GB2521207A - Imaging an internal volume of a subject body - Google Patents

Abstract

A method, device and system are provided for imaging an internal volume of a subject body. The method includes: providing multiple electrodes for locating at selected positions external to a volume of a subject body; applying a source current for imaging of a portion of the internal volume of the subject body through one or more first electrodes; measuring a current received at one or more second electrodes; switching a channel of each second electrode between applying the current source and measuring a voltage at the electrode in order to isolate the voltage measurement from a received current; measuring a voltage at the second electrode whilst providing a current path to a third electrode; and using the measured current and the subsequent measured voltage at each second electrode to provide an impedance for imaging the portion of the internal volume. The method may include simultaneously or sequentially applying a source current for stimulating the portion of the internal volume of the subject body through the one or more first electrodes.

Description

IMAGING AN INTERNAL VOLUME OF A SUBJECT BODY

FIELD OF THE INVENTION

This invention relates to imaging an internal volume of a subject body using S multiple electrodes applied to the external surface of the subject body.

BACKGROUND TO THE INVENTION

Electrical Impedance Tomography (EIT) is used for determining internal tissue impedances or static tissue impedance modelling by spatially mapping the electrical resistance of body tissues associated with the brain, e.g. cortex (white and grey matter), brain fluid, skull and scalp.

In ordinary FIT used as a tool for probing the brain, an array of electrodes is applied to the scalp and it is desirable to provide as many electrodes as possible to create a "dense" array of electrodes. Each electrode is used to "inject" an electrical current into the head, i.e. into the tissues the impedances of which it is desired to ascertain, and the remaining electrodes are used to measure the spatial distribution of the resulting electrical potentials that arise at the scalp. Determining the internal tissue impedances responsible for the measured potentials in view of the known injected currents is what is known as an "inverse boundary value problem".

Magnetic Resonance Electrical Impedance Tomography (MREIT) addresses this challenge. MREIT is also a known technique in which magnetic resonance image is obtained of the injected currents, from which the current density can be determined, which in turn allows for determining impedance.

MREIT does not require solving an inverse problem, and its spatial resolution is superior to that of EIT. However, a drawback of MREIT is that it requires the use of expensive MR imaging machines.

Apart from using ordinary EIT to determine internal tissue impedances, EIT has also been considered as a tool for imaging dynamic neural functions in the brain. When neurons "fire" i.e. depolarize, they transfer ions into the extracellular space, decreasing their soma size and cross-section for conducting current, decreasing their electrical impedance. Conversely, when the neurons polarize they absorb ions from the extracellular space, increasing their soma size and cross-section for conducting current, increasing their electrical impedance. Once the ordinary EIT inverse problem has been solved, the same model can be used to localize changes in impedance associated with neural functions.

n most impementations of HT, a dedicated set of current conthbuting &ectrodes terativ&y appy a sinusoida current. The assodated potenflal s measured at dedicated potenhal measuring eEectrodes and the impedance between the contnbuting and the potentia! sensng electrodes s cacuated.

The set of impedances between aH contribubng and sensing electrodes abng with theft spati ocation is used to determine the characteristics of the intervening tssue.

Transcranial electric brain stimulation is a form of neuro-stimulation of which the techniques include, but are not limited to, transcranial electrical stimulation (TES), transcranial direct current stimulation (tDCS), high-definition transcranial direct current stimulation (HD-tDCS), transcranial alternating current stimulation (tACS), and transcranial random noise stimulation (tRNS).

Transcranial stimulation has been seen to be as effective, if not more effective, than traditional medication for the treatment of depression.

Transcranial Stimulation is also being explored for the implementation of cognitive enhancement (substantially improving cognitive faculties including but not limited to memory, mathematical ability and linguistic ability).

Transcranial Stimulation can be used to improve motor abilities which is of great therapeutic value.

Transcranial stimulation devices utilizing low currents consist of two main components: a waveform generator and electrodes positioned on the head.

S The waveform generator delivers electrical current to the electrodes and the scalp surface electrodes inject currents through the head. The result is an electric field and a current density field generated in the head.

SUMMARY OF THE INVENTION I0

According to a first aspect of the present invention there is provided a method for imaging an internal volume of a subject body, comprising: providing multiple electrodes for locating at selected positions external to a volume of a subject body; applying a source current for imaging of a portion of the internal volume of the subject body through one or more first electrodes; measuring a current received at one or more second electrodes; switching a channel of each second electrode between applying the current source and measuring a voltage at the electrode in order to isolate the voltage measurement from a received current; measuring a voltage at the second electrode whilst providing a current path to a third electrode; using the measured current and the subsequent measured voltage at each second electrode to provide an impedance for imaging the portion of the internal volume.

The method may include providing one or more third electrodes and switching a channel of each third electrode between applying the current source and measuring a voltage at the electrode in opposite switching to the switching of one or more second electrodes for maintaining a current path whilst measuring a voltage at the second electrode.

In one embodiment, the method may simultaneously or sequentially applying a source current for stimulating the portion of the internal volume of the subject body through the one or more first electrodes. The source current for imaging may have a waveform of one of the group of: a direct current, a sinusoidal waveform, orthogonal code, chirp waveform, sinc function waveform, and wherein the source current for stimulating may have a waveform of one of the group of: a direct current, a sinusoidal waveform, a random noise waveform, or other form of waveform suitable for stimulating a characteristic of the internal volume of the subject body.

The method may include controlling the source current for stimulation through multiple electrodes with independent control of each electrode's amplitude, frequency and phase such that a net current field provides stimulation of a target internal volume.

The method may provide a known source current through one or more first electrodes and the measured current and voltage at the one or more second electrodes may be used for imaging the internal volume of the subject body using electrical impedance tomography. The imaging may be carried out in real time in response to applying the source current for stimulating.

The method may include switching between measuring a current and measuring a voltage at multiple second electrodes during simultaneous imaging and stimulation of the internal volume of a subject body, including adjusting an applied source current such that each permutation of electrodes applies a desired stimulating current.

The method may further include using a multiplexing and demultiplexing strategy to discriminate between multiple contributing first electrodes. A known source current may be applied with multiple frequencies, with different frequencies applied at different first electrodes, and the method may use frequency division multiplexing to discriminate different first electrodes. A bandwidth of source current waveforms at each first electrode may span a range of frequencies and the method may use frequency division multiplexing to discriminate different first electrodes.

Providing multiple electrodes may provide cascading groups of electrodes, wherein each group is controlled by a control unit and wherein the control unit enables individual operation of each electrode, the control unit also provides high speed communication between the cascading groups. A group may include an analogue front end component for converting commands from the control unit to source current for an electrode and for measuring current and voltage at an electrode. The control unit may include a field-programmable gate array for simultaneous independent control of all electrodes and multiplexing parallel data paths.

