GB2530355A

GB2530355A - Electric impedance tomographic device

Info

Publication number: GB2530355A
Application number: GB1421948.9A
Authority: GB
Inventors: Joseph Duncanan Farley
Original assignee: Individual
Current assignee: Individual
Priority date: 2014-09-16
Filing date: 2014-12-10
Publication date: 2016-03-23
Also published as: GB201421948D0

Abstract

Monitoring organs (e.g. the brain, strokes, heart, lungs, liver, tumours) using: a current injecting electrode 202_1; a current sinking electrode 202_2; at least one pair of voltage electrodes 203 (505, fig 5) for measuring voltages synchronously with the injection of the current; a remote processor 208 connected to the current electrodes and the voltage electrodes for creating a result, e.g. an image, of the organ. A current is injected at a first position and changes in currents and voltage are measured synchronously at further positions to create a result of the organ. Another aspect refers to a plurality of probe cards for placing on the surface of the organ. The probe card units comprise: a first electrode connected switchably to a first input of a first operational amplifier and a second input of a current sensing resistor; a second electrode connected to a first input of a second operational amplifier, connected to a ground line; a local processor connected to the output of the first and second operational amplifiers; and a current source connected between the ground line and a second input of the first operational amplifier and to a first input of the current sensing resistor.

Description

FIELD OF THE INVENTION

[00011 The present invention relates to the field of instrumentation for detecting and monitoring the bounded organs of patients and in particular for detecting and monitoring patients with brain strokes or brain tumours.

BACKGROUND OF THE INVENTION

[0002j Strokes, also referred to as a cerebrovascular ace/den (CVA), are medical emergencies and occur suddenly and can lead to death if' not treated within -2 to 4 hours of its onset. In the industrialised world strokes are a leading cause of death and disabilities; in the United States alone an estimated 700,000 strokes occur each year making it the third-leading cause of death and the leading cause of disabilities, Hypertension is strongly associated with strokes, so are other risk factors such as previous strokes, smoking, cholesterdi, over-weight and diabetes.

[0003j There are two types of strokes, ischaemic and haemorrhagic. Lichctemic s/rakes represents over 80% of strokes and result after occlusion (blocked blood vessel) via thrombosis (clot due to fatty deposits plaque in the arteries) or arterial embolism (embolus from other parts of the body), or by systemic hypopertiesionjdecrease in blood supply as per in shock). This interruption of blood flow prevents an adequate supply of oxygen and glucose to some brain cells causing them to swell and eventually die, The result is impairment or permanent neurological damage.

[00041 Haemorrhagic strokes result from burst or leaking blood vessels in the brain, This can be caused by rupture due to hypertension or aneuiysms (bursting of outpouched spots of weakened blood vessels). Bleeding is into the brain parenchyma or into the subarachnoid space and is surrounding with oedema. Rupture of the subarachnoid artery on or near the surface of the brain results in an accumulation of blood in the space between the surface of your brain and the skull. This increases the internal cranial pressure, can damage or kill brain cells in the affected area and lead to a loss of normal brain functions such as inability to control the movement of limb(s) on one side of the body, difficulties to understand or formulate speech, or a vision impairment of one side of the field of view.

[0005] The ability to differentiate between ischaemic and haemorrhagic strokes enable rapid life-saving treatment, e.g., administering clot dissolving drug for ischaemic stroke or quickly deciding to operate for haemorrhages.

[0006] Human cancer cells have damaged DNA that prevents self-repair or programmed death. They continue to grow out of control, and grow into other tissues and propagate the damaged DNA. Damaged DNA may be inherited or result from cigarette smoking, radiation damage or other unknown effects.

[0007] Tumours are collections of cancer cells of which there are many kinds; cancer cells can get into the blood stream, travel to other parts of the body (metastases) and form new tumours. Not all tumours are cancerous; benign tumours do not spread, but can grow large enough in the brain, compress the brain tissues and affect blood supply, resulting in disabling or life threatening ischaemic stroke effects, This pathologic result leads doctors to speak of brain tumours as opposed to brain cancers. The most aggressive fast growing tumours are known as glioblastomas; these account for more than 50% of brain tumours, Common symptoms of cerebral tumours are a function of its location and includes, seizures, problems speaking, mood changes, depression, personality changes, weakness or paralysis in parts of the body, changes in senses (vision, hearing smell, taste) etc. [0008] Tumour imaging is used for detection of the structure of the tumour, differentiating between malignant and benign, localisation of the volume of the lesion and any extent of spreading. Many tumours have significantly different electrical properties compared to the surrounding tissue; in the case of the brain there would be formation of new blood vessels to provide increased blood nutrients to aggressive fast-growing tumours. Electrical conductivity and permittivity changes versus the surroundings will give a priori detection by electrical impedance tomography (BIT), BIT impedance slices at varying levels can be compared, The smaller the tumour that can be detected, the earlier tumour treatment can begin, Unfortunately EIT's main disadvantage is its relatively poor image resolution, even using a large number of electrodes.

