Abstract:
The present disclosure relates to a supplementary device for attachment to an injection device including an imaging arrangement configured to capture an image of a moveable number sleeve of the injection device, a plurality of light sources, and a processor arrangement configured to control operation of the imaging arrangement and the plurality of light sources and to receive image data from the imaging arrangement. In some instances, the processor arrangement is configured to activate the plurality of light sources sequentially and to combine multiple images captured by the imaging apparatus under different illumination conditions into a single image.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a U.S. national stage application under 35 USC §371 of International Application No. PCT/EP2015/072905, filed on Oct. 5, 2015, which claims priority to European Patent Application No. 14187695.3 filed on Oct. 6, 2014, the entire contents of which are incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    Certain aspects of the present disclosure relates to a supplementary device for attachment to an injection device, and in particular to a supplementary device comprising a processor arrangement configured to activate a plurality of light sources sequentially and to combine into a single image multiple images captured by an imaging apparatus under different illumination conditions. 
       BACKGROUND 
       [0003]    A variety of diseases exists that require regular treatment by injection of a medicament. Such injection can be performed by using injection devices, which are applied either by medical personnel or by patients themselves. As an example, type-1 and type-2 diabetes can be treated by patients themselves by injection of insulin doses, for example once or several times per day. For instance, a pre-filled disposable insulin pen can be used as an injection device. Alternatively, a re-usable pen may be used. A re-usable pen allows replacement of an empty medicament cartridge by a new one. Either pen may come with a set of one-way needles that are replaced before each use. The insulin dose to be injected can then for instance be manually selected at the insulin pen by turning a dosage knob and observing the actual dose from a dose window or display of the insulin pen. The dose is then injected by inserting the needle into a suited skin portion and pressing an injection button of the insulin pen. To be able to monitor insulin injection, for instance to prevent false handling of the insulin pen or to keep track of the doses already applied, it is desirable to measure information related to a condition and/or use of the injection device, such as for instance information on the injected insulin type and dose. 
       SUMMARY 
       [0004]    A first aspect of the disclosure provides a supplementary device for attachment to an injection device, the supplementary device comprising:
       an imaging arrangement configured to capture an image of a moveable number sleeve of the injection device;   a plurality of light sources; and   a processor arrangement configured to control operation of the imaging arrangement and plurality of light sources and to receive image data from the imaging arrangement,   wherein the processor arrangement is configured to activate the plurality of light sources sequentially and to combine multiple images captured by the imaging apparatus under different illumination conditions into a single image.       
 
         [0009]    The processor may be configured to divide a field of view of the imaging arrangement into a plurality of areas and to associate each of the areas with a respective illumination condition. The processor arrangement may be configured to combine multiple images captured by the imaging apparatus under different illumination conditions into a single image by being configured to combine an image of a first area of the plurality of areas captured under a first illumination condition with an image of a second area of the plurality of areas captured under a second illumination condition. 
         [0010]    The supplementary device may comprise four light sources grouped into first and second pairs and may be configured to activate the plurality of light sources sequentially by being configured to activate the first pair of light sources followed by the second pair of light sources. 
         [0011]    The processor may be configured to control the imaging arrangement to:
       capture a first image of the number sleeve when the first pair of light sources are activated; and   capture a second image of the number sleeve when the second pair of light sources are activated.       
 
         [0014]    The processor may be configured to divide the field of view of the imaging arrangement into first and second halves and to associate the first half with a first illumination condition and the second half with a second illumination condition. The processor may be configured to keep the first half of the first image and discard the second half of the first image and to keep the second half of the second image and discard the first half of the second image. The processor arrangement may be configured to combine multiple images captured by the imaging apparatus under different illumination conditions into a single image by being configured to combine the first half of the first image and the second half of the second image into a single image. 
         [0015]    In some other embodiments, the processor may be configured to divide the field of view of the imaging arrangement into a central section and two peripheral sections and to associate the central section with a first illumination condition and the two peripheral sections with a second illumination condition. 
         [0016]    Each illumination source, when activated, may result in one or more reflections from a transparent window of the injection device being visible in a field of view of the imaging apparatus. 
         [0017]    A second aspect of the disclosure provides a system comprising a supplementary device according to the first aspect of the disclosure and an injection device comprising a moveable number sleeve and being configured to have the supplementary device attached thereto. 
