WO2015136238A1

WO2015136238A1 - Measuring and recording body electrical potentials

Info

Publication number: WO2015136238A1
Application number: PCT/GB2015/050395
Authority: WO
Inventors: Edwin David BYE; Martin Andrew FOREMAN; Ryan James BYE; Megan Marie GLOSTER; Lesley Meredith TURLEY
Original assignee: Bye Edwin David; Foreman Martin Andrew
Priority date: 2014-03-14
Filing date: 2015-02-12
Publication date: 2015-09-17
Also published as: GB2524080B; GB2524080A; GB201404548D0

Abstract

A device (100) for measuring and recording electrical potentials for an area of the body of a subject (124). The device (100) comprises a reference probe (102) for locating at or near a reference location for the body of a subject (124), a measuring probe (104) for locating at or near a plurality of different locations of an area of the body of the subject (124), and processing circuitry (106) in communication with the reference probe (102) and the measuring probe (104). The processing circuitry (106) is configured to measure and record, in association with each particular location of the plurality of different locations, a potential value that is based on a potential difference measured between the reference probe (106) and the measuring probe (104) when the reference probe (106) is at or near the reference location and the measuring probe (104) is at or near that particular location. The device (100) can be used to provide spatial information about the electrical properties of the body of a subject (124).

Description

MEASURING AND RECORDING BODY ELECTRICAL POTENTIALS

The present invention relates to a device for and a method of measuring and recording electrical potentials for an area of the body of a subject.

It is well known that the measurement of electrical activity produced by human bodies can be used to monitor and identify medical conditions and abnormalities. For example, electrocardiography (ECG) is the measurement of temporal variations in the electrical activity of the heart. In electrocardiography, electrodes are placed at various places on the body, primarily on the chest, and a trace of the heart's electrical activity is recorded. Expert analysis of the recorded trace can reveal certain medical conditions or abnormalities. Similarly, electroencephalography (EEG) is the measurement of temporal variations in the electrical activity of the brain. In scalp electroencephalography, a large number of electrodes may be placed on the scalp so that the brain's electrical activity can be recorded and then analysed. Also, electromyography (EMG) is the measurement of temporal variations in the electrical activity of one or more muscles. In surface electromyography, a number of electrodes may be placed on the skin so that muscular electrical activity can be recorded and then analysed.

The above approaches primarily provide temporal information about electrical activity produced by the human body. It is a principal aim of this invention to provide arrangements by which further useful information can be derived from the electrical properties of the bodies of human or animal subjects. Thus, according to an aspect of the present invention there is provided a device for measuring and recording electrical potentials for an area of the body of a subject, the device comprising:

a reference probe for locating at or near a reference location for the body of a subject;

a measuring probe for locating at or near a plurality of different locations of an area of the body of the subject; and

processing circuitry in communication with the reference probe and the measuring probe, the processing circuitry being configured to measure and record, in association with each particular location of the plurality of different locations, a potential value that is based on a potential difference measured between the reference probe and the measuring probe when the reference probe is at or near the reference location and the measuring probe is at or near that particular location.

The present invention also extends to methods of measuring and recording electrical potentials using a device as describe herein.

Thus, according to another aspect of the present invention there is provided a method of measuring and recording electrical potentials for an area of the body of a subject using a device as described herein, the method comprising:

locating the reference probe at or near a reference location for the body of a subject;

locating the measuring probe at or near a plurality of different locations of an area of the body of the subject; and operating the device such that the processing circuitry measures and records, in association with each particular location of the plurality of different locations, a potential value that is based on a potential difference measured between the reference probe and the measuring probe when the reference probe is at or near the reference location and the measuring probe is at or near that particular location.

It will be appreciated from the above that the present invention can be used to provide spatial (rather than temporal) information about the electrical properties of the body of a subject, which spatial information may, for example, be output for spatial presentation using a presentation device or for storage for later spatial presentation or analysis. In particular, the association made by the processing circuitry between potential values and their corresponding locations provides spatial information that can assist in the identification and location of medical conditions and abnormalities, such as breast and gynaecological conditions, muscular disorders, joint issues, wound healing, skin lesions, scar tissue, organ conditions, etc. The spatial information can also assist in the monitoring of medical conditions and abnormalities over time, assist in locating medical features and abnormalities (e.g. prior to an operation being carried out on the subject), or assist in monitoring the effectiveness of treatment or progression of a disease, condition, etc.. Furthermore, the present invention allows such spatial information to be obtained accurately, conveniently and quickly, and with very few contraindications. The approach used is also passive and, in some embodiments, is non-invasive. Such spatial information can therefore be obtained many times over without causing harm to the subject. The subject may be animal or human and the measurements may be taken from the area of the body in vivo or in vitro. The area of the body of the subject (and the various "locations" mentioned above) may be on the skin of the subject, and/or transcutaneous, and/or sub-dermal, and/or on or in an organ of the subject, and/or may be partially or completely within a cavity of the subject (e.g. vaginal cavity, rectal cavity, oral cavity (mouth), nasal cavity, ocular cavity etc.).