According to a second aspect of the present invention there is provided a device for imaging an internal volume of a subject body, comprising: a plurality of electrodes for locating at selected positions external to a volume of a subject body; a control unit including: a source current applying component for applying a current source for imaging of a portion of the internal volume of the subject body through one or more first electrodes; a current measuring component for measuring a current received at one or more second electrodes; a voltage measuring component for measuring a voltage at the one or more second electrodes whilst providing a current path to a third electrode; a channel of each electrode including a switch mechanism to switch between measuring a received current and measuring the voltage in order to isolate the voltage measurement from a received current; wherein each electrode is capable of acting as a first or a second electrode.

In one embodiment, the control unit may include a stimulating current applying component for simultaneously or sequentially applying a source current for stimulating the portion of the internal volume of the subject body through the one or more first electrodes.

The source current for imaging may have a waveform of one of the group of: a direct current, a sinusoidal waveform, orthogonal code, chirp waveform, sinc function waveform, and the source current for stimulating may have a waveform of one of the group of: a direct current, a sinusoidal waveform, a random noise waveform, or other form of waveform suitable for stimulating a characteristic of the internal volume of the subject body.

The control unit may be provided for controlling the source current for stimulation through multiple electrodes with independent control of each electrode's amplitude, frequency and phase such that a net current field provides stimulation of a target internal volume.

The control unit may be for switching between measuring a current and measuring a voltage at multiple second electrodes during simultaneous imaging and stimulation of the internal volume of a subject body, including adjusting an applied source current such that each permutation of electrodes applies a desired stimulating current.

The device may be in the form of a module having a group of electrodes, wherein the module is attachable to one or more other modules in cascading form; and wherein each module is controlled by a control unit enabling individual operation of each electrode and high speed communication between the cascading modules.

The device may include an analogue front end component for converting commands from the control unit to source current for an electrode and for measuring current and voltage at an electrode.

The control unit may include a field-programmable gate array for simultaneous independent control of all electrodes and multiplexing parallel data paths.

According to a third aspect of the present invention there is provided an imaging system for imaging an internal volume of a subject body comprising: one or more device in accordance with the second aspect of the present invention; and a system interface including: a controlling component for controlling the one or more device including controlling device configuration and session parameters and electrode parameters; an electrical impedance tomography imaging component including: an imaging processing component for receiving device output and processing data to provide imaging; a display component for displaying the output of the imaging processing component.

The system interface may include a stimulating component for controlling the application of stimulating currents to the one or more device. The system interface may include a multiplexing and demultiplexing component to discriminate between multiple contributing first electrodes.

According a fourth aspect of the present invention there is provided a method for imaging an internal volume of a subject body, comprising: providing multiple electrodes for locating at selected positions external to a volume of a subject body; applying a source current for imaging of a portion of the internal volume of the subject body through one or more first electrodes; simultaneously or sequentially applying a source current for stimulating the portion of the internal volume of the subject body through the one or more first electrodes; measuring a current received at one or more second electrodes; measuring a voltage at an electrode; using the measured current and the measured voltage to provide an impedance for imaging the portion of the internal volume; controlling the source current for stimulation through the multiple electrodes with independent control of each electrodes amplitude, frequency and phase such that a net current field provides stimulation of a target internal volume.

The method may include switching a channel of each second electrode between applying the current source and measuring a voltage at the electrode in order to isolate the voltage measurement from a received current.

The method may include providing one or more third electrodes and switching a channel of each third electrode between applying the current source and measuring a voltage at the electrode in opposite switching to the switching of one or more second electrodes for maintaining a current pathway whilst measuring a voltage at the second electrode.

The source current for imaging may have a waveform of one of the group of: a direct current, a sinusoidal waveform, orthogonal code, chirp waveform, sinc function waveform, and the source current for stimulating may have a waveform of one of the group of: a direct current, a sinusoidal waveform, a random noise waveform, or other form of waveform suitable for stimulating a characteristic of the internal volume of the subject body.

The method may provide a known source current through one or more first electrodes and the measured current and voltage at the one or more second electrodes is used for imaging the internal volume of the subject body using electrical impedance tomography.

The method may include switching between measuring a current and measuring a voltage at multiple second electrodes during simultaneous imaging and stimulation of the internal volume of a subject body, including adjusting an applied source current such that each permutation of electrodes applies a desired stimulating current.

The method may include a multiplexing and demultiplexing strategy to discriminate between multiple contributing first electrodes.

Providing multiple electrodes may provide cascading groups of electrodes, wherein each group is controlled by a control unit and wherein the control unit enables individual operation of each electrode, the control unit also provides high speed communication between the cascading groups. A group may include an analogue front end component for converting commands from the control unit to source current for an electrode and for measuring current and voltage at an electrode.

According to a fifth aspect of the present invention there is provided a device for imaging an internal volume of a subject body, comprising: a plurality of electrodes for locating at selected positions external to a volume of a subject body; a control unit including: a source current applying component for applying a current source for imaging of a portion of the internal volume of the subject body through one or more first electrodes; a stimulating current applying component for simultaneously or sequentially applying a source current for stimulating the portion of the internal volume of the subject body through the one or more first electrodes; a current measuring component for measuring a current received at one or more second electrodes; a voltage measuring component for measuring a voltage at an electrode; controlling the source current for stimulation through the multiple electrodes with independent control of each electrode's amplitude, frequency and phase such that a net current field provides stimulation of a target internal volume.

The control unit may include a channel of each electrode including a switch mechanism to switch between measuring a received current and measuring the voltage in order to isolate the voltage measurement from a received current.

The control unit may be for switching between measuring a current and measuring a voltage at multiple second electrodes during simultaneous imaging and stimulation of the internal volume of a subject body, including adjusting an applied source current such that each permutation of electrodes applies a desired stimulating current.

The device may be in the form of a module having a group of electrodes, wherein the module is attachable to one or more other modules in cascading form; and wherein each module is controlled by a control unit enabling individual operation of each electrode and high speed communication between the cascading modules.

The device may include an analogue front end component for converting commands from the control unit to source current for an electrode and for measuring current and voltage at an electrode.

The control unit may include a field-programmable gate array for simultaneous independent control of all electrodes and multiplexing parallel data paths.

