Patent Publication Number: US-2017360298-A1

Title: Three-dimensional plantar imaging apparatus and membrane assembly for use in the same

Description:
RELATED APPLICATIONS 
     This present application claims benefit of priority under 35 U.S.C. §120 as a continuation of U.S. application Ser. No. 15/032,273, filed Apr. 26, 2016, which claims priority to International Application No. PCT/CA2015/050453, filed May 20, 2015, which claims priority under 35 U.S.C. §0.119(e) to U.S. provisional patent application No. 62/001,488 filed on May 21, 2014. The above-referenced applications are hereby incorporated by reference into the present application in their entirety. 
    
    
     TECHNICAL FIELD 
     The general technical field relates to techniques for acquiring the plantar foot shape of a patient for manufacturing a patient-specific orthosis and, in particular, to techniques for acquiring a three-dimensional image of the plantar surface of a foot. 
     BACKGROUND 
     Various techniques exist for measuring the three-dimensional (3D) shape of a foot for the production of orthoses. The traditional technique generally involves forming a cast and mold of the foot in a non-weight-bearing condition. Despite having certain advantages in terms of simplicity and cost, the casting techniques can be relatively time consuming and labor intensive, which limit the number of patients that a practitioner can treat daily. 
     More recent techniques have relied on optical imaging techniques to acquire a 3D plantar foot shape, typically using a digital laser scanner. The image data can subsequently be used in a computer-aided design and manufacturing (CAD/CAM) system to fabricate a patient-specific orthosis. Optical imaging techniques can provide time and cost advantages over traditional casting and molding techniques and, depending on the intended application, can allow the 3D plantar image to be acquired in any of a non-weight-bearing, full-weight-bearing and semi-weight-bearing state, each having its own challenges and limitations. 
     For example, measurement techniques that acquire an image of the plantar surface with the foot in a non-weight-bearing state generally cannot account for the natural elongation and deformation of the foot that occur when weight is applied thereto, which can lead to unreliable measurements. Meanwhile, in a full-weight-bearing condition, the deformation imposed on the foot can become significant enough so as to negatively affect the reliability of the scanned image, notably the arch measurements. It can also be difficult to position the foot in a neutral position in a full-weight-bearing condition. A semi-weight-bearing condition can provide an intermediate and, in principle, more accurate configuration to acquire an image of the plantar surface, as this condition is often more representative of the natural elongation and deformation of the foot in the walking stance. However, acquiring a 3D plantar image with the entire length of the foot in a semi-weight-bearing state is not straightforward, as achieving proper soft tissue deformation requires careful positioning of the foot, which can prove challenging using existing techniques. 
     Accordingly, many challenges remain in the development of techniques for acquiring a 3D plantar image with the whole foot in a semi-weight-bearing condition, while also overcoming or at least alleviating some of the drawbacks of existing techniques. 
     SUMMARY 
     In accordance with an aspect, there is provided a membrane assembly for use with a three-dimensional imager to obtain a topographical plantar image of a foot. The membrane assembly includes a support structure having a front end and a rear end, the rear end being elevated relative to the front end; and a flexible membrane suspended from the support structure and configured to receive and support an entire plantar surface of the foot, the flexible membrane defining and enclosing an upper portion of an inflatable chamber, the flexible membrane including a forefoot-receiving region and a rearfoot-receiving region respectively adjacent to the front end and the rear end of the support structure, the rearfoot-receiving region being under less tension than the forefoot-receiving region, the three-dimensional imager being positionable under the flexible membrane in order to acquire the topographical plantar image when the foot is disposed on the flexible membrane. 
     In accordance with another aspect, there is provided an apparatus for obtaining a topographical plantar image of a foot in a semi-weight-bearing condition. The apparatus includes a three-dimensional imager; a support structure having a front end and a rear end, the rear end being elevated relative to the front end; and a flexible membrane suspended from the support structure and configured to receive an entire plantar surface of the foot thereon, the flexible membrane defining and enclosing an upper portion of an inflatable chamber, the flexible membrane including a forefoot-receiving region and a rearfoot-receiving region respectively adjacent to the front end and the rear end of the support structure, the rearfoot-receiving region being under less tension than the forefoot-receiving region, the three-dimensional imager being provided under the flexible membrane in order to acquire the topographical plantar image when the foot is disposed on the flexible membrane. 
     In accordance with a further aspect, there is provided a method for imaging a foot having a front portion and a rear portion. The method includes: providing a flexible membrane suspended from a support structure having a front end and a rear end elevated relative to the front end, the flexible membrane defining and enclosing an upper portion of an inflatable chamber, the flexible membrane including a forefoot-receiving region and a rearfoot-receiving region respectively affixed to the front end and the rear end of the support structure, the rearfoot-receiving region being under less tension than the forefoot-receiving region; adjusting an internal pressure of the inflatable chamber; positioning the foot on the membrane in a semi-weight-bearing condition with an entire plantar surface of the foot being supported by the flexible membrane with the front and rear portions of the foot respectively located in the forefoot and rearfoot-receiving regions of the membrane; and acquiring a topographical plantar image of the foot. 
     In accordance with another aspect, there is provided a use of the membrane assembly as described herein, in conjunction with a three-dimensional imager, for obtaining a topographical plantar image of a foot. 
     In accordance with another aspect, there is provided a use of the apparatus as described herein for obtaining a topographical plantar image of a foot. 