The reference probe is preferably electrically connected to the measuring probe via potential difference measuring circuitry. The potential difference measuring circuitry may comprise one or more analogue to digital converters (ADCs). The communication of the processing circuitry with the reference probe and the measuring probe may comprise wired or wireless communication, and so the potential difference measuring circuitry may or may not be electrically connected to the processing circuitry.

It will be appreciated from the above that each potential value that is recorded in the present invention will represent a substantially invariant (or "background") electrical potential for the location in question. Thus, each potential value may be based on a single (e.g. absolute and/or substantially DC and/or low-pass filtered) potential difference measured for the location in question, or on an average (e.g. mean average) of plural potential differences measured for the location in question, or on a root-mean-squared (rms) of plural potential differences measured for the location in question. In embodiments in which each potential value is based on plural potential differences, the number of plural potential differences for each potential value is preferably at least 10, 100, 1 ,000, 10,000 100,000, or 1 ,000,000 potential differences.

The potential values may each be derived by subtracting an offset (e.g. a lower or minimum potential difference measured for the plurality of different locations) from a potential difference measured for the location in question. The potential values may instead each be derived by subtracting a potential difference measured for the location in question from an offset (e.g. an upper or maximum potential difference measured for the plurality of different locations).

The different locations may be identified by the processing circuitry with reference to a two-dimensional or three-dimensional space. A single measurement or, more preferably, a plurality of measurements may be taken at each location. The plurality of measurements for each location may be processed (e.g. averaged) to give a measurement for that location. Data reconstruction (e.g. forward and/or backward projection) may be used in situations where insufficient measurements for a particular location are made.

The number of different locations that constitute the plurality of different locations will depend on the particular application. However, the number of different locations will typically be at least 10 different locations, but may be many more than this, such as at least 100, 1000, 10,000, 100,000 or 1 ,000,000 different locations. In one embodiment, there are 800x600 (480,000) different locations). The different locations may each correspond to a uniform or nonuniform shaped region of the area of the body. The shapes of the regions preferably tessellate, preferably such that the regions entirely cover the area of the body without substantial gaps or overlapping therebetween. The shapes of the regions are preferably the same size as one another. The shapes of the regions are preferably square.

In preferred embodiments, the reference probe comprises one or more electrodes for electrically contacting the body of the subject at the reference location and/or the measuring probe comprises one or more electrodes for electrically contacting the body of the subject at the plurality of different locations. The electrode of the reference probe and/or measuring probe may comprise, for example, a cup-disc, a plate, a needle, a wire loop, a ball, a hemisphere, etc.

The measuring probe may be moved in use and may, for example, be a stylus having a ball or hemisphere electrode or other suitably shaped electrode for movement across the area in question. Conversely, the reference probe preferably is not moved in use and may have, for example, a cup-disc, a plate, a needle or a wire loop electrode. The reference probe may comprise a self- adhesive pad, with the reference probe being attachable to the body of the subject at the reference location using the self-adhesive pad. In other embodiments, the reference probe may be held in place with adhesive tape, adhesive (e.g. collodion), an elasticated or non-elasticated strap, or an elasticated or non-elasticated band, or may be of the needle, plate or wire loop style or other suitable shape for insertion into and/or retention on or in the body or in a body cavity.

In some embodiments, the reference probe and/or measuring probe has a means for controlling and/or monitoring the contact force to ensure a consistent level of contact with the skin or body is obtained. This means may be a mechanical or electrical pressure switch, force transducer or load cell.

In alternative embodiments, the reference probe may comprise an electric field sensor for sensing the electric field near the reference location and/or the measuring probe may comprise one or more electric field sensors for sensing the electric field near the plurality of different locations. In these alternative embodiments, the reference probe and/or measuring probe may not actually contact the body of the subject at the locations but may merely be near (e.g. directly above) those locations.

