the present invention provides a device for measuring the surface topographys in epithelial tissue that is hand - held , noninvasive and suitable for use on human subjects , particularly for use in outpatient or other clinical settings . fig1 shows a partially transparent perspective view of the hand - held device 8 according to an embodiment of the invention . as can be seen in the figure , there is a push - button actuator 10 at the top of the device attached to , and extending through , positioning handle 12 . positioning handle 12 is designed to be gripped by one hand of an operator in order to position and orient the device , thus it is preferably a spherical shape , but may be any other suitable shape for gripping . the arrangement of the positioning handle 12 with push - button actuator 10 allows an operator to activate and position the device with a single hand by wrapping a finger or fingers around the positioning handle 12 and engaging the push - button actuator 10 with a single finger . at the base of positioning handle 12 is cap 14 that covers and protects the motors 16 and 18 , further discussed below . connected to the motors is probe 20 , which contains sensing and processing electronics for the device , including a current - to - voltage amplifier circuit 62 ( see fig5 a ). probe 20 is vibrated by a vibration unit 24 that may be either a piezoelectric disk or an electromagnetic speaker , shown in more detail in fig5 a and 5b , respectively . as shown in fig6 a , the signal from the probe 20 is sent through a cable 74 to an electronics package 76 , which is connected to a computer 52 , where a microcontroller 70 and a v ptp determining circuit 66 analyze the capacitance formed between the gold plate 22 at the bottom tip of probe 20 and the epidermis of the subject ( not shown in fig1 ). the length of the connecting cable , which is usually several feet ( e . g . a 6 - ft . cable ), allows the device to be easily positioned on any part of the subject being examined . the lower portion of the device , including probe 20 and vibration unit 24 , is enclosed in an outer housing 26 ( fig1 and 2 ). outer housing 26 is joined to cap 14 , forming a covering for the body of the device , and is preferably formed from a plastic material . the bottom of outer housing 26 rests on the skin of the subject and this contact provides stable positioning of the device with respect to the skin surface being examined . using positioning handle 12 , the device may be positioned such that outer housing 26 is placed against a body surface having any orientation . in addition , having outer housing 26 in contact with the skin allows the device to move with the skin as the skin moves due to breathing , circulation , movement of the underlying muscles , or other movement . this matched movement permits the outer housing to hold the skin in a relatively stationary position with respect to the probe 20 and maintains the separation between the skin and sensor tip at a roughly constant distance , which allows the probe 20 to be positioned independently of minor involuntary movement by the subject . of course , the subject should avoid large movements during scanning to allow the outer housing 26 to be held against the skin . the bottom surface of outer housing 26 comprises a lens 28 that is formed from a transparent material and has an aperture 30 ( shown in more detail in fig2 and 3 ). aperture 30 provides access to the skin for the probe 20 to scan and is preferably a slit about 1 mm wide . the preferred narrow width of the aperture 30 optimizes the surface topology for scanning because it minimizes the amount of skin that protrudes up into the aperture . when skin protrudes up into the aperture , it has a convex shape , thus the separation distance between the skin and the probe 20 is not the same for the entire region of skin exposed by the aperture . variations in the separation distance makes positioning of probe 20 in the z direction difficult , and has an adverse affect on the quality of the measurements taken , as further discussed with respect to the positioning mechanism . accordingly , the shape and dimensions of the aperture should be selected to minimize protrusion of the skin into the aperture . thus , when measuring skin that is particularly loose and flexible , a narrow aperture will be preferred . in contrast , when examining a region of skin that is substantially taut , a larger aperture or an aperture of another shape may be acceptable . when measuring the surface topography at a wound site that has any kind of fluid present , such as blood or interstitial fluid , the fluid can interfere with the accurate measurement of the epidermal surface potential by the device due to the differences in the work function characteristics of the fluid in comparison with those of the surrounding tissues the work function , which is the minimum energy needed to remove an electron from the surface of a material , is very different for dry skin than for fluids . thus , when moved from a position over dry skin to one over fluid , the probe will detect a large voltage difference that is due to work function differences alone , rather than from the electric field of interest that is generated by the current flow beneath the epidermis . the effect of these differences in work function can be minimized by placing a thin covering 42 ( fig2 ) over the aperture that is an electrically transparent material , such as polyethylene or other polyvinyls . with the covering 42 in place , the surface work function is the same for all