     Other features and advantages of aspects of the present invention will be better understood upon reading of preferred embodiments thereof with reference to the appended drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is schematic perspective view of an apparatus for obtaining a topographical image of a plantar surface of a foot, in accordance with an embodiment. 
         FIG. 2  is the same as  FIG. 1 , but with a foot received on the flexible membrane. 
         FIG. 3  is a cross-sectional side view of the apparatus of  FIG. 1 , taken along section line  3  and depicting a foot above the flexible membrane. 
         FIG. 4  is the same as  FIG. 3 , but with the foot received on the flexible membrane. 
         FIG. 5  is a partially exploded, cross-sectional side view of the apparatus of  FIG. 1 , taken along section line  3 - 3  and depicting in more detail the configuration of the support structure from which is suspended the flexible membrane. 
         FIG. 6  is a partially exploded perspective view of the apparatus of  FIG. 1 . 
         FIG. 7  is a top plan view of  FIG. 1 , with a foot received on the flexible membrane. 
         FIG. 8  is a schematic perspective view of a membrane assembly, in accordance with an embodiment. 
         FIG. 9  is a cross-sectional side view of an apparatus for obtaining a topographical image of a plantar surface of a foot, in accordance with another embodiment. 
         FIG. 10  is a schematic perspective view of an apparatus for obtaining a topographical image of a plantar surface of a foot, in accordance with a further embodiment. 
         FIG. 11  is a schematic perspective view of an apparatus for obtaining a topographical image of a plantar surface of a foot, in accordance with a still another embodiment. 
         FIG. 12  is the same as  FIG. 11 , but with a foot received on the flexible membrane. 
         FIG. 13  is the same as  FIG. 11 , but with the tension member pivoted from an operative to an inoperative position. 
         FIG. 14  is a schematic perspective view of a membrane assembly, in accordance with another embodiment. 
         FIG. 15  is a schematic cross-sectional side view of an apparatus for obtaining a topographical image of a plantar surface of a foot, in accordance with another embodiment. 
         FIG. 16A  is a schematic, simplified front view of the apparatus of  FIG. 2 .  FIG. 16B  is a schematic, simplified rear view of the apparatus of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, similar features in the drawings have been given similar reference numerals, and, in order to not unduly encumber the figures, some elements may not be indicated on some figures if they were already identified in preceding figures. It should also be understood herein that the elements of the drawings are not necessarily depicted to scale, since emphasis is placed upon clearly illustrating the elements and structures of the present embodiments. 
     The present description generally relates to techniques for obtaining a topographical plantar image of a foot. In particular, in accordance with different aspects, there are provided a membrane assembly for use with a 3D imager, an apparatus including a membrane assembly and a 3D imager, and a method for imaging the plantar surface of a foot. 
     As used herein, the term “topographical plantar image” and variants thereof broadly refer to a 3D relief map or model replicating the plantar foot surface in a certain weight-bearing condition. The topographical plantar image generally consists of arrays of 3D data points, each described by its spatial coordinate Z(x, y), where Z is the local height or elevation of the surface at position (x, y). As described below, a topographical image of the plantar shape can be acquired using optical methods, for example 3D laser scanners, and 3D digital stereo imaging systems. 
     As used herein, the term “plantar surface” has its ordinary meaning and refers to the underside or bottom surface of the foot. 
     As known in the art, topographical plantar images may be acquired with the foot in three main weight-bearing conditions: non-weight bearing, full-weight bearing and semi-weight bearing. First, the term “non-weight bearing” refers to a weight-bearing condition where no body weight or forces are applied to the foot, as if the foot were in suspension. Meanwhile, the term “full-weight bearing” refers to a weight-bearing condition where the foot supports the whole body weight. Finally, the term “semi-weight bearing” refers to a weight-bearing condition where only a certain amount of body weight is applied supported by the foot, such as, for example, between 20% and 50% of the total body weight. Of course, this range is provided for exemplary purposes only, such that values lying outside this range can be used in certain embodiments. It is to be noted that, in the present description, the terms “semi-weight bearing” and “partial-weight bearing” can be used interchangeably. 
     As mentioned above, in some instances, acquiring a 3D plantar image with the foot in a semi-weight-bearing state may be desirable. One reason for this is that the amount of soft tissue deformation under semi-weight bearing can be controlled more accurately and be more representative of the natural physiological deformation of the foot under body weight, for example the height of the medial and lateral arches and the natural deformation of the foot axis. Hence, measuring the 3D plantar shape under some controlled level of deformation can be beneficial, while an absence or excess of deformation, as in non-weight-bearing and full-weight-bearing conditions, can lead to inaccuracies in the measured data. Acquiring a 3D plantar image in a semi-weight-bearing condition can be challenging and can involve providing: (i) a foot-receiving surface which is not locally deformed by another physical part of the system (e.g., a plate-like surface) when the foot is received thereon; (ii) a controlled pressure exerted on the foot which is adapted to the flexibility and dimensions of the foot, and which induces a deformation of the foot that is anatomically similar to the natural physiological deformation of the foot under body weight; and (iii) a configuration that can remain stable over the entire duration of the image acquisition process. 
     The techniques described herein allow for a 3D plantar image to be acquired under semi-weight bearing with the entire plantar surface of the foot received on and supported solely by a flexible and inflatable membrane suspended from a support structure. As will be described in greater detail below, achieving this semi-weight-bearing configuration involves configuring, among other things, the flexible membrane such that the region of the membrane for receiving the rear of the foot (e.g., the heel) is connected higher on the support structure and under less tension than the region of the membrane intended for receiving the front of the foot (e.g., the toes). 