In preferred embodiments, the reference location is not within, or even in proximity to, the area of the body having the different locations. In preferred embodiments, the reference location is at or near to a location that is electrically quiet and relatively free from spontaneous muscle movement, such as on or near to the coccygeal bone. Midway along the coccygeal bone has been found to be a particularly electrically quiet and motionless location of the body, which is generally not within or near to the area of the body having the different locations.

In preferred embodiments, the measuring probe comprises a single electrode or electric field sensor for sequentially measuring the potential differences for the plurality of different locations. In these embodiments, the measuring probe is moved from one of the different locations to the next. However, in other embodiments, the measuring probe may comprise an array of plural electrodes or electric field sensors for simultaneously measuring the potential differences for the plurality of different locations. In these other embodiments, the potential difference measuring circuitry may comprise at least one analogue to digital converter (ADC) for each electrode in the array of plural electrodes. Alternatively, the potential difference measuring circuitry may comprise a multiplexing arrangement to measure the potential differences for the plurality of different locations. These other embodiments allow potential differences for the plurality of different locations to be measured rapidly. In these other embodiments, having taken measurements for the first plurality of different locations for the area of the body, the measuring probe may still later be moved to a different place within the area of the body in order to measure potential differences for a second plurality of different locations for the area of the body.

In any of the above embodiments, the measuring probe may be moveable by hand between different locations or places of the area of the body. The processing circuitry may also or instead be configured to control the movement of the measuring probe between different locations or places of the area of the body either under the remote control of an operator of the device or automatically according to a predetermined path. The movement of the measuring probe between different locations or places of the area of the body may be achieved by fixing the subject and moving the measuring probe, or by fixing the measuring probe and moving the subject (e.g. by moving a support for the subject or a table on which the subject is placed), or by a combination of these approaches.

In preferred embodiments, the processing circuitry is configured to determine the particular location to be associated with each potential value by determining the location of the measuring probe relative to the area of the body. This determination may be achieved in a number of ways. For example, the measuring probe may comprise an accelerometer, the determination being achieved using an output from the accelerometer. Alternatively, the measuring probe may comprise optical (in the visible or non-visible spectrum) tracking means (e.g. an LED and/or photodiodes), and/or acoustic tracking means, and/or electromagnetic tracking means, and/or mechanical tracking means (e.g. a roller), the determination being achieved using an output from the tracking means. The determination may also or instead be achieved by using an output from a camera and by using image processing techniques. The output may be a single frame (e.g. an image) or a series of frames (e.g. a video). The camera may or may not form part of the device. Alternatively, the processing circuitry may be aware of a predetermined path which the operator or processing circuitry will take when moving the measuring probe between the different locations or places. An indicator, marker or template (e.g. an open grid) may be provided on the area of the body to assist or guide the operator in following the predetermined path. Alternatively, a virtual representation may provide this guiding function.

In some embodiments, the processing circuitry is configured to measure and/or record each potential value in response to an indication that the measuring probe is near to or has contacted the area of the body. For example, the indication may be provided by: a manually operable button for the device (e.g. a button on the measuring probe or a foot peddle); or a mechanical or electrical pressure switch, force transducer or load cell for the measuring probe (e.g. the above-described means for controlling and/or monitoring the contact force) upon measuring a pressure that is above a threshold pressure value or between threshold pressure values; or measuring a potential difference that is above or below a threshold potential value.

In preferred embodiments, the processing circuitry is configured to assign a presentation value (e.g. a luminance value or brightness value) or set of presentation values (e.g. a set of colour coding values such as RGB values, YUV values, etc.) to the potential value associated with each particular location and output the presentation values to a presentation device or storage device. The presentation device may present the presentation values as the potential values are being recorded, for example so as to indicate to the operator the amount of the area of the body that has already been measured. Alternatively, the presentation device may present the presentation values once some or all of the potential values for the different locations are recorded. The processing circuitry may also or instead be configured to provide for each of the plurality of locations a visual representation of the number of measurements taken at the location in question and output the visual representation to a presentation device or storage device. This approach can guide the operator in knowing which locations have been covered, but also how thoroughly each location has been covered. The visual representation may be a presentation value or set of presentation values, for example taken from a monochromatic scale (e.g. grey- scale) or polychromatic scale (e.g. electromagnetic scale) that is mapped (e.g. logarithmically, linearly, etc.) to the number of measurements for the location in question. As will be appreciated, the presentation location (e.g. pixel(s)) or paper location used by the presentation device (e.g. display screen or printer) to present the visual representation of the number of measurements taken at each particular location is based on or corresponds to that particular location. Similarly, the storage location (e.g. position in an array) used by the storage device to store the visual representation of the number of measurements taken at each particular location is based on or corresponds to that particular location.