[0009j For a patient in the field, once a stroke occurs and often treatment is not sought until a debilitating stage is reached, or a tumour is suspected, generally an ambulance is called and the patient taken to a hospital. Precious minutes may then be lost in locating a available brain scanner and preparing the patient for the neurological examinations. Diagnostic tools in present use for such cases are computerised tomography (CT) imaging that uses penetrating ionising X-rays or magnetic resonance imaging (MRI) that uses the non-ionising strong magnetic fields. Both CT and IVIRI give excellent special resolution and tissue contrast, however these machines are extremely costly, cumbersome, require special locations and specially trained technicians for their operation and maintenance.

[00010] Electroencephalograms (FEEl) are devices that monitor brain activities at the surface of the brain referred to as the cerebral cortex. By the placement of multiple electrodes on the scalp and analysing the electrical signals from regions of the surface of the brain; skilled practitioners analyse changes of electrical activities for the detection of strokes.

However, it is difficult to ascertain the type of stroke with these devices. Likewise electrocardiogram (ECU sometimes referred to as EKU) monitors and displays electrical activity of several heart beats for interpretation by a specialist by recording the surface voltages at positioned body surface electrodes.

[000111 Relatively recently portable ultrasound devices have therapeutic application as well as control of strokes. US Patent publication No. US 2014/0155788A to I-loelscher eta], describes the use of microbubbles for the treatment of strokes in the field or during the ambulance ride to the hospital. While this is a portable relatively low cost device, it does require the administering intravenously an active agent.

[00012] Patient safety is an important aspect of EIT and EIS. The current safely tolerated by the body is frequency dependant. Below -iO Hz and using currents above 100 jiA (sometimes as low as 100 pA) some individuals feel a periodic stinging sensation that is thought to result from electrolysis at the electrode-tissue interface. At frequencies above 1O Hz, the electrolysis effect lessens and the dominant biological effect is neitnif sf1 nu/ateon when tens of mY appears across a nerve membrane. In the range 10 Hz to 1 kflz, especially between 50 to 60 Hz where there is maximum sensitivity of our nervous system, -1 mA gives the perception of current through the skin, tens of milliamps leads to muscular paralysis and hundreds of milliamps gives ventricular fibrillation leading to death. Above I kHz, the threshold for neural stimulation increases by a factor of 10 for each decade frequency increase. Beyond "-400 kflz no neural stimulation occurs and ohmic heating of the tissue becomes the dominant effect. Transcranial FIT systems inject current across the scalp and measure the resulting surface potential distribution. The (TEC6O6O1-1, 2005) and equivalent British (BS5724, 1979) standards penriit currents to patients of 100 iA rms for frequencies below 1 kHz, and increases of 0.1 mA per kHz up to a maximum of 10 mA rms beyond 100 kHz.

[000131 Bipolar or two electrodes arrangement use the same electrodes for current injection and voltage measurements. The measured voltage therefore includes the voltage across the tissue and the electrode-skin interface impedances which may vary and become large enough to invalidate findings. Teirapolar or four electrodes arrangement inject the current via one pair of electrodes and use a separate pair of electrodes for measurement of the resulting surface voltage. Additionally, in the tetrapolar arrangements only the voltmeter's low current flows through the electrode-skin interface impedances giving negligible voltage loss across it; hence the voltage measured is that across the tissue.

[00014] Imaging the brain involves placing cranial electrodes on the patient's scalp.

The surface voltage distribution is measured by injecting current into the region of interest (ROt) then measuring the voltages at all surface electrodes.

[00015] For shallow mapping, such as investigating the cerebral cortex region, current is injected through adjacent electrodes, For a ring of 18 electrodes sequentially numbered t, 2 3, etc. around the ROT, if the current is passed through electrodes 1 and 2, surface voltage distributions occurs; voltages between electrodes 3 and 4, then 4 and 5 and so on are measured and recorded, This procedure is repeated with current injected through different pairs of electrodes, say 2 and 3, 3 and 4 etc. and the corresponding surface voltages measured for each electrode pair. With p probes, p2 independent voltage measurements can be made.

[00016] Opposite electrodes are used to maximise the amount of current injected into the brain; this offers higher sensitivities to impedance changes deep inside the brain, In cerebral tomography opposite electrodes are used to investigate impedances related to aqueous electrolyte (blood or CSF) changes. The current source is firstly connected to opposite electrodes, say 1 and 9. Surface voltages are measured between say electrodes, 3 and 4, 4 and 5 and so on, and recorded. Current is thereafter injected through a different opposing pair of electrodes, say 2 and 10 and the corresponding surface voltages measured again. For 16 probes (p = 16) probes, up to, 256 independent voltages can be taken.

