Patent Description:
Patients' skin integrity has long been an issue of concern for nurses and in nursing homes. Maintenance of skin integrity has been identified by the American Nurses Association as an important indicator of quality nursing care. Meanwhile, pressure ulcers remain a major health problem particularly for hospitalized older adults. When age is considered along with other risk factors, the incidence of pressure ulcers is significantly increased. Overall incidence of pressure ulcers for hospitalized patients ranges from <NUM>% to <NUM>%, and rates of greater than <NUM>% have been reported for patients in intensive care settings. In a multicenter cohort retrospective study of <NUM>,<NUM> older adults discharged from acute care hospitals with selected diagnoses, <NUM>% (i.e., <NUM> patients) demonstrated an incidence of stage I ulcers. Of those <NUM> patients, <NUM> (<NUM>%) had ulcers that progressed to a more advanced stage. Pressure ulcers additionally have been associated with an increased risk of death one year after hospital discharge. The estimated cost of treating pressure ulcers ranges from $<NUM>,<NUM> to $<NUM>,<NUM> for each ulcer, depending on severity.

Therefore, there is an urgent need to develop a preventive solution to measure moisture content of the skin as a mean to detect early symptoms of ulcer development. Prior art document <CIT> discloses an apparatus for the non-invasive glucose detection comprising an electrical detection device for measuring the response of the tissue or blood to an electric field at low frequencies below <NUM> and at high frequencies above <NUM>. The apparatus further comprises a force or acceleration sensor to detect the pressure of the apparatus against the skin and/or quick movements. Prior art document <CIT> discloses tissue sensors that house one or more sensor elements. Each element has a housing mounted substrate and a superstrate with a planar antenna between. A transitional periphery (TP) of a superstrate outer surface interconnects a base to a plateau. Some of the TP has a generally smooth transition. Plural elements are spaced by the housing. In an alternative embodiment, the superstrate TP is flat, the housing extends to the outer superstrate surface and a shield surrounds the element. The housing is flush with or recessed below the superstrate and defines a TP between the housing and superstrate. Prior art document <CIT> discloses a method for measuring tissue edema. An electromagnetic probe is placed on the skin, and the capacitance of the probe is proportional to the dielectric constant of the skin and subcutaneous fat, which is proportional to the water content of the skin. Prior art document <CIT> describes an apparatus and method for near-field imaging of tissue. Pulsed or continuous-wave sources, broadband electromagnetic energy generally in the <NUM> to <NUM> range is applied through one or a plurality of near-field antennas such as coaxial probe tips in the form of a bundle of antennas. The bundle of antennas is scanned over a surface of the object on a pixel-by-pixel basis to determine the spectra of the sample on a pixel-by-pixel basis, allowing a two dimensional display of the absorption spectra to be provided.

<NPL> describes an apparatus for measuring skin moisture using an interdigital electrode structure.

The above needs are met by an apparatus for in situ Sub-Epidermal Moisture (SEM) sensing of tissue as defined in claim <NUM>.

An aspect of the present disclosure is a smart compact capacitive sensing conforming handheld apparatus configured to measure Sub-epidermal Moisture (SEM) as a mean to detect and monitor the development of pressure ulcers. The device incorporates an array of electrodes which are excited to measure and scan SEM in a programmable and multiplexed manner by a battery-less RF-powered chip. The scanning operation is initiated by an interrogator which excites a coil embedded in the apparatus and provides the needed energy burst to support the scanning/reading operation. Each embedded electrode measures the equivalent sub-epidermal capacitance corresponding and representing the moisture content of the target surface.

An aspect of this disclosure is the in situ sensing and monitoring of skin or wound or ulcer development status using a wireless, biocompatible RF powered capacitive sensing system referred to as smart SEM imager. The present invention enables the realization of smart preventive measures by enabling early detection of ulcer formation or inflammatory pressure which would otherwise have not been detected for an extended period with increased risk of infection and higher stage ulcer development.