As will also be appreciated, the presentation location (e.g. pixel(s)) or paper location used by the presentation device (e.g. display screen or printer) to present the presentation value or set of presentation values for the potential value associated with each particular location is based on or corresponds to that particular location. Similarly, the storage location (e.g. position in an array) used by the storage device to store the presentation value or set of presentation values for the potential value associated with each particular location is based on or corresponds to that particular location.

The processing circuitry may be configured to assign the presentation value or set of presentation values to the potential value associated with each particular location using a range of potential values that are mapped to a scale of presentation values or a scale of sets of presentation values (these scales may be referred to herein as "presentation" scales). The range of potential values for the mapping may be predetermined and/or may be selectable by an operator of the device. The range of potential values for the mapping may be based on or may be between a lower, e.g. minimum, potential value and an upper, e.g. maximum, potential value recorded for the plurality of different locations. Alternatively, the operator may select a lower and/or upper potential value for the range. The presentation value scale may be monochromatic (e.g. a greyscale or brightness scale) or polychromatic (e.g. a "colour" spectrum, such as part of or the entire visible electromagnetic spectrum). The mapping of the scale (e.g. the wavelength values, luminance values, brightness values, presentation values, etc., of the scale) to the potential values may be linear, logarithmic, etc. The mapping may be an inverse mapping.

In alternative embodiments, one or more threshold potential values may be used to assign a presentation value or set of presentation values to potential values. For example, a single threshold potential value may be used to assign either a first presentation value or first set of presentation values, or a second presentation value or second set of presentation values, to a potential value. In general, where there are "n" threshold potential values there may be "n+1 " presentation values or sets of presentation values to which a potential value can be assigned. The threshold potential value(s) used and/or presentation values or sets of presentation values used may be operator selectable. The threshold potential value(s) may be positive, negative or zero.

In alternative embodiments, the processing circuitry may be configured to generate presentation values for the contours of an equipotential map from the potential values associated with the particular locations, and output the presentation values to a presentation device or a storage device.

In any of the above embodiments, the presentation device or storage device may or may not form part of the device. Furthermore, the recording (storing) of each potential value and/or associated location by the processing circuitry prior to outputting the presentation values may be temporary or may be persistent. The presentation device may be, for example, a display screen, projector, printer, etc. The storage device may be, for example, a floppy disc, a hard-drive, a CD, a DVD, non-volatile memory, etc. The format of the data to be stored may be a DICOM format, which can be used in other medical imaging systems.

To orientate the operator, the processing circuitry may be configured to overlay the presentation values either on an (e.g. digitally stored) image (photograph, x-ray, MRI scan, etc.) of the body part that includes the area in question or on a representation of the body part that includes the area in question. The representation (or another regular or irregular shape) may be used as a virtual "mask" that limits the area within which potential values are or can be recorded. The representation of the body part may be a silhouette of the body part or an outline of the body part. The representation may be predetermined and imported from a storage device. The format of the representation may be a DICOM format. Alternatively, the processing circuitry may be configured to derive the representation of the body part from an image of the body part captured by a camera, for example using edge detection and/or using chroma-keying. As discussed above, the camera and/or storage device may or may not form part of the device. In other embodiments, the processing circuitry may be configured to overlay the presentation values onto the area of the body itself (e.g. using a projector). This may be useful as a guide for surgery or other procedures, such as aspiration, drug delivery, biopsy, etc. In embodiments having a camera, a means for calibration (e.g. to correct or compensate for camera position, lens aberrations, etc.) may be provided as part of the processing circuitry. For example, a calibration board, e.g. having black and white squares of known size (e.g. a chequer board), may be placed on the body in the field of view of the camera to enable calibration steps to be taken by the processing circuitry. The calibration board may be placed at various angles and rotations to enable the calibration. Also, in embodiments having a camera, it may be desirable to make virtual distance measurements using the presentation output of the presentation device. Therefore, a similar calibration procedure can be used to scale physical (of the body) distances to virtual (presentation device) distances.

