Patent Publication Number: US-2020281512-A1

Title: Imaging apparatus and method of imaging blood vessels in a target region of tissue

Description:
This disclosure relates to imaging apparatus and a method of imaging blood vessels within a target region of tissue. 
     Wound healing is natural process performed by the human body in response to injury. The amount of time taken for a wound to heal is dependent on many different factors which include the human body&#39;s ability to heal itself and any treatments that are applied to the wound to accelerate wound healing. Understanding the healing status of a wound and being able to monitor the healing process helps to inform decisions on further treatment of the wound and can also assist in the development of future wound therapies. 
     One factor that is known to be associated with wound healing is the amount of blood that is supplied to blood vessels, such as capillaries, within tissue at or near a wound. The process of supplying blood to blood vessels within tissue is known as blood perfusion. Oxygen and nutrients carried by blood within wounded tissue are essential for wound healing and so the amount of blood oxygenated blood within tissue is known to correlate well with wound healing. Conventional techniques for determining the presence of blood within skin tissue require bulky specialist equipment that is typically expensive. 
     It is an aim of the present disclosure to at least partly mitigate the above-mentioned problems. 
     It is an aim of certain embodiments of the present disclosure to image blood vessels within a target region of tissue so that blood vessels within the tissue are clearly identifiable. 
     It is an aim of certain embodiments of the present disclosure to image blood vessels within a target region of tissue so that blood vessels carrying oxygenated blood within the tissue can be distinguished from blood vessels carrying deoxygenated blood. 
     It is an aim of certain embodiments of the present disclosure to image blood vessels within a target region of tissue and to distinguish blood vessels from other features within, on or comprising part of the skin tissue. 
     It is an aim of certain embodiments of the present disclosure to provide a compact apparatus for imaging blood vessels within a target region of tissue. 
     According to some embodiments, there is provided an imaging apparatus for imaging blood vessels within a target region of tissue, comprising: a housing having an aperture which, in use, is placed against a target region of tissue such that the target region of tissue occludes the aperture; a light source arranged to illuminate at least a portion of a target region of tissue occluding the aperture, the light source is configured to provide illuminating light having a predetermined first spectral range and to provide illuminating light having a predetermined second spectral range which is different from the first spectral range; an imaging device arranged to receive illuminating light reflected by the target region of tissue occluding the aperture, wherein the imaging device is configured to generate an image output at the first spectral range and an image output at the second spectral range; and a controller or controlling element arranged to selectively control the imaging device and/or the light source to sequentially capture at least one image generated by the imaging device at the first spectral range and at least one image generated by the imaging device at the second spectral range. 
     The imaging apparatus may be configured such that the first spectral range and the second spectral range do not overlap. 
     The imaging device may be configured to detect light across a continuous spectral range which encompasses the first spectral range and the second spectral range. 
     The controlling element may be configured to control the light source to provide illuminating light at only the first spectral range during capture of the at least one image at the first spectral range and to provide illuminating light at only the second spectral range during capture of the at least one image at the second spectral range. 
     The first spectral range may correspond to a spectral range associated with visible light. Visible light may be regarded as light having a wavelength between 380 nm and 770 nm. 
     The first spectral range may correspond to a spectral range associated with visible red light. Visible red light may be regarded as light having a wavelength of between 600 nm and 750 nm. 
     The second spectral range may correspond to a spectral range encompassing a wavelength absorbed by blood. 
     The second spectral range may correspond to a spectral range associated with infrared light. 
     The second spectral range may correspond to light having a wavelength between 850 nm and 1000 nm. 
     The imaging device may comprise a charge coupled device and/or a complementary metal-oxide semiconductor. 
     The light source may comprise at least a first light emitter configured to emit light having the first spectral range and a second light emitter configured to emit light having the second spectral range. 
     The controlling element may be configured to selectively activate the first light emitter during capture of the image at the first spectral range. The controlling element may be configured to selectively activate the second light emitter during capture of the image at the second spectral range. 
     The light source may be configured to emit light having a spectral range which encompasses the first spectral range and the second spectral range. 