[000171 Electrical Impedance Spectroscopy EIS uses signal current at different frequencies (i.e., a spectrum of frequencies); it frequencies gives up2 independent voltages measurements. Several cycles of the lowest signal frequency may be used to obtain noise reduction. A system of 32 electrodes, S frequencies, and 4 cycles of 100 Hz (40 ms) will have a minimum data acquisition time of 40 * 5*322 ms, that is over 3.3 minutes per image. The choice of frequencies depends on the pathology desired.

[000181 For image reconstruction the boundary surface voltages, knowledge of the boundary shape, the position of the electrodes, the measured surface potential distribution and the magnitudes of the injected currents are needed. The conductivity may be estimated, but for complex nonhomogeneous volumes such as the human head where no analytic solution exists, a numerical method such as using the Finite Element Method (FEM) is used.

[000191 The forward model uses inner conductivity distribution of the brain, the known injected currents, and "predicts" the internal current density (or electric field) distributions for recreating the boundary voltages. This is solved using the generalised Laplace's equation with boundary conditions for the injected currents to give quantitative estimation of the current density within the brain, Software such as 1-DEAS now exists for the production of FEM from a head TvIRI scan.

[00020j The reconstruction process continues with the inverse solution where the voltage distribution and current density distributions are given and the conductivity distribution within the volume is computed. The data (current density) obtained from the forward model calculations is used. The inverse solution involves intensive computations; a specialised commonly used open source software, Electrical Impedance Tomography and Diffuse Optical Tomography Reconstruction Software (FIDORS), uses the 1PM model for forward calculations and a nonlinear solver for a unique, stable inverse solution.

[000211 An example of the proposed wireless data transfer to the remote host computer for image processing is the ZigBee communication protocol. ZigBee follows the IEEE 802.15.4 standards (Institute of Electrical and Electronics Engineers, 2006). ZigBee -originally set up for home networks -is reliable, cost effective and low power. Its transmission rate is 250 Kbps with a long range (l00-400 m). It is simpler, cheaper and more secure than other possible protocols such as Bluetooth and Wi-Fi. ZigBee is well suited for portable wireless brain systems; however care must be taken in Europe where its overlap with the Wi-H and Bluetooth frequency bands make using the ZigBee communication protocol susceptible to interference. However, with improved Bluetooth security, Bluetooth is an alternative having the advantage of a protocol already used by many devices such as smartphones, PDAs etc. [000221 There exists therefore the need of a frontline low cost non-invasive portable imaging system, even with low resolution, that may permit rapid detection of the onset or presence of a stroke or of a brain tumour, to enable early treatment that minimises neurologic damage and even prevent deaths. This system should not use ionising radiation, be stand alone, non-cumbersome, portable, low cost and simple to use, with displays indicating the type of stroke. The system should be capable of monitoring persons with a disposition for the recurrence of strokes, In conjunction with a remote host computer, the system should be capable of imaging the interior of volumes, albeit with low resolution, for the detection, monitor and display of tumours. Such a system is the subject of this disclosure.

SUMMARY OF THE INVENTION

[000231 The device described in this disclosure uses BIT / ETS for diagnosing and imaging inner volumes.

[000241 EIT / EIS injects a current through the volume target; the resulting surface voltage distribution is used in computing the inner conductivity distribution from which image reconstruction of the tissues within the inner volume is computed.

[000251 This device uses a tetrapolar probe arrangement for injecting the current and measuring the surface voltages. The tetrapolar arrangements give improved measurement accuracy as variations in the electrode-skin contact impedances have a lessor voltage drop effect.

[000261 The principle of human BIT is that a safe electrical AC current is injected between two adjacent or opposing surface electrodes. The resulting surface voltage distribution is measured at all electrodes around the volume. Computer programmes use the latter to determine the conductivity distribution within the volume, and correlate the conductivity with different tissue types. An introduction of blood within the brain (a haemorrhagic stroke or brain trauma), for example will modify the intra-cerebral conductivity distribution and be detected by the ELT system. The ELT processor can also output a visual image of the conductivity distribution for analysis.

[00027j This device at the patient side comprises arrangements of interconnected electrode units, non-invasively attached to the scalp for electrical current injection and or for monitoring cerebral surface potentials. Bach electrode unit is attached to a small probe card containing a low current microcontroller such as the TI MSP43OF t61 I (Texas Instruments, Dallas, TX) and other electronic components and form a probe card utt/t (PCU). There is one PCIJ per cranial node and 4-64 interconnected by a conductor bus ( say an 8-wire bus) PCUs within the array of PCTJs. The PCUs placement typically use, but is not limited to, the standard electroencephalogram (PEG) 1 0-20 electrode arrangement. The conductor bus interconnects all of the PCUs and is also connected to one system management processor unit (SMPU) that interfaces with extensive data storage, more powerful processing capability, a a local display unit and a transceiver unit such as the Chipcon 2430 (Texas Instruments, Dallas, TX) system and other units that are described later.