Also, in embodiments having a camera, a means for compensating for movement of the camera or movement of the area of the body may be provided as part of the processing circuitry. The processing circuitry may then, for example, continue to appropriately map the physical locations of the area of the body that correspond to the potential values to virtual locations used by the presentation device to present those potential values, despite small movements of the area of the body and/or camera. For example, the processing circuitry may have means for applying a weighted function to determine the coordinates of a centroid of an initial image captured by the camera and means for tracking the coordinates of the centroid in later images. Movement of the centroid in later images can then be interpreted by the processing circuitry as a corresponding movement of the area of the body. The virtual locations used by the presentation device to present the potential values that are obtained subsequent to a movement of the camera and/or area of the body can then be adjusted accordingly. In an alternative example, rather than using a centroid, the processing circuitry may have means for tracking the coordinates of two known and recognisable points or markers for the area of the body.

In embodiments, the processing circuitry may include means for controlling the functions of the camera. The functions that can be controlled may include, for example, white balance, gain, focus, shutter speed etc. The processing circuitry may include means for controlling the positioning, rotation and/or angle of the camera, for example so as to achieve a desired orientation.

In embodiments, the processing circuitry may comprise means for presenting or storing text, lines and/or markers with the presentation values, for example to indicate anatomical features or other features of interest. The style, e.g. size, colour, shape and/or appearance (dotted, dashed, solid, etc.), of the text, lines and/or markers may be adjustable.

In embodiments, the processing circuitry may comprise means for enhancing a region of the presentation values using regular (e.g. rectangular or circular) geometric shapes or irregular shapes so as to focus only on that region. The processing circuitry may comprise means for zooming in so as to magnify either all of the presentation values or a selected region of the presentation values.

In embodiments, the processing circuitry may comprise means for processing the presentation values to reduce resolution to achieve a compromise between scanning time and detail. Some smoothing or averaging may also be applied to blur edge transitions between regions of the presentation values that provide different appearances. In embodiments, the processing circuitry may comprise means for altering the overall appearance of the presentation values, e.g. means for adjusting the brightness, contrast, colour balance and/or for applying filters.

In embodiments, the processing circuitry may comprise means for including statistical data (e.g. a histogram) of the potential differences or potential values with the presentation values and/or for including a scale specifying the correspondence of potential differences or potential values to the presentation values.

Any of the above means may be under the control of the operator or may be automatic means.

In any of the above embodiments, to appropriately illuminate the area of the body for the image of the body part, which includes the area to be captured, the processing circuitry may be configured to automatically control one or more light sources. The one or more light sources may or may not form part of the device.

By way of example only, embodiments of the invention will now be described in detail with reference being made to the accompanying drawings in which:

Figure 1 shows a device for measuring and recording electrical potentials according to an embodiment of the present invention;

Figure 2 illustrates a method of using the device of figure 1 ; Figure 3 shows a first exemplary result obtained using a device for measuring and recording electrical potentials according to an embodiment of the present invention; and

Figure 4 shows a second exemplary result obtained using a device for measuring and recording electrical potentials according to an embodiment of the present invention.

Figure 1 shows an overview of a device 100 for measuring electrical potentials for an area of skin of a subject 124. The device 100 includes a reference probe 102, a measuring probe 104, and processing circuitry 106.

The reference probe 102 has an electrode that is attached to the body of the subject 124 at a reference location. In this embodiment, the reference location is midway along the coccygeal bone of the subject 124. The reference probe 102 comprises a disc-cup, which is attached to the skin of the subject 124 with adhesive tape to hold the reference probe 102 in place.

The measuring probe 104 has a stylus electrode that contacts a plurality of different locations on an area of skin of the subject 124. The measuring probe 104 is moved by the operator by hand between the different locations on the area of skin. However, in other embodiments, the movement of the measuring probe 104 may be remote controlled or automated via the processing circuitry 106.

The processing circuitry 106 comprises measurement circuitry 108, movement circuitry 1 12, synchronisation circuitry 1 10, control circuitry 1 14 and illumination circuitry 120. The reference probe 102 and the measuring probe 104 are electrically connected to the measurement circuitry 108. The measurement circuitry 108 is configured to measure the potential difference between the reference probe 102 and the measuring probe 104 and provide potential values based on the potential difference to the control circuitry 1 14. In this embodiment, plural potential difference measurements are taken for each location using an analogue to digital converter (ADC) of the measurement circuitry 108. The plural potential difference measurements for each location are mean averaged by the measurement circuitry 108 to give a potential value for that location.

