Pressure sensing systems and methods

Abstract

A pressure sensing system (100) can include an ultrasound responsive polymer element which resonates at a resonance frequency when exposed to ultrasound waves (112) at an input frequency, at least one sensor (114) configured to directly or indirectly detect the resonance frequency, and at least one memory device (116) that has instruction that, when executed by at least one processor, cause the memory device (116) to correlate the resonance frequency detected to a pressure. Additionally, a method of detecting pressure can include identifying an area where pressure monitoring is desired, orienting an ultrasound responsive element (110) adjacent to that area, directing ultrasound waves (112) toward the ultrasound responsive element (110), detecting the resonance frequency produces by the ultrasound responsive element, and correlating that to a pressure.

Description

[0001] PATENT APPLIC TION Attorney Docket No. 00846-U8563. PCT

[0002] PRESSURE SENSING SYSTEMS AND METHODS

[0003] C OSS REFERENC TO R L ED APPLICATIO S

[0004] This application claims priority to U. S. Provisional Patent Application No.

[0005] 63 / 741,846, filed January 4. 2025 which is incorporated herein by reference.

[0006] STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0007] lliis invention was made with government support under R43 NS 127733 awarded by the National Institutes of Health. The government has certain rights in the invention.

[0008] BACKGROU D

[0009] Elevated Intracranial pressure (1CP) often occurs due to underlying conditions such as traumatic brain injury or hydrocephalus and results in an excess buildup of cerebral spinal fluid (CSF). Untreated, these medical conditions can lead to fatal outcomes or severe negative consequences for the patient, such as neurological defects or irreversible tissue damage. Thus, monitoring ICP can dramatically decrease mortality rate and allow for provision of improved medical treatment for the patient. Current state-of-the-art monitoring techniques include insertion of a strain gauge or optical fiber pressure sensors intraventricularly. These current approaches tend to increase risk of infection and hemorrhages, and impact tire sensor performance through misplacement, mishandling, or electrostatic discharges. Also, these methods limit the use of imaging techniques such as magnetic chromatography (MRI) as the devices are not compatible with MRI magnetic fields and pose further risk for the patient.

[0010] SUMMA Y

[0011] A pressure sensing system can include an ultrasound responsive polymer element. This ultrasound responsive polymer element can be configured to resonate at a resonance frequency when exposed to ultrasound waves at an input frequency. The system can also include at least one sensor configured to detect the resonance frequency directly or indirectly.The system can further include at least one memory device. The at least one memory device can have instructions that, when executed by at least one processor, cause the memory device to correlate the resonance frequency detected by the at least one sensor to a pressure.

[0012] A method of detecting pressure can include identifying an area where pressure monitoring is desired. The method can also include orienting an ultrasound responsive element adjacent to or within the area where pressure monitoring is desired. Additionally, the method can include directing ultrasound waves at an input frequency toward the ultrasound responsive element to produce a response at a resonance frequency. The method can further include detecting the resonance frequency of the ultrasound waves. Furthermore, the method can include correlating the detected resonance frequency of the ultrasound waves to a pressure.

[0013] There has thus been outlined, rather broadly, the more important features of the invention so that the detailed description thereof that follows may be better understood, and so that the present contribution to the art may be better appreciated. Other features of the present invention will become clearer from tire following detailed description of the invention, taken with die accompanying drawings and claims, or may be learned by the practice of the invention.

[0014] BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic of a pressure sensing system in accordance with one example. FIG. 2A is a schematic of an ultrasound responsive element in tire form of a single polymer layer atached to a support substrate in accordance with one example.

[0015] FIG. 2B is a schematic of an ultrasound responsive element having a multi-layer polymer stack attached to a support substrate in accordance with another example.

[0016] FIG. 3 is a schematic of an ultrasound responsive element being compressed as a result of applied pressure in accordance with one example.

[0017] FIG.4 is a graph of a raw' sensor response showing mean pixel intensity as a function of ultrasound image acquisitions with pressure overlaid in a gradient format in accordance with one example.

[0018] FIG. 5 is a flowchart depicting a method of detecting pressure in accordance with another example.FIG. 6A is a graph of raw sensor response at HC7 MHz in accordance with an example.

[0019] FIG. 6B is a graph of mean sensor response showing mean pixel intensity as a function of pressure in accordance with the example of FIG. 6A.

[0020] FIG. 6C is a graph of raw sensor response at 6MHz in accordance with still another example.

[0021] FIG. 6D is a graph of mean sensor response at 6MHz showing mean pixel intensity as a function of pressure in accordance with tire example of FIG. 6C.