[00028] Away from the patient side is a host computer, also equipped with a similar transceiver (such as the Chipcon 2430); it contains the software programmes such as of tumour and stroke detection for wireless data transfers with the patient's SMPU and controls frmnctions, such as imaging, storage, distribution etcetera.

[00029] The PCU and SMPIJ system architecture enables cranial electrode current injection and surface voltages at each electrode in the array to be measured synchronously instead of being multiplexed to a central measurement instrument as is illustrated in Fig. t, the prior art. Synchronous measurements give the important benefit of speeding-up the time for a complete set of data ("image") by a factor of the number of electrodes e.g., a 32 electrode system has the potential for a 32x faster image time. Other advantages will be addressed later; a prior art 180 sec acquisition time is thus reduced to 6 secs.

[00030] h haernorrhagic strokes, blood typically accumulates towards the surface of the brain. Cranial stimulating currents are therefore injected across each hemisphere with shorter electrode spacing for less deep measurements, then the impedances of regions around the left hemisphere are compared to those of the right hemisphere; Cole-Cole parameters are computed and low impedance anomalies correlating to blood tissue close to the surface of the brain are interpreted as haemorrhagic stroke.

[00031] is'chae;nic strokes occur more towards the interior of the brain, Trans-cranial currents are therefore injected across each hemisphere with a wide spacing for increased penetration depths and the impedances of the left hemisphere compared to that of the right hemisphere; Cole-Cole parameters are computed and high impedance anomalies correlating to the absence of blood tissue are interpreted as ischaemic stroke.

[00032] At the onset of the diagnosis, the pathology -stroke or of tumour -is unknown and is important for rapid treatment (required within 3-4 hours to avoid neurological damage or even death), The proposed system must therefore execute the ischaemic, haemorrhagic and diagnostic procedures, and if negative, execute locally or at the host computer sequences, using wireless data exchanges, to provide imaging, Bluetooth transfer image data for display on, for example a PDA or smartphone devices or ZigBee or other wireless transfers to the host for imaging, distribution archiving etc. After the diagnostic measurement sequence, the go-no-go stroke detection is computed by the patient's SMPU -without intervention by the host; the results are indicated visually (e.g., flashing LEDs or audibly or a combination thereof). The type of stroke, ischaemic or haemorrhagic or request for image scan will also be displayed.

[00033] This system is also applicable to bedside patient monitoring for possible recurrence of strokes and can have applications in other diagnosing areas such as ±1w monitoring the conductivity integrity of neonates' organs, the adult lungs, liver and other organs -after the array of electrodes are modified for compatibility with the region of interest. This system configurable by software, can accommodate programmes such as, but not limited to, for obtaining EEG, EKO data from, say, the placement of an array of electrodes around the ROl and making selective synchronous surfice voltage measurements.

[00034] In one aspect of the disclosure, there is provided a system for the monitoring of organs, for example in a human body, comprising a pair of current electrodes for injecting a current into the monitored organs, at least one pair of voltage electrodes for measuring surface voltages about the monitored organs synchronously with the injection of the curre$, and a system processor connected to the at least one pair of voltage electrodes for creating a result of the monitored organs based on the measured injected current(s) and the resultant surface voltages. This enables a simple, portable device for the monitoring of organs to be created. The result could be an image, information related to the organ, or an output from one or all of the voltage electrodes.

[00035] The system can flirther comprise a first microprocessor that is connected to a first one of the pair of current electrodes for controlling the injection of the current and a first one of the pair of voltage electrodes for monitoring the injected voltage. The system further comprises a second microprocessor connected to a second one of the pair of current electrodes configured to receive the injected current and to a second one of the pair of voltage electrodes for measuring the surface voltages around the monitored organ. A local data transmitter is connected to the first microprocessor and the second microprocessor and is used to transfer data, for example by wireless, to the remote processor. The data transfer to the remote processor is controlled, for example, by a system controller.

[00036] In one aspect of the disclosure, the system frirther comprises a plurality of additional microprocessor units for the synchronous measurement of surface voltages around the monitored organ [00037j The remote processor comprises a plurality of software modules having logic instructions to operate the system for identification of medical issues. These medical issues include, but are not limited to, at least one of detection of tumours, strokes, lung functions, liver functions, heart functions, e.g. ECG, brain functions, e.g. EEG, [000381 The system further comprises, in one aspect, a sinusoidal current generator for generating the current at a plurality of frequencies. This creates a large number of data points that can be interpreted when monitoring the organ. The choice of the plurality of frequencies depends on the pathology.