     The imaging device may comprise at least a first filter arranged to transmit light within the first spectral range and a second filter arrange to transmit light within the second spectral range, wherein the controlling element is configured to selectively apply the first filter during capture of the image at the first spectral range and to apply the second filter during capture of the image at the second spectral range. 
     The housing may be a rigid housing and the imaging device is secured to the housing such that, when the aperture is placed against the target region of tissue, the imaging device is spaced from the target region of tissue by a predetermined distance. 
     The imaging device may comprise a lens having a predefined focal length and the predetermined distance is such that the lens is spaced from the target region of tissue by a distance that is equal to the focal length. 
     The housing may be opaque to light having a wavelength which is within the first spectral range and may be opaque to light having a wavelength which is within the second spectral range. 
     The housing may define a light path extending from the light source to the aperture and from the aperture to the imaging device and the housing is arranged to shield the light path from ambient light. 
     The light source and/or the imaging device may be disposed within the housing. 
     The apparatus may be a hand-held device comprising the light source, the imaging device, the housing and the integrated screen. 
     According to some embodiments, there is provided an imaging apparatus for imaging blood vessels within a target region of tissue, comprising: a housing having an aperture which, in use, is placed against a target region of tissue such that the target region of tissue occludes the aperture; a light source arranged to illuminate at least a portion of a target region of tissue occluding the aperture, the light source is configured to provide illuminating light having a predetermined first spectral range and to provide illuminating light having a predetermined second spectral range which is different from the first spectral range; an imaging device arranged to receive illuminating light reflected by the target region of tissue occluding the aperture, wherein the imaging device is configured to generate an image output at the first spectral range and an image output at the second spectral range; and a controller or controlling element arranged to selectively control the imaging device and/or the light source to sequentially capture at least one image generated by the imaging device at the first spectral range and at least one image generated by the imaging device at the second spectral range, the controlling element further arranged to combine the at least one image captured at the first spectral range and the at least one image captured at the second spectral range to produce a composite image in which blood vessels within the target region of skin tissue can be distinguished. 
     According to some embodiments, there is provided a method of imaging blood vessels within a target region of tissue using an imaging apparatus comprising a housing having an aperture, comprising the steps: holding the housing against a target region of tissue such that the target region of tissue occludes the aperture; illuminating the target region of tissue occluding the aperture using light having at least a predetermined first spectral range; capturing at least one image of the target region of tissue at the first spectral range; illuminating the target region of tissue using light having at least a predetermined second spectral range which is different from the first spectral range; and capturing at least one image of the target region of tissue at the second spectral range. 
     The light having at least the predetermined first spectral range may be light having only the first spectral range. 
     The light having at least the predetermined second spectral range may be light having only the second spectral range. 
     The step of capturing at least one image of the target region of tissue at the first spectral range comprises the step of filtering the light having at least the first spectral range such that only light having the first spectral range is transmitted for image capture. 
     The step of capturing at least one image of the target region of tissue at the second spectral range may comprise the step of filtering the light having at least the second spectral range such that only light having the second spectral range is transmitted for image capture. 
     The first spectral range and the second spectral range may not overlap. 
     The first spectral range may correspond to a spectral range associated with visible light. The first spectral range may correspond to a spectral range associated with visible red light. 
     The second spectral range may correspond to a spectral range encompassing a wavelength absorbed by blood. The second spectral range may correspond to a spectral range associated with infrared light. The second spectral range may correspond to a light having a wavelength between 850 nm and 1000 nm. 
     The method may further comprise the step of automatically combining the at least one image captured at the first spectral range and the at least one image captured at the second spectral range to produce a composite image in which blood vessels within the target region of skin tissue can be distinguished. 
     According to some embodiments, there is provided a method of imaging blood vessels within a target region of tissue using an imaging apparatus comprising a housing having an aperture, comprising the steps: illuminating a target region of tissue occluding the aperture of the housing held against the target region of tissue using light having at least a predetermined first spectral range; capturing at least one image of the target region of tissue at the first spectral range; illuminating the target region of tissue using light having at least a predetermined second spectral range which is different from the first spectral range; and capturing at least one image of the target region of tissue at the second spectral range. 