[0022] These drawings are provided to illustrate various aspects of the invention and are not intended to be limiting of the scope in terms of dimensions, materials, configurations, arrangements or proportions unless otherwise limited by the claims.

[0023] DET ILED DESCRIPTION

[0024] While these exemplar}' embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, it should be understood that other embodiments may be realized and that various changes to tire invention may be made without departing from the spirit and scope of the present invention. Thus, the following more detailed description of the embodiments of the present invention is not intended to limit the scope of the invention, as claimed, but is presented for purposes of illustration only and not limitation to describe the features and characteristics ofthe present invention, to set forth the best mode of operation of the invention, and to sufficiently enable one skilled in the art to practice the invention. Accordingly, the scope of the present invention is to be defined solely by the appended claims.

[0025] Definitions

[0026] In describing and claiming the present invention, the following terminology will be used.

[0027] Hie singular forms “a,” “an,’’ and ‘"the"’ include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a polymer layer” includes reference to one or more of such materials and reference to “implanting”' refers to one or more of such actions.

[0028]

[0029] As used herein with respect to an identified property or circumstance, ’'substantially” refers to a degree of deviation that is sufficiently small so as to not measurably detract from the identified roperty or circumstance. The exact degree of deviation allowable may in some cases depend on the specific context.

[0030] As used herein, ‘’adjacent” refers to the proximity of two structures or elements. Particularly, elements that are identified as being ‘‘adjacent” may be either abutting or connected. Such elements may also be near or close to each other without necessarily contacting each other. Hie exact degree of proximity may in some cases depend on the specific context.

[0031] As used herein, the term “about” is used to provide flexibility and imprecision associated with a given term, metric or value. The degree of flexibility for a particular vanable can be readily determined by one skilled in the art. However, unless otherwise enunciated, the term “about” generally connotes flexibility’ of less than 2%, and most often less than 1 %, and in some cases less than 0.01%.

[0032] As used herein, a plurality of items, structural elements, compositional elements, and / or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary.

[0033] As used herein, the term “at least one of’ is intended to be synonymous with “one or more of.” For example, “at least one of A. B and C” explicitly includes only A, only B, only C, or combinations of each.

[0034] Numerical data may be presented herein in a range format. It is to be understood that such range format is used merely for convenience and brevity and should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example, anumerical range of about 1 to about 4.5 should be interpreted to include not only the explicitly recited limits of 1 to about 4.5, but also to include individual numerals such as 2, 3, 4, and subranges such as 1 to 3, 2 to 4, etc. The same principle applies to ranges reciting only onenumerical value, such as ‘'less than about 4 5,” which should be interpreted to include all of the above-recited values and ranges. Further, such an interpretation should apply regardless of the breadth of the range or the characteristic being described.

[0035] Any steps recited in any method or process claims may be executed in any order and are not limited to the order presented in the claims. Means-plus-function or step-plus-function limitations will only be employed where for a specific claim limitation all of the following conditions are present in that limitation: a) "'means for” or "step fbr” is expressly- recited; and b) a corresponding function is expressly recited. The structure, material or acts that support the means-plus function are expressly recited in the description herein Accordingly, the scope of the invention should be determined solely by the appended claims and their legal equivalents, rather than by the descriptions and examples given herein. Example Embodiments

[0036] Referring generally to FIG. 1, a pressure sensing system 100 can include an ultrasound responsive element 110 which is configured to resonate at a resonance frequency upon exposure to ultrasound waves 112 at an input frequency-. As described later, the ultrasound responsive element can be oriented in a location where pressure monitoring is desired. An ultrasound source can also be provided as an integrated ultrasound transducer (i.e. production of ultrasound waves 112 and detection of reflected waves at the resonance frequency in a common device), although these can be provided as separate units in some alternatives. The pressure sensing system 100 can also include at least one sensor 114. Hie at least one sensor 114 can be configured and oriented to directly or indirectly detect the resonance frequency of reflected waves resonated by the ultrasound responsive element. Tire pressure sensing system 100 can further include at least one memory device 116. The memoiy device can include instructions, that when executed by at least one processor, cause the memory device to correlate the resonance frequency detected by the at least one sensor to a pressure.