[000391 A method for monitoring of organs is also disclosed. This method comprises injecting a current at a first position into the organs to be monitored and measuring changes synchronously in voltage at further positions about the organ. The measured injected current and changes in voltage are used to create a result of the monitored organs. As noted above, the injection of the current can be at a plurality of frequencies to create a number of data points.

[000401 Computations using the measured injected current and surface voltages can be compared with threshold values to indicate a medical issue.

[000411 In one further aspect, the measuring of the current and voltage is carried out at a second position. In other (third) positions and so on, only the surface voltage needs to be measured.

[000421 The system can be implemented with a plurality of probe card units for placing on the surface around the organ to be monitored. At least one of the probe card units comprises a first electrode connected switchably to a first input of a first operational amplifier and a second input of a current sensing resistor. A second electrode is connected to a first input of a second operational amplifier and the second input of the second operational amplifier is connected to a ground line. A local processor is connected to the output of the first operation amplifier and the second operational amplifier.

A current source is connected between the ground line and switchably to a second input of the first operational amplifier and to a first input of the current sensing resistor.

[000431 The plurality of probe card units can both be used to measure current and voltage as follows. A first one of the probe card units as adapted to inject current into the surface of the organ at a first position. A second one of the probe card units is adapted to measure the flowing current about the organ and the voltage about the organ at a second position and further ones of the probe card units are adapted to measure the voltage at further positions. In other words the current is only measured between two of the probe card units, whereas the vohage about the organ is measured at multiple probe card units. The function of the probe card units can be easily controlled by software. However, there are instances where it may be desired to inject the current by more that one current electrode so as to form a complex resultant waveform.

BRIEF DESCRIPTION OF THE DRAWINGS

[000441 The invention will be better understood from the following description when taken in conjunction with the accompanying drawings. EIT and EIS (both hereinafter generically described as EIT for ease of description) is not to be understood as the only application of this invention.

[00045] FIG. 1 is a simplified block diagram of prior art of an Eli system showing the multitude of electrode wires connected to a multiplexer block, the output of which is connected to the measurement system then to a processing unit.

[00046] FIG, 2 is one exemplary block diagram of the patient side array of probe card units (hereinafter PCIJ) and their interfacing with the patients' scalp and the System Management Processor Unit (hereinafter SMPU), according to the aspects of the present invention.

[00047] FIG. 3 is one exemplary block diagram of the principal sub-blocks within a PCU, according to the aspects of the present invention.

[00048] FIG. 4 is one exemplary block diagram of the SMPTJ, according to the aspects of the present invention.

[00049] FIG. 5 is a novel compact exemplary three terminal electrode assembly that includes distributed processing PCTJ, an adequate number of PCBs that can accommodate the PCU's circuit components, provide electrical interfacing to the electrodes and to the interconnecting cable bus according to the aspects of the present invention, The two voltage electrodes may be conneted together as desired.

[00050] FIG. 6 is an exemplary cranial application of a single of several rows, for ease of description, of the electrode assembly that include PCU units, SMPTJ and the interconnecting cable bus according to the aspects of the present invention.

DETAILED DESCRIPTION

[00051] The FIG. 2 shows a block diagram of the system of the disclosure, For simplicity, only a four node system with current supplied by PCU1 205 and measured at PCU3 211 is illustrated, The element 20 t represents an inner cranial abnormality. The tetra probe electrodes are 202_I, 203, 2023 and 2033 (as all of the PCUs contain similar circuitry, the number after the underscore corresponds to the PCU number). It will be understood that the system can be easily expanded to 8, 16, 32, 64 or more electrodes, [00052] The measurement program can be developed on a host computer 208, which has wireless transmitting and receiving capabilities through an antenna 209, The host computer 208 also has imaging software for recreating the inner image of tissue distribution from measured surface potentials; such imaging software can also be ported to the system management processor unit (hereinafter SIVIPU) 400.

[000531 The requirements at the patient side are the SPMU 400 and an array of nodal probe card units (hereinafter PCUs) such as PCTJI 205, PCU2 210, PCTJ3 211 etc. each bearing two probe electrodes 2021 and 2031, 2022 and 2032 etc. The probe electrodes 2021 and 203_i, 2022 and 2032 of the array of PCUs may be connected as per the standard EEC 10/20 layout for cranial applications of the invention. Each measurement node comprises the two nodal electrodes 202, 203, for the case ofPCU1, one for current injection, one for current reception at PCU3 and the other PCUs for voltage measurement; such that measuring between the nodes realise effectively a tetrapolar electrode arrangement e.g. 202_i, 2031, 2023, 2033.