     The light having at least the predetermined first spectral range may be light having only the first spectral range. 
     The light having at least the predetermined second spectral range may be light having only the second spectral range. 
     The step of capturing at least one image of the target region of tissue at the first spectral range comprises the step of filtering the light having at least the first spectral range such that only light having the first spectral range is transmitted for image capture. 
     The step of capturing at least one image of the target region of tissue at the second spectral range may comprise the step of filtering the light having at least the second spectral range such that only light having the second spectral range is transmitted for image capture. 
     The first spectral range and the second spectral range may not overlap. 
     The first spectral range may correspond to a spectral range associated with visible light. The first spectral range may correspond to a spectral range associated with visible red light. 
     The second spectral range may correspond to a spectral range encompassing a wavelength absorbed by blood. The second spectral range may correspond to a spectral range associated with infrared light. The second spectral range may correspond to a light having a wavelength between 850 nm and 1000 nm. 
     The method may further comprise the step of automatically combining the at least one image captured at the first spectral range and the at least one image captured at the second spectral range to produce a composite image in which blood vessels within the target region of skin tissue can be distinguished. 
     According to some embodiments, there is provided a method of imaging blood vessels within a target region of tissue using an imaging apparatus comprising a housing having an aperture, comprising the steps: illuminating a target region of tissue occluding the aperture of the housing held against the target region of tissue using light having at least a predetermined first spectral range; capturing at least one image of the target region of tissue at the first spectral range; illuminating the target region of tissue using light having at least a predetermined second spectral range which is different from the first spectral range; capturing at least one image of the target region of tissue at the second spectral range; and automatically combining the at least one image captured at the first spectral range and the at least one image captured at the second spectral range to produce a composite image in which blood vessels within the target region of skin tissue can be distinguished. 
     Certain embodiments of the present disclosure allow for images to be obtained of a target region of tissue in which blood vessels within the tissue are identifiable. 
     Certain embodiments of the present disclosure allow for images to be obtained of a target region of tissue in which blood vessels carrying oxygenated blood within the tissue are distinguishable from blood vessels carrying deoxygenated blood within the tissue. 
     Certain embodiments of the present disclosure allow for a portable handheld device to be provided which comprises readily available components, typically referred to as off-the-shelf components, for imaging blood vessels within skin tissue. Such a device is convenient to use and relatively inexpensive. 
    
    
     
       Embodiments of the present disclosure will now be described, by way of example only, with reference to the accompanying drawings in which: 
         FIG. 1  shows imaging apparatus for imaging a target region of tissue; 
         FIG. 2  is a schematic representation of part of the imaging apparatus shown in  FIG. 1  comprising an imaging unit; 
         FIG. 3  shows a portion of the imaging apparatus shown in  FIGS. 1 and 2  comprising a sensor module; 
         FIG. 4  shows spectral distributions for the sensor module shown in  FIG. 3 ; 
         FIG. 5  is a schematic representation of key components of the apparatus shown in  FIG. 1 ; 
         FIG. 6  is a flow chart of a method of imaging a target region using the imaging apparatus shown  FIG. 1 ; 
         FIG. 7A  is a representation of a first example image captured using the imaging apparatus shown in  FIG. 1 ; 
         FIG. 7B  is a representation of a second example image captured using the imaging apparatus shown in  FIG. 1 ; 
         FIG. 8  shows spectral distributions for a further embodiment of a sensor module; and 
         FIG. 9  is a schematic representation of key components of a further embodiment of imaging apparatus. 
     
    
    
       FIG. 1  shows apparatus  2  for imaging blood perfusion at a target region of skin tissue being used to image blood perfusion at a region of a patient&#39;s wrist  4 . Other areas of a persons or animals body and other types of tissue such as wound tissue could, of course, be investigated. The apparatus comprises an inspection unit  6  and a display unit  8 . The display unit  8  in the embodiment shown comprises a portable device, in particular, a tablet device, having an integrated screen  10 . The inspection unit  6  and the display unit  8  are connected by a lead  12 . A wireless connection could of course be utilised. 