[0037] Hie ultrasound responsive element can be configured to resonate at a resonance frequency when exposed to ultrasound waves atari input frequency. Design of the resonance frequency for a given element can be a function of one or more of the following variables: material composition, structure (i.e. combination of materials, shape, etc), dimensions (e.g. thickness), and temperature. Hie ultrasound responsive element 110 can be formed from acompliant. biocompatible polymer or other biocompatible material. In some embodiments, the ultrasound responsive element 110 can be a single layer, although in other cases tire ultrasound responsive clement can be a composite layer comprising a stacked multi-layer configuration. Further, in some cases, the ultrasound responsive element 110 can be freestanding and unsupported. Optionally, the ultrasound responsive element 110 can be secured to a support substrate for increased mechanical strength. In some cases, the ultrasound responsive element 110 is a solid homogeneous layer (i.e. uniform composition). In some examples, the ultrasound responsive element can be substantially flat on an exposed frequency receiving side such that there are no openings, recessed or other surface features. In some cases, the exposed frequency receiving side can include recessed patterns or a controlled surface roughness. As a general guideline, the polymer layer can have a thickness which provides mechanical integrity, any coupled materials or layers, and also allows for resonant response as described herein. Accordingly, thicknesses can vary but can be from about 0.01 ram to about 1 mm thick, from about 0.1 mm to about 5 mm thick, from about 0.05 mm to about 2 mm thick, or from about 2 mm to about 6 mm thick. The ultrasound responsive polymer can also be formed of any polymer which is compressible at the input frequency. Non-limiting examples of suitable polymers can include an inorganic polymer, an organic polymer, an elastomer (e.g.. a silicone elastomer), a biopolymer (e.g. cellulose based polymer such as cellophane or the like), rubber (e.g natural or artificial), polydimethylsiloxane (PDMS), polyimide, parylene, benzocyclobutene (BCB), polyethylene, polyurethane, polytetrafluoroethylene (PTFE), acrylics, hydrogels, and combinations thereof.

[0038] In some alternatives associated with implantable devices, the ultrasound responsive polymer can be formed of a biodegradable material such that invasive recovery of the device is not necessary. More specifically, the biodegradable material can be designed to degrade over a desired time. In this case, the biodegradable polymer can be chosen to degrade over a desired target use time ranging from days to months. Choice of biodegradable polymers, ratios ofpolymers, degree of cross-linking (i.e. lower degrades faster), molecular weight (i.e. lower degrades faster), increased degree of crystallinity, increased porosity, additives (e g. plasticizers, fillers, bioactive glass, stabilizers, etc), and other factors can be varied in order to adjust degradation time. For example, esters such as PLA'PLGA, carbonates andanhydrides have hydrolytically labile bonds which tend to degrade, while more hydrophobic polymers tend to degrade more slowly. Non-limiting examples of suitable biodegradable polymers can include polyacctal, chitosan, alginate, polylactidc, polycaprolactonc, polyethylene glycol, polyglycolic acid, polyvinyl alcohol, polyvinyl pyrrolidone, polyacrylic acid. carboxymethyl cellulose. methyl cellulose, ethyl cellulose, polyoxyethylene / polyoxypropylene copolymers, polylactides, polyglycolides, polydioxanones, polysaccharides, hyaluronic acid polymers, starches, acacia gum, agar, alginates, carrageenan, cassia gums, cellulose gums, chitin, chitosan, curdlan, gelatin, dextran, fibrin, fulcelleran, gellan gum, gliatti gum, guar gum, tragacanth, karava gum, locust bean gum, pectin, tara gum, xanthan gum, combinations thereof, and the like.

[0039] As mentioned above, resonance can be dependent on material stiffness, speed of sound, temperature, and thickness. Thus, different materials will show different resonance frequencies at identical layer thicknesses. In this manner, multiple layers of differing materials can be stacked to provide a greater signal than others at the same resonance frequency. Higher signal amplitude will allow for better pressure monitoring (e.g. improved SNR). Similarly, different materials can be mixed to obtain varied resonance performance at given dimensions and expected operating temperatures. Layers and optional coatings can also be chosen to enhance reflective surfaces, interface behavior, and to increase ultrasound wraves traveling back to the probe. As an example, different device configurations and choice of ultrasound responsive polymers can also be responsive as a function of temperature. Accordingly, multiple devices can be configured to operate at different temperature ranges. In some cases, resonance responses can be used from multiple devices to calculate whether a given response is due to temperature changes or pressure changes. For example, devices can be calibrated independently to determine how its resonance response shifts with temperature alone (at constant pressure) and with pressure alone (at constant temperature). Tliis results in a measured pressure sensitivity and temperature sensitivity for each device configuration. As a general rule, during a measurement, multiple devices can be interrogated simultaneously. Because temperature affects all devices to some extent, while pressure affects each device differently depending on its geometry’ and material, the pattern of resonance shifts across devices can be used to determine whether a change is driven by temperature, pressure, or a combination of both. In practice, the measured shifts can becompared against the calibration data to separate the pressure-induced component from the temperature-induced component. In one specific simplified implementation, one device can be designed to be strongly pressure -sensitive and relatively insensitive to temperature compared to a second device, while the second device can act primarily as a temperature reference with minimal pressure sensitivity compared to the first device. The temperature-induced shift measured by a reference device can then be used to correct the response of the pressure-sensitive device. Tins approach enables temperature effects to be accounted for without die need for active temperature sensors or electronics, instead relying on differential calibration and correlation between multiple passive, ultrasound-responsive devices. As an example, such configurations can be useful since the ultrasound probe may induce heat transfer to the sensor, when monitoring pressure for a longer time.

