Abstract:
Various improvements to inflatable membranes are disclosed. These improvements include, among other things, features on the membrane that can mitigate hazards such as bubble formation or frictional damage during inflation of the membrane.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Prov. App. No. 61/501,600 filed on Jun. 27, 2011. This application is also a continuation-in-part of U.S. application Ser. No. 12/508,955, filed on Jul. 24, 2009, which application claims the benefit of U.S. Provisional Patent Application No. 61/083,394 filed on Jul. 24, 2008 and U.S. Provisional Patent Application No. 61/165,708 filed on Apr. 1, 2009. Each of the foregoing applications is incorporated herein by reference in its entirety. 
     
    
     FIELD OF INVENTION 
       [0002]    This document relates to an inflatable membrane with features for mitigating hazards of inflation within a cavity, such as trapped bubbles or frictional damage. 
       BACKGROUND 
       [0003]    Techniques have been disclosed for capturing thickness measurements inside an inflated membrane, as described for example in commonly-owned U.S. Pat. No. 8,107,086 and reconstructing three-dimensional images from these measurements. 
         [0004]    While these techniques are generally useful for measuring interior cavities, there remains a need for improved inflatable membranes adapted to capturing such data in particular environments such as within a human ear canal. 
       SUMMARY 
       [0005]    Various improvements to inflatable membranes are disclosed for use in three-dimensional imaging of interior spaces based upon distance measurements. These techniques may be used alone or in combination for improved data capture. 
         [0006]    In one aspect, a device disclosed herein includes an inflatable membrane having a proximal end with an opening, a distal end, and an interior accessible through the opening, wherein the inflatable membrane has an inflation characteristic that is non-uniform, thereby causing the membrane to inflate in a predetermined manner; a supply of a medium coupled to the interior through the opening; and a three-dimensional scanning system including at least one scanner element disposed within the interior to capture data from the interior and a processor programmed to calculate a three-dimensional shape of the interior based upon the data. 
         [0007]    The device may include a pump configured to controllably deliver the medium into the interior. The pump may be configured to deliver the medium at a controlled pressure. The device may include an illumination source disposed within the interior and positioned to illuminate a surface of the interior. The three-dimensional scanning system may calculate a distance through the medium to a point on the interior using a ratio of two different wavelengths of light. The medium may selectively absorbs one wavelength of light more than another wavelength of light. The medium may include at least one of a liquid, a gas, and a gel. The inflatable membrane may have a gross geometry corresponding to a human ear canal. The inflatable membrane may have a gross geometry corresponding to human anatomy selected from a group consisting of a stomach, an esophagus, and a bladder. The predetermined manner of inflation may include inflation at the distal end before inflation at the proximal end. The inflation characteristic may include a thickness of the inflatable membrane. The inflation characteristic may include a hardness of the inflatable membrane. The device may include a reinforcing sheath about a portion of the inflatable membrane to impart the non-uniform inflation characteristic to the inflatable membrane. The sheath may be disposed near the proximal end of the inflatable membrane. The inflation characteristic may include a pattern of relatively inelastic material disposed on a portion of the inflatable membrane. The inflation characteristic may include a bellows formed into a portion of the inflatable membrane. A portion of the inflatable membrane may be exercised prior to use to alter an elasticity of the portion, thereby imparting the inflation characteristic to the inflatable membrane. The inflatable membrane may have an oval cross section. The inflatable membrane may have a circular cross section. The inflatable membrane may be formed of an elastic material. 
         [0008]    In another aspect, disclosed herein is a device including an inflatable membrane having a proximal end with an opening, a distal end, and an interior accessible through the opening, wherein the inflatable membrane has one or more fiducials on the interior; a supply of a medium coupled to the interior through the opening; and a three-dimensional scanning system including at least one scanner element disposed within the interior to capture data from the interior and a processor programmed to calculate a three-dimensional shape of the interior based upon the data, wherein the processor uses the one or more fiducials to calculate the three-dimensional shape. 
         [0009]    The device may include a pump configured to controllably deliver the medium into the interior. The pump may be configured to deliver the medium at a controlled pressure. The device may include an illumination source disposed within the interior and positioned to illuminate a surface of the interior. The three-dimensional scanning system may calculate a distance through the medium to a point on the interior using a ratio of two different wavelengths of light. The medium may selectively absorb one wavelength of light more than another wavelength of light. The medium may include at least one of a liquid, a gas, and a gel. The one or more fiducials may be used to register multiple frames of image data acquired from the at least one scanner element. The one or more fiducials may include predetermined patterns printed on the interior. The one or more fiducials may include predetermined patterns embedded in a material of the inflatable membrane. The one or more fiducials may include predetermined three-dimensional shapes on the interior of the inflatable membrane. 