     Apparatus for Acquiring a 3D Plantar Image and Membrane Assembly 
     Referring to  FIGS. 1 to 7 , there is illustrated an exemplary embodiment of an apparatus  20  configured for obtaining a topographical image of a plantar surface  22  of a foot  24 . Broadly described, the apparatus  20  generally includes a support structure  26 , a flexible membrane  28  suspended from the support structure  26  and configured to receive and support at least partially a weight of the foot  24  thereon, and a 3D imager  30  provided under the flexible membrane  28  to acquire the topographical image of the plantar surface  22  of the foot  24  when the foot  24  is placed on the flexible membrane  28  (see  FIGS. 2, 4 and 7 ). Furthermore, the flexible membrane  28  defines and encloses an upper portion of an inflatable chamber  32 . More details regarding the various operational and structural features of the apparatus will be discussed further below. 
     As used herein, the term “support structure” refers broadly to any structure that can hold and mechanically support the flexible membrane, generally via its periphery, in a manner such that the flexible membrane hangs from the support structure while hermetically sealing the inflatable chamber. 
     As used herein, the term “flexible membrane” is intended to refer to any sheet-like or otherwise relatively thin layer of elastic and stretchable material which is mechanically deformed in response to the action of an applied load, for example, the force exerted by the weight of the foot received on the membrane. It is noted that for simplicity, the term “flexible membrane” may, in some instances, be shortened to “membrane”. In an embodiment, the membrane may have an ultimate elongation greater than 300%, for example 600%, although different values of ultimate elongation may be used in other embodiments. As known in the art, the term “ultimate elongation” refers to the percentage increase in the length of a material that occurs before the mechanical properties of the material change irreversibly (e.g., due to breakage under tension or to the onset of crystallization). It is to be noted that, for the purpose of the present description and unless stated otherwise, the terms “flexible”, “elastic”, “stretchable”, “foldable” and variants thereof can be used interchangeably to designate the ability of the membrane to be deformed under an applied load. 
     Referring still to  FIGS. 1 to 7 , the flexible membrane  28  may be made of any suitable flexible material including, without limitation, polymers, plastics, thermoplastics, rubber, synthetic rubbers, elastomers, and the like. For example, in an embodiment, the flexible membrane  28  is made of a silicone-based flexible material. The flexible membrane  28  can be made by casting, molding, extrusion, thermoforming, 3D printing, or any other suitable manufacturing process or technique. The flexible membrane  28  may have a thickness ranging from about 0.5 millimeter (mm) to about 4 mm, and particularly between about 0.8 mm and about 1.2 mm. For example, in the illustrated embodiment, the thickness of the membrane  28  is 0.8 mm. It is to be noted that the flexible membrane  28  may, but need not, have a uniform thickness. Also, the membrane  28  may be flat or have a preformed shape (e.g., concave or convex), or have a different configuration on each side thereof. More details regarding the shape and configuration of the flexible membrane will be discussed further below. 
     The support structure  26  includes a front end  34   a  and a rear end  34   b , which are provided such that rear end  34   b  is elevated relative to front end  34   a . As used herein, the term “elevated” refers to the rear end of the support structure being vertically higher than the front end when measured upwardly from the bottom of the apparatus. In an embodiment, the elevation angle of the rear end  34   b  of the support structure  26  relative to the front end  34   a  thereof ranges between about 5 degrees and about 30 degrees, and in another embodiment between about 5 degrees and about 6 degrees, although other elevation angle values may be used in other embodiments. It will be understood that, when referring to the relative position of the front and rear ends  34   a ,  34   b  of the support structure  26 , the term “elevation angle” of the support structure  26  is defined as the tangent of the elevation angle which is equal to the ratio of the vertical distance to the horizontal distance between the front end  34   a  and the read end  34   b.    
     The flexible membrane  28  includes a forefoot-receiving region  36   a  and a rearfoot-receiving region  36   b  proximate and affixed to the front end  34   a  and the rear end  34   b  of the support structure  26 , respectively. It is understood that, when designating the regions of the flexible membrane  28 , the terms “forefoot” and “rearfoot” refer to the fact that the forefoot and the rearfoot-receiving regions  36   a ,  36   b  are intended to receive and support the front and rear portions  38   a ,  38   b  of the foot  24 , respectively. As a result of the rear end  34   b  of the support structure  26  being elevated relative to the front end  34   a , the flexible membrane  28  is downwardly inclined toward the forefoot-receiving region  36   a . In particular, the inclination angle of the suspended membrane  28  corresponds to the elevation angle of the support structure  26  thereof. In an embodiment, the configuration of the support structure  26  may optionally allow for the elevation angle of the support structure  26 , and thus for the inclination angle of the membrane  28 , to be adjusted over a certain angular range. More details regarding the advantages of suspending the membrane  28  in a downwardly inclined manner toward the forefoot-receiving region  36   a  will be discussed further below. 