The measuring probe 104 is also in communication with the movement circuitry 1 12. The movement circuitry 1 12 is configured to determine the location of the measuring probe 104 on the area of skin and provide two dimensional location co-ordinates for the measuring probe 104 to the control circuitry 1 14. In this embodiment, the measuring probe 104 comprises an accelerometer, the output of which is used to track the location of the measuring probe 104. Alternatively, a digital camera 1 18 may output a video that shows the movement of the measuring probe 104. Imaging processing techniques may then be used to track the location of the measuring probe 104.

In response to the operator pressing a button on the measuring probe 104, the control circuitry 1 14, via the synchronisation circuitry 1 10, instructs the measurement circuitry 108 to take potential difference measurements and instructs the movement circuitry 1 12 to provide location co-ordinates for associating with the resultant potential value. The measurement circuitry 108 then provides the resultant potential value to the control circuitry 1 14 and the movement circuitry 1 12 provides the associated location co-ordinates to the control circuitry 1 14. The control circuitry 1 14 then records the potential value in association with the location co-ordinates. The operator of the device 100 then moves the measuring probe 104 to another location on the area of skin. This process of measuring and recording is repeated at different locations on the area of skin until a desired and suitable number of potential values and associated locations are recorded for the area of skin.

As the potential values and associated locations are being obtained, the control circuitry 1 14 assigns a set of RGB presentation values to each of the recorded potential values. In this embodiment, this is done by mapping each recorded potential value to a polychromatic scale in the form of the visible electromagnetic spectrum. This mapping produces an "electrical potential map" for the area of skin, which can be output to a display screen 1 16.

In this embodiment, the electrical potential map is overlaid on a silhouette representation of the body of the subject 124. The silhouette is derived from an image of the body of the subject 124 that is obtained using the camera 1 18. The camera 1 18 is under the control of the control circuitry 1 14 and provides digital images to the control circuitry 1 14 for processing. The control circuitry 1 14, via the illumination circuitry 120, is also able to adjust the light level by automatically controlling the output of a light source 122 so that a suitable amount of illumination of the subject 124 is provided.

The process 200 of deriving the silhouette representation of the body and overlaying the electrical potential map will now be explained with reference to figure 2. Initially, in step 202, any surrounding equipment and parts of the subject, except for the subject's back 212, are covered in blue cloth 210. The device 100 is then calibrated by placing a calibration board 220 on the subject's back 212 and taking a calibration image using the camera 1 18. The calibration image is used by the control circuitry 1 14 to scale "real world" distances on the subject's back 212 with distances within images obtained using the camera 1 18 or representations derived by the control circuitry 1 14.

In step 204, the calibration board 220 is removed and an image of the subject's back 212 is obtained. In step 206, any sets of presentation values for the image of step 204 that indicate "blue" are given a set of "black" presentation values 214 using chroma-key thresholding. In step 208, the image of step 206 is transformed into a silhouette 216 by setting any sets of "black" presentation values to be "white" and all other sets of presentation values to be "black". The black area is used as a virtual "mask" to limit the area within which measurements can be taken and displayed, and provides a representation of the subject's body part under investigation, in this case, the back. Finally, in step 210, potential values and locations are acquired as discussed above, and RGB presentation values for one or more maps are progressively built up at the appropriate locations within the silhouette mask 216.

In some embodiments, as shown in figure 2 for step 210, a "coverage" map 218 is progressively shown. This can assist the operator in effecting the scan. For example, RGB presentation values are derived that represent the number of measurements made at each location, and these presentation values are progressively overlaid at appropriate locations on the silhouette 216, gradually forming a coverage map 218 of how well the area has been covered. In these embodiments, the electrical potential map as discussed above may be progressively and concurrently shown together with the coverage map 218. Alternatively, the (completed) electrical potential map may only be provided once sufficient coverage has been obtained, as determined by the operator from the coverage map 218. In other embodiments, in step 210, the electrical potential map may be progressively shown rather than the coverage map 218.

In any of the above embodiments, the electrical potential map can then be used by the operator to identify and locate possible medical conditions and abnormalities.

Figure 3 shows a first exemplary result obtained using a device in accordance with the present invention. In this example, the subject is a female who is aged 59. Eight years prior to this scan, she underwent unilateral skin sparing mastectomy to her left side with immediate reconstruction using tissue removed from her abdomen (the Transverse Rectus Abdominis Myocutaneous flap or "TRAM flap" procedure). The procedure was performed by removing the Areola Nipple Complex (ANC) and working through the opening created. Breast tissue was then removed and replaced with abdominal tissue. Finally, the incision was stitched.