In one beneficial embodiment, the handheld capacitive sensing imager apparatus incorporates pressure sensing components in conjunction with the sensing electrodes to monitor the level of applied pressure on each electrode in order to guarantee precise wound or skin electrical capacitance measurements to characterize moisture content. In summary, such embodiment would enable new capabilities including but not limited to: <NUM> ) measurement capabilities such as SEM imaging and SEM depth imaging determined by electrode geometry and dielectrics, and <NUM>) signal processing and pattern recognition having automatic and assured registration exploiting pressure imaging and automatic assurance of usage exploiting software systems providing usage tracking.

One major implication of this sensor-enhanced paradigm is the ability to better manage each individual patient resulting in a timelier and more efficient practice in hospitals and even nursing homes. This is applicable to patients with a history of chronic wounds, diabetic foot ulcers, pressure ulcers or postoperative wounds. In addition, alterations in signal content may be integrated with the activity level of the patient, the position of patient's body and standardized assessments of symptoms. By maintaining the data collected in these patients in a signal database, pattern classification, search, and pattern matching algorithms can be developed to better map symptoms with alterations in skin characteristics and ulcer development. This approach is not limited to the specific condition of ulcer or wound, but may have broad application in all forms of wound management and even skin diseases or treatments.

One aspect of the present disclosure is apparatus for sensing sub-epidermal moisture (SEM) from a location external to a patient's skin. The apparatus includes a bipolar RF sensor embedded on a flexible substrate, and a conformal pressure pad disposed adjacent and underneath the substrate, wherein the conformal pressure pad is configured to support the flexible substrate while allowing the flexible substrate to conform to a non-planar sensing surface of the patient's skin. The apparatus further includes interface electronics coupled to the sensor; wherein the interface electronics are configured to control emission and reception of RF energy to interrogate the patient's skin.

Another aspect, which is not claimed, is a method for monitoring the formation of pressure ulcers at a target location of a patient's skin. The method includes the steps of positioning a flexible substrate adjacent the target location of the patient's skin; the flexible substrate comprising one or more bipolar RF sensors; conforming the flexible substrate to the patient's skin at the target location; exciting the one or more bipolar RF sensor to emit RF energy into the patient's skin; and measuring the capacitance of the skin at the target location as an indicator of the Sub-Epidermal Moisture (SEM) at the target location.

Further aspects of the disclosure will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing preferred embodiments of the invention without placing limitations thereon.

The invention will be more fully understood by reference to the following drawings which are for illustrative purposes only:.

In one exemplary embodiment, a smart handheld capacitive sensing device according to the present invention employs a programmable sensing electrode array. This is based on methods that use an interrogator to excite the embedded electrodes.

<FIG> illustrates an SEM scanning/sensing apparatus <NUM> according to the present disclosure. The scanner <NUM> comprises five main components, including a top silicone edge sealing gasket <NUM> encircling a Kapton-based sensing substrate <NUM>, which rests on a conformal silicone pressure pad <NUM>. A thick annular silicone spacer <NUM> is disposed under pressure pad to provide free space for the pressure pad to deform. The bottom layer comprises an interface electronics package enclosure <NUM> that houses interface circuitry for interrogating and transmitting data for evaluation. These five main components are described in further detail below.

In the embodiment shown in <FIG>, an array <NUM> of individual RF electrode sensors <NUM> and <NUM> is embedded on a flexible biocompatible substrate <NUM>. Substrate <NUM> may comprise a laminated Kapton (Polyimide) chip-on-flex.

<FIG> illustrates one embodiment of a Kapton sensor substrate 16a that comprises an array <NUM> of differing sized concentric sensing electrodes. A flexible biocompatible Polyimide or Kapton substrate <NUM> comprises a layer of sensing pads <NUM> and <NUM> coated on one side with an ultra thin cover layer <NUM> of Polyimide (e.g. CA335) to isolate pads electrodes <NUM>,<NUM> from direct moisture contact and also to provide a uniform contact surface.