According to a sixth aspect of the present invention there is provided an imaging system for imaging an internal volume of a subject body comprising: one or more device as defined in the fifth aspect of the present invention; and a system interface including: a controlling component for controlling the one or more device including controlling device configuration and session parameters and electrode parameters; an electrical impedance tomography imaging component including: an imaging processing component for receiving device output and processing data to provide imaging; a display component for displaying the output of the imaging processing component; and a stimulating component for controlling the application of stimulating currents to the one or more device.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:-Figure 1 is a schematic block diagram of an embodiment of a system for imaging an internal volume of a subject body in accordance with the present invention; Figure 2 is a schematic block diagram of an embodiment of a portion of the system of Figure 1 including an analogue electrode channel; Figure 3 is a schematic block diagram of an embodiment of a portion of the system of Figure 1 including a control unit; Figure 4 is a schematic diagram of a further embodiment of a system for imaging an internal volume of a subject body in accordance with the present invention; Figure 5 is a circuit diagram of a further embodiment of an aspect of the system for imaging an internal volume of a subject body in accordance with the present invention; and Figure 6 is a block diagram of a block diagram of an embodiment of a computing system in which aspects of the present invention may be implemented.

DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS

It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numbers may be repeated among the figures to indicate corresponding or analogous features.

In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, and components have not been described in detail so as not to obscure the present invention.

Referring to Figure 1, an embodiment is shown of a system (100) for imaging an internal volume of a subject body. The imaging may be carried out by Electrical Impedance Tomography (EIT) by the application of a current to the internal volume of the subject body for calculating and imaging impedances of the internal volume. The subject body may be part of a human or animal body requiring imaging for biomedical application or, alternatively, the subject body may be of a non-living form for imaging for industrial applications.

In one embodiment, the system (100) includes, in addition to imaging, stimulating the internal volume of the subject body by applying additional current waveforms. One form of stimulation is transcranial electric brain stimulation which is a form of neuro-stimulation.

Both EIT imaging and current stimulation require the application of source currents from multiple electrodes applied to the external surface of a subject body. In the case of EIT source current may be applied in the form of a direct current, a sinusoidal waveform, orthogonal code, chirp waveform, sinc function waveform, or other appropriate form. A source current for stimulating may have a waveform of a direct current (for transcranial direct current stimulation tDCS), a sinusoidal waveform (for transcranial alternating current stimulation tAGS), a random noise waveform (for transcranial random noise stimulation tRNS), or other form of waveform suitable for stimulating a characteristic of the internal volume of the subject body.

The system (100) includes a system interface (103) allowing user interaction with an imaging component (107) and an optional stimulating component (101). The system (100) also includes a module (150) including a control unit (102) including hardware and software components and an analogue front end (139).

The system (100) may include an interface (130), for example, a Universal Serial Bus (USB) interface, connected to the control unit (102) for operative connection to the system interface (103).

The control unit (102) may include a current applying component (104), a current measuring component (105), and a voltage measuring component (106). The control unit (102) is connected to a plurality of electrodes (108, 110, 112) having contact elements (109, 111, 113) via analogue electrode channels (116, 118, 120) that make up an analogue front end (139). The electrodes (108, 110, 112) are operatively attached to the external surface of a subject body (114) via the contact elements (109, 111, 113) respectively.

The control unit (102) may also be connected to a reference electrode (140) attached to the external surface of the subject body (114).

In one embodiment, the analogue electrode channels (116, 118, 120) are each provided with switches (122, 124, 126) that enable each electrode to operate in a current sourcing or current sinking mode when a switch is in a closed state, and a voltage measuring mode when the switch is in an open state.

The current applying component (104) is configured to apply either an imaging excitation current component, or a stimulating current component, or both. The excitation current component is characterised in that it is small enough not to provoke a discernable brain response, and for sake of clarity, should be understood to include any current component that is applied to the subject (114) through the electrodes (108, 110, 112) and from which measurements are taken for the purpose of performing Electrical Impedance Tomography (EIT).

The stimulating current component is typically of several magnitudes larger than the excitation current component and should be understood to include any current component applied to the subject (114) through the electrodes (108, 110, 112). For example, the stimulating current may be for neuro-stimulation applied to the head of a person for the purpose of performing neuro-therapy, for example in transcranial direct current stimulation (tDCS) therapy.

For illustrative purposes, this particular embodiment shows four electrodes, and it should be appreciated that an array of many electrodes may be provided.

Each electrode channel (116, 118: 120) and associated electrode (108, 110, 112) may be operable to provide more than one function from the following: * applying a current; * alternately measuring a received current and measuring a voltage; * providing a sink for a current path when measuring a voltage.

In order to provide these optional functions each electrode may include a switch (122, 124, 126) to enable the electrode to switch between a closed switch for current delivery or received current measuring, and an open switch for voltage measuring.

These different functions of electrodes are described by referencing the electrodes as "first", "second", or "third" electrodes although it should be appreciated that each electrode channel (116, 118, 120) and associated electrode (108, 110, 112) may act as any one of a first, second, or third electrode.

A first electrode (108) may function as an electrode through which a source current is applied and in this function, the switch (122) will be closed.

A second electrode (110) may function as an electrode at which a received current is measured in alternation with a measurement of the voltage at the electrode (110). When the second electrode (110) has its switch (124) closed it may provide a received current measurement and when it has its switch (124) open it may provide a voltage measurement (as shown in Figure 1). Providing a switch (124) at an electrode to enable voltage measurement at the same electrode as the received current is measured has the advantage that the voltage may be measured immediately following a received current measurement.

A third electrode (112) may function as an electrode providing a sink for a current path whilst the voltage is being measured at a second electrode (110). Therefore, a third electrode (112) may use its switch (126) in opposing position to a second electrode (112).

Providing electrodes (108, 110, 112) with a switching capability enables increased resolution of an imaging system due to the multi-function of the electrodes.

The scenario illustrated in Figure 1 is described. An excitation current component is applied through a first electrode (108) causing the first electrode (108) to act in current sourcing mode.

It is desired to obtain a return current and voltage measurement from a second electrode (110) in order to measure electrical impedance in the subject (114) between the first electrode (108) and the second electrode (110). A reference electrode (140) is also provided at the subject (114) for voltage reference.

The switch (122) of a first electrode (108) is in a closed state and an excitation current component is applied through a first electrode (108) to a second electrode (110) having its switch (124) in a closed state and the received current at the second electrode (110) is measured. The second electrode (110) as illustrated has changed its switch (124) to an open state in order to measure voltage at the second electrode.

An excitation current component continues to be applied through the first electrode (108), causing first electrode (108) to act in current sourcing mode and a third electrode (112) to act in current sinking mode. In this illustrated scenario, the second electrode (110) has its switch (124) in an open state to enable voltage measurement at the second electrode (110).

A return current and a voltage measurement in response to the excitation current component (for FIT) are taken at the second electrode (110) having its switch in an open state and thus operating in voltage measurement mode.