         [0010]    In another aspect, a device disclosed herein includes an inflatable membrane having a proximal end with an opening, a distal end, and an interior accessible through the opening, wherein the inflatable membrane may includes an optical coating on the interior; a supply of a medium coupled to the interior through the opening; and a three-dimensional scanning system including at least one scanner element disposed within the interior to capture data from the interior and a processor programmed to calculate a three-dimensional shape of the interior based upon the data, wherein the optical coating may be selected to improve performance of the three-dimensional scanning system. 
         [0011]    The optical coating may include a matte finish. The optical coating may include a fluorescent dye. The optical coating may include an optically absorptive coating. The optical coating may include a predetermined color. 
         [0012]    In another aspect, the device disclosed herein includes an inflatable membrane having a proximal end with an opening, a distal end, and an interior accessible through the opening, wherein the inflatable membrane may include an optical material disposed within a wall of the inflatable membrane; a supply of a medium coupled to the interior through the opening; and a three-dimensional scanning system including at least one scanner element disposed within the interior to capture data from the interior and a processor programmed to calculate a three-dimensional shape of the interior based upon the data, wherein the optical material may be selected to improve performance of the three-dimensional scanning system. 
         [0013]    The optical material may include a fluorescent dye or a luminescent material. The optical material may include a black pigment. The optical material may be disposed in a pattern to form one or more fiducials for the three-dimensional scanning system. 
         [0014]    In another aspect, a device disclosed herein includes an inflatable membrane having a proximal end with an opening, a distal end, and an interior accessible through the opening; a supply of a medium coupled to the interior through the opening; a proximity sensor configured to provide a signal indicative of a proximity of the distal end to an external object; and a three-dimensional scanning system including at least one scanner element disposed within the interior to capture data from the interior and a processor programmed to calculate a three-dimensional shape of the interior based upon the data, wherein the processor may be further programmed to receive the signal from the proximity sensor and generate an alert under one or more predetermined conditions. 
         [0015]    The device may include a pump configured to controllably deliver the medium into the interior. The pump may be configured to deliver the medium at a controlled pressure. The device may include an illumination source disposed within the interior and positioned to illuminate a surface of the interior. The three-dimensional scanning system may calculate a distance through the medium to a point on the interior using a ratio of two different wavelengths of light. The medium may selectively absorb one wavelength of light more than another wavelength of light. The medium may include at least one of a liquid, a gas, and a gel. The alert may activate an audible alarm. The alert may activate a visual alarm. The alert may activate a tactile alarm. The proximity sensor may be disposed in the interior of the inflatable membrane. The proximity sensor may be disposed on an exterior of the inflatable membrane. The proximity sensor may include an ultrasound transducer. 
         [0016]    In another aspect, a device disclosed herein includes an inflatable membrane having a proximal end with an opening, a distal end, and an interior accessible through the opening; a supply of a medium coupled to the interior through the opening; and a three-dimensional scanning system including one or more optical sensors disposed within the interior to capture image data from the interior and a processor programmed to calculate a three-dimensional shape of the interior based upon the data, wherein the one or more optical sensors include a coating having a first index of refraction matched to a second index of refraction of the medium. 
         [0017]    The device may include a pump configured to controllably deliver the medium into the interior. The pump may be configured to deliver the medium at a controlled pressure. The device may include an illumination source disposed within the interior and positioned to illuminate a surface of the interior. The three-dimensional scanning system may calculate a distance through the medium to a point on the interior using a ratio of two different wavelengths of light. The medium may selectively absorb one wavelength of light more than another wavelength of light. The medium may include at least one of a liquid, a gas, and a gel. 
         [0018]    In another aspect, a device disclosed herein includes an inflatable membrane having a proximal end with an opening, a distal end, and an interior accessible through the opening; a window of transparent material in the distal end providing a view from the interior of the inflatable membrane to an exterior of the inflatable membrane; a supply of a medium coupled to the interior through the opening; and a three-dimensional scanning system including one or more scanner elements disposed within the interior to capture data from the interior and a processor programmed to calculate a three-dimensional shape of the interior based upon the data, at least one of the one or more scanner elements including a camera oriented toward the window. 
         [0019]    The device may include a pump configured to controllably deliver the medium into the interior. The pump may be configured to deliver the medium at a controlled pressure. The device may include an illumination source disposed within the interior and positioned to illuminate a surface of the interior. The three-dimensional scanning system may calculate a distance through the medium to a point on the interior using a ratio of two different wavelengths of light. The medium may selectively absorb one wavelength of light more than another wavelength of light. The medium may include at least one of a liquid, a gas, and a gel. The device may include a display coupled to the camera and configured to display video images from the camera. The device may include an optical coating on the camera having a first index of refraction matched to a second index of refraction of the medium. The device may include a proximity sensor configured to provide a signal indicative of a proximity of the distal end to an external object. 