positions scanned by the probe , while the underlying electric field is easily detected through the electrically transparent material . the probe 20 examines the skin exposed by the aperture 30 as its position is controlled by the first stepper motor 16 in the x direction , which follows the length of aperture 30 . in a preferred embodiment , adjustments in the y direction are not necessary because of the narrow width of aperture 30 ( see fig3 ). in addition , if measurements of regions to either side of the aperture 30 are required , the device may easily be repositioned such that the aperture 30 exposes those regions for subsequent scans . as shown in fig2 , first stepper motor 16 includes a positioning arm 34 that moves probe 20 , along with vibration unit 24 , incrementally in the x direction . the first stepper motor 16 is electrically connected to and controlled by the computer 52 ( fig6 a ) via signal wires 54 a extending through connection handle 32 ( fig2 ). the first stepper motor 16 is capable of moving with a 40 μm step size and allows the collection of surface potential data over a linear region of the skin . the second stepper motor 18 is responsible for maintaining the position of probe 20 in the z direction ( fig3 ), which is roughly perpendicular to the skin surface . the outer housing 26 and lens 28 keep the device steady with respect to movements of the skin ; however , the device requires that the distance between the closest approach of probe 20 and the skin be precisely maintained in order to accurately determine the surface topography of the skin , thus the second stepper motor 18 provides the necessary fine adjustments . the feedback control mechanism employed by the second stepper motor 18 is discussed in further detail below . vibration of the probe 20 , caused by vibration unit 24 , also occurs in the z direction , thus second stepper motor 18 controls the distance of closest approach , as defined above . the vibration units used in the device are preferably either a piezoelectric disk 36 ( fig5 a ) or an electromagnetic speaker 38 ( fig5 b ). the piezoelectric disk is composed of two piezoelectric ceramics , each bonded to a brass disk , that are in turn attached together . the electromagnetic speaker is composed of a speaker element that vibrates on an axis normal to the skin or other epithelium . the vibration unit 24 vibrates probe 20 at 800 hz or greater . currently , frequencies in the range of 800 to 1200 hz are used , but higher frequencies may be used as faster , quieter vibration techniques and devices are developed . in general , the highest frequency available is preferred as higher frequencies generate a stronger signal . the high frequency vibration used here represents an almost twenty - fold increase over the vibration frequency used in the bench - mounted bfi , allowing for faster data acquisition and overall shorter scanning times . this is advantageous for the subjects because it minimizes the time that they need to remain relatively still . fig2 and 4 show a color video camera 40 located inside connection handle 32 that allows the operator performing the scan to see the area over which the device is positioned . connection handle 32 is comprised of a camera housing 44 , right - hand and left - hand adapter rings 46 and 48 , and a two part cylinder portion 50 ( fig4 ). the camera 40 images a view through lens 28 , as shown in the upper right portion of the graphical interface depicted in fig8 . an led ( 78 in fig5 b ) provides illumination to the area . the camera display allows the device to be precisely positioned over a wound or a skin lesion , which reduces the number of scans that do not cover the intended region . in addition to housing camera 40 , connection handle 32 provides a conduit for connection of the device to a computer 52 via cable 74 and the electronics package 76 ( fig6 a ). signal wires extend into connection handle 32 ( fig2 ) from the motors 16 and 18 ( 54 a and 54 b in fig6 a ), the vibration unit 24 ( 56 in fig6 a ) and the probe 20 ( 58 in fig6 a ). returning to fig2 , probe 20 has an outer portion 60 that forms a conductive metal layer that electrically shields the electronics inside and the gold plate 22 at the bottom . the gold plate 22 and the subject &# 39 ; s epidermis ( not shown in fig2 ) form plates of a parallel - plate capacitor . because the surface potential of each plate is different , charges will build up on the plates and a voltage will develop across the capacitor ( the contact potential ). a series of reference ( biasing ) voltages of ± 5 - 10 v , preferably ± 10 v , are applied to either the skin or to the gold plate 22 , which causes the charges on the plates to change , meaning that a current flows from one plate to the other via the connection formed across the applied voltage . in a preferred embodiment , the reference voltages are applied to the skin via a conventional skin surface electrode ( such as those used in electrocardiography ). application of the reference voltage to the skin results in fewer switching artifacts compared with application to the probe , which allows data acquisition to begin more quickly . the reference voltages are applied in pairs ( e . g . + 10 v and − 10 v ) in an alternating sequence during the measurement period . at the same time , the probe 20 is vibrated in the z direction by vibration unit 24 , changing the distance separating the plates of the capacitor . the capacitance of a parallel - plate capacitor depends on the distance between the plates , thus the capacitance is very