Due to interference impedance caused by contact elements (109, 113) while their associated switches (122, 126) are in the closed states, the voltage measurements at first and third electrodes (108, 112) would be inaccurate for the purpose of EIT and it is thus desirable to supply and sink the excitation current component through first and third electrodes (108, 112) operating in current supply and sinking modes, whilst a voltage in response to the excitation current component is measured at second electrode (110) operating in voltage measuring mode. Accordingly, by measuring the return current and voltage at second electrode (110) of which the switch (124) is in an open state, interference impedance caused by contact element (111) is not detected and a clean voltage measurement is obtained by the voltage measuring component (106) in response to the excitation current applied to the subject (114) by the stimulating current applying component (104) of the control unit (102).

The system (100) of the present embodiment, and accordingly the stimulating current applying component (104), is configured to also apply a stimulating current component by imposing a stimulation current component on the excitation current component. This may be imposed by superimposing the currents or by sequential application of the currents. In this case, a return current and a voltage in response to both the excitation current component and the stimulation current component are measured at the second electrode (110), and the desired voltage and return current components are subsequently extracted from the combined measurement.

It should be apparent from the description of the present embodiment that the first, second and third electrodes (108, 110, 112) of the system (100) may be used interchangeably to either obtain current and voltage measurements with reference to the reference electrode (140), or apply excitation and stimulation current components such that measurements may be made by like electrodes of which the switches operate in alternate states as those being used for measurement. Advantageously, the interchangeable use of electrodes may provide for higher resolution measurements as that obtained by traditional [IT systems.

In the above embodiments, an EIT imaging method and system are described with switchable individual electrodes providing improved imaging spatial resolution due to the electrodes being able to switch between current sources and voltage monitors and thus providing double the current measurement.

EIT imaging requires the calculation of impedance, which is the ratio between voltage and current. The voltage referred to here is that at the electrode end of the sense resistor. As mentioned, current contribution from the current source generates a voltage across the contact impedance which distorts the voltage measurement. Even if the current source is instructed to provide zero current, it still provides a conductive path for currents injected elsewhere as the amplifier implementing the current source has a finite output impedance (dependent on frequency). So the switch isolates the amplifier from the subject, ensuring that the voltage measurement is uncorrupted. The intention is not to measure the contact impedance.

The voltage measurement is also necessary in order to ensure that the administered current is within safety parameters. A sense resistor is placed in series with the output and the current is measured by measuring the voltage across it, i.e. before and after it, and then dividing by the known resistance.

Voltage measurement also ensures that the outputs are not saturating, i.e. being asked to provide a current outside of the capabilities such as when the local potential at the output is near either supply voltage.

In the context of simultaneous EIT imaging and current stimulation, it is possible to selectively alternate individual electrodes between current contributing (stimulating and providing [IT waveforms) to voltage measuring states mid-session, as the current contribution from other electrodes can be adjusted to ensure that the net current field remains within the required parameters.

Switching between voltage measurement and current source during simultaneous imaging and stimulation may take advantage of the multi-electrode imaging, while adjusting the current output of the contributing electrodes such that in each permutation of electrode states the desired stimulating current field is as per the required parameters for effective stimulation of the of the cortical current.

Current outputs can implement high resolution and speed general purpose signal generation. Voltage sensing provides high resolution and speed general purpose data acquisition. Active monitoring of outputs allows implementation of output limits.

Referring now to Figure 2, an analogue electrode channel (200) for a single electrode (108) is shown generally as an example of the analogue electrode channels (116, 118, 120) of the electrodes (108, 110, 112) of the system (100) of Figure 1.

The electrode (108) is attached to the external surface of the subject body (114) by the contact element (109) and connected to the control unit (102), the control unit being configured to apply the current components and collect voltage measurements for the imaging or stimulating currents, or both. The measurements are operatively taken with reference to the reference electrode (140) attached to another part of the surface of the subject body (114).

Control of the analogue channel (200) is effected by a Field Programmable Gate Array (FPGA) (206) implemented by the control unit (102). The FPGA (206) is configured to selectively transmit an excitation current command (202) to a current source (204) to deliver the excitation current component to an electrode (108) via the switch (122).

The switch (122) is shown in its closed state and it should thus be evident that the analogue channel (200) and the electrode (108) attached thereto would operate in current sourcing mode.

Before reaching the current source (204), the excitation current command (202) is converted to an analogue signal by a digital to analogue converter (DAC) (208), and subsequently passed through a current to bipolar voltage converter (210) and anti-imaging filter (212). In one embodiment, the DAC is implemented by four AD5447 double output 21MS/s twelve bit DACs providing eight channels.

The analogue channel (200) of the electrode (108) includes a return path for measuring a return current (214) across a resistor (216), amplified by an instrumentation amplifier (218), passed through an anti-aliasing filter (220) and subsequently converted to a digital return current signal by an analogue to digital converter (ADC) (222) before being operatively received at an input of the FPGA (206). The return current (214) requires the switch (122) to be in a closed state.

The analogue channel (200) of the electrode (108) includes a return path for measuring a voltage measurement (226). The voltage measurement (226) requires the switch (122) to be in an open state. The voltage measurement (226) is passed through a differential converter (228), an anti-aliasing filter (230) and subsequently converted into a digital signal by an ADC (232) before being operatively received at the FPGA (206).

An advantage of the described system is its scalability through cascading of multiple modules (150) with each module having multiple electrodes. The cascading of modules (150) is described further below in relation to Figure 4.

An increased number of electrodes provide greater spatial resolution up to a limit. A major advantage of the described system is that it is easily scaled according to the required cost/capability ratio of the application. The system can implement arbitrarily large numbers of electrode channels, with the primary limitation being the data throughput to the host computer. The ability to increase the number of electrodes to higher numbers has definite application for implementation of EIT imaging.

In the case of a combined imaging and stimulation system, simulation indicates that the minimum number of electrodes is 10 for effective multi-electrode transcranial stimulation.

The aim of the system is not to provide as many channels as physically possible, but to allow scaling of the output channels depending on the requirements of the application.

The use of modules with on board FPGA which is inherently parallel opens up simultaneous advanced imaging modularities. The on board ERGA in the module (150) is completely reconfigurable thus it may be used for any application requiring high resolution and high speed data acquisition or signal generation, especially in biomedical applications as it is designed with biomedical safety as a priority.

An embodiment of the control unit (102) is now described in more detail with reference to Figure 3. The control unit (102) includes the FPGA (206) having an on-board Random Access Memory (RAM) module (250) and is programmed via a Complex Programmable Logic Device (CPLD) (252) connected to the USB interface (130) for operative connection to the system interface (103).

