Abstract:
A skin marker for providing a reference point for a plurality of different medical imaging procedures, said marker incorporating one or more substances having one or more of radiance and/or hydration and/or radiopaque and/or radio luminescent and/or radioactive properties for detection by X-ray and/or Computer Tomography (CT) and/or MRI and/or Ultrasonic scanning processes and/or Positron Emission Tomography (PET), and one or more markings recognizable by an optical imaging process such as 3D surface scanning.

Description:
FIELD OF THE INVENTION 
     This invention relates to a skin/body marker and in particular to a trans-modal/multi-modal skin marker for use as a reference marker for mapping anatomical landmarks when using a range of invasive and non-invasive imaging methods. Applications may include medical imaging processes for measurement, diagnostic and therapeutic procedures, posture mapping for spinal analysis and biomechanics purposes and as a measurement reference for anthropometrics, sports science, fitness and fashion industries. 
     BACKGROUND OF THE INVENTION 
     A variety of imaging techniques are available for imaging different anatomical structures of the body, such as X-ray imaging, typically used for imaging bones, Computer Tomography (CT), typically used for generating a three-dimensional image of the inside of an object from a large series of two-dimensional X-ray images taken around a single axis of rotation, Magnetic Resonance Imaging (MRI), or Nuclear Magnetic Resonance Imaging (NMRI), used most commonly to visualize the internal structure and function of the body, including soft tissues as well as bones, Diagnostic sonography (ultrasound scanning), used to visualize subcutaneous body structures including tendons, muscles, joints, vessels and internal organs for possible pathology or lesions and Positron Emission Tomography (PET), where a three-dimensional image or picture of functional processes in the body is produced by creating images of the passage of a radioactive tracer through the body. 
     It is often desirable to register images produced by such modalities, for example for full spine imaging, and there is an emerging trend to register images produced by different techniques to each other. To do this, reference points are required to register the various images. Different skin markers are available to suit each imaging technique. However, these markers are all different and may not be transferable between modalities, meaning that they need to be removed and alternative ones replaced between different scanning operations, leading to a risk of placement error and mis-registration of the various images produced. 
     Many markers also have difficulty in attaching to the skin, due to hair and moisture, and some have very small surface areas, increasing this problem. Furthermore, none of the known markers are suitable for reliable recognition by 3D surface scanning technologies, which are increasingly used in volumetric analysis and surface profiling/measurement operations. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, there is provided a skin marker for providing a reference point for a plurality of different medical imaging procedures, said marker incorporating one or more substances having one or more of radiance and/or hydration and/or radiopaque and/or radio luminescent and/or radioactive properties for detection by X-ray and/or Computer Tomography (CT) and/or MRI and/or Ultrasonic scanning processes and/or Positron Emission Tomography (PET), and one or more markings recognisable by an optical imaging process such as 3D surface scanning. 
     In one embodiment said substance may comprise a radiopaque material having a radiographic density sufficient to produce a discernable shadow on a radiographic image. 
     In one embodiment said markings may comprise at least one first marking recognisable by Moiré Fringe 3D scanning processes or other optical scanning processes and at least one second marking recognisable by a colour recognition imaging process. Said first marking may comprise a substantially non-reflective image, such as a matt black printed image. Said second marking may comprise a coloured image, for example a blue or green image. 
     The marker may include a 3D surface formation. Such surface formation may be adapted to be recognisable by ultrasound and 3D surface scanning processes, including photogrammetry and laser scanning, or other optical imaging processes and/or may comprise a chamber or reservoir within which said one or more substances may be located. 
     Preferably said one or more substances are encapsulated within said 3D surface formation. In one embodiment said 3D surface formation comprises a hollow body containing a liquid, semi-liquid or solid material, said material containing and/or comprising said one or more substances. The material may comprise an oil based liquid (such as vitamin E fish oils), an oil-based semi-solid material or a gelled material. Such gelled material may comprise either an oil or aqueous base having a rheological structure, which may be achieved by way of high polymeric concentration, incorporation of stiffening agents, induced hydrogen bonding or covalent cross-linking using molecular or ionic species. One suitable material may be a hydrogel, such as a PVA (poly vinyl alcohol) hydrogel. 
     In one embodiment said 3D surface formation comprises a dome shaped member defining a substantially hemi-spherical surface formation. Preferably said dome shaped member is located on a central portion of the marker. At least a portion of the dome shaped member may be optically transparent to define a magnifying lens to assist correct location of the marker on the skin. Alternatively the dome may be coloured and/or possess markings to provide enhanced visibility. 
     Said one or more markings may comprise one or more concentric rings located around said dome shaped member. 