       FIG. 2  shows schematic representation of the inspection unit  6 . The inspection unit  6  comprises an oblong housing  14 . The housing  14  has an opening at one end, which defines a viewing aperture  16  of the inspection unit  6 , and a sensor module  18  at the other end. The housing  14  comprises four side walls  14   a ,  14   b ,  14   c ,  14   d  and an end wall  14   e  to which the sensor module  18  is secured such that the sensor module  18  is located within the space  20  defined by the walls  14   a ,  14   b ,  14   c ,  14   d ,  14   e . The walls  14   a ,  14   b ,  14   c ,  14   d ,  14   e  of the housing  14  are opaque and are substantially not reflective. In the embodiment shown, the walls  14   a ,  14   b ,  14   c ,  14   d ,  14   e  are formed from rigid black plastic. The housing  14  provides structural support for the sensor module  18  when the inspection unit  6  is held against the patient&#39;s wrist while shielding the area enclosed by the housing  14  from ambient light. The housing  14 , or the portion of the housing  14  at which the aperture  16  is provided, may be disposable so that it may be replaced after use and/or between use on different patients or when used repeatedly on the same patient. 
     The sensor module  18  is shown in  FIG. 3 . The sensor module  18  comprises a light source  22  and an imaging device comprising a camera module  24 . 
     The light source  22  comprises two sets of light emitting diodes (LEDs)  26 ,  28  which are mounted to the front of the camera module  24  such that they emit light at least in a direction which is away from the camera module  22  towards the aperture  16 . The first set of LEDs  26  comprises eight LEDs which are arranged about the circumference of a lens  30  of the camera module  24 . In the embodiment shown, the LEDs of the first set of LEDs  26  are arranged in diametrically opposed pairs. The second set of LEDs  28  also comprises eight LEDs which are also arranged about the circumference of the lens  30 . The second set of LEDs  28  are spaced radially further outwardly from the lens  30  than the first set of LEDs  26  and are also arranged in diametrically opposed pairs. The first and second sets of LEDs  26 ,  28  are arranged to provide reasonably uniform illumination of a target region of issue placed at the aperture  16  from within the housing  14 . The sets of LEDs  26 ,  28  are connected by power supply wires  32 , which comprise part of the lead  12 , to the display unit  8 . 
     A shield  34  is located between the sets of LEDs  26 ,  28  and the camera module  24  to inhibit light emitted by the LEDs from being transmitted to the camera module  24  directly (i.e. prior to being absorbed or reflected) and helps shield the camera module  24  from any ambient light which may enter the housing  14 . In the present embodiment, both sets of LEDs  26 ,  28  have an angular emission range of between +/−45 degrees and so emit light in a direction away from the camera module  24  towards the aperture  16 . In addition, both sets of LEDs  26 ,  28  are located in front of the camera module  24 . Consequently, very little light is transmitted from the LEDs  26 ,  28  directly towards the camera module  24 . Therefore, in other embodiments, a shield may not be required. The optics of the camera module  24  may also be configured to reduce the impact of directly transmitted light and/or other light which would have an adverse impact on images captured by the camera module  24 . The camera module  24  is connected by a flex cable  36 , which comprises part of the lead  12 , to the display unit  8 . In the embodiment shown, the camera module  24  has a fixed focal length and is arranged within the housing such that when the housing  14  is held against the target region of tissue, the cameras module  24  is spaced from the target region at a distance which corresponds to the focal length. The target region of tissue is therefore in focus. 
     Each LED of the first set of LEDs  26  is configured to emit light having a predefined first spectral range. In the embodiment shown, the first spectral range of the light emitted by the first set of LEDs is light having at distribution of wavelengths between 600 nm and 750 nm. The range is within the visible red spectrum. The normalized intensity profile  1010  of the light emitted by the first set of LEDs  26  over the spectral range is shown in  FIG. 4  (not shown to scale). Light is emitted by each of the LEDs of the first set of LEDs  26  over the entire first spectral range. That is to say, each of the LEDs of the first set of LEDs emits light having a distribution of wavelengths between 600 nm and 750 nm in accordance with the intensity profile shown in  FIG. 4 . The normalized intensity profile has a peak wavelength at 660 nm and the intensity drops from the peak to substantially zero at each of the limits, 600 nm and 750 nm respectively, of the spectral range. 
