intensity of the light received. In this way the dynamic range of the measurement system can be greatly increased.

The devices <NUM> in some examples may all have the same hardware and the same software and/or firmware other than the address code for the devices <NUM>. Each device <NUM> has a unique address so it can be individually addressed by the base unit <NUM>, which is made possible by virtue of the devices <NUM> each having their own controller <NUM>. Devices <NUM> can therefore easily be added to or removed from the bus <NUM>, and this can be done even while the apparatus <NUM> is in use. If the base unit <NUM> addresses a device <NUM> which is not connected to the bus <NUM>, the command will fail and no signals will be returned. The base unit <NUM> will then address the next device <NUM>. The physical order in which devices <NUM> are connected to the bus <NUM> is therefore irrelevant, which is convenient for technicians using the system in practice. In an example, each device <NUM> has a <NUM>-pin programming feature. (The programming pins are located on the device <NUM> and are not part of or connected to the shared bus <NUM>. ) The <NUM>-pin programming feature on each device <NUM> facilitates the programming of each device controller <NUM>.

At least some of the devices <NUM> may also have an electroencephalography (EEG) electrode <NUM>, which can be used for non-invasively measuring electrical potentials on the scalp resulting from underlying neuronal activity. EEG is known as a complimentary technique to fNIRS. The EEG electrode <NUM> may be controlled by the device controller <NUM>. Providing EEG electrodes <NUM> on the same device <NUM> as the light sources and detectors for monitoring changes in concentration of a chromophore enables EEG measurements to be obtained at the same time, which can provide further useful information.

The examples described herein are to be understood as illustrative examples of embodiments of the invention. Further embodiments and examples are envisaged.

For example, instead of using a protocol that enables the devices <NUM> to be addressed individually, a time division multiple access scheme may be used in which each device <NUM> is accessed sequentially in turn. This may enable higher data transfer speeds to be achieved, which in turn allows a larger number of devices <NUM> to be used. As another alternative, a daisy chained bus (described above) using a serial shift register may be used. In this example, the physical medium is not shared but is connected to each device <NUM> in turn. Hence, there is a data-in connection and a data-out connection at each device <NUM>. Although in this example the devices <NUM> cannot be removed while the system is running, the serial shift register ensures high data rates, and so can support a larger number of devices <NUM>.

As another example, a combination of a small photodiode detector <NUM> and a large photodiode detector <NUM> within the same detector unit <NUM> can be used to improve the dynamic range of the apparatus <NUM>. The added dynamic range is proportional to the ratio of the detection areas of the large and small photodiode detectors <NUM>.

Another example of a device for use with apparatus for measuring changes in concentration of a chromophore in a biological medium, and a dock and a light guide arrangement for use with the device, will be described with reference to <FIG>. Much of the description of the various features and options of the first example discussed above is applicable to the second example and will therefore not be repeated in detail here. Likewise, many of the various features and options of the second example discussed below are applicable to the first example and can be incorporated therein.

<FIG> shows a side view of an assembly of the second example of a device <NUM> for use with apparatus for measuring changes in concentration of a chromophore in a biological medium assembled with a dock <NUM> and a light guide arrangement <NUM>. <FIG> shows a cross-sectional view on VII-VII of the assembly of <FIG>. As will be discussed further below, in an example, the device <NUM> is removably received in and connectable to the dock <NUM>. The dock <NUM> itself may be one of a number of docks <NUM>, each for receiving a respective device <NUM> and which may be carried on or fixed to some carrier. A specific example of this, in the form of a cap or headgear, will be discussed with reference to <FIG>.

The device <NUM> in this example is hexagonal in shape/footprint. Correspondingly, the dock <NUM> into which the device <NUM> is fitted in use is also hexagonal in shape. The light guide arrangement <NUM> is also generally hexagonal in shape. The hexagonal shape is of advantage as it makes it easier to cover a particular area or region that is to be subject to study. In an example, the side of each hexagon of the device <NUM> is <NUM>. A smaller size is preferred as it enables more of the devices <NUM> to be used to cover a particular area or region, which enables the resolution of the imaging to be greater.