         [0018]    A third aspect of the disclosure provides a method of operating a supplementary device for attachment to an injection device, the supplementary device having an imaging arrangement configured to capture an image of a moveable number sleeve of the injection device, a plurality of light sources and a processor arrangement configured to control operation of the imaging arrangement and the plurality of light sources, the method comprising:
       activating the plurality of light sources sequentially;   receiving image data from the imaging arrangement; and   combining multiple images captured by the imaging apparatus under different illumination conditions into a single image.       
 
         [0022]    Embodiments of the disclosure will now be described, by way of example only, with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0023]    The figures show: 
           [0024]      FIG. 1 a   : an exploded view of an drug delivery device; 
           [0025]      FIG. 1 b    shows a perspective view of some detail of the drug delivery device of  FIG. 1   a;    
           [0026]      FIG. 2 a   : a schematic illustration of a supplementary device to be releasably attached to the drug delivery device of  FIGS. 1 a  and 1 b    according to an aspect of the present disclosure; 
           [0027]      FIG. 2 b   : a perspective view of a supplementary device to be releasably attached to the drug delivery device of  FIGS. 1 a  and 1 b    according to various aspects of the present disclosure; 
           [0028]      FIG. 2 c   : a perspective view of a supplementary device to be releasably attached to the drug delivery device of  FIGS. 1 a  and 1 b    according to other aspects of the present disclosure; 
           [0029]      FIG. 3 : a schematic view of a supplementary device attached to a drug delivery device showing components of the supplementary device; 
           [0030]      FIG. 4 : a schematic illustration of the injection device and supplementary device showing reflections from a dose window of the injection device; 
           [0031]      FIG. 5 a   : a first embodiment of a typical field of view of an optical sensor of the supplementary device, showing the position of LEDs and resulting reflections; 
           [0032]      FIG. 5 b   : a final image created by combining partial images of the field of view of  FIG. 5   a;    
           [0033]      FIGS. 6 a  and 6 b   : a second embodiment of a field of view of an optical sensor of the supplementary device, showing the position of LEDs and resulting reflections; 
           [0034]      FIGS. 7 a  and 7 b   : a third embodiment of a field of view of an optical sensor of the supplementary device, showing the position of LEDs and resulting reflections; 
           [0035]      FIG. 8 : an embodiment in which a number appears in the centre of the field of view of the optical sensor. 
       
    
    
     DETAILED DESCRIPTION 
       [0036]    In the following, embodiments of the present disclosure will be described with reference to an insulin injection device. The present disclosure is however not limited to such application and may equally well be deployed with injection devices that eject other medicaments, or with other types of medical devices. 
         [0037]      FIG. 1  is an exploded view of an injection device  1  (also referred to herein as a drug delivery device  1 , injection pen  1  or pen device  1 ), which may for instance represent Sanofi&#39;s Solostar (R) insulin injection pen. 
         [0038]    The injection device  1  of  FIG. 1  is a pre-filled, disposable injection pen that comprises a housing  10  and contains an insulin container  14 , to which a needle  15  can be affixed. The needle is protected by an inner needle cap  16  and an outer needle cap  17 , which in turn can be covered by a cap  18 . An insulin dose to be ejected from injection device  1  can be selected by turning the dosage knob  12 , and the selected dose is then displayed via dosage window  13 , for instance in multiples of so-called International Units (IU), wherein one IU is the biological equivalent of about 45.5 micrograms of pure crystalline insulin ( 1/22 mg). An example of a selected dose displayed in dosage window  13  may for instance be 30 IUs, as shown in  FIG. 1 . It should be noted that the selected dose may equally well be displayed differently. A label (not shown) is provided on the housing  10 . The label includes information about the medicament included within the injection device, including information identifying the medicament. The information identifying the medicament may be in the form of text. The information identifying the medicament may also be in the form of a color. The information identifying the medicament may also be encoded into a barcode, QR code or the like. The information identifying the medicament may also be in the form of a black and white pattern, a color pattern or shading. 
         [0039]    Turning the dosage knob  12  causes a mechanical click sound to provide acoustical feedback to a user. The numbers displayed in dosage window  13  are printed on a sleeve that is contained in housing  10  and mechanically interacts with a piston in insulin container  14 . When needle  15  is stuck into a skin portion of a patient, and then injection button  11  is pushed, the insulin dose displayed in display window  13  will be ejected from injection device  1 . When the needle  15  of injection device  1  remains for a certain time in the skin portion after the injection button  11  is pushed, a high percentage of the dose is actually injected into the patient&#39;s body. Ejection of the insulin dose also causes a mechanical click sound, which is however different from the sounds produced when using dosage knob  12 . 