     The skin marker may further include two or more tabs or wings, such as tabs or wings extending radially from said central portion of the marker, to enable the marker to be attached to the body. Said tabs or wings may be provided with a suitable adhesive, which may be covered by a releasable cover material, and/or may define locations or carriers for the attachment of surgical tape to enable the marker to be affixed to the skin. Each tab may have a semi-circular indent at their respective hinge point to allow better flexion and positioning over the human anatomy. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
         FIG. 1  is a plan view of a skin marker according to a first embodiment of the present invention; 
         FIG. 2  is a side view of the skin marker of  FIG. 1 ; 
         FIG. 3  is a plan view of a skin marker according to an alternative embodiment of the present invention; 
         FIG. 4  is a plan view of a skin marker according to a further alternative embodiment of the present invention, with various surface patterns; 
         FIG. 5  is a plan view of a skin marker according to a further embodiment of the present invention; and 
         FIG. 6  is a sectional view through the skin marker of  FIG. 5  on line A-A. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The skin marker  10  is made from 0.125 mm thick polycarbonate (PC) or polyester (PET) film (or a comparable flexible carrier suitable for graphic printing) comprising a circular central portion  12  and having two or more radially extending attachment wings or tabs  14  provided to allow the marker to be attached to the skin. The tabs  14  may be coated with a suitable adhesive, such as a hypoallergenic pressure sensitive adhesive (for example Duplomed 2806), which may be covered by a protective releasable covering, or may simply be used to receive surgical tape to secure the marker to the skin, particularly in areas of excessive hair. As shown in  FIGS. 1 ,  3 , and  4 , different versions of the marker  10  may be produced having a different number of tabs  14  to suit different anatomical locations on the body of the patient. The tri-form shape shown in  FIG. 4  may provide the best adhesion on most locations. However, any other number or arrangement of tabs may be provided to suit the location to which the marker is to be attached. Unevenly spaced or odd numbered tabs may be provided to provide a better distribution of forces at particular locations. 
     The width of each tab  14  is reduced at the junction of the tab  14  with the central portion  12  of the marker by means of cut-outs  16  to provide a hinge joint for flexion. This assists the central circular portion  12  of the marker  10  to retain its profile and provides enhanced adhesion at this area. The distal ends of the tabs  14  are wider to provide a greater surface area for adhesion. 
     A raised hemispherical dome  18  is formed in the centre of the marker  10 , such as shown in  FIGS. 1 and 2 . The dome  18  may have a diameter of between 5 mm and 25 mm, although a prototype has been made with a 10 mm diameter dome. The dome  18  comprises a hollow body encapsulating an oil based liquid or PVA hydrogel containing substances or additives which have a desired combination of radiance and/or hydration and/or radiopaque and/or radio luminescent properties and/or radioactive properties. These substances can be imaged using ionizing radiation, electro-magnetic fields and the hemispherical form of the dome can be recognised by ultrasound and/or 3D surface scanning processes, including photogrammetry and laser scanning. For example, such substances may comprise Barium Sulphate to be recognisable by X-Ray techniques and/or all forms of gadolinium, such as a salt, a covalently bound compound, lattice or co-ordination complex, a chelate or ionic solution, to be recognised by MRI techniques. Chelates may be ustilised (e.g. Gadolinium III Chelate) to enhance the water solubility and reduce toxicity of such substances. The oil based liquid may comprise a mineral oil or any other liquid hydrocarbon oil of synthetic or natural origin, which may be cross-linked or thickened with styrenic copolymer, such as polystyrene blocks and/or rubber blocks (comprising polybutadiene, polyisoprene or their hydrogenated equivalents). In a particular example the liquid within the dome may comprise a paraffin based cross-linked hydrogel. 
     The dome  18 , containing a liquid/gel, may have an embodiment where both are (at least in part) transparent whereby the dome may function as a lens, magnifying the skin location upon which the marker  10  is placed. For example, such magnifying effect may assist in locating the marker over a cross or other mark previously placed on the skin to assist accurate placement of the marker. 
     In a modified embodiment shown in  FIGS. 5 and 6 , to preserve the lens effect with the use of radiopaque substances within the dome  18  (which are visually opaque), a conical section  24  of the dome  18  may be moulded with a non-radiopaque transparent material, as shown in  FIG. 6 . This maintains the sphere-like reference of radiopaque substance  26 . 
     In an alternative embodiment the dome  18  may be coloured or patterned to enhance its visibility. For example, the surface of the dome may be black, preferably matt black, to provide enhanced contrast and thus visibility. 
     A coloured graphic surface image  20  (preferably blue or green) is formed on the central portion  12  of the marker  10  around the dome  18  for recognition by colour imaging processes, such as Red, Green and Blue (RGB) or Cyan, Yellow, Magenta and Key (CYMK) colour recognition algorithms. Using pixel recognition methods similar to “blue screen technology”, the coloured graphic image  20 , in a colour absent from the human body, can be isolated using video and still image processing systems. In the embodiment shown, the coloured graphic image  20  comprises a coloured ring arranged concentrically around the dome  18 . 
     A further printed surface image  22 , in the preferred embodiment in the form of a matt black ring surrounding the coloured graphic image  20 , is provided on the central portion of the marker for recognition by Moiré Fringe 3D scanning processes or other optical scanning processes. The substantially non-reflective black pattern of the image  22  absorbs the light from an optical scanning process, resulting in a gap/blank on the surface model geometry. This gap clearly highlights the location of the 3D dome of the marker, which may also be detected as a 3D surface feature. The geometric centre of the dome  18  can thereby be easily calculated using simple algorithms. 
     Thus the present invention provides a skin reference marker that can be recognised by multi-modal imaging processes to assist diagnosis and operative planning. The skin markers may be used to identify regions for reference purposes and for image registration (for example for registering or aligning multiple images produced by different imaging techniques). The skin marker in accordance with the present invention allows a more seamless workflow and better image registration across a wider range of modalities than presently available. 
     The present invention also provides a skin marker that can be more easily, reliably and accurately placed on the skin of the patient by means of the radially extending attachment wings. This design does not depress the skin surface. 
     The invention is not limited to the embodiment(s) described herein but can be amended or modified without departing from the scope of the present invention. The present invention is not limited to the imaging modalities described above and encompasses other substances recognisable by other imaging modalities beyond the aforementioned modalities.