     Referring still to  FIGS. 1 to 7 , the support structure  26  can form part of a housing  48 , which generally defines the overall shape of at least an upper portion of the apparatus  20 . The housing  48  has a top wall  50 , a bottom wall  52 , and a sidewall  54  interconnecting the top and bottom walls  50 ,  52 . The sidewall  54  includes four wall panels, but this number may differ in other embodiments. In the illustrated embodiment, one or more transparent windows  66  may optionally be provided on the sidewall  54  to allow for the podiatric physician to better see the foot received on the flexible membrane  28  and more conveniently adjust its position as well as to allow for a camera (not shown) to acquire an image of the membrane  28  when the foot  24  is received thereon. The transparent windows  66  may also be provided to reduce the weight of the apparatus  20 . In another embodiment, transparent windows may be omitted and an optional positioning system (not shown) may be provided inside the housing  48  to facilitate the positioning of the foot  24  on the flexible membrane  28 . The housing  48  may be made of light yet sturdy and durable material including, without being limited to, molded plastic or lightweight metals alloys. The housing  48  may also be compact and have an ergonomic shape (e.g., rounded corners and smooth surfaces) to facilitate its use and operation. 
     In the illustrated embodiment, the top wall  50  is inclined at a slope angle θ, which corresponds to the elevation angle of the support structure  26  and, thus, to the inclination angle of the flexible membrane  28 . Accordingly, the slope angle θ of the top wall  50  relative to the bottom wall  52  may range between about 5 degrees and about 30 degrees, although other slope angle values may be used in other embodiments. It is also to be noted that, in other embodiments, the angle, if any, between the top and the bottom wall  50 ,  52  of the housing  48  need not be equal to the elevation angle of the support structure  26 . 
     In the illustrated embodiment, the support structure  26  includes a peripheral frame  42  that encloses an opening  40  formed through the top wall  50  of the housing  48 . The flexible membrane  28  is affixed to the peripheral frame  42  in a way such as to extend across and hermetically seal the opening  40 . As a result of the opening  40  being hermetically sealed, the flexible membrane  28  and the housing  48  together define and enclose the inflatable chamber  32 . In this regard, it will be understood that, in some embodiments, the support structure  26  need not form part of a housing, as long as the flexible membrane  28  is suspended from the support structure  26  and defines and encloses an upper portion of the inflatable chamber  32 . 
     In the illustrated embodiment, the opening  40  generally has an ovoid shape, with a width that increases from the front end  34   a  toward the rear end  34   b  of the support structure  26 . Of course, in other embodiments, the opening  40  may have another shape, for example an ellipse (see  FIG. 10 ) or a rectangle (see  FIG. 11 ), or any other suitable regular or irregular shape. Moreover, in other embodiments, the opening  40  may have a substantially uniform width, as depicted in  FIGS. 10 and 11 . It is to be noted that the term “width” and variants thereof refer herein to a linear dimension that extends perpendicularly to a line extending between the front and the rear ends of the support structure or, equivalently, perpendicularly to the longitudinal axis of the foot when received on the flexible membrane (see, e.g.,  FIG. 7 ). More details regarding the advantages of varying the width of the opening enclosed by the peripheral frame of the support structure will be discussed further below. 
     Turning now to  FIGS. 3 to 5 , in the illustrated embodiment, the peripheral frame  42  of the support structure  26  includes an upper frame member  44   a  and a lower frame member  44   b , the lower frame member  44   b  being received in a peripheral groove  46  formed in the top wall  50  of the housing  48 . As illustrated in  FIGS. 3 to 5 , the upper and lower frame members  44   a ,  44   b  cooperate to sealingly clamp the periphery of the flexible membrane  28  therebetween and against the outer wall of the peripheral groove  46 . In one embodiment, either or both of the upper and lower frame members  44   a ,  44   b  are detachably connected to the top wall  50  of the housing  48 . 
     Of course, those skilled in the art will appreciate that the flexible membrane can be held by and connected to the support structure using a number of fastening or anchoring mechanisms or arrangements, as long as, in the intended use of the apparatus, the membrane remains suspended from the support structure and hermetically seals the inflatable chamber. In some implementations, it may also be desirable that the support structure allows for the flexible membrane to be conveniently removed and reinstalled (e.g., following a rupture of the membrane or for cleaning the membrane). Furthermore, in some embodiments, the flexible membrane  28  may be intended to be releasably affixed to the support structure  26 , which can allow the membrane  28  to be conveniently cleaned, replaced, repaired, repositioned, tighten or loosen, or otherwise serviced. 
     Referring still to  FIGS. 3 to 5 , in the illustrated embodiment, the flexible membrane  28  is clamped continuously along the entire periphery thereof by the peripheral frame  42 , which can improve the strength of the connection and the integrity of the seal therebetween. However, in other embodiments, the periphery of the flexible membrane  28  may be connected to the support structure  26  at a plurality of discrete anchoring points, which can be regularly spaced or not, while maintaining inflatable chamber  32  hermetically sealed from the outside. It will be understood that by adjusting how the flexible membrane  28  is suspended from the support structure  26 , it may be possible to adjust the value and/or the uniformity of the tension of the membrane  28 . More details regarding how locally adjusting the tension of the flexible membrane can help achieving a semi-weight-bearing state when the foot is received on the membrane will be discussed further below. 
     Referring still to  FIGS. 3 to 5 , in the illustrated embodiment, the apparatus  20  may include an inflation unit  58  in fluid communication with the inflatable chamber  32 . The inflation unit  58  is configured to selectively supply or discharge a pressurized fluid into or from the inflatable chamber  32 , using valves or other suitable actuators, so as to regulate an internal pressure of the inflatable chamber  32  and, thereby, selectively inflate or deflate the inflatable chamber  32  and thereby adjust the pressure applied on the flexible membrane  28 . In other words, when the inflatable chamber  32  is pressurized, the flexible membrane  28  can form an air cushion for receiving and supporting the foot in a semi-weight-bearing condition, as described further below. It is to be noted that the pressurized fluid is generally a gas, for example air, although the techniques described herein would not preclude the use of a liquid. 