sensitive to changes in that distance . as the capacitance changes , the charge on the plates is also changed in accordance with the equation q = cv ( here , voltage can be assumed to be relatively constant ). the current corresponds with the change in charge over time , given by i = dq / dt , thus the combination of the applied voltage and vibration of the probe induce an oscillating current . in one embodiment of the present invention , the oscillating current is measured by the probe 20 and immediately converted to a voltage via a current - to - voltage or transimpedance amplifier 62 ( fig6 a ). to reduce the input capacitance of the current - to - voltage amplifier 62 , the gold plate 22 is mounted directly on the amplifier chip and the chip is embedded in plastic and shielded . the output voltage of the amplifier varies periodically as the probe vibrates ( an oscillating voltage ), and the peak - to - peak voltage ( v ptp ) depends on the difference between the contact potential and the reference voltage . the signal from the probe 20 is sent via cable 74 to an electronics package 76 , where the signal is further amplified through a voltage amplifier 64 to generate an amplitude of approximately 2 v peak - to - peak . the amplified signal is then sent to a circuit 66 , where one of two methods may be used to determine the v ptp . in the first method , the oscillating voltage is accumulated over a fixed sample time by an integrator circuit 68 ( fig6 b ). because the voltage signal is oscillating about 0 volts , it is necessary to invert the signal from negative to positive when the signal is in the negative range in order to integrate . the microcontroller 70 instructs the integrator circuit 68 to invert the signal at the appropriate times in this phase - dependent inversion method . the then - positive signal allows the integrator circuit 68 to sum the total area between the voltage wave and the time axis . integrator circuit 68 integrates the signal for a fixed number of periods , beginning from the minimum signal level , which is zero in this ease , further reducing noise . the integrated signal is proportional to the peak - to - peak value of the vibrating capacitor - induced signal . in an alternative embodiment , the signal may be rectified by an amplifier 80 ( e . g . an ad8037 , a wide bandwidth , low distortion clamping amplifier ) before integration , such that the negative portions of the signal are reflected about the time axis ( x - axis ) and made positive ( fig6 c ). however , the rectified signal tends to have a lower signal - to - noise ratio compared to the signal produced using phase - dependent inversion . in the second method , a peak detector circuit 82 averages the positive peak signals and the negative peak signals ( fig6 d ). this method is less sensitive to slight changes in frequency than the integration method , while providing a high signal - to - noise ratio . the output of the integrator circuit 68 or peak detector 82 is sensed by the microcontroller 70 via an analog - to - digital converter ( adc ) 72 ( fig6 a ). datasets are measured and transmitted from the microcontroller 70 to the computer 52 at a rate of approximately 21 hz . each dataset consists of a data value and integration time versus each applied reference voltage ( e . g . a data value and integration time for the + 10 v reference and a data value and integration time for the − 10 v reference ). from the datasets , the average v ptp for each reference voltage is calculated and plotted against the reference voltage values . the resulting line will intercept the reference voltage axis at a point that corresponds to the voltage at which there would be no current flow between the two surfaces , which also provides the voltage created by the electric field of the subject &# 39 ; s skin at the location measured . as described above , after determining the surface potential at several points in a given region , the electric field between any two points is given by the difference in surface potential at these points divided by the distance between them . in addition , the line of v ptp plotted against the reference voltages is used in the control of the positioning of the probe 20 in the z direction by second stepping motor 18 . the slope of the line is inversely proportional to the distance between the closest approach of the probe and the skin surface , thus by maintaining the slope , the distance is also maintained . the computer 52 uses the slope data to send feedback signals to the second stepper motor 18 via the microcontroller 70 . when the slope varies from a target slope value , the computer 52 provides the slope information to microcontroller 70 , which generates a control signal for the second stepper motor 18 to adjust the z position of probe 20 before each measurement . the data sampling rate of 21 hz allows the microcontroller 70 to provide the control signal to the second stepper motor 18 at a rate of 1 - 5 hz , as a proportional controller . the amount of adjustment of the probe &# 39 ; s position is based on the slope value at that time compared to the target slope value . the stepper the slope of the line , the more change will result from a given adjustment of the probe . accordingly , the computer 52 continually monitors the separation distance as it evaluates new datasets and produces the line of v ptp plotted against the reference voltages . the surface topography is then displayed by plotting the z motor step adjustments required to maintain the constant distance between the probe and the skin . as shown in more detail in the flowchart of fig7 , the feedback control mechanism begins with the acquisition of the calculated average v ptp values 100 . as described above , these values are then plotted against their corresponding reference voltages 102 . the slope of the voltage line is determined 104 and compared with a target slope value 106 . the feedback control mechanism next determines if the slope is within the tolerance range 108 . if it is in the tolerance range , the slope is monitored for a predetermined amount of time 110 to ensure that it remains in the range . if it remains in the range as evaluated at step 112 , then the slope can be accepted as a data point 114 and measurements may be taken in order to determine the electric field of the epithelium . as stated above , the position of the probe in the z direction must be established prior to taking any measurements . if the slope does not remain within the tolerance range for the specified period , then the process begins again at step 100 as new v ptp values are acquired . if the slope was determined not to be in the tolerance range at step 108 , then the microcontroller 70 determines how far the probe needs to be moved 116 and generates the appropriate control signal 118 for the second stepper motor 18 . the second stepper motor 18 then moves the probe in accordance with the control signal 120 . next , the microcontroller 70 determines how far the probe is from the target 122 and allows a period of time to elapse based on that determination 124 . if the probe is far from the target , a short amount of time is required , but if the probe is close to the target , then the amount of time is longer . this variable waiting time allows the slope to stabilize when it is near the target ( where it is most important ), but also allows the probe to be moved quickly when it is farther away . after the time period has elapsed , the control mechanism returns to step 100 to acquire new v ptp values to continue to evaluate the slope until the positioning of the probe in the z direction is acceptable . because the microprocessor 70 generates the control signals for the second stepper motor 18 based on feedback from the probe itself , it is important that the probe &# 39 ; s signal contains accurate information about the distance between the probe and the skin surface . the surface topology of the skin can be rather complex near wounds , lesions , and wrinkles thus the distance between the skin and the probe must be adjusted before every measurement to ensure that the distance of closest approach is maintained . fig8 depicts one embodiment of a graphical interface used on the computer . in the top center panel a real - time video image from camera 40 of the probe 20 and the epithelium being scanned is displayed . to the right of the video image , the probe &# 39 ; s real - time output is displayed as it scans across a lancet wound . the average surface potential is displayed in blue ( peaking downwardly ) and the topographical information is displayed in red ( peaking upwardly ). the increase in potential present as the device scans - over the wound indicates a lateral electric field on either side of the wound region and the red plot indicates that the wound region is higher that the surrounding surface probably due to swelling of the wounded dermis . fig9 a - 9c show scans of different surface profiles . fig9 a shows the dermacorder scan of a 2 mm wide dome shape that is 380 um high in the center . it was scanned using a probe tip that was a disk 500 um in diameter . the red bar indicates the position of the dome on this plot and the inset shows a photograph of the dome with a scale bar indicating 1 mm . fig9 b shows the dermacorder scan of a 4 mm wide depression that is 400 um deep in the center scanned with the same probe described in 9 a . the red bar indicates the position of the depression . fig9 c shows the dermacorder scan of a forehead wrinkle shown in the left inset . the probe used here was 100 um by 2 mm long as shown in the right inset . the scale bar in the right inset is 1 mm long . a polymer replica of this wrinkle indicated a depth of 160 um . that the dermacorder measured only 90 um is due to the fact that resting the dermacorder on the skin tends to flatten the wrinkle profile somewhat . in additional embodiments of the invention , a series of measurements are taken in the x direction in order to obtain data in two dimensions , rather than the linear measurements described above . in one embodiment , the probe 20 is replaced by multiple probes in order to provide simultaneous measurements at multiple locations . in another embodiment , the probe 20 is provided with multiple sensors to achieve similar measurements .
the present invention provides a hand - held , noninvasive diagnostic device for measuring the electric fields in mammalian skin and other epithelial structures . the device includes an outer housing that contacts the skin , providing stability and allowing the device to move along with minor movement of the skin . recessed within the outer housing is a probe that acts as a sensor to measure the electric field in the skin through an aperture in the bottom surface of the outer housing . by applying a series of known voltages while the probe is vibrating , the skin &# 39 ; s local surface potential can be measured and the lateral electric field can be calculated from the spatial distribution of surface potential measurements . active feedback is used to maintain a constant distance between the probe and the skin surface .