In <FIG>, sample capacitive sensing electrodes <NUM> are shown in different sizes (e.g. <NUM>, <NUM>, and <NUM>), which are manipulated to achieve and sense different depths of skin. Sensing electrodes <NUM> may comprise any number of different shape and configurations, such as the concentric circles of array <NUM>, or the interdigitating fingers of sensor <NUM>.

<FIG> illustrates a close-up top view of a concentric sensing pad <NUM> in accordance with an embodiment of the present invention. Pad <NUM> comprises a bipolar configuration having a first electrode <NUM> comprising an outer annular ring disposed around a second inner circular electrode <NUM>. Outer ring electrode <NUM> has an outer diameter D<NUM> and an inner diameter D, that is larger than the diameter Dc of the circular inner electrode <NUM> to form annular gap <NUM>. Inner circular electrode <NUM> and outer ring electrode <NUM> are coupled electrically to interface electronics in the interface electronics package <NUM>. As shown in greater detail in <FIG> and <FIG>, electrodes <NUM> and <NUM> are disposed on separate layers within the substrate assembly <NUM>.

The dimensions of the sensor pads <NUM>, <NUM> generally correspond to the depth of interrogation into the derma of the patient. Accordingly, a larger diameter pad (e.g. pad <NUM> or <NUM>) will penetrate deeper into the skin than a smaller pad. The desired depth may vary depending on the region of the body being scanned, or the age, skin anatomy or other characteristic of the patient. Thus, SEM scanner <NUM> may comprise an array of different sized pads (e.g. small pads <NUM> and medium sized pads <NUM> shown in <FIG>) each individually coupled to the interface electronics package <NUM>.

<FIG> illustrates side view of a flex stack-up for a Kapton based substrate assembly <NUM>, where thin adhesive layers <NUM> are used to attach a Kapton layer <NUM> in between copper layers <NUM> and <NUM>, all of which are disposed between upper coverlay <NUM> and lower coverlay <NUM>. A stiffener <NUM> is disposed under lower coverlay <NUM>, being positioned directly under copper layer <NUM> of the sensing pads. The stiffener <NUM> forms a rigid portion of the substrate where sensing pad array <NUM>, connectors (e.g. connectors <NUM>, <NUM>, or <NUM> shown in <FIG>) and interfacing (e.g. lead wires <NUM>) are located, so that these areas do not deform, whereas the rest of the substrate is free to deform. The top copper layer <NUM> is used to etch out electrode array <NUM> and corresponding copper routing <NUM> to the connectors. The bottom copper layer <NUM> preferably comprises a crisscross ground plane to shield electrode array <NUM> from unwanted electromagnetic interference.

In one embodiment, the flex substrate <NUM> assembly comprises Pyralux FR material from Dupont. In an exemplary configuration, approximately <NUM> (5mil) thick FR9150R double-sided Pyralux FR copper clad laminate is used as the Kapton substrate. Top coverlay <NUM> comprises Pyralux <NUM> (5mil) FR0150 and the bottom coverlay <NUM> comprises <NUM> (<NUM> mil) FR01 <NUM> Pyralux. The thickness of the top FR0150 coverlay <NUM> is an important parameter as it affects the sensitivity of sensing electrodes in measuring skin moisture content. Copper layers <NUM>, <NUM> are generally <NUM> (<NUM>. 4mil) thick, while adhesive layers <NUM> are generally <NUM> (<NUM> mil thick). The stiffener <NUM> shown in <FIG> is approximately <NUM> (<NUM> mil) thick.