[00054] The PCUs 204, 205, 210, 211 etc. are also linked by the interconnecting bus 212. Each one of the PCUs 204, 205, 210, 211 comprise signal lines 301, 302. 303, 304, 305, 306, 307, 308 (as shown on Fig. 3), the functions of waveform generation 315, voltage controlled current source (hereinafter VCCS) 316, instrumentation amplifiers 318, 319 filters 320, 321, calibration RC networks 329, current sensing resistor 317, digitally controlled solid state switches 322, 323, 324, 325, 326, 327, 328, a local processor 314 with current and voltage measurement ADCs and data storage capabilities, and other supporting components for biasing and for obtaining functionality of each sub-block details of which a person skilled in this discipline would appreciate.

[00055] The analogue ground (AGND) signal line 306 and the analogue supply signal lines (AVCC+ 305 and AVCC-307) connections are shown in the Fig. 3. A spare signal line 304 is shown which may be required as a power up signal or synchronising signal. Separating the AGND signal line 306 from a digital ground (DGND) signal line 308 improves the noise performance of the system. These GNDs, i.e. the AUND arid the DGND, may be connected for example at the SMPU.

[00056] There are two probe electrodes labelled, Ii 2021 and Vi 203_i which are shown to contact the skin at node 1. The probe electrode Ii 202 can be programmed to sink or source currents depending on the positions of the electronic switches SWIA to SW1 312, [00057] The output of the waveform generator 315 is connected to the VCCS 316, which is as an example a modified Howland circuit. The amplitude of the current programmed by design does not exceed the safe limit of 100 MA rms below t kHz, and this safe limit increases by 0.1 mA per kHz up to a maximum of 10 mA rms for frequencies beyond tOO kHz. The amplitude, frequency and waveform of the current can be programmed.

With the electronic switches, SWIA 322 and S\Vic 324 closed and SWIB 323 and SWW 326 open, the programmed sinusoidal current will flow from the VCCS 316 through the precision current sensing resistor RS 1 317 and appears across the differential inputs of the gain programmable instrumentation amplifier 318 ADC] 3 1 therefore measures the amplitude and time variation of the sending current.

[00058] At the current receiving end, say the probecard unit at node 3 2 t t, the switches SW1B 323, SW1D 326 are closed and the switches SW1A 322 and SW1c 324 opened.

The sinusoidal current flows through 202_3 then the current sensing resistor RS 1 317 and then to the analogue ground line 316. The sending and receiving current values can thus be measured by the respective ADCs, stored, copied to the SMPU and also compared for fail safe current amplitude control, In this illustration, the PCUI sending node voltage is measured by Vi 203_i after closing SW1E 325. At the receiving side, in this example at PCU3 211, the voltage is received at Vi 2033 converted to digital data and stored for eventual transmission to the host via the SMIPU 400. The system configuration permits all other node voltages at the probe electrodes to be synchronously measured without activating their current sink switches. Synchronous measurements permit the amplitude and phase of the sending current and voltage to be compared with those at the other node positions.

[00059] For the single signal stimulation case, the PCU at one of the nodes will be in the current stimulation mode, while one of the PCUs in the current sinking mode with the resistor 317 selected. The other ones of the PCUs are in voltage measurement mode with resistor 317 not selected. This current and voltage measurements procedure is repeated for different frequencies in the desired frequency range. Another current stimulation (and if desired, sinking) node then undergoes the same current and voltage measurement procedure at the other PCUs. A complete set of data is collected after all of the nodes in turn singly act as the current stimulating node and the surface voltage distribution for each case measured and recorded.

[000601 The voltage gain of each instrumentation amplifier 318, 319 can be adjusted for adequate signal levels by selecting the value of the external resistor as detailed in their product specification. Matching of readings of the multiple current sources at each PCU, is achieved through the use of matched 0,1% sense resistors as recommended by (Boone & Holder, 1996). The output of the instrumentation amplifier 318 represents the magnitude of the injected current; this output is passed through the filter 320 and is sampled by an ADC 311 of the PCU's local processor 314 at a high enough frequency such that the phase information with the surface voltage can be computed with the desired precision. The output of the second instrumentation amplifier 319 represents the magnitude of the surface voltage and is similarly sampled and converted to digital data and stored for eventual transmission to the host via the SMPU 400. After all the data stored by the PCUs local processors 314 are passed on to the SMPIJ 400 for data storage, computations, and optionally transferred over by wireless signals with the host computer 208 or other intelligent display devices.