         [0020]    In another aspect, a device disclosed herein includes an inflatable membrane having a proximal end with an opening, a distal end, and an interior accessible through the opening; a window of transparent material in the distal end providing a view from the interior of the inflatable membrane to an exterior of the inflatable membrane; a fixture in the interior of the inflatable membrane shaped and sized to receive an imaging device and to align the imaging device to the window to provide a view of the exterior through the window with the imaging device; a supply of a medium coupled to the interior through the opening; and a three-dimensional scanning system including one or more scanner elements disposed within the interior to capture data from the interior and a processor programmed to calculate a three-dimensional shape of the interior based upon the data. 
         [0021]    The device may include a pump configured to controllably deliver the medium into the interior. The pump may be configured to deliver the medium at a controlled pressure. The device may include an illumination source disposed within the interior and positioned to illuminate a surface of the interior. The three-dimensional scanning system may calculate a distance through the medium to a point on the interior using a ratio of two different wavelengths of light. The one or more scanner elements may include the imaging device. The medium may include at least one of a liquid, a gas, and a gel. The device may include a display coupled to the imaging device and configured to display video images from the imaging device. The imaging device may have a lens with an optical coating having a first index of refraction matched to a second index of refraction of the medium. The device may include a proximity sensor configured to provide a signal indicative of a proximity of the distal end to an external object. 
         [0022]    In another aspect, a device disclosed herein includes an inflatable membrane having a proximal end with an opening, a distal end, and an interior accessible through the opening, wherein the inflatable membrane has a textured exterior including one or more features to permit passage of air around an exterior of the inflatable membrane from the distal end to the proximal end when the inflatable membrane may be inflated within a passage; a supply of a medium coupled to the interior through the opening; and a three-dimensional scanning system including one or more scanner elements disposed within the interior to capture data from the interior and a processor programmed to calculate a three-dimensional shape of the interior based upon the data. 
         [0023]    The device may include a pump configured to controllably deliver the medium into the interior. The pump may be configured to deliver the medium at a controlled pressure. The device may include an illumination source disposed within the interior and positioned to illuminate a surface of the interior. The three-dimensional scanning system may calculate a distance through the medium to a point on the interior using a ratio of two different wavelengths of light. The medium may selectively absorbs one wavelength of light more than another wavelength of light. The medium may include at least one of a liquid, a gas, and a gel. 
         [0024]    In another aspect, there is disclosed herein a device including an inflatable membrane having a proximal end with an opening, a distal end, and an interior accessible through the opening, wherein the inflatable membrane has a vent tube on an exterior including a channel to permit a passage of air through the vent tube from the distal end to the proximal end when the inflatable membrane may be inflated within a passage; a supply of a medium coupled to the interior through the opening; and a three-dimensional scanning system including one or more scanner elements disposed within the interior to capture data from the interior and a processor programmed to calculate a three-dimensional shape of the interior based upon the data. 
         [0025]    The device may include a pump configured to controllably deliver the medium into the interior. The pump may be configured to deliver the medium at a controlled pressure. The device may include an illumination source disposed within the interior and positioned to illuminate a surface of the interior. The three-dimensional scanning system may calculate a distance through the medium to a point on the interior using a ratio of two different wavelengths of light. The medium may selectively absorb one wavelength of light more than another wavelength of light. The medium may include at least one of a liquid, a gas, and a gel. 
         [0026]    In another aspect, there is disclosed herein a device including an inflatable membrane having a proximal end with an opening, a distal end, and an interior accessible through the opening, wherein the inflatable membrane has a lubricant on an exterior surface thereof to facilitate movement of the inflatable membrane along a surface of a cavity while the inflatable membrane may be inflating within the cavity; a supply of a medium coupled to the interior through the opening; and a three-dimensional scanning system including one or more scanner elements disposed within the interior to capture data from the interior and a processor programmed to calculate a three-dimensional shape of the interior based upon the data. 
         [0027]    The device may include a pump configured to controllably deliver the medium into the interior. The pump may be configured to deliver the medium at a controlled pressure. The device may include an illumination source disposed within the interior and positioned to illuminate a surface of the interior. The three-dimensional scanning system may calculate a distance through the medium to a point on the interior using a ratio of two different wavelengths of light. The medium may selectively absorb one wavelength of light more than another wavelength of light. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0028]    The invention and the following detailed description of certain embodiments thereof may be understood by reference to the following figures: 
           [0029]      FIG. 1  illustrates an imaging system including an inflatable membrane. 