     Each LED of the second set of LEDs  28  is configured to emit light having a predefined second spectral range. In the embodiment shown, the second spectral range of the light emitted by the first set of LEDs is light having at distribution of wavelengths between 850 nm and 1000 nm. The range is within the near-infrared spectrum. The normalized intensity profile  1020  of the light emitted by the second set of LEDs  28  is shown in  FIG. 4  (not to scale). The normalized intensity profile has a peak wavelength at 890 nm. 
     As referred to above,  FIG. 4  shows a normalized intensity distribution profile  1010  of light emitted by the first set of LEDs  26  and a normalized distribution profile  1020  of light emitted by the second set of LEDs  28 . The distribution profiles  1010 ,  1020  are not to scale, but demonstrate that the spectral ranges of light emitted by each of the two sets of LEDs  26 ,  28  do not overlap. 
       FIG. 5  is a schematic representation of some of the components of the apparatus  4 . Components of the inspection unit  6  and the display unit  8  are enclosed, respectively, by broken lines. 
     The display unit  8  further comprises a power source  38 , such as a battery, mains connection or the like, a controller or controlling element in the form of a processor  40  configured to drive each set of LEDs  26 ,  28  independently (i.e. each set of LEDs  26 ,  28  may be activated independently of the other set of LEDs  26 ,  28 ) and to process an output of the camera module  24 , and an output device  42  which is configured to display an output from the processor  40  on the screen  10  of the display unit  8 . 
     As illustrated in  FIG. 5 , the sets of LEDs  26 ,  28  and the camera module  24  are arranged such that at least some of the light emitted by the LEDs travels within the housing  14  in the direction of the aperture  16  and at least some of the light reflected by skin tissue of the wrist at the aperture  16  travels back within the housing  16  to be received by the camera module  24 . Light received by the camera module  24  passes through the lens  30  (shown in  FIG. 3 ) before being received by an imaging sensor (not shown) within the camera module. The imaging sensor is configured to detect light emitted by LEDs from both the first set of LEDs  26  and the second set of LEDs  28 . In the embodiment shown, the camera module  24  comprises an imaging sensor in the form of a charge coupled device (CCD). Other sensors such as a complementary metal-oxide semiconductor (CMOS) or the like configured to detect light across a broad spectral range could of course be utilised. For example, the imaging sensor may be a sensor configured to detect light over a spectral range of wavelengths between 380 nm and 1350 nm. 
     A flow chart illustrating a method of imaging blood within a target region of skin tissue is shown in  FIG. 6 . 
     In use, at step S 1010 , the inspection unit  6  is held in contact with a target region of skin tissue which is to be imaged such that the skin tissue occludes the aperture  16 , as shown in  FIG. 1 . The target region of skin tissue therefore seals against the edges of the housing  14  defining the aperture  16  so that the amount of ambient light which enters the housing  16  through the aperture  16  is restricted or ambient light is prevented from entering the housing altogether. 
     At step S 1020 , the first set of LEDs  26  is activated to illuminate the target region of skin tissue at the aperture  16  with light having the spectral distribution  1010  shown in  FIG. 4 . At least some of the light emitted by the first set of LEDs  20  is transmitted directly to the skin tissue. The remaining light is transmitted to the walls  14   a ,  14   b ,  14   c ,  14   d ,  14   e  of the housing  14 , which are black and substantially not reflective (i.e. highly absorbent) and so absorb substantially all or all of the light which is not transmitted directly to the skin tissue. Light which reaches the skin tissue is either absorbed or reflected by the skin tissue. At least some of the light reflected by the skin tissue is reflected towards the camera module  24 . The housing  14  therefore defines a light path that extends from the light source  22  to the aperture  16  and from the aperture  16  to the camera module  24 . The housing  14  is opaque to the wavelengths of light at which analysis occurs and so provides a shroud that prevents all or substantially all ambient light from entering the housing  14  and reaching the camera module  24 . Any light received at the camera module  24  originated from the first set of LEDs  26  and so has a wavelength within the spectral range  1010  shown in  FIG. 4 . Although ingress of some ambient light can be tolerated, the amount should be small compared with the intensity of the light emitted by the LEDs  26 . The ratio of light emitted by the first set of LEDs  26  received at the cameral module to ambient light received at the camera module should be not less than 5:1, for example not less than 10:1. In other embodiments, any adverse effect of ambient light entering the housing  14  could be mitigated by obtaining a preliminary image of the target region without any illumination from by either the sets of LEDs  26 ,  28 . The preliminary image can be used to calibrate the subsequent images obtained for analysis of the target region or used to inform a user that the housing should be repositioned to reduce the amount of ambient light entering the housing  14 . 