As shown most clearly in <FIG>, the device <NUM> has at least one light source unit <NUM> and at least one light detector unit <NUM>. In the specific example shown, the device <NUM> has three light source units <NUM> and four light detector units <NUM>. The three light source units <NUM> are symmetrically arranged on the device <NUM>, in this example being located towards alternating corners of the hexagon. The four light detector units <NUM> are likewise symmetrically arranged on the device <NUM>, in this example with three being located towards the other alternating corners of the hexagon and the fourth being located centrally of the hexagon.

Each light source unit <NUM> has or contains at least one light source <NUM> for emitting light. In an example a light source unit <NUM> has a plurality of light sources <NUM>. In the specific example shown, each light source unit <NUM> has three light sources <NUM>. Each light source <NUM> may emit light having a wavelength in the range of for example around <NUM> to <NUM>. The light sources <NUM> may emit light having different wavelengths. That is, in an example, each light source unit <NUM> has a first light source <NUM> which can emit light at a first wavelength, a second light source <NUM> which can emit light at a second wavelength, and a third light source <NUM> which can emit light at a third wavelength, each wavelength being different. In an example, the three wavelengths might be <NUM> nanometres, <NUM> nanometres and <NUM> nanometres. The light sources <NUM> may be for example light-emitting diodes (LEDs). In use in an example, each of the light sources <NUM> is powered in turn such that, at least within a particular light source unit <NUM>, only one light source <NUM> is emitting light at a time.

Each light detector unit <NUM> has at least one light detector <NUM>, which may be for example a photodiode, for detecting light. In the example shown, each light detector unit <NUM> has a single light detector <NUM>. The light detectors <NUM> are arranged to detect light having a wavelength that is emitted by the light sources <NUM>. In use in an example, each light detector <NUM> is continually able to detect light.

In the example shown, the light source units <NUM> and light detector units <NUM>, and specifically the light sources <NUM> and light detectors <NUM> contained therein, are mounted directly on a printed circuit board (PCB) <NUM>. An advantage of mounting the light source units <NUM> and light detector units <NUM>, and specifically the light sources <NUM> and light detectors <NUM> contained therein, directly on the PCB <NUM> is that it avoids (relatively) long connecting wires from the PCB to the light sources <NUM> and light detectors <NUM>, which therefore reduces noise and interference. The light detector units <NUM> are arranged on the PCB close to their respective amplifier circuits, which again helps to keep down noise arising in the device <NUM>. (Examples of arrangements for the amplifier circuits are discussed above in relation to the first example.

A Faraday cage encloses the light detector units <NUM> and their amplifier circuits (the amplifier circuits therefore not being visible in the drawings for this example). The Faraday cage consists of two main parts, a first part <NUM> on the top of the PCB <NUM> and a second part <NUM> on the bottom of the PCB <NUM>. In an example, the Faraday cage can be made from copper coated with a thin layer of tin. The close proximity of the detectors units <NUM> and their respective amplifier circuits together with the Faraday cage <NUM>, <NUM> provides a low noise detection system, which maximises the signal-to-noise ratio of the device <NUM>. As mentioned above, the signal strength is often very low whilst noise levels can be very high, and so increasing the signal-to-noise ratio of the device <NUM> is very important.

In an example, the Faraday cage part <NUM> on the underside of the PCB <NUM> has holes <NUM>, which may be cut into the part <NUM> during manufacture, to allow light to reach the detector units <NUM>. The entrances to these holes <NUM> in one example are covered with a layer of material which is transparent to the light being used and which is electrically conductive, to maintain the integrity of the Faraday cage <NUM>, <NUM> whilst still allowing light to reach the detector units <NUM>. An example of a suitable material is indium tin oxide.

In an example, the PCB <NUM> has a number of conducting pads (not shown) which enable connection to a number of "pogo targets" <NUM>, which in turn enable connection to a number of "pogo pins" <NUM> mounted on a suitable docking system, such as the dock <NUM> discussed further below. (As is known, a "pogo pin" is a device used in electronics to establish a (usually temporary) connection between two printed circuit boards, devices, etc. A pogo pin is typically in the form of a slender cylinder containing two sharp, spring-loaded pins. ) Spring connectors <NUM> are provided for each pogo target <NUM>. The spring connectors <NUM> in this example are soldered on their undersides to conducting pads on the PCB <NUM>, with the upper spring portion providing the electrical connection to the pogo targets <NUM>. This docking system provides both a mechanical and electrical connection for the PCB <NUM>. In the example shown, there are six pogo pins <NUM> on the dock <NUM> which correspond to six pogo targets <NUM> on the device <NUM>, each being arranged in two groups of three on opposite sides of the dock <NUM> and device <NUM> respectively. One group of three pogo pins <NUM> and pogo targets <NUM> in an example provide respectively for power, clock and ID (identification) connections. The ID connection may connect to an integrated circuit or chip on the (flexible) PCB <NUM> of the dock <NUM> discussed below that provides each dock <NUM> with its own unique ID for addressing purposes. The other group of three pogo pins <NUM> and pogo targets <NUM> in an example provide respectively for ground and for bus <NUM> and bus <NUM> which form a differential bus, as used in for example an RS <NUM> bus.