In this embodiment, the CPLD (250) is of the lattice MachXO2 type. The selected FPGA (206) is of the lattice ECP3-95 type, having 92k look-up tables, 128 multiplier blocks and an integrated four channel Serializer/Deserializer (SERDES) allowing full duplex 3.12Gb/s Low Voltage Differential Signalling (LVDS). The particular implementation of the FPGA (206) enables four data paths for derivation of EIT impedance data, each channel path including a 512 point Fast Fourier Transform (FFT) block for de-multiplexing inputs, each block sharing two of the electrodes (for example first electrode (108) and second electrode (110)), the data paths having a latency of approximately 2Oms.

Output waveforms of the stimulating current command may be generated by interpolating lookup tables stored in the RAM (250), instead of using Direct Digital Synthesis (DDS), thereby conserving resources of the FPGA (206).

In this embodiment of the control unit (103), an FPGA (206) is selected over a standard microcontroller, to advantageously provide inherent concurrency in processing, allowing for simultaneous control of the analogue front end (139) associated electrode channels (116, 118, 120). Naturally, the advantage would be more apparent in arrays of large numbers of electrodes, and again, only the three channels (116, 118, 120) are discussed here for illustrative purposes. Furthermore, processing resource constraints are mitigated by multiplexing parallel data paths and using LVDS Serializer/Deserializer (SERDES) facilitates the implementation of high speed interfaces; and that microcontrollers having integrated ADCs and DACs suffer from low performance.

In a particular embodiment of the control unit (102), the USB interface (130) is implemented as a single IC USB transceiver of the F14232H type. The transceiver interfaces with the CPLD (252) via four Serial Peripheral Interface connections and three isolators (shown collectively by 262) of the ADUM2400 galvanic isolator type, which conform to IEC-60601 requirements and allow a communication speed of 90Mb/s through each connection.

The RAM module (250) contains high speed DDR RAM that allows local storage and high speed access of output parameters while also providing lookup tables in order to simplify calculations and temporary storage for FPGA (206) EIT calculations, thus reducing the FPGA's (206) resource usage. Each electrode channel (116, 118, 120) has a dedicated queue of output current values implemented in RAM. These are updated from the system interface and are routed synchronously by the FPGA (206) to the appropriate analogue electrode channels. A plurality of Serial Advanced Technology Attachment (SATA) compatible external devices (254, 256, 258, 260) may be connected to the FPGA (206).

A system illustrating the cascading option of modules (150) is shown in Figure 4. This cascading arrangement may be used in only imaging systems or in combined imaging and stimulating current systems. In addition, the individual electrode channel switching described in relation to Figure 1 may be used in this cascading system, alternatively dedicated current source and voltage measurement channels may be provided.

Turning now to Figure 4, a system (400) is shown according to another embodiment of the system (400) including a plurality of modules (402, 404, 406, 408, 410, 412, 414, 416). As can be seen from module (402), each module includes a control unit (102) connected to an analogue front end (139) having a group of a plurality of electrodes (420) (in this example, eight electrodes) connected to the analogue front end (139). The control unit (102) interfaces with the system interface (103) via the USB interface (130).

To provide the cascading feature, the control unit (102) of module (402) is connected to like control units of modules (404, 406, 414, 416), for example, via an LVDS communications bus (422), and the control units of modules (404) and (406) are in turn connected to like control units of modules (408, 410, 412) in cascade, for example, via a subsidiary LVDS communications bus (424).

Galvanic isolation of modules provides electrical safety as per 1EC60601 standards.

Current contribution may be made using the cascading modules through multiple electrodes with each electrode amplitude, frequency and phase independently controlled. In the combined imaging and stimulation system, such independent control may be harnessed such that the net current field provides focal and effective stimulation of an internal volume target.

The efficacy of sUmulation is dependent on the polahty, magnitude and duration of the electrical field induced by the appHed current at the target, abng with the orientation of the field relative to the axons at this target.

These factors are in turn dependent on the current contribution, piacement, electrical properties and physical dimensions of the applied electrodes along with the eectrical properties of the subject body.

n the context of neuro-stimuation, the dimensions of the electrodes, their location on the scap a'ong with the anatomical and eecthca characteristics of the oca sca'p, skufi. cerebrospina fluid, white and grey matter determne the distribution of the induced eectric fled and thus the current density at the target. Therefore optima rnodukition of a spechc neurologca function can be performed by adjusting the size and position of the &ectrodes (known as the &ectrode montage) and the amphtude of irected current such that the magnitude of the &ectric fieid is maximized at the target region whde aso being negligible elsewhere, thus preventing unintended modulation of other functions.

With reference to Figure 5 of the drawings, the circuitry (500) of four front end analogue channels of electrodes applied to the subject (114) is shown. Each electrode (512, 522, 532, 542) is connected to the subject (114) via a contact element (511, 521, 531, 541) and has a switch (514, 524, 534, 544) and depending on whether the switch is in a closed or open position, the electrodes (512, 522, 532, 542) can perform either a current supply function, a voltage measuring function, a return current measuring function, or a current sink function.

To perform a current supply function, a voltage is applied at (516, 526, 536, 546), converted by a converter (513, 523, 533, 543) and passed through a closed switch (514, 524, 534, 544) of the electrode (512, 522, 532, 542).

To perform a voltage measuring function, the switch is opened and a voltage measurement taken at (519, 529, 539, 549).

To perform a return current measuring function, the switch (514, 524, 534, 544) is closed and a voltage drop over the resistor (518, 528, 538, 548) is measured between a point (517, 527, 537, 547) and a point (519, 529, 539, 549).

To perform a current sink function, no measurement needs to be taken at the particular electrode (512, 522, 532, 542) and the switch (514, 524, 534, 544) may be switched to a ground position.

In the present embodiment, the first electrode (512) operates as a current supply, the second electrode (522) and the fourth electrode (542) to measure voltage, whilst the third electrode (532) acts as a current sink and is grounded.

Reference numerals 560, 561, 562, 563, 564 and 565 represent various impedances within the subject body (114). Depending on the state of electrodes described above, any one or more of the impedances are measured.

Imaging described herein may be provided through Electrical Impedance Tomography (EIT) although the architecture of the system allows more advanced modalities utilizing multiple frequencies and wideband waveforms.

The impedances of different tissues are frequency dependent Therefore excitation with different frequencies albws more fine-grained classification of tissue. A further advantage is that if different frequency current waveforms are simuftaneously applied at different electrodes, Frequency Division Multiplexing may be used to discriminate the source &ectrodes thus increasing temporal resolution. Furthermore, so long as there is an appropriate dc-multiplexing strategy for discriminating between contributing electrodes, the bandwidth of the waveforms at each electrode can span a range of frequencies increasing thus capitalizing on both the advantages mentioned. Of the multiple possible energizing waveforms it can further be shown that they have different discriminatory attributes and computational requirements which lend themselves to different applications.