           [0030]      FIG. 2  shows a scanner with an inflatable membrane placed for use in an ear canal. 
           [0031]      FIG. 3  shows a scanner with an inflatable membrane placed for use in an ear canal. 
           [0032]      FIG. 4  shows an inflatable membrane with a substantially conical profile. 
           [0033]      FIG. 5  shows an inflatable membrane. 
           [0034]      FIG. 6  shows an inflatable membrane. 
       
    
    
     DETAILED DESCRIPTION 
       [0035]    Disclosed herein are various modifications to inflatable membranes such as balloons for use in three-dimensional imaging systems, and more particularly, modifications for use with three-dimensional imaging systems designed for imaging of interior spaces. While emphasis in the following description is on imaging of the human ear canal, it will be understood that the principles of the invention have broader applicability, and may be usefully employed for imaging of any other interior spaces including organs such as the bladder or stomach, and any other non-biological cavities where accurate three-dimensional data is desired. 
         [0036]    Throughout this disclosure, various terms of quantitative and qualitative description are used. These terms are not intended to assert strict numerical boundaries on the features described, but rather should be interpreted to permit some variability. Thus for example where a medium is described as being transparent at a particular wavelength, this should be understood to mean substantially transparent or sufficiently transparent to permit measurements yielding accurate thickness calculations, rather than absolutely transparent at the limits of measurement or human perception. Similarly, where a target surface is described as having uniform color or a dye is described as fluorescing at a particular wavelength, this should not be interpreted to exclude the variability typical of any conventional material or manufacturing process. Thus in the following description, all descriptive terms and numerical values should be interpreted as broadly as the nature of the invention permits, and will be understood by one of ordinary skill in the art to contemplate a range of variability consistent with proper operation of the inventive concepts disclosed herein, unless a different meaning is explicitly provided or otherwise clear from the context. 
         [0037]    In the following description, the term wavelength is used to describe a characteristic of light or other electromagnetic energy. It will be understood that the term wavelength may refer to a specific wavelength, such as where the description refers to a center frequency or a limit or boundary for a range of frequencies. The term may also or instead refer generally to a band of wavelengths, such as where a wavelength is specified for a sensor, pixel, or the like. Thus in general the term wavelength as used herein should be understood to refer to either or both of a specific wavelength and a range of wavelengths unless a more specific meaning is provided or otherwise clear from the context. 
         [0038]    All documents mentioned herein are hereby incorporated by reference in their entirety. References to items in the singular should be understood to include items in the plural, and vice versa, unless explicitly stated otherwise or clear from the text. Grammatical conjunctions are intended to express any and all disjunctive and conjunctive combinations of conjoined clauses, sentences, words, and the like, unless otherwise stated or clear from the context. 
         [0039]    Although the following disclosure includes example embodiments, these examples are provided for illustration only and are not intended in a limiting sense. All variations, modifications, extensions, applications, combinations of components, and the like as would be apparent to one of ordinary skill in the art are intended to fall within the scope of this disclosure. 
         [0040]      FIG. 1  illustrates an imaging system including an inflatable membrane. In general, the system  100  may include an inflatable membrane  102 , a supply of a medium  104 , and a three-dimensional scanner  106 . 
         [0041]    The system  100  may have a variety of form factors. For example, the system  100  may include a standalone handheld enclosure including a processor and other hardware for independent operation as a handheld scanner. The system  100  may also or instead include a handheld probe coupled to a computer or other computing device as shown in  FIG. 2 . The computing device  108  may include a processor programmed to receive data from a sensor within the inflatable membrane and calculate three-dimensional data from the data, and to perform other functions associated with the imaging systems described herein. The computing device  108  may also include a display  110  for displaying three-dimensional images, as well as providing a user interface for operation of the system  100  and so forth. It will be understood that in general, processing functions associated with the system  100  may be performed by the computing device  108 , the handheld probe, or some combination of these. 
         [0042]    The inflatable membrane  102  may in general be any inflatable membrane suitable for insertion into a cavity and inflation therein. The inflatable membrane  102  may, for example, be formed of an elastic material that permits the inflatable membrane  102  to conform to such a cavity as it expands. For ear canal imaging in particular, the inflatable membrane  102  may have a gross geometry, i.e., overall inflated three-dimensional shape and size, generally adapted to any cavity in which the inflatable membrane  102  is to be inserted for use. For example, the inflatable membrane  102  may be shaped and sized to have a gross geometry corresponding to a human ear canal. The inflatable membrane  102  may instead be shaped and sized to have a gross geometry corresponding to other human anatomy such as a stomach, an esophagus, a bladder, and so forth. It will be understood that in some implementations, this correspondence may include some degree of over-sizing so that the inflatable membrane  102  can be inflated to fully occupy a cavity and press against interior walls of the cavity, e.g., with a predetermined or measured pressure. Alternatively, in some implementations, this correspondence may include some degree of under-sizing, to mitigate the potential of the inflatable membrane  102  folding over itself during deployment. 