Referring particularly now to the exploded view of the device <NUM> in <FIG>, in an example, a black-out layer <NUM> is attached to the bottom surface of the PCB <NUM>. The black-out layer <NUM> has a central cut-out <NUM> for the second part <NUM> of the Faraday cage and three peripheral cut-outs <NUM> for the light source units <NUM>. The black-out layer <NUM> prevents light travelling directly from a light source unit <NUM> to a detector unit <NUM> within the device <NUM>. In an example, the black-out layer <NUM> is made from silicone.

The PCB <NUM> and black-out layer <NUM> are enclosed in a two part housing <NUM>, <NUM> of the device <NUM>. The housing parts <NUM>, <NUM> may be made of ABS for example. The two housing parts <NUM>, <NUM> may for example be a push fit or may be clipped together. The top housing part <NUM> contains the pogo target mechanisms, including the pogo targets <NUM> and the spring connectors <NUM>.

In an example, the bottom housing part <NUM> contains band pass interference filters <NUM>, one for each light detector unit <NUM> and positioned underneath the respective light detector unit <NUM>, which permit passage of light in the range emitted by the light source units <NUM>. In a specific example, the band pass interference filters <NUM> for the light detector units <NUM> pass near-infra red light in the range <NUM> to <NUM> nanometres. In an example, the band pass interference filters <NUM> for the light detector units <NUM> are made from glass. A transparent cover <NUM> of for example a thin layer of ordinary glass is positioned under each light source unit <NUM>. The bottom housing part <NUM> has apertures <NUM> for each light source unit <NUM> and each light detector unit <NUM> to allow light to exit and enter the housing. The band pass interference filters <NUM> and the covers <NUM> are a similar size and shape as the apertures <NUM> in the bottom housing part <NUM> which they cover and/or fill.

Referring now to <FIG>, this shows an exploded view of the example of the dock <NUM> discussed briefly above. The dock <NUM> removably receives a device <NUM> and acts as a mechanical support and retainer for the device <NUM>. The dock <NUM> and the device <NUM> may be a friction fit or a snap fit, with ridges and recesses, etc. The dock <NUM> in this example also provides power and data connections for the device <NUM>.

The dock <NUM> is generally in the form of an open container or receptacle with upstanding walls <NUM> and into which a device <NUM> can be passed. Two opposed sides <NUM> of the dock <NUM> are open, which allows a user to grip the device <NUM> to remove the device <NUM> from the dock <NUM> when required.

The pogo pins <NUM> of the dock <NUM>, which provide the data and power connections with the device <NUM> via the pogo targets <NUM><NUM> of the device <NUM>, in this example are carried by two pogo pin plates <NUM>, each carrying three pogo pins <NUM>. The pogo pin plates <NUM> are partially received in and retained by internally facing recesses <NUM> which are provided in opposed walls <NUM> of the dock <NUM>. The pogo pins <NUM> face inwardly so as to engage the pogo targets <NUM> of the device <NUM> when the device <NUM> is inserted into the dock <NUM>. In an example, a (flexible) PCB <NUM> is attached to the underside of the dock <NUM>. The PCB <NUM> provides an electrical connection between the main serial bus and the six pogo pins <NUM> that connect to the device <NUM>. It also provides for individually identifying each dock <NUM>, via a suitable integrated circuit or chip mounted on the PCB <NUM> which has a unique ID stored in its on-board memory, as mentioned above. The main serial bus may connect to the front and rear tabs of the PCB <NUM> shown in <FIG>.