         [0040]    Injection device  1  may be used for several injection processes until either insulin container  14  is empty or the expiration date of injection device  1  (e.g. 28 days after the first use) is reached. 
         [0041]    Furthermore, before using injection device  1  for the first time, it may be necessary to perform a so-called “prime shot” to remove air from insulin container  14  and needle  15 , for instance by selecting two units of insulin and pressing injection button  11  while holding injection device  1  with the needle  15  upwards. 
         [0042]    For simplicity of presentation, in the following, it will be exemplarily assumed that the ejected doses substantially correspond to the injected doses, so that, for instance when making a proposal for a dose to be injected next, this dose equals the dose that has to ejected by the injection device. Nevertheless, differences (e.g. losses) between the ejected doses and the injected doses may of course be taken into account. 
         [0043]      FIG. 1 b    is a close-up of the end of the injection device  1 . This Fig. shows a locating rib  70  that is located between the viewing window  13  and the dosage knob  12 . 
         [0044]      FIG. 2 a    is a schematic illustration of an embodiment of a supplementary device  2  (also referred to herein as an additional device  2 , clip-on device  2  or sensor device  2 ) to be releasably attached to injection device  1  of  FIG. 1 . Supplementary device  2  comprises a housing  20  with a mating unit configured and embrace the housing  10  of injection device  1  of  FIG. 1 , so that supplementary device  2  sits tightly on housing  10  of injection device  1 , but is nevertheless removable from injection device  1 , for instance when injection device  1  is empty and has to be replaced.  FIG. 2 a    is highly schematic, and details of the physical arrangement are described below with reference to  FIG. 2   b.    
         [0045]    Supplementary device  2  contains optical and acoustical sensors for gathering information from injection device  1 . At least a part of this information, for instance a selected dose (and optionally a unit of this dose), is displayed via display unit  21  of supplementary device  2 . The dosage window  13  of injection device  1  is obstructed by supplementary device  2  when attached to injection device  1 . 
         [0046]    Supplementary device  2  further comprises at least one user input transducer, illustrated schematically as a button  22 . These input transducers  22  allow a user to turn on/off supplementary device  2 , to trigger actions (for instance to cause establishment of a connection to or a pairing with another device, and/or to trigger transmission of information from supplementary device  2  to another device), or to confirm something. 
         [0047]      FIG. 2 b    is a schematic illustration of a second embodiment of a supplementary device  2  to be releasably attached to injection device  1  of  FIG. 1 . Supplementary device  2  comprises a housing  20  with a mating unit configured and embrace the housing  10  of injection device  1  of  FIG. 1 , so that supplementary device  2  sits tightly on housing  10  of injection device  1 , but is nevertheless removable from injection device  1 . 
         [0048]    Information is displayed via display unit  21  of supplementary device  2 . The dosage window  13  of injection device  1  is obstructed by supplementary device  2  when attached to injection device  1 . 
         [0049]    Supplementary device  2  further comprises three user input buttons or switches. A first button  22  is a power on/off button, via which the supplementary device  2  may for instance be turned on and off. A second button  33  is a communications button. A third button  34  is a confirm or OK button. The buttons  22 ,  33 ,  34  may be any suitable form of mechanical switch. These input buttons  22 ,  33 ,  34  allow a user to turn on/off supplementary device  2 , to trigger actions (for instance to cause establishment of a connection to or a pairing with another device, and/or to trigger transmission of information from supplementary device  2  to another device), or to confirm something. 
         [0050]      FIG. 2 c    is a schematic illustration of a third embodiment of a supplementary device  2  to be releasably attached to injection device  1  of  FIG. 1 . Supplementary device  2  comprises a housing  20  with a mating unit configured to embrace the housing  10  of injection device  1  of  FIG. 1 , so that supplementary device  2  sits tightly on housing  10  of injection device  1 , but is nevertheless removable from injection device  1 . 
         [0051]    Information is displayed via display unit  21  of the supplementary device  2 . The dosage window  13  of injection device  1  is obstructed by supplementary device  2  when attached to injection device  1 . 