         [0043]    The medium  104  may be any liquid, gas, gel, or combination of the foregoing, and may include additives dissolved into or suspended in the medium  104  as appropriate to a particular imaging technology. For example, the medium  104  may selectively absorb one wavelength of light more than another wavelength of light, such as with the use of a colored dye or other wavelength-selective additive. The medium  104  may also or instead include luminescent or fluorescent substances used by the three-dimensional scanner  106  to determine shape or distance in three-dimensions. 
         [0044]    The three-dimensional scanner  106  may use any suitable techniques for recovering three-dimensional data from the interior of the inflatable membrane  102 . A variety of useful techniques are described by way of examples in U.S. Pat. No. 8,107,086 for recovering three-dimensional data from a single frame of image data; however, numerous other useful techniques may be adapted to imaging as contemplated herein, including without limitation techniques using structured light, laser line scanning, confocal imaging, shape from motion, plenoptic light fields, and so forth. All such techniques that are suitable for capturing the three-dimensional shape of the interior of an inflatable membrane may be used as the three-dimensional scanner  106  described herein. 
         [0045]    A display  110  may be provided for viewing two-dimensional images from the system  100 , reconstructed three-dimensional images from the system  100 , a user interface for controlling the system  100 , and so forth. 
         [0046]      FIG. 2  shows a scanner with an inflatable membrane placed for use in an ear canal. The inflatable membrane  202  includes a proximal end  204  nearer to a handheld probe  206  for using the inflatable membrane  202 , and a distal end  208  away from the handheld probe  206  for insertion into an ear canal  210 . In use, the inflatable membrane may be inserted into the ear canal  210 , and then inflated with medium from an external supply, e.g., from a reservoir and pump within the handheld probe  206 . 
         [0047]    The inflatable membrane  202  may generally include one or more scanner elements  212  for a three-dimensional scanning system disposed within an interior  214  of the inflatable membrane  202  to capture data from the interior  214 . The scanning elements  212  may be fixed to a rigid rod  214  or the like to facilitate steering of a field of view, or otherwise disposed in any manner and at any location within the inflatable membrane  202 . 
         [0048]    It will be noted that a three-dimensional scanner may in general include a variety of sensors and other components, along with a processor, light sources, optical components, transducers (e.g., for ultrasound) and so forth, all depending upon the particular three-dimensional scanning technique deployed, and that such components may be distributed in various ways inside and outside of the inflatable membrane  202 . In general, for the uses contemplated herein, such a system includes at least one “scanner element” disposed within the inflatable membrane  102 . This may be a digital component such as a charge-coupled device, complementary metal oxide semiconductor device, or other light sensor positioned within the inflatable membrane  102  and coupled to external components such as a processor. This may also or instead include an optical component such as one or more fibers, lenses and so forth that optically transfer images to an external acquisition and processing system. This may also or instead include a transducer such as an ultrasonic transducer or any other combination of active and passive elements used to acquire three-dimensional information non-optically. Thus it will be appreciated that the term scanner element is intended to be used broadly, and is not intended to imply any particular type of scanner element, scanner, or scanning technology, except inasmuch as such a scanner element is positioned within the inflatable membrane  102  to acquire data from the interior  214  for three-dimensional processing. 
         [0049]      FIG. 3  shows a scanner with an inflatable membrane placed for use in an ear canal. The inflatable membrane  302  may in general be as described above. 
         [0050]    A backing plate  304  may be provided to couple the inflatable membrane  302  to a handheld probe (not shown) or the like to permit positioning and other manipulation of the inflatable membrane  302  and associated hardware. 
         [0051]    The proximal end of the inflatable membrane  302  may include an opening  306  so that an interior  307  of the inflatable membrane  302  is accessible through the opening  306 . In this manner, the opening  306  may provide a port for accessing components within the interior such as one or more scanner elements  308 . A supply of medium  310  may be coupled (e.g. through a pump  312 ) to the interior  307  through the opening  306  as well. The pump  312 , which may be a manual, automatic, or semi-automatic pump, may be configured to deliver the medium  310  at a controlled pressure or volume such as to inflate the inflatable membrane  302  to a predetermined pressure or volume within the ear canal  318 . 