In an example, the internal face of the base wall <NUM> of the dock <NUM> has upstanding ridges <NUM> which help to prevent light travelling directly between light source units <NUM> and light detector units <NUM> of the device <NUM> received in the dock <NUM>. In the example shown, there are three ridges <NUM>, one round each region where a light source unit <NUM> is located when the device <NUM> is received in the dock <NUM>. The base wall <NUM> also has seven through holes <NUM>, one for each of the light source units <NUM> and light detector units <NUM> of the device <NUM>, and which allow the light guide arrangement <NUM> to be clicked into place.

Referring particularly to <FIG>, the light guide arrangement <NUM> comprises seven short lengths of light guides <NUM>, in the form of optical fibres <NUM>, one for each light source unit <NUM> and light detector unit <NUM> of the device <NUM>, supported in and passing through a generally planar sheet <NUM>. The planar sheet <NUM> may be made of for example compression moulded silicone. These light guides <NUM> channel the light from the light source units <NUM> to the tissue under investigation and back from the tissue to the light detector units <NUM>.

Similarly to the example described above with reference to <FIG>, each light guide <NUM> in this example has an inner core and at least one coating or cladding layer. In a specific example, the light guide <NUM> has an inner core of for example (poly(methyl methacrylate) or PMMA). The inner core has a cladding of lower refractive index, made from polytetrafluoroethylene (PTFE). This helps to contain the light within the inner core. The outer coating is an opaque medium to prevent light from outside the light guide <NUM> passing into the light guide. The outer coating also prevents light transmission from within the light guide <NUM> to the outside of the light guide <NUM>. The outer coating may be formed of for example transparent silicone mixed with a black, or substantially dark, pigment to provide an opaque surface. The black pigment may be for example charcoal powder. In another example, the outer coating may be formed of a material such as PC/ABS, which is a mixture of polycarbonate and acrylonitrile butadiene styrene. The outer coating may alternatively be formed of a material such as polypropylene or a fluorinated polymer.

<FIG> also shows a portion of a retaining member or sheet <NUM>, which may be a flexible sheet, such as a fabric. The retaining sheet <NUM> has a number of holes <NUM> corresponding to the light source units <NUM> and the light detector units <NUM>. <FIG> also shows a backing plate <NUM> for the dock <NUM> which will be discussed further below.

In an example, the device <NUM> is push-fitted into the dock <NUM>. The connection between the pogo pins <NUM> on the dock <NUM> and the pogo targets <NUM> and the spring connectors <NUM> on the device <NUM> may be used to provide a secure connection for the device <NUM> in the dock <NUM>. The light guide arrangement <NUM> is push-fitted into the main body of the dock <NUM> from the underside of the retaining sheet <NUM>. The uppermost portions <NUM> of some or all of the light guides <NUM> may flare outwardly or be frustoconical or the like so as to engage with correspondingly shaped portions around the through holes <NUM> of the base wall <NUM> of the dock <NUM>, thereby to retain the light guide arrangement <NUM> in close engagement with the dock <NUM>.

<FIG> shows an example of a portion of a measuring arrangement <NUM> for fitting to an animal body for measuring changes in concentration of a chromophore in the animal body. This example is in the form of a cap or headgear to be worn on the subject's head. Other configurations and arrangements are possible. For example, the measuring arrangement <NUM> may be in the form of a sleeve for fitting over a limb or a more simple sheet for placing over or wrapping round some other body part.

The measuring arrangement <NUM> has a sheet-like portion <NUM>. (A portion of this corresponds to the retaining member or sheet <NUM> discussed with reference to <FIG> above. ) The sheet-like portion <NUM> may conveniently be a flexible, stretchable fabric. An example is neoprene.

A number of docks <NUM> for receiving devices <NUM> are arranged over the sheet-like member <NUM>. The docks <NUM> are located at positions that correspond to the region(s) to be studied. In this example, the docks <NUM> are arranged so as to cover the entire cortex of the (human) subject. Each dock <NUM> is secured to the sheet-like member <NUM> in this example by first holding the backing plate <NUM> against the interior of the sheet-like member <NUM>. As shown most clearly in <FIG>, the backing plates <NUM> have a number of upstanding projections or pins <NUM> which pass through the sheet-like member <NUM>. Corresponding holes <NUM> may be provided in the sheet-like member <NUM> to receive the pins <NUM>. In addition, holes <NUM> corresponding to the light guides <NUM> may also be provided in the sheet-like member <NUM>. The docks <NUM> are then pushed up against the respective backing plates <NUM> from the exterior of the sheet-like member <NUM>. The pins <NUM> of the backing plates <NUM> are received in and lock against recesses provided in the docks <NUM> in for example a snap-fit connection. The light guide arrangement <NUM> for each device <NUM> is then push-fitted into the main body of the dock <NUM> from the underside of the sheet-like member <NUM>, the light guides <NUM> themselves passing through corresponding holes <NUM> in the backing plates <NUM>.