     In some implementations, the inflation unit  58  can include a pressure sensor  80  (see, e.g.,  FIG. 3 ) in fluid communication with the inflatable chamber  32  for measuring the internal pressure in the inflatable chamber  32  which, in an embodiment, can be increased up to 5 kilopascals, although other internal pressure values may be used in other embodiments. It will be understood that the inflation unit  58  can be embodied using a variety of techniques, equipment and components known to those skilled in the art. Hence, its structure and operation need not be discussed in further detail herein. 
     Referring back to  FIGS. 1 to 7 , the apparatus  20  further includes a 3D imager  30 , the 3D imager being provided under the flexible membrane  28  in order to acquire the topographical image of the plantar surface  22  when the foot  24  is disposed on the flexible membrane  28 , as better illustrated in  FIG. 4 . As used herein, the term “3D imager” refers broadly to any component, device or system capable of acquiring a topographical image of the plantar surface when the foot is received on and supported by the flexible membrane. As mentioned above, the topographical image of the plantar surface of the foot provides a 3D model that replicates the plantar foot surface and generally consist of an array of data points, each designated by a spatial coordinate Z(x, y), where Z is the local height or elevation of the surface at position (x, y), generally measured from a reference plane of the 3D imager. It should be mentioned that, as used herein, the terms “light”, “optical” and variants thereof are intended to refer to electromagnetic radiation in any appropriate region of the electromagnetic spectrum, and are not limited to visible light. 
     By way of example, in the illustrated embodiment, the 3D imager is a 3D laser scanner, such as the iQube™ scanner commercially available from Delcam Plc., Birmingham, UK. It will be appreciated, however, that various other conventional or specialized imaging devices, whether active or passive, may be used in other embodiments, depending on performance requirements or constraints of the device, for example in terms of its field of view, spatial resolution, sensitivity, image acquisition speed, size, weight, cost, and the like. Examples of suitable types of 3D imaging devices include, without limitation, 3D structured-light cameras, 3D time-of-flight cameras, 3D stereoscopic cameras, and other imaging devices capable of acquiring 3D depth images. 
     In the illustrated embodiment, the housing  48  is mounted onto the 3D imager  30 , with the bottom wall  52  of the housing  48  in contact with the top surface  60  of the 3D imager. It will be understood that, in the illustrated embodiment, the 3D imager is configured to acquire the topographical image of the plantar surface  22  through the bottom wall  52  of the housing  48 . Therefore, the bottom wall  52  of the housing  48  should be made of an optically transparent material (e.g., glass or another suitable material) on at least portion thereof sufficiently large to allow a topographical image of the entire plantar foot surface to be captured in one acquisition by the 3D imager  30 . 
     It will be understood that, in the illustrated embodiment, the 3D imager  30  is releasably connected to the rest of the apparatus  20 . In such a case, and referring to  FIG. 8 , the support structure  26  and the flexible membrane  28  suspended therefrom and defining an upper portion of the inflatable chamber  32  can define a membrane assembly  56  for use with, but manufactured independently of, the 3D imager  30 . 
     Referring to  FIG. 15 , in another embodiment, the 3D imager  30  may alternatively be positioned inside the housing  48 , so that no part or component of the apparatus  20  is interposed between the 3D imager  30  and the flexible membrane  28 . It will be understood that in such a case, the 3D imager  30  would be provided inside the inflatable chamber  32  and be formed integrally with the other components of the apparatus  20 . 
     In an embodiment, the flexible membrane may be partially or fully opaque to the optical radiation used by the 3D imager, in which case the 3D imager actually acquires an image of the flexible membrane deformed by the foot received thereon. However, in another embodiment, the flexible membrane may be optically transparent to the optical radiation used by the 3D imager, so that the image of the plantar surface itself is acquired by the 3D imager. 
     As mentioned above, a general aim of the techniques described herein consists in controlling the forces exerted on the forefoot by the membrane, in order to reduce the deformation of the forefoot which, if significant, can have repercussions on the overall shape of the plantar surface and, potentially, degrade the reliability and accuracy of the 3D plantar image. In particular, it is desirable that the toes are neither excessively dorsiflexed (i.e., not overly curled up) nor forming “artificial” lateral arches (i.e., either concave or convex), so as to ensure that the medial and lateral arches, whose shape is to be acquired, are not adversely deformed. At the same time, a certain amount of deformation in the rear foot region may be beneficial, especially as it can allow the 3D plantar image to be more representative of the natural physiological deformation of the medial and lateral arches. As will now be described, in the techniques described herein, the control of the forces exerted on and deformation experienced by the foot may be achieved by carefully selecting the structure and configuration of the flexible membrane and/or the support structure including the opening. 
     Referring to  FIGS. 1 to 7 , and more particularly to  FIG. 4 , in the techniques described herein, the flexible membrane  28  is configured to receive and support alone and autonomously the foot  24 . Stated otherwise, during the acquisition of the topographical plantar image, the entire plantar surface of the foot  24  is supported solely by the inflatable suspended flexible membrane  28 , without contact with other physical parts or components of the apparatus  20 . This condition can be achieved, for example, by properly selecting the shape and the elasticity of the flexible membrane  28 , as well as the configuration in which it is suspended from the support structure  26  (e.g., the inclination of the membrane  18  due to the rear end  34   b  of the support structure  26  being elevated relative to the front end  34   a  thereof). 