[0040] Similarly, such resonance responses from multiple devices can allow for operation across a wider range of temperatures when the multiple devices are configured for operation at different temperature ranges. Tirus, in some cases, tire pressure sensing system can include an array of ultrasound responsive elements where groups of elements or each individual element is configured to resonance at a target resonance frequency and / or temperature. In these cases, the ultrasound responsive elements can resonate at a common frequency, or at different frequencies from one another. Similarly, the ultrasound responsive elements can resonate within a common temperature range, or at different temperature ranges Further, additives can be added to adjust polymer properties such as resilience, resistance to corrosion, ultrasound resonance, stability, temperature compensation (i.e. to adjust resonance response to a desired operating temperature), etc. Non-limiting examples of additives can include, but are not limited to, plasticizers, stabilizers, degradation accelerators (i.e. especially for biodegradable polymer devices), anti-inflammatory agents, neural growth factors, antibiotics, therapeutic agents, fillers, colorants, and the like. in another alternative, the polymer layer can include protective coatings which are relevant to an intended use environment. Such protective coatings can also reduce or prevent agglomeration. For example, in biological environments coatings such as polyurethanes, polyethylene glycols, polyether ether ketone (PEEK), combinations thereof, and the like can be used Similarly, in corrosive industrial environments coatings can be useful. Regardless, the polymers themselves can also be chosen for compatibility with the intended environment.The ultrasound responsive polymer element can also be provided in any suitable shape which allows for resonant response to the input frequency. As a general guideline, the ultrasound responsive polymer element can be provided as a layer, and in some cases a uniformly thick layer, hi th csv examples, the layer can be planar having a thickness which is less than about 8 times a width of the element, and in some cases less than 10 times the width. The layer can be shaped as a disc, ellipse, quadrilateral, rounded quadrilateral, star, regular or irregular polygonal, or other suitable shape. In some cases, die layer can be curved, i.e. convex or concave over all or a portion of die layer. Alternatively, die layer can further include surface features such as protrusions, dimples, or the like in order to allow further tailoring of the resonant frequency and the frequency response, and to aid in securing ti e device in place.

[0041] Referring to FIG. 2A, the ultrasound responsive element 110 can include a single polymer layer 120. When provided as an unsupported ultrasound polymer layer (single or multiple layers), the layer can experience both compression and bending in response to the incoming ultrasound waves. Optionally, a support substrate 130 can be provided to increase mechanical strength of the polymer layer when die ultrasound responsive element 110 is free standing. Alternatively, the support substrate can act as a mounting surface if the ultrasound responsive element is intended to be secured to a solid object during use. The support substrate can generally mean that although the device will have increased mechanical integrity, bending in response to the ultrasound waves will be suppressed or eliminated.

[0042] The support substrate 130 can generally be formed having a thickness which is greater than the ultrasound responsive polymer layer, or in some cases having a higher stiffness. The support substrate can be formed of any suitable material which can be bonded to die ultrasound responsive polymer layer. In some cases, the support substrate can be ultrasound transparent at the desired operating temperatures and input ultrasound frequencies. As a general guideline, materials which are ultrasound transparent can have a transmission percentage of greater than 80%, and in some cases greater than 90% at the target resonance frequency. As with resonance, the ultrasound transparency of a particular material (re, support substrate) will be a function of composition, temperature, dimensions (e.g. thickness across ultrasound path), frequency, acoustic barriers (e.g. pores, material nonhomogeneities, surface features, etc), and the like. However, in odier cases, such as whenpressure sensing is done on a surface of an implant deeper within the body, it can be beneficial for the support substrate to be ultrasound reflective so a reflective ultrasound measurement can be obtained. In other words, an ultrasound reflective material can be one having a transmission percentage less than 80%, in some cases less than 60%, and in other cases less than 20%. Non-limiting examples of suitable materials for the support substrate can include polymethylmethacrylate (PMMA), polyester-acrylic, polyimide, polyacrylates, polycarbonates, polysiloxanes, ceramics, metals (e.g. aluminum etc), and combinations thereof. In some cases, tire support substrate can have a thickness from 1 to 10 times that of the ultrasound responsive polymer layer.