     At step S 1030 , light reflected by the skin tissue which passes through the lens  30  of the camera module  24  is received by the image sensor and processed by the processor  40 . In the present embodiment, the camera module is configured to have an ISO setting of 100 and a shutter speed of 72 ms when the first set of LEDs  26  is used to illuminate the target region of tissue. Other imaging settings could of course be utilised in order to obtain an image of the target region of tissue. The first set of LEDs  26  are activated using a drive current of 1 mA during image capture. The image is then sent by the output device  42  to the imaging unit  8  for storage and/or display on the screen  10 . The first set of LEDs  26  is then deactivated at step S 1040 . 
     At step S 1050 , the second set of LEDs  28  is activated to illuminate the target region of skin tissue at the aperture  16  with light having the spectral range  1020  shown in  FIG. 4 . At least some of the light reflected by the skin tissue is reflected towards the camera module  24 . The remaining light is absorbed by the walls  14   a ,  14   b ,  14   c ,  14   d ,  14   e  of the housing  14 , or the skin tissue, as described above. 
     At step S 1060 , light reflected by the skin tissue which passes through the lens  30  of the camera module  24  is received by the image sensor and processed by the processor  40 . In the present embodiment, the camera module is configured to have an ISO setting of 100 and a shutter speed of 48 ms when the second set of LEDs  28  is used to illuminate the target region. Other imaging settings could of course be utilised in order to obtain an image of the target region of tissue. The second set of LEDs  26  are activated using a drive current of 1 mA during image capture. The image is then sent by the output device  42  to the imaging unit  8  for storage and/or display on the screen  10 . The second set of LEDs  28  is then deactivated, at step S 1070 . 
     Once an image at each spectral range has been captured, steps S 1020  through S 1070  can be repeated to capture multiple images at each spectral range, if desired. 
     Once one or more images at each spectral ranged has been captured, the images may be optionally processed at step  1080 , for example, to produce a combined image. Successive images taken at each spectral range may be paired. At step S 1090 , the images are subsequently displayed, stored and/or transmitted individually, or as paired images (for example, displayed side-by-side) or as a combined image. 
     At step S 1100 , the inspection unit  6  is removed from the target region of skin tissue once inspection is complete. 
       FIG. 7A  and  FIG. 7B  are illustrative diagrams of images captured using light emitted by the first and second sets of LEDs  26 ,  28 . 
       FIG. 7A  illustrates a first image captured by the camera module  24  using light emitted by the first set of LEDs  26  having the normalized intensity distribution profile  1010  shown in  FIG. 4 . The image has a central oval portion A 1  which corresponds to the portion of the target region of skin tissue which is illuminated by the first set of LEDs  26 . The image has a peripheral portion B 1  corresponds to a less-well illuminated region. The boundary between the two regions may be well defined, as shown in  FIG. 7A , graduated or even non-existent if the whole area is sufficiently well illuminated. 
     Within the central portion of the image, there are lighter regions C 1  and darker regions D 1  (which appear as isolated lines on the image). The amount of light received by the camera module  24  is inversely proportional to the amount of light absorbed by the skin tissue. Therefore, darker regions of an image indicate areas of high absorbance (i.e. low reflectivity) whereas lighter regions of the image indicate areas of low absorbance (i.e. high reflectivity). The image, which is captured over the red spectral range of visible, therefore shows features such as skin defects, scarring, moles and underlying blood vessels carrying deoxygenated haemoglobin as dark regions on the image. Although other blood vessels are discernible as lines D 1  on the image, their appearance is very faint and it is extremely difficult, or impossible, to distinguish between vessels and other features clearly. 