     In contrast to certain known systems (see, e.g., U.S. Pat. No. 7,392,559), in the present apparatus  20 , when the foot  24  is placed on the flexible membrane  28  and the inflatable chamber  32  is pressurized, the membrane  28  does not become stretched to such an extent that the front portion  38   a  of the foot  24  impinges on and bears against an underlying solid surface (e.g., the bottom wall  52  of the housing  48  in  FIG. 4 ) while the rear portion  38   b  of the foot  12  remains suspended. Indeed, if the front portion  38   a  of the foot were to abut against the bottom wall  52  of the housing  48  during the image acquisition process, the resulting deformation of the front portion  38   a  of the foot  24  would create a full-weight-bearing condition and improper deformation of the overall plantar surface  22 , which could in turn negatively affect the reliability of the acquired image data. Hence, in the embodiment of  FIGS. 1 to 7 , the vertical separation between the suspended membrane  28  and the bottom wall  52  is such that no portion of the foot  24  will impinge on and bear against the bottom wall  52  when the foot  24  is received on the flexible membrane  28  and the pressure inside the inflatable chamber  32  is raised to a value that produces a semi-weight-bearing condition, for example, and without limitation, between 3 and 7 kilopascals. 
     Referring still to  FIGS. 1 to 7 , in addition to being configured for supporting the entire plantar surface  22  of the foot  24  alone and unaided by another physical component, the flexible membrane  28  is configured such that the rearfoot-receiving region  36   b  is under less tension than the forefoot-receiving region  36   a . Indeed, it will be understood that by having a higher tension in the forefoot-receiving region  36   a  than in the rearfoot-receiving region  36   b  the deformation undergone by the front portion  38   a  of the foot  24  will be smaller than that undergone by the rear portion  38   b , thus making it easier for the foot  24  to reach a semi-weight-bearing condition. 
     As will now be described, a non-uniform tension in the flexible membrane  28  can be achieved by adjusting the physical properties of the flexible membrane  28  itself and/or the manner by which it is suspended from the support structure  26  (e.g., whether the tension imposed on the membrane  28  by the support structure  26  is uniform or not). 
     Referring more specifically to  FIGS. 5 and 6 , in the illustrated embodiment, the flexible membrane  28  is preformed so that its upper surface  62  includes an upwardly concave recessed area  64  formed in the rearfoot-receiving region  36   b . As used herein, the term “preformed” is used to indicate that the flexible membrane has been subjected, prior to being affixed to the support structure, to a manufacturing process to confer to the flexible membrane a form having a predetermined size and shape and, generally, a non-flat cross-section. The term “preformed” also refers to the fact that the flexible membrane retains shape conferred thereto when disposed on a flat surface. Of course, since it is made of an elastic material, the flexible membrane will nevertheless be deformed when a sufficient load is applied thereto (e.g., the weight of a foot). 
     Referring still to  FIGS. 5 and 6 , in the illustrated embodiment, the flexible membrane  28  is under less tension in the rearfoot-receiving region  36   b  than in the forefoot-receiving region  36   a  as a result of the extra “slack” or “looseness” deliberately introduced in the rearfoot-receiving region  36   b  by the concave recessed area  64 . It is noted that in the illustrated embodiment, the width of the membrane  28  is greater in the rearfoot-receiving region  36   b  than in the forefoot-receiving region  36   a  due not only to the slack or looseness created by the concave recessed area  64 , but also to the fact that the width of the opening  40  enclosed by the peripheral frame  42 , and across which is supported the flexible membrane  28 , has a width that increases from the front end  34   a  toward the rear end  34   b  of the support structure  26 . 
     Referring to  FIG. 10 , in another embodiment, a semi-weight-bearing condition may be achieved with a flexible membrane  28  preformed to be less tensioned in the rearfoot-receiving region  36   b , but with the opening  40  enclosed by the peripheral frame  42  having a substantially uniform width. 
     Referring to  FIG. 9 , in still another embodiment, the tension in the flexible membrane  28  may be controlled by providing the membrane  28  with a non-uniform thickness. In particular, in the embodiment of  FIG. 9 , the membrane has a thickness greater in the forefoot-receiving region  36   a  than in the rearfoot-receiving region  36   b , thereby increasing the tension in the former compared to the latter. 
     Turning now  FIGS. 16A and 16B , there are shown a front view and a rear view, respectively, of the apparatus  20  depicted in  FIG. 2 , which illustrate that the front portion  38   a  and the rear portion  38   b  of the foot  24  are under different conditions when received on the flexible membrane  28 . First, referring to  FIG. 16A , it can be seen that the forefoot-receiving region  36   a  of the flexible membrane  28  is under relatively high tension and presents a rather uniform and flat receiving surface to the front portion  38   a  of the foot  24 . As a result, the deformation of the front portion  38   a  of the foot  24  due to either vertical or lateral compressive loads remains relatively small. In particular, turning briefly to  FIG. 7 , the toes  76  are neither overly curled up nor forming artificial lateral arches, which otherwise would negatively impact the measurements of the medial and lateral arches  78   a ,  78   b . Second, referring to  FIG. 16B , the rearfoot-receiving region  36   b  is under reduced tension and receives the rear portion  38   b  of the foot  24  in the concave recessed area  64 . As a result, the rearfoot-receiving region  36   b  of the flexible membrane  28  produces larger lateral and vertical compressive forces and envelops the foot  12  more than does the forefoot-receiving region  36   a  (see  FIG. 16A ). It will be understood that in such a configuration, the foot  24  can be placed more readily in a semi-weight-bearing condition. 