[00061] The function of the SMPU 400 is to interface with the host processor 208 and the array of PCUs 205 microcontrollers at the measurement nodes. The SMPU 400 shown in Fig. 4 comprises a system microcontroller unit 401 with digital signal processing capabilities, non-volatile storage memory 406, an RF transceiver 402, antenna 407, LCD, LED, audio indicators 403, power management circuits 404 and the power source 405 for all the nodal PCUs, [00062] The host computer 208 transmits by wireless means the programme detailing calibration sequences, current magnitudes, frequencies, measurement electrode signal injection electrode configurations, measurement sequences and other requirements to the SMPU 400 where the requirements are stored. The SMPU 400 manages the communication with the host processor as well as for all PCU node operations.

[00063] On acquiring the measured surface voltages distribution data and the injected current data from the each of the nodal PCU 205, the SMPU 400 also derives (e.g. by quadrature detection and computations) Cole-Cole tissue parameters; stroke type is extracted from the measured information and the SMPU displays system status and its findings via LCD, LED and or Audio means 403 and also passes the data over to the host computer 208 where the specialised imaging and other algorithms reside, for imaging and archival purposes. Implementing Bluetooth protocol also permits imaging data derived by the SJVIPU 400 to be passed over to PDAs, smartphones and devices with such protocols.

[00064j One embodiment of the probe card unit (PCU) is illustrated in Fig. 5, The components defined for each node are contained in element 500. These components are mounted on the printed circuit boards (PCBs) 501 and 502 or other workable supports, in order to realise the electrical circuit of the PCU; these PCBs may be double sided with several interconnecting layers. For compactness component assembly directly onto the PCBs or multi-chip packages 512 that house integrated circuits and passive components may be used. Although two PCBs 501 and 502 are shown, more of the PCBs may be required to accommodate all the components. The bottom PCB 502 sits on an interchangeable base unit 503 that connects the large current electrode 506 and the small voltage electrodes 505, 507 to the circuit inputs 202 and 203 respectively. The small voltage electrodes 505 and 507 are acceptable as the input current to the voltage measuring operational amplifiers are very small.

A housing unit 508 electrically separates the electrodes 505, 506, 507. The housing unit 508 furthermore is designed to permits gel or dry skin contacting of the small voltage electrodes 505 and 507 as well as the large current electrode 506.

[000651 Calibration is carried out by opening the switches 324, 325 to isolate the circuit from the tissue and closing the stches 327 328 and running the calibration software for representative tissue networks in a calibration controller 329. Switches for connection to the VCCS 316 and amplifiers 318, 319 are programmed appropriately.

[000661 It is envisaged that components within 310 are integrated into a front end ASIC chip for performance and compactness. The power management block 404 assures all correct voltage levels are available for the chips, references and manages the powerdown and current reduction modes. Low dropout linear regulators can be used -if needed-for intermediate voltages instead of switching regulators which can introduce noise and degrade the SNR. The power source 405 can be, e.g., 2x 3.6 V. I Ah lithium coin cells, one for each of a positive and a negative rail, A screened switched mode regulator at the SMPIJ allows generation of the negative rail voltage thereby making the requirement for only one cell at the patient side.

[000671 The main advantages of this proposed system over those described in the literature are outlined as follows: [000681 There are no multiplexing of the electrodes from skin contact to the measurement system, hence one cable per node is not needed and there is therefore no large cable bundle or capacitance on the current sources and surface nodes under measurement are not present. Such capacitances often lead to complex cable screen charging schemes.

[000691 Cerebral surface voltages can be measured in parallel; this greatly reduces the acquisition times by a factor of the number of electrodes, e.g., for say a 48 electrodes arrangement, the acquisition time at each measured frequency is reduced from 80 secs to a few seconds, This parallel measurement system has a potential for improved SNR.

[00070] Autonomous (no host required) for yes-no and type of stroke detection from positioning and spacing of the PCUs and making local analysis of the volume conductivity levels and locations and correlate with tissue types.

[00071] The SMPU can send data wirelessly to a host for more in-depth processing of the volume conductivity permifting an image of the inner tissue to be derived and displayed.

The host can also distribute and archive the results, [00072] There are two electrodes at each node interconnected by a set of conductors, This arrangement enables a tetrapolar measurement system where the probe contact impedances and their variations has less effect on the results.

[00073] The system can be easily (re-)programmed for new sequences for injecting the current, and collection of the measured boundary surface voltages.

[00074] The system permits simultaneous current injection into multiple electrodes, The injected currents can also be analysed so any amplitude and/or phase effects of the current generators is recorded and can be compensated.

[00075] An original interchangeable original dual electrode probe contacting distributed processing system is described that does not require a power source at each node.

[00076] The system is easily adaptable for the acquisition of EEG data that can give functionality of inner areas of the brain.

[00077] The system is fbrthermore easily adaptable to neonatal heart, liver and lung, adult heart, liver and lung and other organs through the use of say of a belt electrode assembly. The belt electrode assembly comprises a plurality of PCUs placed on a fabric belt.