       FIG. 7B  illustrates a second image captured by the camera module  24  using light emitted by the second set of LEDs  28  having the normalized distribution profile  1020  shown in  FIG. 4 . The image has a central portion A 2  and an outer portion B 2  similar to the first image. Within the central portion A 2  there are light regions C 2  bounded by darker regions D 2  (which, although not darker in the representation, are the narrow reticulated “pathways” in the second image). The darker regions D 2  in the second image are blood vessels within the skin tissue carrying oxygenated blood. In the embodiment shown, the LEDs comprising the second set of LEDs  28  emit light having a spectral range which corresponds with a peak in the absorption spectra of oxygenated haemoglobin. The second image therefore provides a clear indication of the quantity and location of oxygenated blood vessels. Furthermore, since the amount of light absorbed is proportional to the amount of oxygenated blood within the vessels, the second image provides a reliable indication of the amount of oxygenated blood within the vessels. 
     Features having prominence in the image shown in  FIG. 7A  are unlikely to be blood vessels carrying oxygenated blood. They may, for example, be features such as skin defects, moles, tissue or de-oxygenated blood, for example, that absorb light equally at the first spectral range and the second spectral range, for example. Such features can therefore be disregarded either by a clinician or automatically by processing the images obtained using image recognition software. 
     Images obtained at either or both of the first and second spectral ranges can be processed to enhance features of interest. For example, the brightness of an image can be adjusted or the contrast enhanced. An image may also be adjusted to enhance or mute particular colours. Images may also be filtered for noise. Image recognition techniques may also be utilised to identify certain features of interest. 
     In a further embodiment, the LEDs of the first set of LEDs  26  may comprise LEDs that emit white light having a relatively wide spectral range between 380 nm and 770 nm. Illumination using white light produces a high-quality image that is visible to the naked eye and may utilise the full sensing range of typical CCD imaging sensors thereby maximising the amount of light processed to produce an image.  FIG. 8  shows an example of the spectral ranges of white light and infrared light. 
     In order to identify blood vessels, the LEDs of the second set of LEDs  28  may comprise LEDs that emit light having a spectral range of wavelengths in region that is absorbed or reflected by blood. For example, LEDs which emit light in the green spectral range of between 495 nm and 570 nm, and/or the red spectral range of between 600 nm and 750 nm, and or the near-infrared spectral range of between 850 nm and 1000 nm. Furthermore, LEDs may be used that emit light having a spectral range within the near-infrared window of biological tissue of between 650 nm and 1350 nm. Such light is absorbed poorly by tissue surrounding blood vessels and so will provide good tissue penetration, but will be absorbed well by blood within the tissue. The LEDs of the second set of LEDs  28  may have a peak wavelength of 890 nm, as described with respect to the embodiment shown or 910 nm or 950 nm may be used. In further embodiments, a third set of LEDs may be provided for illuminating the target region with light having a third spectral range that is different from the spectral range of the first and second sets of LEDs  26 ,  28  and for capturing an image or images at the third spectral range. The third spectral range may be associated with high absorption by other chemical species within tissue and so can be used to identify the presence of other chemical species within tissue. Steps S 1050  to S 1070  can be repeated using the third set of LEDs. 
       FIG. 9  is a schematic representation of a variation of the embodiment described above in which the two sets of LEDs are replaced with a single set of LEDs  44  which emits light over a single broad spectral range which encompasses both visible and infrared light. First and second filters  46 ,  48  are arranged within the housing  14  such that they can be placed sequentially in front of the camera module  24 . For example, the first filter  46  may restrict light passing through the filter to light within the red visible spectral band having a spectral range between 600 nm and 750 nm (i.e. corresponding to the spectral range emitted by the first set of LEDs described in connection with the embodiment described above). The second filter  48  may restrict light passing through the filter to light within the infrared region having a spectral range between 850 nm and 1000 nm (i.e. corresponding to the spectral range emitted by the second set of LEDs described in connection with the embodiment described above). 