<FIG> shows a side view of a preferred alternative flex stack-up for a Kapton based substrate <NUM>, where thin adhesive layers <NUM> (<NUM> or <NUM> mil) are used to attach an <NUM> (<NUM> mil) Kapton layer <NUM> in between <NUM> (<NUM>. <NUM> mil) copper layers <NUM> and <NUM>, all of which are disposed between <NUM> (<NUM> mil) upper coverlay <NUM> and <NUM> (<NUM> mil) lower coverlay <NUM>. A stiffener <NUM> is disposed under lower coverlay <NUM>, being positioned directly under copper layer <NUM> of the sensing pad. The <NUM> (<NUM> mil) FR4 stiffener <NUM> forms a rigid portion of the substrate under the array <NUM> of sensing pads, connectors <NUM> and interfacing <NUM>. A <NUM> (<NUM> mil) layer of PSA adhesive <NUM> is used between the bottom coverlay <NUM> and stiffener <NUM>. The layering of assembly <NUM> is configured to provide proper shielding from interference.

<FIG> shows a top view of three separate and adjacently arranged concentric bipolar electrode sensing Kapton-based flex pads <NUM>, <NUM> and <NUM> having different sized capacitive sensing concentric electrodes. Pad <NUM> comprises a substrate having two large concentric electrodes <NUM> wired through substrate <NUM> via connectors <NUM> to lead line inputs <NUM>. Pad <NUM> comprises a substrate having two medium concentric electrodes <NUM> wired through substrate <NUM> to lead line inputs <NUM>. Pad <NUM> comprises a substrate having two small concentric electrodes <NUM> wired through substrate <NUM> to lead line inputs <NUM>. The configuration shown in <FIG> is optimized for cutting/manufacturing and also to avoid interference between data lines and sensors. Each of the bipolar electrode pads is individually wired to the electronics package <NUM> to allow for independent interrogation, excitation, and data retrieval.

<FIG> illustrates an exploded perspective component view of the SEM scanner <NUM>. The silicone edge sealing gasket <NUM> is applied over the Kapton sensor substrate assembly <NUM> to seal and shield the edge interface connectors through which interface electronics package <NUM> excite and controls the sensing electrode array <NUM>. The Kapton sensor substrate assembly <NUM> rests on a conformal silicone pressure pad <NUM> that provides both support and conformity to enable measurements over body curvature and bony prominences.

In one beneficial embodiment, pressure sensor <NUM><NUM> may be embedded under each sensing electrode <NUM>, <NUM> (e.g. in an identical array not shown), sandwiched between Kapton sensor substrate <NUM> and the conformal silicone pressure pad <NUM> to measure applied pressure at each electrode, thus ensuring a uniform pressure and precise capacitance sensing.

Lead access apertures <NUM> provide passage for routing the connector wires (not shown) from the substrate connectors (e.g. <NUM>, <NUM>, <NUM>) through the pressure pad <NUM>, annular spacer <NUM> to the interface electronics <NUM>.

The annular silicone spacer <NUM> comprises a central opening <NUM> that provides needed spacing between the conformal silicone pressure pad <NUM> and the interface electronics package <NUM> to allow the pressure pad <NUM> and flexible substrate to conform in a non-planar fashion to conduct measurements over body curvatures or bony prominences.

In one embodiment, the interface electronics package <NUM> is connected to a logging unit or other electronics (not shown) through wire-line USB connector <NUM>.

The interface electronics package <NUM> preferably comprises an enclosure that contains all the electronics (not shown) needed to excite, program and control the sensing operation and manage the logged data. The electronics package <NUM> may also comprise Bluetooth or other wireless communication capabilities to allow for transfer of sensing data to a computer or other remote device. Docked data transfer is also contemplated, in addition to real-time Bluetooth transfer. A gateway device (not shown) may be used for communicating with the SEM device <NUM> and data formatting prior to upload to a computer or backend server.

<FIG> is a schematic side view of the SEM scanner <NUM> in the nominal configuration, showing the edge gasket <NUM> over Kapton substrate <NUM>, and lead access apertures <NUM>, which provide access through annular spacer <NUM> and conformal pad <NUM> to electronics <NUM>.