Neurological activity of the brain is accompanied by local blood flow changes at the location where the function is being effected. This increased blood flow is accompanied by changes in local impedance as blood has a much lower impedance than cortical grey matter. In order to capture brain function, not only must these impedance changes be detectable, but the EIT measurement sample rate must be fast enough to reconstruct the dynamics of the activity. Both these criteria have been seen to be achievable with regard to significant neurological functions.

Using multiple actively controlled electrodes in a transcranial stimulation system and precisely adjusting the montage along with the polarity and magnitude of their current contribution such that the mutual addition and subtraction of the contributing currents is controlled, a resultant current field can be created whereby the current density and orientation through the cortex provides optimal stimulation of a target.

Determining the appropriate montage and electrode current contributions resulting in the required intensity, focality and electric field orientation without exceeding safety constraints in order to optimally stimulate a cortical target is a non-trivial problem. This is primarily due to unique and complex anatomical structure of the head. Therefore for optimal stimulation administration, high resolution imaging of the subjects head is required in order to determine these optimum parameters.

Wth regard to tDCS administration there are no significant sources or sinks of current within the head. Therefore all current sources and sinks are the electrodes at the boundary of the volume. Thus the electric potential within the volume can be computed as it obeys Laplace's equation: V (aVG) = 0, where a is the tensor representing anisotropic conductivity within the volume and 0 is the induced potential.

The current flow perpendicular to boundary surface is zero everywhere, except at the &ectrodes. where known currents are apped. Therefore Newmann boundary conditions can he defined and the calcuation becomes a boundary value problem. A boundary condition s defined as zero current density perpendicular to the boundary surface at every point on the boundary induding at afi electrodes except for positive one unit current density applied at a single active electrode and negative one unit current density at the reference. The complete set of boundary conditions consists of the previous criteria appUed to each active &ectrode.

Converting the conductivity model into a mesh of appropriate geometry and connectivity (especiafly to account for anisotropic conductivity) of finite elements aUows efficient evaluation of the electric field within the volume using the Finite Element Method (FEM). The computation of the FEM with an appropriate solver results in a system of linear equations which map a vector of the induced electric field at each point in the volume to a vector of the current applied at each electrode.

Safety criteria, focality, intensity parameters along with the maximum electrode count are used to guide an optimisation algorithm which attempts to converge on an optimum electrode montage and associated current contribL.ltions.

Due to the use of multiple actively controlled electrodes accuracy and effectiveness is better than legacy systems. The modules are seamlessly cascadable allowing the number of electrodes to be increased up to an arbitrarily large number, thus the system capabilities and cost can be custom ised to the application.

The system may combine electrical stimulation and imaging using intrinsically safe low currents. The system uses multiple active electrodes in order to increase effectiveness over legacy systems. As all the electrodes are independently controlled, the system may provide not only direct current stimulation, but stimulation with arbitrary waveforms.

The described system is capable of achieving both stimulation and imag!ng whHe also amehorahng the shortcomings of legacy systems. Both these functions require muRiple independently controHed &ectrodes distributed on the subject body arid have cornphrneritary functional requrements. therefore minimal additional resources are required to achieve both goals. Meeting these requirements also results in the abihty to improve on legacy modalities.

The described system exceeds aU appropriate safety requirements and is implemented with a modular architecture enabling cascading of the hardware such that the system capahflity and cost can be scaled according to the requirements of the apphcation.

Each electrode channel may also switch between current source or a voltage measurement functionality which increases the spatial resolution of EIT imaging.

With regard to stimulation, the described system provides high sample rates of data acquisition and output signals.

The system can be used in practically any application where low current stimulation and/or imaging is required. This may be for biomedical applications, but also for industrial applications.

The multi-electrode system is capable of high fidelity and high speed generation of waveforms (for both stimulation and imaging).

Figure 6 illustrates an example of a computing device (600) in which various aspects of the disclosure may be implemented, in particular the system interface (103). The computing device (600) may be suitable for storing and executing computer program code. The various participants and elements in the previously described system diagrams may use any suitable number of subsystems or components of the computing device (600) to facilitate the functions described herein.

The computing device (600) may include subsystems or components interconnected via a communication infrastructure (605) (for example, a communications bus, a cross-over bar device, or a network). The computing device (600) may include at least one central processor (610) and at least one memory component in the form of computer-readable media.

The memory components may include system memory (615), which may include read only memory (ROM) and random access memory (RAM). A basic input/output system (BIOS) may be stored in ROM. System software may be stored in the system memory (615) including operating system software.

The memory components may also include secondary memory (620). The secondary memory (620) may include a fixed disk (621), such as a hard disk drive, and, optionally, one or more removable-storage interfaces (622) for removable-storage components (623).

The removable-storage interfaces (622) may be in the form of removable-storage drives (for example, magnetic tape drives, optical disk drives, floppy disk drives, etc.) for corresponding removable storage-components (for example] a magnetic tape, an optical disk, a floppy disk, etc.), which may be written to and read by the removable-storage drive.

The removable-storage interfaces (622) may also be in the form of ports or sockets for interfacing with other forms of removable-storage components (623) such as a flash memory drive, external hard drive, or removable memory chip, etc. The computing device (600) may include an external communications interface (630) for operation of the computing device (600) in a networked environment enabling transfer of data between multiple computing devices (600). Data transferred via the external communications interface (630) may be in the form of signals, which may be electronic, electromagnetic, optical, radio, or other types of signal.

The external communications interface (630) may enable communication of data between the computing device (600) and other computing devices including servers and external storage facilities. Web services may be accessible by the computing device (600) via the communications interface (630).

The external communications interface (630) may also enable other forms of communication to and from the computing device (600) including, voice communication, near field communication, Bluetooth, etc. The computer-readable media in the form of the various memory components may provide storage of computer-executable instructions, data structures, program modules, and other data. A computer program product may be provided by a computer-readable medium having stored computer-readable program code executable by the central processor (610).

A computer program product may be provided by a non-transient computer-readable medium, or may be provided via a signal or other transient means via the communications interface (630).

Interconnection via the communication infrastructure (605) allows a central processor (610) to communicate with each subsystem or component and to control the execution of instructions from the memory components, as well as the exchange of information between subsystems or components.

Peripherals (such as printers, scanners, cameras, or the like) and input/output (I/O) devices (such as a mouse, touchpad, keyboard, microphone, joystick, or the like) may couple to the computing device (600) either directly or via an I/O controller (635). These components may be connected to the computing device (600) by any number of means known in the art, such as a serial port.

One or more monitors (645) may be coupled via a display or video adapter (640) to the computing device (600).