         [0052]    A three-dimensional scanning system  320  including the scanner element(s)  308 , along with a computer or other computing device having a processor  338 , a display  340 , and so forth, may in general acquire data from the scanner element(s)  308 . The processor may be programmed to calculate a three-dimensional shape of the interior  307  based upon the data. As noted above, this may employ any of a variety of three-dimensional processing techniques known in the art. For example, using the techniques disclosed in U.S. Pat. No. 8,107,086, the three-dimensional scanning system  320  may calculate a distance through the medium  310  (which is used to inflate the inflatable membrane  302 ) to a point  322  on the interior  307 , or more specifically on the surface  309  of the interior  307 , using a ratio of intensity of two different wavelengths of light. By combining this information for a number of points with information about the direction of such points from the scanner element  308 , a three-dimensional image of the interior  307  can be reconstructed using simple geometry. 
         [0053]    The scanning system  320  may include an illumination source  330  disposed within the interior  307  and positioned to illuminate a surface  309  of the interior  307 . The illumination source  330  may provide any type of illumination such as white light to permit viewing of images on a display  340  or the like, or any narrow wavelength, range of wavelengths, or set of ranges of wavelengths suitable to a particular imaging technology being used. 
         [0054]    In general, the inflatable membrane  302 , which may be any of the inflatable membranes described above, may have a circular cross section, or any other suitable cross-sectional shape, such as an oval cross section, or a cross section that varies in shape along its length. 
         [0055]    The inflatable membrane  302  may also or instead have an inflation characteristic that is non-uniform. As used herein, the term inflation characteristic is intended to refer to any characteristic or property of the inflatable membrane  302 , or materials disposed on or in the material of the inflatable membrane  302 , that affects the manner in which the inflatable membrane  302  inflates under pressurization. For example, the inflatable membrane  302  may have an inflation characteristic such as a thickness or hardness that varies about the surface of the inflatable membrane  302 , thus causing the inflatable membrane to inflate in a predetermined manner when pressurized. For example, when inflating in the ear canal  318 , it may be desirable for the inflatable membrane  302  to inflate from the distal end (away from the opening  306 ) to the proximal end in order to reduce or mitigate pressurization of the ear canal  318  during inflation. By forming a seal within the ear canal  318  at the distal end first, this can also mitigate trapping of air bubbles or the like along the contact surface between the inflatable membrane  302  and the ear canal  318 . To achieve this end, the proximal end may be formed of a thicker layer or a harder material than the distal end so that the predetermined manner of inflation includes inflation at the distal end before inflation at the proximal end. 
         [0056]    In another aspect, the inflatable membrane  302  may be formed of an elastic material that is exercised (e.g. at the distal end) by stretching, straining, heating, or other manipulation to alter elasticity, thus imparting the desired inflation characteristic (e.g., a localized, reduced spring constant of an elastic material) to the inflatable membrane  302  for inflation in a predetermined manner (e.g., the exercised regions can inflate before unexercised regions). The inflatable membrane  302  may be exercised in this manner immediately prior to use, or at any other time prior to use such as prior to packaging for shipping to an end user. 
         [0057]    In some implementations, the thickness of the inflatable membrane  302  may accounted for in obtaining the three-dimensional image data. The thickness of the inflatable membrane  302  may be determined in any manner. For example, the thickness of the inflatable membrane  302  may be known or assumed a priori. However, the thickness of the inflatable membrane  302  may change in unpredictable ways after it is inflated in a cavity of unknown dimensions. To account for such changes, a number of other techniques are possible. 
         [0058]    For example, the rough geometry of the cavity can be assumed in advance to be a cylinder, sphere, or other convenient shape. The increase in volume of the inflatable membrane after deployment can be used, in combination with the assumed geometry, to determine an average decrease in the thickness of the membrane  302 . This average decrease can then be assumed to uniformly take place over the entire surface the membrane  302 . 
         [0059]    In another example, the relative positions of fiducials (described below) on the inflatable membrane  302  can be compared in a deployed state vs. an undeployed state or other state in which the thickness of the inflatable membrane is known. This comparison, in combination with known material properties of the inflatable membrane  302  (compressibility, Poisson ratio, etc.) can be used to model the potentially varying thickness of the inflatable membrane. This has the advantage of accounting for potentially non-uniform variation of thickness the membrane  302  experiences in its deployed state. 
         [0060]    For optically based three-dimensional imaging techniques, the inflatable membrane may include an optical coating on the interior  309  thereof selected to improve performance of the three-dimensional scanning system. For example, the optical coating may include a matte finish to prevent light scattering and resulting imaging artifacts that might otherwise be caused by a glossy surfaces. The optical coating may also or instead include a fluorescent dye. The optically coating may also or instead include an optically absorptive coating, such as a black or other highly absorptive pigment or combination of pigments. In another aspect, the optical coating may include a predetermined color, which, as described in U.S. Pat. No. 8,107,086, for example, may be used in combination with a medium that differentially absorbs different wavelengths to resolve three-dimensional data. Particular colors may provide other advantages in varying conditions, and no particular predetermined color is intended to be required by the foregoing description. 