     The processor  40  is configured to drive the single set of LEDs  44  and to automatically move the filters sequentially in front of the camera module  24  when capturing images. Alternatively, the positioning of the filters may be controlled manually. 
     In use, sequential images are captured with each of the filters  46 ,  48  disposed in front of the camera module  24  respectively. The images are then processed as described above. 
     In the embodiments described above, LEDs are used for illumination. However, it will be appreciated that a wide range of light sources could be used such as incandescent light sources, discharge lamps, fluorescent lamps, solid state light sources, organic LEDs, polymer LEDs, laser diodes or super-luminescent diodes. Surface-mount LEDs may be suitable because of they are compact, widely available, inexpensive, reliable, easily integrated and have a low power consumption. Although the described embodiments describe sets of LEDs comprising multiple LEDs, a set of LEDs could comprise a single LED. A set of LEDs may be comprise a chip on which multiple LEDs having different spectral ranges are mounted. Such devices are compact and cost-effective. In the embodiments described above, the first and second spectral ranges do not overlap. In other embodiments, there may be an overlap of the first and second spectral ranges provided that there are sufficient differences in the absorption of light by tissue across each of the spectral ranges so that images produced at each of the spectral ranges are sufficiently different to distinguish features within the images. 
     A diffuser or lens arrangement configured to diffuse light emitted by the first and or second LEDs may be provided in order to provide a uniform illumination of the target region of tissue. 
     The housing may be made from a variety of suitable materials including non-transparent materials or other materials that are painted or covered by a non-transparent material. For example, the housing may comprise plastic, metal, cardboard or paper. In the embodiments described, the housing is oblong having a single aperture at one end. Other shapes could of course be utilised. Likewise the shape and number of apertures could be different. 
     The embodiments described above comprise a power source in the form or a battery, mains connection or the like. Alternative or additional power sources may be used such as one or more capacitors, fuel cells or energy generators, which generate energy, for example, from the movement of the wearer, e.g. based on some piezo elements or the like, from temperature differences and heat generated by the user or the environment, using, for example, thermopiles, or from light, using, for example, photovoltaic cells, or other energy generating systems, for example clockwork type mechanisms which can be charged by the user. Any battery used may be non-rechargeable or rechargeable. Recharging may be conducted using wired or contactless charging techniques. 
     The embodiments described above comprise an inspection unit that is movable with respect to the display unit. The display unit is a portable device having an integrated touch-screen which forms a control interface with a user for selecting analysis functions and displaying captured/processed images and data. In other embodiments, the display unit may have dedicated buttons for selecting analysis functions. In further embodiments, the inspection unit and display unit may be incorporated into a portable hand-held device having a single housing in which the components of the inspection unit and the display unit are housed. 
     It will be appreciated that throughout this specification reference is made to a wound. It is to be understood that the term wound is to be broadly construed and encompasses open and closed wounds in which skin is torn, cut or punctured or where trauma causes a contusion, or any other superficial or other conditions or imperfections on the skin of a patient or otherwise that benefit from reduced pressure treatment. A wound is thus broadly defined as any damaged region of tissue where fluid may or may not be produced. Examples of such wounds include, but are not limited to, abdominal wounds or other large or incisional wounds, either as a result of surgery, trauma, sterniotomies, fasciotomies, or other conditions, dehisced wounds, acute wounds, chronic wounds, subacute and dehisced wounds, traumatic wounds, flaps and skin grafts, lacerations, abrasions, contusions, burns, diabetic ulcers, pressure ulcers, stoma, surgical wounds, trauma and venous ulcers or the like. 
     In the drawings like reference numerals refer to like parts. 
     Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of them mean “including but not limited to” and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise. 
     Features, integers, characteristics or groups described in conjunction with a particular aspect, embodiment or example of the disclosure are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of the features and/or steps are mutually exclusive. The disclosure is not restricted to any details of any foregoing embodiments. The disclosure extends to any novel one, or novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed. 
     The reader&#39;s attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference in their entireties.