     Referring still to  FIGS. 1 to 7 , it is often desirable that, in a semi-weight-bearing state, the upwardly directed reaction force acting on the foot  24  in response to the downwardly directed force exerted by the foot  24  received on the flexible membrane  28  be as uniform as possible over the foot plantar surface  22 . In a non-limitative embodiment, the patient may be in a sitting position when he or she places his or her foot  24  on the flexible membrane  28 . This configuration generally results in the force exerted by the rear portion  38   b  of the foot  24  on the rearfoot-receiving region  36   b  of the flexible membrane  28  being greater than the force exerted by the front portion  38   a  of the foot  24  on the forefoot-receiving region  36   a  of the flexible membrane  28 , due to the additional downwardly directed force generally applied by the podiatric physician on the patient&#39;s knee. It will be understood that by providing the rear end  34   b  of the support structure  26  higher than the front end  34   a  such as to suspend the membrane  28  at an inclination angle, it may be possible to compensate at least partially for this excess of force acting on the rear portion  38   b  of the foot  24 . As a result, the plantar surface  22  of the foot  24  may advantageously be oriented substantially parallel to the image plane of the 3D imager  30  during the image acquisition procedure. 
     Referring now to  FIGS. 11 to 13 , there is illustrated another embodiment of an apparatus  20  for a topographical image of a plantar surface  22  of a foot  24  in a semi-weight-bearing condition. As for the embodiment of  FIGS. 1 to 7 , the apparatus  20  in  FIGS. 11 to 13  includes a support structure  26  having a front end  34   a  and a rear end  34   b  elevated relative to the front end  34   a , a flexible membrane  28  suspended from the support structure  26  and configured to receive and support the entire plantar surface  22  of the foot  24  thereon, and a 3D imager  30  provided under the flexible membrane  28  in order to acquire the topographical image of the plantar surface  22  when the foot  24  is disposed on the flexible membrane  28 . The flexible membrane  28  defines and encloses an upper portion of an inflatable chamber  32 , and includes a forefoot-receiving region  36   a  and a rearfoot-receiving region  36   b , where the rearfoot-receiving region  36   b  is under less tension than the forefoot-receiving region  36   a .  FIG. 14  is a membrane assembly  56  which can be used with a 3D imager to form an apparatus such as that illustrated in  FIGS. 11 to 13 . 
     In contrast to the embodiment of  FIGS. 1 to 7 , in the embodiment of  FIGS. 11 to 13 , the difference in tension between the forefoot-receiving region  36   a  and the rearfoot-receiving region  36   b  is not achieved by preforming the flexible membrane  28 . Rather, the difference in tension is achieved by anchoring the flexible membrane  28  non-uniformly along the peripheral frame  42  of the support structure  26  so as to create a “slack” or “looseness” in the rearfoot-receiving region  36   b . By way of example, in an embodiment, this can be achieved first by placing the flexible membrane  28  on a preformed surface (not shown) in such a way as to make the rearfoot-receiving region  36   b  looser than the forefoot-receiving region  36   a . Then, while still located on the preformed surface, the flexible membrane  28  can be affixed to the peripheral frame  42  forming the support structure  26  in a manner such as to maintaining looseness in the rearfoot-receiving region  36   b . Finally, the support structure  26  with the flexible membrane  28  affixed thereto can be installed on the top wall  50  of the housing  48 . 
     Referring still to  FIGS. 11 to 13 , the apparatus  20  further includes a tension member  70  configured to be urged against and exert a downwardly directed force on a peripheral portion  68  of the forefoot-receiving region  36   a  of the flexible membrane  28 . In the illustrated embodiment, the tension member  70  is U-shaped and includes two legs  72   a ,  72   b  between which can be received the front portion  38   a  of the foot  24  (see  FIG. 12 ). The tension member  70  may, but need not, be made of a transparent material so as not to interfere with the image acquisition process. Furthermore, in the illustrated embodiment, the tension member  70  is pivotable about a pivot axis  74  between an operative position, where the tension member  70  is urged against and exerts the downwardly directed force onto the peripheral portion  68  of the forefoot-receiving region  36   a  of the membrane  28 , and an inoperative position, where the tension member  70  is pivoted away from the membrane  28 . 
     Referring still to  FIGS. 11 to 13 , when tension member  70  is in the operative position, it is pushed against the flexible membrane  28 , thereby increasing the slope between the forefoot-receiving region  36   a  and the rearfoot-receiving region  36   b . It will be understood that the tension member  70  acts to increase the tension applied to the membrane  28  in the forefoot-receiving region  36   a , which in turn, reduces the pressure on and the deformation experienced by the front portion  38   a  of the foot  24  when supported by the flexible membrane  28  in a semi-weight-bearing condition (see  FIG. 12 ). This reduction in pressure on and deformation of the front portion  38   a  of the foot  24  ensures that the toes  76  are not overly curled up, which otherwise could adversely deform the medial and lateral arches  78   a ,  78   b  of the foot  24  and render the image acquisition process difficult and imprecise. It is to be noted that as for the embodiment described above in connection with  FIGS. 1 to 7 , the entire plantar surface  22  of the foot  24  is supported by the membrane  28  in the embodiment of  FIGS. 11 to 13 , without any part of the foot  24  being in contact with or supported by a solid surface provided below the flexible membrane  28 . 