The fabric belt can be adjusted in size to encompass adults, children and babies as well as neonates, The size of the fabric belt can also be adj usted to the part of the body of interest, A waist, for example, requires a larger fabric belt (with more PCU5) than the chest.

[00078] The belt array of electrodes can additionally be programmed for electrocardiogram data storage for analysis and display.

[00079] One example of the belt array is shown in Fig. 6 which illustrates the belt array 600 placed about the cranium of the patient and can be used to measure brain function as well as identify strokes, The drawing is not to scale The belt array 600 comprises a plurality of current electrodes 202 and 506 and voltage electrodes 203 and 505 as well as a plurality of microprocessors 314. The SMPU 400 is also mounted on the fabric belt 600 and is connected to eight probes in this non-limiting example. The SMPU 400 is connected wirelessly to the remote processor 208, The SMPU 400 is used to receive all of the measurements from the current electrodes 202, 506 and the voltage electrodes 203, 505 rather than having a plurality of data transmitters mounted on the fabric belt.

Claims

Claims A system for the monitoring organs comprising: a first current electrode (2021, 506_i) for injecting a current into the monitored organs; a second current electrode (2022, 506_2) for sinking the injected curent; at least one pair of voltage electrodes (203, 505) for measuring voltages in the monitored organs synchronously with the in] ection of the current; a remote processor (208) connected to the first current electrode (202_I, 506_I), the second current electrode (2022, 5062) and the at least one pair of voltage electrodes (203, 505) for creating a result of the monitored organs based on the measured currents and voltages.
2 The system of claim i, further comprising: a first microprocessor (3i4) connected to the first current electrode (2021, 506_i) for controlling the injection of the current and a first one of the pair of voltage electrodes (2031, 505t) for the monitoring of the inj ected voltage; a second microprocessor (314) connected to the second current electrode (2022, 5062) and a second one of the pair of voltage electrodes (2032, 5052) for controlling the measurement of the surface voltages around the monitored organs; and a local data transmitter (407) connected to the first microprocessor (3 t4) and the second microprocessor (3 t4), the local data transmitter being connectable to the remote processor (208).
3 The system of claim 2, further comprising a system processor (400) connected to the first microprocessor (314) and the second microprocessor (314) and the remote processor (208).
4 The system of claim 3, wherein the connection between the system processor (400) and the remote processor (208) is a wireless connection.
The system of claim 2, further comprising of a plurality of additional microprocessor units (204, 205, 210, 211) connected to further pairs of voltage electrodes for the synchronous measurement of the surface voltages at a plurality of locations around the monitored organ.
6 The system of any one of claims 2 to S further comprising a system controller (401) connected to the local data transmitter (407).
7 The system of any of the above claims, wherein the remote processor (208) comprises a plurality of software modules having logic instructions to operate the system for identification of medical issues.
8 The system of claim 6, wherein the medical issues comprise at least one of detection of tumours, strokes, lung functions, liver frmnctions, heart and brain functions.
9 The system of any of the above claims further comprising a sinusoidal current generator for generating the current at a plurality of frequencies.
The system of any of the above claims, wherein the result is an image.
11 A method for monitoring organs comprising: injecting a current at a first position into the organs to be monitored; measuring changes synchronously in currents and voltage at further positions about the monitored organ; using the measured changes in the currents and the voltage to create a result of the organs.
12 The method of claim 11, wherein the injection of the current is at a single or plurality of frequencies.
13 The method of claim 11 or 12, wherein the creation of the result is a creation of an image.
14 The method of one of claims 11 to 13, further comprising comparing the computations using the measured currents and the voltages with threshold values to indicate a medical issue.
The method of any one of claims t 1 to t4, further comprising measuring the current and voltage at a second position.
16 The method of any one of claims ii to 15 further comprising measuring the voltage at third and further positions.
17 A plurality of probe card units for placing on the surface around an organ to be monitored where at least one of the probe card units comprises: a first electrode (202) connected switchably to a first input of a first operational amplifier (318) and a second input of a current sensing resistor (317); a second electrode (203) connected to a first input of a second operational amplifier (3 t9), wherein the second input of the second operational amplifier is connected to a ground line (306); a local processor (314) connected to the output of the first operation amplifier (318) and the second operational amplifier; -a current source (316) connected between the ground line (306) and switchably to a second input of the first operational amplifier (3 18) and to a first input of the current sensing resistor (317).
18 The plurality of probe card units of claim 17, wherein first one of the probe card units as adapted to inject current into the surface of the organ at a first position, a second one of the probe card units is adapted to measure the flowing current about the organ and the voltage about the organ at a second position, and further plurality of the probe card units are adapted to measure the voltage at the plurality positions.