As can be seen in Figure 3, an electrical potential map 318 has been overlaid on a silhouette 316 of the thoracic and abdominal region of the body. Identified at 302 is a region corresponding to the right breast. Similarly, at 304, is a region corresponding to the left breast. It can be seen that the potentials over region 302 are mainly uniform and distinct from the potentials surrounding the right breast. However, over region 304, there is only a small distal area 306 that shows similar potentials to those encountered on the right breast. The remaining area 308 of the left breast, although predominantly uniform in potential, is generally consistent in potential to that of the areas surrounding the breasts, especially as encountered in the abdominal region 310. Thus, a clear divide can be seen between the upper part and the lower part of the left breast.

The electrical potential map 318 of figure 3 illustrates the ability of the device of the present invention to assist in identifying a medical abnormality in breast tissue.

As can also be seen in Figure 3, the device displays an area 312 for providing information relating to the scan, an area 314 for providing statistical information, a scale 320 showing minimum and maximum potentials recorded during the scan, and an area 322 showing the settings that the operator applied when using the device.

Figure 4 shows a second exemplary result obtained using a device in accordance with the present invention. In this example, the subject is a female who is aged 35. Three years prior to this scan, she was diagnosed with a cancerous growth on her right outer breast extending to the axilla and underwent lumpectomy. At the time of scanning she was still on chemotherapeutic agents.

As can be seen in Figure 4, a series of three electrical potential maps 402,404,406 were obtained on the anterior and both lateral thoracic regions of her body. In each case, the electrical potential map 402,404,406 is overlaid on an image of the thoracic region in question. Electrical potential map 402 covers the right lateral thoracic region. The right breast is outlined at 408. At the interface with the chest wall, there is an area 410 that extends to the axilla of differing electrical potentials to that encountered on the right breast. This is the area where cancer was diagnosed and treated by lumpectomy and ongoing chemotherapeutic agents. Electrical potential map 404 covers the anterior thoracic region. The potentials for the breasts 408,412 are clearly distinguishable from the potentials of the abdomen. There is a good degree of uniformness between the potentials of the breasts 408,412. Electrical potential map 406 covers the left lateral thoracic region. The left breast is outlined at 412. On the left breast 412 the potentials are generally uniform, whereas on the right breast 408 different regions of potentials can be seen extending up to the axilla.

The electrical potential maps 402, 404, 406 again illustrate the ability of the device of the present invention to assist in identifying a medical abnormality in breast tissue.

Claims

1 . A device for passively measuring and recording electrical potentials for an area of the body of a subject, the device comprising:

a measuring probe for locating at or near a plurality of different locations of an area of the body of the subject, wherein the measuring probe is moveable by hand between different locations of the area of the body; and

processing circuitry in communication with the reference probe and the measuring probe, the processing circuitry being configured to measure and record, in association with each particular location of the plurality of different locations, a potential value that is based on a potential difference measured between the reference probe and the measuring probe when the reference probe is at or near the reference location and the measuring probe is at or near that particular location, wherein the processing circuitry is configured to determine the particular location to be associated with each potential value by determination of the location of the measuring probe relative to the area of the body.

2. A device as claimed in claim 1 wherein the reference probe comprises one or more electrodes for electrically contacting the body of the subject at the reference location and/or the measuring probe comprises one or more electrodes for electrically contacting the body of the subject at the plurality of different locations.

3. A device as claimed in claim 2 wherein the reference probe and/or measuring probe has a means for controlling and/or monitoring the contact force to ensure a consistent level of contact with the body is obtained.

4. A device as claimed in claim 1 , 2 or 3 wherein the reference probe comprises: a self-adhesive pad, the reference probe being attachable to the body of the subject at the reference location using the self-adhesive pad; a cup- disc; a plate; a needle; and/or a wire loop.

5. A device as claimed in claim 1 wherein the reference probe comprises an electric field sensor for sensing the electric field near the reference location and/or the measuring probe comprises one or more electric field sensors for sensing the electric field near the plurality of different locations.

6. A device as claimed in any one of the preceding claims wherein the measuring probe comprises a single electrode or electric field sensor for sequentially measuring the potential differences for the plurality of different locations.

7. A device as claimed in any one of claims 1 -5 wherein the measuring probe comprises an array of plural electrodes or electric field sensors for simultaneously measuring the potential differences for the plurality of different locations.