         [0061]    An optical material may be disposed within a wall of the inflatable membrane to similar affect. The optical material may for example include a fluorescent dye, a luminescent material, a black material, a pigment or the like. The optical material may be distributed throughout the entire inflatable membrane  302 , or in a pattern to form one or more fiducials for the three-dimensional scanning system. 
         [0062]    Where the scanner element  308  is an optical sensor such as an active (e.g., charge-coupled device) or passive (e.g., lens or fiber optic tip) imaging device, the optical sensor may usefully include a coating having an index of refraction matched to the index of refraction of the medium  310 . In this manner, optical distortion can be mitigated at the interface between the optical sensor and the medium. 
         [0063]    In another aspect, the inflatable membrane  302  may include a window  350  of transparent material in the distal end  352  providing a view from the interior  307  of the inflatable membrane to an exterior of the inflatable membrane  302  such as the ear canal  318 . This can provide visibility for positioning of the inflatable membrane  302 , such as to ensure that the inflatable membrane  302  is inserted sufficiently deep into the ear canal  318 , or to avoid collisions with sensitive tissue such as the tympanic membrane. In such embodiments, the scanner element  308  may include a camera or other imaging device oriented toward the window  350 , and the display  340  may be coupled to the camera by the scanning system  320  in order to display video images from the camera. The camera or other imaging device may have an optical coating with an index of refraction matched to the index of refraction of the medium  310 . 
         [0064]    At certain times, such as during insertion of the inflatable membrane  302  into the ear canal  318 , it may be desirable to have a view from the distal end  352  of the inflatable membrane  302  to facilitate manual navigation of the tip. To facilitate this navigation, the distal end  352  may include a fixture in the interior  307  shaped and sized to receive an imaging device such as an endoscope or an otoscope, and to align the imaging device to the window  350  in order to provide a view of the exterior through the window  350  with the imaging device. The imaging device may be the scanner element  308 , or may be an additional imaging device separate and independent from the scanning system  320 . The display  340  may be coupled to the imaging device and configured to display video images therefrom. The imaging device may have an optical coating having an index of refraction matched to the medium  310 . 
         [0065]      FIG. 4  shows an inflatable membrane  402  with a substantially conical profile. The inflatable membrane  402  may be used with any of the systems described above. The inflatable membrane  402  may include a reinforcing sheath  404  of a second elastic material or a non-elastic band or the like about a portion of the inflatable membrane  402  to impart a non-uniform inflation characteristic to the inflatable membrane  402 . That is, by reinforcing one or more regions of the inflatable membrane  402 , the reinforced regions will tend to inflate after regions without such reinforcement. The sheath  404  may be adhered to the inflatable membrane  402 , and/or may wrap fully around the inflatable membrane  402 . The sheath  404  may be disposed near the proximal end  406  of the inflatable membrane  402 , or at any other suitable location(s) according to the predetermined manner of inflation that is intended. 
         [0066]    In one aspect, the inflatable membrane  402  may include a vent tube  408  on an exterior  410  thereof, the vent tube  408  including a channel to permit a passage of air through the vent tube  408  from the distal end to the proximal end  406  when the inflatable membrane  402  is inflated within a passage such as an ear canal. In this manner, if the membrane inflates to the walls of a cavity to seal in a chamber at the distal end, air within the chamber can remain at an ambient pressure even as the chamber volume is reduced by expansion of the inflatable membrane  402  toward the distal end. 
         [0067]    In another aspect, a lubricant may be disposed on the exterior  410  surface of the inflatable membrane  402  to facilitate movement of the inflatable membrane  402  along a surface of a cavity while the inflatable membrane  402  is inflating within the cavity. This may advantageously avoid frictionally imposed distortions in the expansion of the inflatable membrane  402  so that the inflatable membrane  402  can fully expand along any adjacent surfaces of the cavity. 
         [0068]      FIG. 5  shows an inflatable membrane. The inflatable membrane  502  may be used with any of the systems described above. The inflatable membrane  502  may include a bulbous region  504  to form a seal within a cavity, or to accommodate the gross geometry of a cavity such as the ear canal. A pattern  506  of relatively inelastic material may be disposed on a portion of the inflatable membrane, which may provide an inflation characteristic (inelasticity) in the area of the pattern  506  to control the manner in which the inflatable membrane  502  inflates. The pattern  506  may include any size, shape, and number of patterns suitable for controlling inflation of the inflatable membrane  502 . For example, the pattern  506  may include circumferential bands about the inflatable membrane  502  or lateral bands at various locations to urge a curved manner of inflation. 