[0043] Alternatively, as displayed in FIG. 2B, the ultrasound responsive element 110 can include an ultrasound responsive polymer layer 120 which is a multi-layer stack. As previously mentioned, the ultrasound responsive polymer layer and optional support substrate 130 can be made from a biocompatible polymer or other biocompatible material as previously listed. However, the multi-layer stack can be made from one or more materials with compliant or non-compliant properties to modify longevity, ultrasound reflection, resonance, bending, and compression. In the illustrated example Hie multi-layer stack 120 can include four layers. As a general guideline, a multi-layer stack can include from two to ten layers, in some cases two to four layers. However, there is no theoretical limit on the number of layers that can be used. Each of these layers can be formed of a common polymer or can be different polymers from one another. Similarly', each lay er can have a common thickness or different thicknesses. The selection of polymer type and thickness for each layer can depend on the desired resonance, adhesion between layers, environmental compatibility, acoustic impedance, mechanical properties (expansion coefficients), liquid permeability, and the like. The multi-layer stack can be held together using a suitable adhesive and / orthrough inherent adhesion between polymer layers. The layers can be formed independently and then adhered or laminated together, or can be formed in place onto one another by any suitable technique such as, but not limited to, additive printing (e.g. jetting, FDM, SLA, SLS, etc.), screen printing, roll forming, coating (e.g. spray, spin, dip, blade, etc), vapor deposition (e.g. CVD. PVD, ALD, etc,), electrospinning, and the like.

[0044] Regardless of whether the ultrasound responsive element is a single layer or a multilayer stack, the ultrasound responsive element can be non-suspended. In other words, theultrasound responsive element can operate independent of surrounding fluid, cavities, solid material, or other elements. For example, the ultrasound responsive element and / or the ultrasound responsive polymer layer can be freestanding (i.c. along inner portions and outer portions of exterior surfaces) during use, or can be contacted with a desired support surface without forming enclosed cavities. The ultrasound responsive element can optionally also include a mounting mechanism to allow securing to a surface. Non-limiting examples of suitable mounting mechanisms can include an adhesive layer, clips or other elements which correspond to and couple with a complimentary receiving feature on tire surface, or the like. As previously mentioned, the pressure sensing system does not require a cavity, but rather can be effective when loose and unsecured in a fluid medium, or secured and / or oriented on a flat or solid area of interest. Therefore, in one example, the single layer or multi-layer stack can have its entire surface area in contact with a flat or solid area of interest. Providing a nonsuspended layer without adjacent cavities reduces failure risks associated with manufacturing, fluid ingress or membrane rupture, increasing long-term stability and longevity of the sensor’s performance, In another alternative, the ultrasound responsive element can include a locator feature which can be readily identified in ultrasound images.

[0045] Referring again to FIG. 1, the pressure sensing system 100 can further include an ultrasound transducer 114 as a source of the ultrasound waves. In this example, the ultrasound transducer 114 also includes an integrated ultrasound sensor. Optionally, the least one sensor can be separate units from the ultrasounds source. In one specific example, an ultrasound source such as a resonator can be integrated on top of an encapsulated transducer as an integrated pressure sensor such that imaging is not needed or produced. Regardless, the ultrasound transducer or source can be configured to emit ultrasound waves at the input frequency and can be any suitable ultrasound source configuration such as. but not limited to linear, curvilinear, or the like.

[0046] The input frequency can be specifically selected to vibrate the ultrasound responsive element, or corresponds to one of the ultrasound responsive element's resonance frequencies, hi some examples, the input frequency can be sweeping over a larger area in order to detect the resonance frequency to a high degree. In other examples, a fixed frequency readout can be used where the input frequency is slightly off resonance to get a stronger response signal. Tire degree of difference from resonance depends on the FWHM (full width half maximum)

[0047] IIof the resonance curve and thus a Q-Factor of the particular ultrasound responsive polymer element structure. As a general guideline, the input frequency can be 10% of the FWHM of resonance for the intensity-based measurements, and in some cases 2-20%. and in other cases 5-15%. This results in the ultrasound responsive element resonating at a resonance frequency. The resonance frequency is generally not measured directly. Rather, the change or shift in frequency can be detected by locking onto the phase of the resonance, directly by sweeping the excitation frequency and thus measuring the intensity resonance curve and extracting the resonance frequency, or indirectly by measuring at a fixed frequency and observing the changes in the intensity response.