Some portions of this description describe the embodiments of the invention in terms of algorithms and symbolic representations of operations on information. These algorithmic descriptions and representations are commonly used by those skilled in the data processing arts to convey the substance of their work effectively to others skilled in the art. These operations, while described functionally, com putationally, or logically, are understood to be implemented by computer programs or equivalent electrical circuits, microcode, or the like. The described operations may be embodied in software, firmware, hardware, or any combinations thereof.

The software components or functions described in this application may be implemented as software code to be executed by one or more processors using any suitable computer language such as, for example, Java, C++, or Perl using, for example, conventional or object-oriented techniques. The software code may be stored as a series of instructions, or commands on a non-transitory computer-readable medium, such as a random access memory (RAM), a read-only memory (ROM), a magnetic medium such as a hard-drive or a floppy disk, or an optical medium such as a CD-ROM. Any such computer-readable medium may also reside on or within a single computational apparatus, and may be present on or within different computational apparatuses within a system or network.

Any of the steps, operations, or processes described herein may be performed or implemented with one or more hardware or software modules, alone or in combination with other devices. In one embodiment, a software module is implemented with a computer program product comprising a non-transient computer-readable medium containing computer program code, which can be executed by a computer processor for performing any or all of the steps, operations, or processes described.

Finally, the language used in the specification has been principally selected for readability and instructional purposes] and it may not have been selected to delineate or circumscribe the inventive subject matter. It is therefore intended that the scope of the invention be limited not by this detailed description, but rather by any claims that issue on an application based hereon. Accordingly, the disclosure of the embodiments of the invention is intended to be illustrative, but not limiting, of the scope of the invention, which is set forth in the following claims.

Claims (45)