<FIG> illustrates a schematic side view of the SEM scanner <NUM> in contact with the target subject <NUM>. The annular silicone spacer <NUM> provides enough spacing for conforming silicone pad <NUM> to conform to the target surface <NUM>. The conforming silicone pad <NUM> enables continuous contact between the substrate <NUM> and patient's skin <NUM>, thus minimizing gaps between the substrate <NUM> and patient's skin <NUM> that could otherwise result in improper readings of the patient anatomy. Electrode array <NUM>, which is embedded in substrate16, is shown interrogating into the derma of tissue <NUM> by directing emission of an RF signal or energy into the skin and receiving the signal and correspondingly reading the reflected signal. The interrogator or electronics package <NUM> excites electrode coil <NUM> by providing the needed energy burst to support the scanning/reading of the tissue. Each embedded electrode <NUM> measures the equivalent sub-epidermal capacitance corresponding to the moisture content of the target skin <NUM>.

While other energy modalities are contemplated (e.g. ultrasound, microwave, etc.), RF is generally preferred for its resolution in SEM scanning.

<FIG> illustrates a perspective view of an assembled SEM scanner <NUM> with an alternative substrate 16b having an array <NUM> of ten sensors dispersed within the substrate 16b. This larger array <NUM> provides for a larger scanning area of the subject anatomy, thus providing a complete picture of the target anatomy in one image without having to generate a scanning motion. It is appreciated that array <NUM> may comprise any number of individual sensors, in be disposed in a variety of patterns.

The SEM scanner <NUM> was evaluated using a number of different sized and types of sensors <NUM>. Table <NUM> illustrates electrode geometries are used throughout the following measurements. As shown in <FIG> the outer ring electrode diameter D<NUM> varied from <NUM> for the XXS pad, to <NUM> for the large pad. The outer ring electrode inner diameter D, varied from <NUM> for the XXS pad, to <NUM> for the large pad. The inner electrode diameter Dc varied from <NUM> for the XXS pad, to <NUM> for the large pad. It is appreciated that the actual dimensions of the electrodes may vary from ranges shown in these experiments. For example, the contact diameter may range from <NUM> to <NUM>, and preferably ranges from <NUM> to <NUM>.

To measure the properties of each sensor size listed in Table <NUM> , the sensors were fabricated using both Kapton and rigid board. In testing with the rigid sensor pads, lotion was applied to the thumb continuously for <NUM> minutes.

<FIG> is a plot of normalized responses of the tested electrodes of the present disclosure. The four sensors' (XXS, XS, S, M) normalized responses are compared in <FIG> and Table <NUM>.

As can be seen in <FIG> and Table <NUM>, the S electrode appears to be most responsive overall to the presence of moisture. Both the M and S electrodes seem to exhibit a peak. This suggests a depth dependency of the moisture being absorbed into the skin, as the roll-off from the M electrode occurs about <NUM> minutes after the peak for S electrode.

The SEM scanner <NUM> was also tested on the inner arm. A resistive pressure sensor (e.g. sensor <NUM><NUM> shown in <FIG>) was also used to measure pressure applied on sensor to the arm. This way, constant pressure is applied across measurements. First, the dry inner arm was measured using the XS, S and M electrodes. Then, the same area was masked off with tape, and moisturizer lotion was applied for <NUM> minutes. Subsequent measurements were made on the same location after cleaning the surface.

<FIG> is a graph of measured equivalent capacitance for dry Volar arm for three different sized (M, S, XS) concentric sensor electrodes before applying the commercial lotion moisturizer.

<FIG> is a plot of time dependent fractional change in capacitance relative to dry skin for three different concentric sensor electrodes (after <NUM> minutes of applying lotion).