         [0052]    Supplementary device  2  further comprises a touch-sensitive input transducer  35 . It also comprises a single user input button or switch  22 . The button  22  is a power on/off button, via which the supplementary device  2  may for instance be turned on and off. The touch sensitive input transducer  35  can be used to trigger actions (for instance to cause establishment of a connection to or a pairing with another device, and/or to trigger transmission of information from supplementary device  2  to another device), or to confirm something. 
         [0053]      FIG. 3  shows a schematic view of the supplementary device  2  of  FIG. 2 a    in a state where it is attached to injection device  1  of  FIG. 1 . 
         [0054]    With the housing  20  of supplementary device  2 , a plurality of components are contained. These are controlled by a processor  24 , which may for instance be a microprocessor, a Digital Signal Processor (DSP), Application Specific Integrated Circuit (ASIC), Field Programmable Gate Array (FPGA) or the like. Processor  24  executes program code (e.g. software or firmware) stored in a program memory  240 , and uses a main memory  241 , for instance to store intermediate results. Main memory  241  may also be used to store a logbook on performed ejections/injections. Program memory  240  may for instance be a Read-Only Memory (ROM), and main memory may for instance be a Random Access Memory (RAM). 
         [0055]    In embodiments such as those shown in  FIG. 2 b   , processor  24  interacts with a first button  22 , via which supplementary device  2  may for instance be turned on and off. A second button  33  is a communications button. The second button may be used to trigger establishment of a connection to another device, or to trigger a transmission of information to another device. A third button  34  is a confirm or OK button. The third button  34  can be used to acknowledge information presented to a user of supplementary device  2 . In embodiments such as those shown in  FIG. 2 c   , two of the buttons  33 ,  34  may be omitted. Instead, one or more capacitive sensors or other touch sensors are provided. 
         [0056]    Processor  24  controls a display unit  21 , which is presently embodied as a Liquid Crystal Display (LCD). Display unit  21  is used to display information to a user of supplementary device  2 , for instance on present settings of injection device  1 , or on a next injection to be given. Display unit  21  may also be embodied as a touch-screen display, for instance to receive user input. 
         [0057]    Processor  24  also controls an optical sensor  25 , embodied as an Optical Character Recognition (OCR) reader, that is capable of capturing images of the dosage window  13 , in which a currently selected dose is displayed (by way of numbers printed on the sleeve  19  contained in injection device  1 , which numbers are visible through the dosage window  13 ). OCR reader  25  is further capable of recognizing characters (e.g. numbers) from the captured image and to provide this information to processor  24 . Alternatively, unit  25  in supplementary device  2  may only be an optical sensor, e.g. a camera, for capturing images and providing information on the captured images to processor  24 . Then processor  24  is responsible for performing OCR on the captured images. 
         [0058]    Processor  24  also controls light-sources such as light emitting diodes (LEDs)  29  to illuminate the dosage window  13 , in which a currently selected dose is displayed. A diffuser may be used in front of the light-sources, for instance a diffuser made from a piece of acrylic glass. Furthermore, the optical sensor may comprise a lens system, for instance including two aspheric lenses. The magnification ratio (image size to object size ratio) may be smaller than 1. The magnification ratio may be in the range of 0.05 to 0.5. In one embodiment the magnification ratio may be 0.15. 
         [0059]    Processor  24  further controls a photometer  26 , that is configured to determine an optical property of the housing  10  of injection device  1 , for example a color or a shading. The optical property may only be present in a specific portion of housing  10 , for example a color or color coding of sleeve  19  or of an insulin container comprised within injection device  1 , which color or color coding may for instance be visible through a further window in housing  10  (and/or in sleeve  19 ). Information on this color is then provided to processor  24 , which may then determine the type of injection device  1  or the type of insulin contained in injection device  1  (e.g. SoloStar Lantus with purple color and SoloStar Apidra with blue color). Alternatively, a camera unit may be used instead of photometer  26 , and an image of the housing, sleeve or insulin container may then be provided to processor  24  to determine the color of the housing, sleeve or insulin container by way of image processing. Further, one or more light sources may be provided to improve reading of photometer  26 . The light source may provide light of a certain wavelength or spectrum to improve color detection by photometer  26 . The light source may be arranged in such a way that unwanted reflections, for example by dosage window  13 , are avoided or reduced. In an example embodiment, instead of or in addition to photometer  26 , a camera unit may be deployed to detect a code (for instance a bar code, which may for instance be a one- or two-dimensional bar code) related to the injection device and/or the medicament contained therein. This code may for instance be located on the housing  10  or on a medicament container contained in injection device  1 , to name but a few examples. This code may for instance indicate a type of the injection device and/or the medicament, and/or further properties (for instance a expiration date). 