1. CLAIMS: 1. A method for imaging an internal volume of a subject body, comprising: providing multiple electrodes for locating at selected positions external to a volume of a subject body; applying a source current for imaging of a portion of the internal volume of the subject body through one or more first electrodes; measuring a current received at one or more second electrodes; switching a channel of each second electrode between applying the current source and measuring a voltage at the electrode in order to isolate the voltage measurement from a received current; measuring a voltage at the second electrode whilst providing a current path to a third electrode; using the measured current and the subsequent measured voltage at each second electrode to provide an impedance for imaging the portion of the internal volume.
2. 2. The method as claimed in claim 1, including providing one or more third electrodes and switching a channel of each third electrode between applying the current source and measuring a voltage at the electrode in opposite switching to the switching of one or more second electrodes for maintaining a current path whilst measuring a voltage at the second electrode.
3. 3. The method as claimed in claim 1 or claim 2, including simultaneously or sequentially applying a source current for stimulating the portion of the internal volume of the subject body through the one or more first electrodes.
4. 4. The method as claimed in claim 3, wherein the source current for imaging has a waveform of one of the group of: a direct current, a sinusoidal waveform, orthogonal code, chirp waveform, sinc function waveform, and wherein the source current for stimulating has a waveform of one of the group of: a direct current, a sinusoidal waveform, a random noise waveform, or other form of waveform suitable for stimulating a characteristic of the internal volume of the subject body.
5. 5. The method as claimed in any one of the preceding claims, including: controlling the source current for stimulation through multiple electrodes with independent control of each electrode's amplitude, frequency and phase such that a net current field provides stimulation of a target internal volume.
6. 6. The method as claimed in any one of the preceding claims, wherein the method provides a known source current through one or more first electrodes and the measured current and voltage at the one or more second electrodes is used for imaging the internal volume of the subject body using electrical impedance tomography.
7. 7. The method as claimed in any one of claims 3 to 6, wherein the imaging is carried out in real time in response to applying the source current for stimulating.
8. 8. The method as claimed in claim 7, including: switching between measuring a current and measuring a voltage at multiple second electrodes during simultaneous imaging and stimulation of the internal volume of a subject body, including adjusting an applied source current such that each permutation of electrodes applies a desired stimulating current.
9. 9. The method as claimed in any one of the preceding claims, including using a multiplexing and demultiplexing strategy to discriminate between multiple contributing first electrodes.
10. 10. The method as claimed in any one of the preceding claims, wherein a known source current is applied with multiple frequencies, with different frequencies applied at different first electrodes, and the method uses frequency division multiplexing to discriminate different first electrodes.
11. 11. The method as claimed in any one of the preceding claims, wherein a bandwidth of source current waveforms at each first electrode spans a range of frequencies and the method uses frequency division multiplexing to discriminate different first electrodes.
12. 12. The method as claimed in any one of the preceding claims, wherein providing multiple electrodes provides cascading groups of electrodes, wherein each group is controlled by a control unit and wherein the control unit enables individual operation of each electrode, the control unit also provides high speed communication between the cascading groups.
13. 13. The method as claimed in claim 12, wherein a group includes an analogue front end component for converting commands from the control unit to source current for an electrode and for measuring current and voltage at an electrode.
14. 14. The method as claimed in claim 12 or claim 13, wherein the control unit includes a field-programmable gate array for simultaneous independent control of all electrodes and multiplexing parallel data paths.
15. 15. A device for imaging an internal volume of a subject body, comprising: a plurality of electrodes for locating at selected positions external to a volume of a subject body; a control unit including: a source current applying component for applying a current source for imaging of a portion of the internal volume of the subject body through one or more first electrodes; a current measuring component for measuring a current received at one or more second electrodes; a voltage measuring component for measuring a voltage at the one or more second electrodes whilst providing a current path to a third electrode; a channel of each electrode including a switch mechanism to switch between measuring a received current and measuring the voltage in order to isolate the voltage measurement from a received current; wherein each electrode is capable of acting as a first or a second electrode.
16. 16. The device as claimed in claim 15, wherein the control unit includes: a stimulating current applying component for simultaneously or sequentially applying a source current for stimulating the portion of the internal volume of the subject body through the one or more first electrodes.
17. 17. The device as claimed in claim 16, wherein the source current for imaging has a waveform of one of the group of: a direct current, a sinusoidal waveform, orthogonal code, chirp waveform, sinc function waveform, and wherein the source current for stimulating has a waveform of one of the group of: a direct current, a sinusoidal waveform, a random noise waveform, or other form of waveform suitable for stimulating a characteristic of the internal volume of the subject body.
18. 18. The device as claimed in claim 16 or claim 17, wherein the control unit is for: controlling the source current for stimulation through multiple electrodes with independent control of each electrode's amplitude, frequency and phase such that a net current field provides stimulation of a target internal volume.
19. 19. The device as claimed in any one of claims 15 to 18, wherein the control unit is for: switching between measuring a current and measuring a voltage at multiple second electrodes during simultaneous imaging and stimulation of the internal volume of a subject body, including adjusting an applied source current such that each permutation of electrodes applies a desired stimulating current.
20. 20. The device as claimed in any one of claims 15 to 19, wherein the device is in the form of a module having a group of electrodes, wherein the module is attachable to one or more other modules in cascading form; and wherein each module is controlled by a control unit enabling individual operation of each electrode and high speed communication between the cascading modules.
21. 21. The device as claimed in any one of claims 15 to 20, including an analogue front end component for converting commands from the control unit to source current for an electrode and for measuring current and voltage at an electrode.
22. 22. The device as claimed in any one of claims 15 to 21, wherein the control unit includes a field-programmable gate array for simultaneous independent control of all electrodes and multiplexing parallel data paths.
23. 23. An imaging system for imaging an internal volume of a subject body comprising: one or more device as claimed in any one of claims 15 to 22; a system interface including: a controlling component for controlling the one or more device including controlling device configuration and session parameters and electrode parameters; an electrical impedance tomography imaging component including: an imaging processing component for receiving device output and processing data to provide imaging; a display component for displaying the output of the imaging processing component.
24. 24. The imaging system as claimed in claim 23, wherein the system interface includes: a stimulating component for controlling the application of stimulating currents to the one or more device.
25. 25. The imaging system as claimed in claim 23 or claim 24, wherein the system interface includes: a multiplexing and demultiplexing component to discriminate between multiple contributing first electrodes.
26. 26. A method for imaging an internal volume of a subject body, comprising: providing multiple electrodes for locating at selected positions external to a volume of a subject body; applying a source current for imaging of a portion of the internal volume of the subject body through one or more first electrodes; simultaneously or sequentially applying a source current for stimulating the portion of the internal volume of the subject body through the one or more first electrodes; measuring a current received at one or more second electrodes; measuring a voltage at an electrode; using the measured current and the measured voltage to provide an impedance for imaging the portion of the internal volume; controlling the source current for stimulation through the multiple electrodes with independent control of each electrode's amplitude, frequency and phase such that a net current field provides stimulation of a target internal volume.
27. 27. The method as claimed in claim 26, including: switching a channel of each second electrode between applying the current source and measuring a voltage at the electrode in order to isolate the voltage measurement from a received current.
28. 28. The method as claimed in claim 27, including providing one or more third electrodes and switching a channel of each third electrode between applying the current source and measuring a voltage at the electrode in opposite switching to the switching of one or more second electrodes for maintaining a current pathway whilst measuring a voltage at the second electrode.
29. 29. The method as claimed in any one of claims 26 to 28, wherein the source current for imaging has a waveform of one of the group of: a direct current, a sinusoidal waveform, orthogonal code, chirp waveform, sinc function waveform, and wherein the source current for stimulating has a waveform of one of the group of: a direct current, a sinusoidal waveform, a random noise waveform, or other form of waveform suitable for stimulating a characteristic of the internal volume of the subject body.
30. 30. The method as claimed in any one of claims 26 to 29, wherein the method provides a known source current through one or more first electrodes and the measured current and voltage at the one or more second electrodes is used for imaging the internal volume of the subject body using electrical impedance tomography.
31. 31. The method as claimed in any one of claims 26 to 30, including: switching between measuring a current and measuring a voltage at multiple second electrodes during simultaneous imaging and stimulation of the internal volume of a subject body, including adjusting an applied source current such that each permutation of electrodes applies a desired stimulating current.
32. 32. The method as claimed in any one of claims 26 to 31, including using a multiplexing and demultiplexing strategy to discriminate between multiple contributing first electrodes.
33. 33. The method as claimed in any one of claims 26 to 32, wherein providing multiple electrodes provides cascading groups of electrodes, wherein each group is controlled by a control unit and wherein the control unit enables individual operation of each electrode, the control unit also provides high speed communication between the cascading groups.
34. 34. The method as claimed in claim 33, wherein a group includes an analogue front end component for converting commands from the control unit to source current for an electrode and for measuring current and voltage at an electrode.
35. 35. A device for imaging an internal volume of a subject body, comprising: a plurality of electrodes for locating at selected positions external to a volume of a subject body; a control unit including: a source current applying component for applying a current source for imaging of a portion of the internal volume of the subject body through one or more first electrodes; a stimulating current applying component for simultaneously or sequentially applying a source current for stimulating the portion of the internal volume of the subject body through the one or more first electrodes; a current measuring component for measuring a current received at one or more second electrodes; a voltage measuring component for measuring a voltage at an electrode; controlling the source current for stimulation through the multiple electrodes with independent control of each electrode's amplitude, frequency and phase such that a net current field provides stimulation of a target internal volume.
36. 36. The device as claimed in claim 35, wherein the control unit includes: a channel of each electrode including a switch mechanism to switch between measuring a received current and measuring the voltage in order to isolate the voltage measurement from a received current.
37. 37. The device as claimed in claim 36 or claim 37, wherein the source current for imaging has a waveform of one of the group of: a direct current, a sinusoidal waveform, orthogonal code, chirp waveform, sinc function waveform, and wherein the source current for stimulating has a waveform of one of the group of: a direct current, a sinusoidal waveform, a random noise waveform, or other form of waveform suitable for stimulating a characteristic of the internal volume of the subject body.
38. 38. The device as claimed in any one of claims 35 to 37, wherein the control unit is for: switching between measuring a current and measuring a voltage at multiple second electrodes during simultaneous imaging and stimulation of the internal volume of a subject body, including adjusting an applied source current such that each permutation of electrodes applies a desired stimulating current.
39. 39. The device as claimed in any one of claims 35 to 38, wherein the device is in the form of a module having a group of electrodes, wherein the module is attachable to one or more other modules in cascading form; and wherein each module is controlled by a control unit enabling individual operation of each electrode and high speed communication between the cascading modules.
40. 40. The device as claimed in any one of claims 35 to 39, including an analogue front end component for converting commands from the control unit to source current for an electrode and for measuring current and voltage at an electrode.
41. 41. The device as claimed in any one of claims 35 to 40, wherein the control unit includes a field-programmable gate array for simultaneous independent control of all electrodes and multiplexing parallel data paths.
42. 42. An imaging system for imaging an internal volume of a subject body comprising: one or more device as claimed in any one of claims 35 to 41; a system interface including: a controlling component for controlling the one or more device including controlling device configuration and session parameters and electrode parameters; an electrical impedance tomography imaging component including: an imaging processing component for receiving device output and processing data to provide imaging; a display component for displaying the output of the imaging processing component; and a stimulating component for controlling the application of stimulating currents to the one or more device.
43. 43. A method substantially as hereinbefore described with reference to the accompanying drawings.
44. 44. A device substantially as hereinbefore described with reference to the accompanying drawings.
45. 45. A system substantially as hereinbefore described with reference to the accompanying drawings.