<FIG> is a plot of time dependent fractional change in capacitance relative to dry skin for three different concentric sensor electrodes (after <NUM> minutes of applying lotion) on two subjects. This experiment was performed with faster sampling intervals and with lotion applied for <NUM> minutes only on forearms of two test subjects. Again, a resistive pressure sensor was used to measure pressure applied on sensor to the arm. This way, constant pressure is applied across measurements. First the dry inner arm was measured using the XS, S and M electrodes. Then the same area was masked off with tape, and lotion was applied for <NUM> minutes. Subsequent measurements were made on the same location every <NUM> minutes. Pressure was maintained at <NUM> Ohms, and the forearm was tested again. We noticed an interesting observation for the case "F" in comparison to case "A" and also compared to previous measurements. Case "F" took a shower right before running the measurements and hence as a result his skin was relatively saturated with moisture. As a result, we observed less degree of sensitivity to the applied deep moisturizer for case "F".

The experiment was performed again for case "F", with a time resolution of <NUM> minutes, knowing that the subject did not shower in the morning before the test. The lotion was applied to the inner forearm for <NUM> minutes. Pressure was maintained at <NUM> Ohms. The results confirm the sensitivity of the measurement to the residual skin moisture.

<FIG> is a plot of results for fractional change vs. time for M, S and XS electrodes.

<FIG> shows a preferred embodiment of a layered SEM scanner electrode system <NUM> having a first electrode pad <NUM> and second electrode pad <NUM>. Pad <NUM> is connected to lead line inputs <NUM><NUM> via wiring <NUM> along curved path <NUM><NUM>. Pad <NUM> is connected to lead line inputs <NUM><NUM> via wiring <NUM> along curved path <NUM>. A stiffener layer (e.g. layer <NUM> in <FIG>) is provided directly under lead inputs <NUM><NUM> and <NUM><NUM> (see footprint <NUM> and <NUM><NUM> respectively) and under pads <NUM> and <NUM> (see footprint <NUM> and <NUM> respectively).

In this embodiment, the electrode size is approximately <NUM> (<NUM> mil) in width by <NUM> (<NUM> mil) in height.

<FIG> illustrates the SEM Scanner mechanical compliance (force-displacement relationship) for electrodes of system <NUM>, developed to enable probing of bony prominence. The diamond symbols show the upper electrode <NUM> response, square symbols show the lower electrode <NUM> response.

The SEM scanner device <NUM> may also include other instruments, such as a camera (not shown), which can be used to take pictures of the wound, or develop a scanning system to scan barcodes as a login mechanism or an interrogator.

Patients using the SEM scanner device <NUM> may wear a bracelet (not shown) that contains data relating to their patient ID. This ID can be scanned by the camera embedded in the SEM scanner <NUM> to confirm correct patient ID correspondence. Alternatively, a separate RF scanner (not shown) may be used for interrogating the bracelet (in addition to the camera).

The SEM scanner device <NUM> is preferably ergonomically shaped to encourage correct placement of the device on desired body location.

The SEM Scanner device <NUM> of the present invention is capable of generating physical, absolute measurement values, and can produce measurements at multiple depths.

Although the description above contains many details, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of this invention. Therefore, it will be appreciated that the scope of the present invention is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean "one and only one" unless explicitly so stated, but rather "one or more.

Claim 1:
An apparatus for in situ Sub-Epidermal Moisture (SEM) sensing of tissue, comprising:
a flexible substrate (<NUM>, <NUM>),
an array of bipolar sensors, each bipolar sensor consisting of a first electrode (<NUM>) and a second electrode (<NUM>) that are both embedded on a common side of the flexible substrate (<NUM>, <NUM>);
an insulating cover layer (<NUM>) coupled to the flexible substrate (<NUM>, <NUM>) and configured to act as a barrier between the tissue being measured and the first and second electrodes (<NUM>, <NUM>);
a pressure sensor (<NUM>) configured to sense applied pressure coupled to the flexible substrate (<NUM>, <NUM>) and disposed in line with the first and second electrodes (<NUM>, <NUM>); and
an electronics package (<NUM>) that is individually wired to each of the first and second electrodes (<NUM>, <NUM>) and configured to:
excite and control the first and second electrodes (<NUM>,<NUM>) so as to measure an equivalent sub-epidermal capacitance, wherein the equivalent sub-epidermal capacitance is an indicator of SEM.