[0048] In some examples, tire ultrasound transducer can be positioned either in the front or the back of the ultrasound responsive element with respect to an ultrasound source. As a general guideline, a surface of the ultrasound source and sensor (e.g. ultrasound transducer) can be in acoustic contact with a surface such that an acoustic pathway is maintained between the surface and the ultrasound responsive element. In the case oftherapeutic diagnostics with a patient, the ultrasound transducer can be placed directly in contact with skin or other tissue such that the acoustic pathway includes biological fluids, tissues, etc. which can translate the ultrasound waves, hi the case of non-biological applications such as industrial monitoring, the surfaces can be ultrasound transparent at the intended input frequencies. Generally, the ultrasound transducer can be oriented a distance which allows for transmission, reflection and collection of sufficient ultrasound signal to allow detection ofthe resonance frequency. This distance can vary depending on the ultrasound frequencies, material, temperature and other factors. However, as a general guideline the distance can be less than 30 cm from the ultrasound responsive element and in some cases from 0.5 cm to 20 cm. and in other cases 1 cm to 12 cm. For materials with higher ultrasound absorption, higher frequencies can be used to achieve further distances. However, in biological environments frequencies can be limited due to safety concerns.

[0049] FIG. 3 is an illustration which shows exposure of the ultrasound responsive element 210 to a pressure change. When exposed to pressure, tire ultrasound responsive element 210 can be configured to bend or compress uniformly, resulting in a compressed ultrasound responsive element 220 However, because ultrasound waves 230 are being emitted toward the ultrasound responsive element 210 while being compressed, the frequency resonated bythe ultrasound responsive element changes, resulting in an altered resonance frequency. An ultrasound system, either the ultrasound transducer that can be included in the pressure sensing system, or an outside ultrasound system, can be configured to detect these changes in resonance frequency based on ultrasound waves that are reflected and received at die ultrasound system. This change in resonance frequency, or frequency shift, can be captured as a change in pixel intensity of a medical ultrasound image, for example. In some examples, analysis of a selected region of interest (ROI) of the medical ultrasound image can show a relationship between applied pressure and change in mean pixel intensity (MPI). FIG. 4 shows a theoretical raw sensor response as mean pixel intensity as a function of ultrasound image captures over time while pressure is intentionally varied. The underlying gradient shows the change in pressure, while the data shows mean pixel intensity in the region of interest. This shows that the mean pixel intensity can be correlated to pressure. Alternatively, when non -imaging measurement methods are used, the frequency shift can be captured as a change of the ultrasound intensity. In other words, a full image need not be reconstructed and raw pixel intensity in a selected area can be directly correlated with pressure rather than reconstructed as an image. If an outside ultrasound system is used, it can be a commercially available ultrasound or a custom-built ultrasound system. An advantage of using commercially available ultrasound systems is the overall simplicity and low cost.

[0050] Once the changes in resonance frequency are detected directly or indirectly, the memory device can correlate the resonance frequency to a pressure. Pixel intensity of the ultrasound image is proportional to the absorption rate of the material. Lower ultrasound wave absorption corresponds to darker portions of the image (e.g. water) and higher ultrasound wave absorption materials shows as lighter portions of the image (e.g. bone, implants, etc). Regardless, this correlation can be calculated using one or more of a lookup table, a fitted curve, or an algorithm. The memory device can be integrated with the ultrasound transducer or data can be communicated wirelessly or wired to a separate computing device such as a handheld device, portable tablet, desktop computer, or the like.

[0051] Once calculated, the pressure can be analyzed in situations where monitoring of pressure is desired. In some examples, the pressure readout, can be available in a medical facility, at a worksite, or in any environment where the pressure monitoring is desired. In some examples, the pressure readout can be sent to a mobile device for more convenientmonitoring. Additionally, the memory device and processor can be configured to notify when the pressure being monitored reaches a predetermined level.

[0052] hi one example, the pressure sensing system can be used as a medical implant. The medical implant can be used to monitor elevated intracranial pressure. The pressure sensing system can be implanted in the skull. The pressure can then be monitored during a surgical procedure, during recovery and / or other times as needed. If biodegradable materials are used for the ultrasound responsive polymer element, the element can be left in place and allowed to degrade over time. Alternatively, the ultrasound responsive polymer element can be surgically removed after the procedure is completed. In another application, the system can be used in any environment where pressure measurement is desired, such as in the hydrocarbon fields, industrial pipelines, reactors, etc. In general, the devices can be placed adjacent ultrasound translucent material (i.e. at desired operating temperatures and frequencies). This can allow pressure measurements in corrosive or difficult-to-access environments. In another example, pressure can be monitored in pipelines e.g. buried under the ground or surrounded by water.