         [0069]    More generally, a variety of useful coatings to the exterior may be provided. Pad printing (e.g., 2d image onto 3d surface) or the like may be employed, for example to print fiducials, nonstretching dots or lines, or patterns that reduce reflections on the interior surface of the inflatable membrane. Pad printing may also usefully be employed to reduce elasticity of the inflatable membrane in certain regions, so that certain portions of the inflatable membrane  502  inflate before others, e.g., under lower pressure. This technique may be used, for example to print bands about the inflatable membrane  502  that encourage a tip-to-base inflation. 
         [0070]    In one aspect, the inflatable membrane  502  may be instrumented with a sensor such as a proximity sensor  508 . The proximity sensor  508  may be configured to provide a signal indicative of a proximity of the distal end to an external object such as an eardrum. The proximity sensor  508  may be wired or wireless, and may be disposed on an interior or an exterior of the inflatable membrane  502 . The proximity sensor  508  may include an infrared source/detector, an ultrasonic transducer, or any other device(s) suitable for measuring distance or otherwise detecting proximity. A processor of a three-dimensional scanning system may receive a signal from the proximity sensor  508  and generate an alert under one or more predetermined conditions, e.g., when a collision of the distal end of the inflatable membrane  502  with a wall of a cavity is imminent. The alert may activate an audible alarm, a visual alarm, a tactile alarm, or the like. The alert may also or instead, trigger other actions such as pausing inflation of the inflatable membrane  502 . 
         [0071]      FIG. 6  shows an inflatable membrane. The inflatable membrane  602  may be used with any of the systems described above, and may include an inflation characteristic for the inflatable membrane  602  to inflate in a predetermined manner. In one aspect, the inflation characteristic may include a bellows  604  formed into a portion of the inflatable membrane, or any other shape or combination of shapes to encourage a predetermined inflation pattern. 
         [0072]    The inflatable membrane  602  may include one or more fiducials  606  disposed on the interior thereof. The fiducials  606  may be used by a processor of the three-dimensional scanning system to calculate three-dimensional shape. The use of fiducials is well known in three-dimensional processing arts, and is not described in detail here except to generally note that recognizable features can assist in resolving particular locations within an image and/or across multiple images to facilitate more efficient processing. The one or more fiducials  606  may for example be used to register multiple frames of image data acquired from the scanner element(s) in order to provide a single three-dimensional model from multiple images. The fiducials  606  may include predetermined patterns such as cross-hairs, circles, squares, lines, or any other patterns, and combinations of the foregoing, printed on the interior of the inflatable membrane  602 . The fiducials  606  may also or instead include any such pattern(s) embedded into a material of the inflatable membrane during fabrication. In another aspect, the fiducials  606  may include predetermined three-dimensional shapes such as ridges or hemispheres on the interior of the inflatable membrane  602 . 
         [0073]    The inflatable membrane  602  may include a textured exterior  608  including one or more features to permit passage of air around an exterior of the inflatable membrane from the distal end to the proximal end when the inflatable membrane is inflated within a passage. The textured exterior  608  may include bumps, ridges, or any other features to create intermittent spacing between the inflatable membrane  602  and a wall of a cavity in which the inflatable membrane  602  is inflated. 
         [0074]    It will be appreciated that the above computing devices and processors may be realized in hardware, software, or any combination of these suitable for the control, data acquisition, and data processing described herein. This includes realization in one or more microprocessors, microcontrollers, embedded microcontrollers, programmable digital signal processors or other programmable devices, along with internal and/or external memory. This may also, or instead, include one or more application specific integrated circuits, programmable gate arrays, programmable array logic components, or any other device or devices that may be configured to process electronic signals. It will further be appreciated that a realization of the processes or devices described above may include computer-executable code created using a structured programming language such as C, an object oriented programming language such as C++, or any other high-level or low-level programming language (including assembly languages, hardware description languages, and database programming languages and technologies) that may be stored, compiled or interpreted to run on one of the above devices, as well as heterogeneous combinations of processors, processor architectures, or combinations of different hardware and software. At the same time, processing may be distributed across devices such as a camera and/or computer and/or server or other remote processing resource in a number of ways, or all of the functionality may be integrated into a dedicated, standalone device. All such permutations and combinations are intended to fall within the scope of the present disclosure. 
         [0075]    While the invention has been disclosed in connection with the preferred embodiments shown and described in detail, various modifications and improvements thereon will become readily apparent to those skilled in the art. Accordingly, the spirit and scope of the present invention is not to be limited by the foregoing examples, but is to be understood in the broadest sense allowable by law.