         [0060]    Processor  24  further controls (and/or receives signals from) an acoustic sensor  27 , which is configured to sense sounds produced by injection device  1 . Such sounds may for instance occur when a dose is dialed by turning dosage knob  12  and/or when a dose is ejected/injected by pressing injection button  11 , and/or when a prime shot is performed. These actions are mechanically similar but nevertheless sound differently (this may also be the case for electronic sounds that indicate these actions). Either the acoustic sensor  27  and/or processor  24  may be configured to differentiate these different sounds, for instance to be able to safely recognize that an injection has taken place (rather than a prime shot only). 
         [0061]    Processor  24  further controls an acoustical signal generator  23 , which is configured to produce acoustical signals that may for instance be related to the operating status of injection device  1 , for instance as feedback to the user. For example, an acoustical signal may be launched by acoustical signal generator  23  as a reminder for the next dose to be injected or as a warning signal, for instance in case of misuse. Acoustical signal generator may for instance be embodied as a buzzer or loudspeaker. In addition to or as an alternative to acoustical signal generator  23 , also a haptic signal generator (not shown) may be used to provide haptic feedback, for instance by way of vibration. 
         [0062]    Processor  24  controls a wireless unit  28 , which is configured to transmit and/or receive information to/from another device in a wireless fashion. Such transmission may for instance be based on radio transmission or optical transmission. In some embodiments, the wireless unit  28  is a Bluetooth transceiver. Alternatively, wireless unit  28  may be substituted or complemented by a wired unit configured to transmit and/or receive information to/from another device in a wire-bound fashion, for instance via a cable or fiber connection. When data is transmitted, the units of the data (values) transferred may be explicitly or implicitly defined. For instance, in case of an insulin dose, always International Units (IU) may be used, or otherwise, the used unit may be transferred explicitly, for instance in coded form. 
         [0063]    Processor  24  receives an input from a pen detection switch  30 , which is operable to detect whether the pen  1  is present, i.e. to detect whether the supplementary device  2  is coupled to the injection device  1 . A battery  32  powers the processor  24  and other components by way of a power supply  31 . 
         [0064]    The supplementary device  2  of  FIG. 3  is thus capable of determining information related to a condition and/or use of injection device  1 . This information is displayed on the display  21  for use by the user of the device. The information may be either processed by supplementary device  2  itself, or may at least partially be provided to another device (e.g. a blood glucose monitoring system). 
         [0065]      FIG. 4  shows schematically a cross-section of the injection device  1  and components of the supplementary device  2 , including an exemplary position of the LEDs  29  (also referred to herein as illumination sources) with respect to the optical sensor  25  and dose window  13 .  FIG. 4  also illustrates the problem caused by reflections from the surface of the dose window  13 . Due to manufacturing requirements and costs considerations, the dose window  13  is not usually made of a highly non-reflective material or provided with a non-reflective coating. The dose window may be made of a clear Polycarbonate. Therefore some of the light incident on the dose window  13  will be reflected from the dose window  13 , rather than passing through to be incident on the number sleeve  19 . In particular, it can be seen that light emitted from the LEDs  29  may be reflected from the lower surface of the dose window  13  towards the optical sensor  25  without reaching the number sleeve  19  of the injection device  1 . These reflections lead to glare in the image captured by the optical sensor  25 . As the LEDs  29  are point light sources, this glare generally takes the form of bright spots. The glare leads to areas of over exposure and impacts the ability of the optical sensor  25  to capture a high quality image of the numbers printed on the number sleeve  19 , which in turn affects the ability of the processor  24  to perform a successful optical character recognition process on the numbers. It can be particularly hard to avoid glare in the captured image because the dose window  13  is curved and so the light is incident on the dose window  13  over a range of angles. LEDs  29  are the preferred choice of illumination because of their small size and cost and their radiation characteristics. However, an alternative source, such as a light bulb, diode laser or an organic LED may be used. 