     Method 
     In accordance with another aspect, there is provided a method for imaging a plantar surface of a foot having a front portion and a rear portion. By way of example, the method described herein can be performed with an apparatus such as those illustrated in  FIG. 1 to 7, 9, 10, 11 to 13 or 15 , or another apparatus. 
     A flexible membrane, suspended from a support structure and enclosing an upper portion of an inflatable chamber, is first provided. The flexible membrane has a front end and a rear end, elevated relative to the front end. The flexible membrane includes a forefoot-receiving region and a rearfoot-receiving region respectively affixed to the front end and the rear end of the support structure. The rearfoot-receiving region is under less tension than the forefoot-receiving region. 
     In some implementations, the step of providing the flexible membrane suspended from the support structure includes preforming the flexible membrane so that the flexible membrane has a concave recessed area in the rearfoot-receiving region and, consequently, having the rearfoot-receiving region under less tension than the forefoot-receiving region. 
     In some implementations, the step of providing the flexible membrane includes securing the flexible membrane to the support structure. 
     Then, internal pressure in the inflatable chamber is increased. Internal pressure can be increased by blowing gas, such as air, in the inflatable chamber. 
     In some implementations, the step of increasing the pressure in the inflatable chamber is carried out until an internal pressure threshold is reached. The value of the internal pressure threshold can be determined such as to induce a deformation of the foot received on the flexible membrane that leads to a semi-weight-bearing state in which the foot arch and the heel are properly enveloped by the flexible membrane. The internal pressure threshold can be determined by the podiatric physician manually sensing the internal pressure in the pressure chamber or based on pressure data provided by a pressure sensor operatively connected to the inflatable chamber. The internal pressure threshold can also be predetermined, based on, for example and without being limited to, patient&#39;s characteristics, the elasticity of the membrane and/or the inclination angle of the suspended membrane. For instance, the apparatus can include a pressure sensor operatively connected to the inflatable chamber, a controller operatively connected to the pressure sensor and a blower, for instance, configured to blow gas in the inflatable chamber. Using pressure data provided by the pressure sensor, the controller can control the blower and, more particularly, stop gas injection in the inflatable chamber when the predetermined internal pressure threshold is reached. 
     Then, when the inflatable chamber is under pressure, the patient&#39;s foot is positioned on the flexible membrane in a semi-weight-bearing condition with the front and rear portions of the foot respectively located in the forefoot and rearfoot-receiving regions of the membrane, that is, with the entire plantar surface of the foot supported by the flexible membrane, without contact with other physical parts or components. 
     In some implementations, the patient&#39;s foot is positioned on the flexible membrane by the podiatric physician. The podiatric physician manipulates the patient&#39;s foot to ensure that the latter is configured in the semi-weight-bearing condition. By way of example, in a non-limitative embodiment, the podiatric physician can perform one or more of the following manipulations: (i) moving the foot vertically downwardly onto the membrane with the front and the rear portions of the foot received in the forefoot- and rearfoot-receiving regions of the membrane, respectively; (ii) setting at or near 90 degrees each one of the angle between the foot and the tibia, the angle between the tibia and the femur and the angle between the femur and the torso, while keeping the foot, the tibia and the femur in a same vertical plane; (iii) adjusting the internal pressure inside the inflatable chamber based on the rigidity of the foot; (iv) positioning the subtalar joint in a neutral position; (v) exerting a downwardly directed forced on the patient&#39;s knee to achieve a desired semi-weight-bearing state; and (vi) maintaining the desired semi-weight-bearing state while acquiring the 3D plantar image. 
     In some implementations, following an initial positioning of the patient&#39;s foot on the flexible membrane, the pressure in the inflatable chamber can be adjusted, that is, it can either be decreased or increased. The pressure in the inflatable chamber can be adjusted manually by the podiatric physician or automatically. Further positioning of the patient&#39;s foot on the flexible membrane can be performed following adjustment of the internal pressure of the inflatable chamber. The steps of positioning of the patient&#39;s foot on the flexible membrane and adjusting the internal pressure of the inflatable chamber can be carried out as an iterative process until the position of the patient&#39;s foot on the flexible membrane in the semi-weight-bearing condition is satisfactory. 
     In some implementations, positioning of the patient&#39;s foot on the flexible membrane can include exerting a downwardly directed force on the foot when the foot is received on the flexible membrane. For instance, the downwardly directed force can be applied by the podiatric physician while maintaining the patient&#39;s foot in the semi-weight-bearing condition. 
     In some implementations, either prior to inflating the inflatable chamber or the initial positioning of the patient&#39;s foot on the flexible membrane or the initial positioning of the patient&#39;s foot on the flexible membrane, the method can include applying a compressive load on the flexible membrane along a peripheral portion of the forefoot-receiving region. For instance, in an embodiment such as that illustrated in  FIGS. 11 to 13 , it can include configuring the tension member  70  in the operative position to increase the tension applied on the forefoot-receiving region  36   a  of the flexible membrane  28 . 
     Then, when the patient&#39;s foot is positioned on the flexible membrane in the semi-weight-bearing condition, the method includes acquiring a topographical image of the plantar surface of the foot and saving the acquired plantar surface data on a data support. In a non-limitative embodiment, the 3D imager is manually activated by the podiatric physician. 
     As mentioned above, the topographical plantar image can be used to design and manufacture a patient-specific orthosis. 
     Of course, numerous modifications could be made to the embodiments described above without departing from the scope of the present invention.