[0053] hi yet another example, the ultrasound responsive element, which can be made from a compliant, biocompatible polymer, can be positioned either in direct contact or adjacent to cerebrospinal fluid. Additionally, in this example, the system can include an ultrasound transducer, positioned either in the front or back of the ultrasound responsive element A sensor can be incorporated in the ultrasound transducer. The ultrasound transducer can emit ultrasound waves at an input frequency, causing the ultrasound responsive element to resonate a resonance frequency. If the intracranial pressure becomes elevated, the ultrasound responsive element will bend or compress uniformly with the elevated pressure. This will result in an altered resonance frequency during exposure to ultrasound waves, which can be detected by the sensor in the ultrasound transducer as a change in pixel intensity' of a medical ultrasound image. At least one memory device, that can be incorporated in the sensor, can correlate the change in pixel intensity detected to a pressure using a lookup table, algorithm, or fitted curve. This correlation can be the result of a processor executing this instruction.

[0054] FIG 5 depicts a method 500 of detecting pressure which can include identifying an area where pressure monitoring is desired 510. As previously mentioned, this area can include any environments where pressure measurement is desired, such as in hydrocarbonfields, industrial pipelines, reactors, medicine (e g. various locations within a patient), etc. Tire methods 500 can also include orienting an ultrasound responsive element adjacent the area where pressure monitoring is desired 520. In one example, if the area where pressure monitoring is desired is in the skull of a patient to monitor elevated intracranial pressure, the ultrasound responsive element can be oriented within or adjacent to cerebrospinal fluid or other important pressure indicators in the cranium. In some examples, the ultrasound responsive element can be non -suspended. In other words, the ultrasound responsive element can respond independently of any cavities, solids or other adjacent features. More specifically, the ultrasound responsive element can generally be freestanding such that it can be free-floating in a fluid, or secure to a surface without necessarily creating any gaps or voids adjacent the ultrasound responsive element. As previously mentioned, the pressure sensing system does not require a cavity, but rather can be effective on a flat or solid area of interest. Therefore, the ultrasound responsive element as a single layer or multi-layer stack¬ can have its entire surface area in contact with the flat or solid area of interest. The ultrasound responsive element can be formed from a compliant, biocompatible polymer or other biocompatible material when using within a patient, hi some embodiments, the ultrasound responsive element can be a single layer. Alternatively, the ultrasound responsive element can be a multi-layer polymer stack. The multi-layer stack can be made from one or more materials with compliant or non-compliant properties to modify longevity, ultrasound reflection, oscillation, vibration, bending, and / or compression.

[0055] The methods 500 can additionally include directing ultrasound waves at an input frequency toward the ultrasound responsive element 530. This can be accomplished by using commercially available ultrasound devices or a custom-built ultrasound solution. The input frequency can be specifically selected to vibrate the ultrasound responsive element, or corresponds to or is close to at least one resonance frequency of the ultrasound responsive element at the desired operating temperature or temperature range. As described above, the input frequency can be selected to correspond to be close to an expected resonance frequencies of the ultrasound responsive element at the given pressure and temperature conditions. Directing ultrasound waves at an input frequency toward the ultrasound responsive element can result in the ultrasound responsive element producing a response at a resonance frequency as previously discussed in more detail above.Methods of detecting pressure 500 can also include detecting the resonance frequency of the ultrasound waves 540 and correlating the detected resonance frequency of the ultrasound waves to a pressure 550. In some examples, this detection can be done using at least one sensor. The detection can be accomplished by capturing the resonance frequency of the response of the ultrasound waves as a change in pixel intensity of a medical ultrasound image. Alternatively, when non-imaging measurement methods are used, the resonance frequency can be captured as a change of the ultrasound intensity. Once detected, at least one memory device that is in data communication with the sensor can correlate the pixel intensity or change in ultrasound intensity to pressure. This correlation can be accomplished by using a lookup table, a fitted curve, or an algorithm. Once pressure is calculated, the pressure can be monitored, reported or otherwise used in further actions. For example, if intracranial pressures exceed a predetermined safety threshold, a healthcare provider or system can be alerted so that corrective action can be taken. Similar corrective actions can be taken in other healthcare or industrial applications when a measured pressure falls outside of a predetermined acceptable range (i.e. excessively high or excessively low).

[0056] Examples

[0057] Preliminary data was gathered using five ultrasound responsive elements. The five ultrasound responsive elements were multi-layer stacks, each being a three-layer stack. One layer was composed of polymethylmethacrylate (PMMA) and was 3.175 mm thick. Another layer was a flexible polyester-acrylic polymeric structure, which was 0.126 mm thick. The other layer was a polyimide (PI) sheet, being 0.025 mm thick.