In the example shown, a multi-conductor cable <NUM>, acting as a bus, connects each dock <NUM> to the next dock <NUM> in turn. This allows all devices <NUM> received in use in the docks <NUM> to be controlled from a single electrical bus or cable <NUM>. This means that the amount of electrical wiring needed in the imaging array is greatly reduced, again improving the signal-to-noise ratio. Nevertheless, other arrangements for data and power connections to and between the devices <NUM> are possible, as discussed above. The cable <NUM> may for example be located on top of the material of the sheet-like member <NUM> or sandwiched between two layers of the sheet-like member <NUM>.

It may be noted that not all of the docks <NUM> have to be filled with a device <NUM>. Moreover, the configuration of docks <NUM> that are filled with devices <NUM> may be varied, optionally on the fly during an investigation, to vary the image and the nature of the image that can be obtained.

This arrangement therefore provides for a measuring arrangement <NUM> that is flexible and (reasonably) comfortable for the subject of any study. A large number of devices <NUM> can be used, which improves the depth and quality generally of the measurements and images that can be obtained. The arrangement of the devices <NUM> can be easily and quickly changed. The light guide arrangement <NUM> for each device <NUM> can easily be removed, for example for cleaning either during use on a particular subject or prior to use on a different subject, and/or replaced.

In an example, the electrical serial bus multi-conductor cable <NUM> is terminated in a "stem" module which is positioned at the back of the measuring arrangement <NUM>. This stem module may contain a circuit that converts the bus for the devices <NUM> (which may be for example a RS <NUM> bus) into a USB bus, which enables simple connection of the imaging array provided by the measuring arrangement <NUM> to a suitable laptop PC, which provides power, control and data collection for the entire imaging array.

In another example, the connecting module to the measuring arrangement <NUM> is known as a "hub" and provides more functionality than a "stem" module. (A similar base unit or hub <NUM> is discussed above in relation to the example shown in overview in <FIG>. ) Such a hub may contain batteries to provide power to the measuring arrangement <NUM>. The hub again provides bus conversion, in one example between the (RS <NUM>) bus <NUM> and a suitable wireless link (<NUM> in <FIG>) which in turn connects to a laptop PC or the like (<NUM> in <FIG>). In an example, the hub may also contain an SD card for local storage of imaging data. The hub may have a user interface, consisting of for example buttons and LEDs, to enable user control and monitoring of basic functions. In an example the hub may also have a USB port to allow tethered operation, and a power socket to allow continuous operation without reliance on battery power.

There may also be provided a light guide for use with apparatus for measuring changes in concentration of a chromophore in a biological medium using at least one light source and at least one light detector, the light guide comprising:.

Claim 1:
A measuring apparatus (<NUM>, <NUM>) for fitting to an animal body for measuring changes in concentration of a chromophore in the animal body, the measuring apparatus (<NUM>, <NUM>) comprising:
a plurality of devices (<NUM>, <NUM>), each device (<NUM>, <NUM>) having a light source (<NUM>, <NUM>) for emitting light towards an animal body to which the measuring apparatus (<NUM>, <NUM>) is fitted in use, a light detector (<NUM>, <NUM>) for detecting light returning from said animal body, and a device controller (<NUM>) for receiving signals from and sending signals to a main controller (<NUM>); characterised by,
a bus (<NUM>, <NUM>) to which the device controllers (<NUM>) of the plural devices (<NUM>, <NUM>) are respectively connected, said bus (<NUM>, <NUM>) connecting each device (<NUM>, <NUM>) to each other device (<NUM>, <NUM>) in a linear manner, starting at the main controller (<NUM>), passing through each device (<NUM>, <NUM>) and terminating at the device (<NUM>, <NUM>) furthest from the main controller (<NUM>).