8. A device as claimed in any one of the preceding claims wherein the measuring probe comprises a stylus.

9. A device as claimed in any one of the preceding claims wherein the processing circuitry is configured to control the movement of the measuring probe between different locations of the area of the body either under the remote control of an operator of the device or automatically according to a predetermined path.

10. A device as claimed in any one of claims 1 -9 wherein the measuring probe comprises an accelerometer, the determination being achieved using an output from the accelerometer.

1 1 . A device as claimed in any one of claims 1 -9 wherein the measuring probe comprises optical tracking means, and/or electromagnetic tracking means, and/or acoustic tracking means, and/or mechanical tracking means, the determination being achieved using an output from the tracking means.

12. A device as claimed in any one of claims 1 -9 wherein the determination is achieved using an output from a camera and image processing techniques.

13. A device as claimed in any one of the preceding claims wherein the processing circuitry is configured to measure and/or record each potential value in response to an indication that the measuring probe is near to or has contacted the body.

14. A device as claimed in claim 13 wherein the indication is provided by: a manually operable button for the device; a mechanical or electrical pressure switch, force transducer or load cell for the measuring probe upon measuring a pressure that is above a threshold pressure value or between threshold pressure values; or measuring a potential difference that is above or below a threshold value.

15. A device as claimed in any one of the preceding claims wherein the processing circuitry is configured to assign a presentation value or set of presentation values to the potential value associated with each particular location and output the presentation values to a presentation device or storage device.

16. A device as claimed in claim 15 wherein the processing circuitry is configured to assign a presentation value or set of presentation values to the potential value associated with each particular location by comparison of the potential value with one or more threshold potential values.

17. A device as claimed in claim 16 wherein the one or more threshold potential values are predetermined and/or are selectable by an operator of the device; and/or

wherein the presentation value or set of presentation values are predetermined and/or are selectable by an operator of the device.

18. A device as claimed in claim 15 wherein the processing circuitry is configured to assign the presentation value or set of presentation values to the potential value associated with each particular location using a range of potential values that are mapped to a scale of presentation values or scale of sets of presentation values.

19. A device as claimed in claim 18 wherein the range of potential values for mapping is predetermined and/or is selectable by an operator of the device.

20. A device as claimed in claim 18 or 19 wherein the range of potential values for mapping is based on or is between a lower potential value and an upper potential value recorded by the processing circuitry for the plurality of different locations.

21 . A device as claimed in claim 18, 19 or 20 wherein the presentation value scale is monochromatic or polychromatic.

22. A device as claimed in any one of claims 15-21 wherein the presentation location to be used by the presentation device to present the presentation value or set of presentation values for the potential value associated with each particular location is based on or corresponds to that particular location.

23. A device as claimed in any one of claims 15-22 wherein the processing circuitry is configured to overlay the presentation values either on an image of a body part or on a representation of a body part.

24. A device as claimed in claim 23 wherein the representation of the body part is a silhouette of the body part or an outline of the body part.

25. A device as claimed in claim 23 or 24 wherein the processing circuitry is configured to derive the representation of the body part from an image of the body part captured by a camera.

26. A device as claimed in claim 23, 24 or 25 wherein the processing circuitry comprises means for compensating for movement of a or the camera that provides images of the area of the body and/or for movement of the area of the body.

27. A device as claimed in any one of the preceding claims wherein the processing circuitry is configured to provide for each of the plurality of locations a visual representation of the number of measurements taken at the location in question and output the visual representation to a or the presentation device or storage device.

28. A device as claimed in any preceding claim wherein the processing circuitry is configured to automatically control one or more light sources for illuminating the area of the body.

29. A method of passively measuring and recording electrical potentials for an area of the body of a subject using a device as claimed in any one of the preceding claims, the method comprising:

locating the measuring probe at or near a plurality of different locations of an area of the body of the subject, wherein the measuring probe is moved by hand between different locations of the area of the body; and

operating the device such that the processing circuitry measures and records, in association with each particular location of the plurality of different locations, a potential value that is based on a potential difference measured between the reference probe and the measuring probe when the reference probe is at or near the reference location and the measuring probe is at or near that particular location, wherein the processing circuitry determines the particular location to be associated with each potential value by determination of the location of the measuring probe relative to the area of the body.

30. A device for measuring and recording electrical potentials for an area of the body of a subject substantially as hereinbefore described with reference to and as illustrated in figures 1 -4.

31 . A method of measuring and recording electrical potentials for an area of the body of a subject substantially as hereinbefore described with reference to and as illustrated in figures 1 -4.