[0058] The ultrasound responsive elements underwent four pressure cycles, iterating from 5 cmH₂O to 50 cmH₂O and back to 5 cmH₂O in 5 cmH₂O steps. After data analysis, two sensors showed a pressure response, as seen in FIGS. 6A-6D. FIGS. 6A-6B, are the raw sensor response and the mean sensor response at 7 MHz, show a linear, proportional relationship between applied pressure and mean pixel intensity (MPI). FIGS. 6C-6D, are the raw sensor response and the mean sensor responses at 6 MHz, show a linear, inverse¬ proportional relationship between applied pressure and MPI. Baseline represents a measurement of a plain acrylic disc followingthe same measurementprotocol as the sensors. The acrylic disc ofthis thickness was chosen because it is ultrasound translucent at the tested frequencies. Standard deviations are presented as error bars and linear regression slope asdotted line Data was normalized and outliers smaller 25thpercentile and larger 75thpercentile were removed. Removed data is indicated as missing datapoint. With applied pressure a change in mean pixel intensity is detected, resulting in a good linear sensor response when averaged across the pressure cycles.

[0059] While the flowcharts presented for this technology may imply a specific order of execution, the order of execution may differ from what is illustrated For example, the order of two more blocks may be rearranged relative to the order shown. Further, two or more blocks shown in succession may be executed in parallel or with partial parallelization.

[0060] Reference was made to the examples illustrated in the draw ings and specific language was used herein to describe the same. It will nevertheless be understood that no limitation of the scope of the technology is thereby intended. Alterations and further modifications of the features illustrated herein and additional applications of the examples as illustrated herein are to be considered within the scope of the description.

[0061] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more examples, hr the preceding description, numerous specific details were provided, such as examples of various configurations to provide a thorough understanding of examples of the described technology. It will be recognized, however, that the technology may be practiced without one or more of the specific details, or with other methods, components, devices, etc. fa other instances, well-known structures or operations are not shown or described in detail to avoid obscuring aspects of the technology.

[0062] Although the subject matter has been described in language specific to structural features and / or operations, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features and operations described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims. Numerous modifications and alternative arrangements may be devised without departing from the spirit and scope of the described technology.

Claims

CLAIMSWhat is claimed is:

1. A pressure sensing system, comprising:an ultrasound responsive polymer element configured to resonate at a resonance frequency upon being exposed to ultrasound waves at an input frequency;at least one sensor configured to directly or indirectly detect the resonance frequency: andat least one memory device including instructions that, when executed by at least one processor, cause the memory device to correlate the resonance frequency detected by the at least one sensor to a pressure.

2. The system of claim 1, wherein the ultrasound responsive polymer element is non -suspended3. The system of claim 1, wherein the ultrasound responsive polymer element is a single polymer layer.

4. The system of claim 3, wherein the single polymer layer is from about 0.1 mm to about 5 mm thick.

5. The system of claim 1, wherein the ultrasound responsive polymer element is a multi-layer stack.

6. The system of claim 5. wherein the multi-layer stack is from about 0.05 mm to about 6 mm thick.

7. The system of claim 1, wherein the ultrasound responsive polymer element is a biocompatible material that bends or compresses uniformly with applied pressure.

8. The system of claim 7. wherein when the ultrasound responsive polymer element is compressed, an altered resonance frequency is resonated.

9. The system of claim 8, wherein the altered resonance frequency is detected as a change in pixel intensity of a medical ultrasound image.

10. The system of claim 8. wherein the altered resonance frequency is detected as a change in ultrasound intensity.

11. The system of claim 1, wherein the correlation of tire resonance frequency to pressure is calculated using one or more of a lookup table, fitted curve, algorithm12. The system of claim 1. further comprising an ultrasound transducer, configured to emit ultrasound waves at the input frequency.

13. The system of claim 12, wherein the input frequency is 10% of a FWHM of the resonance frequency of the ultrasound responsive polymer element.

14. The system of claim 1, wherein the system is used as a medical implant.15 The system of claim 14, wherein the medical implant is used to monitor elevated intracranial pressure.

16. A method of detecting pressure, comprising:identifying an area where pressure monitoring is desired:orienting an ultrasound responsive element adjacent to or within the area where pressure monitoring is desired;directing ultrasound waves at an input frequency toward tire ultrasound responsive element to produce a response at a resonance frequency;detecting the resonance frequency of the ultrasound waves; andcorrelating the detected resonance frequency of the ultrasound waves to a pressure.17 The method of claim 16, wherein the area where pressure monitoring is desired is a head of a patient to monitor elevated intracranial pressure.

18. The method of claim 16. wherein the ultrasound responsive element is a single polymer layer or a multi-layer polymer stack.

19. The method of claim 16, wherein the ultrasound responsive element is non¬ suspended.

20. The method of claim 16, w herein the resonance frequency is detected as pixel intensity of a medical ultrasound image.

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