         [0066]    The supplementary device  2  may also comprise a protection window (not shown). The primary function of the protection window is to seal the supplementary device  2  and prevent the ingress of dust and debris. However the protection window may also be shaped to provide magnification and/or focusing for the optical sensor  25 . 
         [0067]      FIG. 5 a    shows a typical field of view  500  of the optical sensor  25 . In general the field of view of the optical sensor  25  is large enough to capture an image of the entire dose window  13 . In this embodiment the supplementary device  2  is provided with two LEDs  29  located above and below the dose window  13 . When the upper LED  502  is activated, a first reflection  504  is seen by the optical sensor  25 . When the lower LED  506  is activated, a second reflection  508  is seen by the optical sensor  25 . Thus if both the upper and lower LEDs  502 ,  506  are activated, the optical sensor  25  sees two reflections in its field of view  500 . If the reflections are located over a number, then they negatively impact the ability of the optical sensor  25  to capture a high quality image of these numbers. This can make it difficult to perform an accurate OCR process on the captured image, since information about the numbers has effectively been erased through over exposure. 
         [0068]    It should be noted that the number  88  is used in this exemplary embodiment and in other embodiments described herein. In general this number occupies the greatest amount of space and is therefore the best candidate for assessing whether the reflections from the dose window  13  are located over the numbers. The skilled person will appreciate that the numbers printed on the number sleeve  19  represent a dose of medicament dialed into the injection device  1  and will therefore be sequential. For example, the numbers printed on the number sleeve  19  may be ascending even numbers. In some embodiments, the maximum dose which can be dialed into the injection device  1  is 80 units. 
         [0069]    In order to eliminate the negative effects of the reflections  504 ,  508  on the image capture and decoding processes, there is provided a system and method in which multiple images of the number sleeve  19  are captured by the optical sensor  25  under different illumination conditions. These images are then combined to create a final image which is free from reflections. In the embodiment of  FIG. 5 a   , the processor  24  is configured to divide images captured by the optical sensor  25  into two halves. The processor  24  is configured to control activation and deactivation of the upper and lower LEDs  502 ,  506  and to control the image capture process of the optical sensor  25 . 
         [0070]    The processor  24  first activates the upper LED  502 , which in general causes a first reflection  504  from the dose window  13 . The processor  24  controls the optical sensor  25  to capture an image of the number sleeve  19 . The processor  24  then discards the upper half  510  of this image and keeps only the lower half  512  of the image. Due to the position of the upper LED  502  relative to the optical sensor  25  no reflections are seen in the lower half  512  of the captured image. The processor  24  then deactivates the upper LED  502  and activates the lower LED  506 . The processor  24  again controls the optical sensor  25  to capture an image of the number sleeve  19 . In this second image the second reflection  508  in the lower half  512  is visible, but the first reflection  504  does not appear. Thus the processor  24  keeps the upper half  510  of this second image and discards the lower half  512 . The processor  24  then executes an algorithm to combine the lower half  512  of the first image and upper half  510  of the second image to create a final image  514 , illustrated in  FIG. 5 b   . In practice, the image halves captured in the first and second images may overlap. This may be done to ensure that no image information is lost. The processor  24  may execute software which uses edge detection techniques to determine the appropriate place in each image for the combination to occur. The processor  24  then passes the final image  514  to an optical character recognition module, or performs the OCR process itself in order to identify the numbers visible in the image. OCR techniques are in general well known, and the skilled person will be aware of a number of OCR methods which could be applied in aspects of this disclosure. 
         [0071]      FIGS. 6 a  and 6 b    illustrate a second embodiment of the disclosure. In this embodiment the supplementary device  2  comprises four LEDs  29 , arranged in pairs above and below the dose window  13 . The position of the lens of the optical sensor is indicated by the dashed circle  602 . As can be seen in these figures, the LEDs are located closer to the dose window  13  than in the first embodiment. Due to the relative position of the LEDs and optical sensor  25 , each LED produces two reflections from the dose window  13  which are within the sensor&#39;s field of view  600 . 
         [0072]    In this embodiment the processor  24  divides the field of view of the optical sensor  25  vertically, into a left half  604  and a right half  606 . The processor  24  controls the LEDs to be activated in left and right pairs. The processor  24  first activates the left LEDs  608 . This causes reflections  609  to appear on the left half  604  of the field of view of the optical sensor  25 . The processor  24  controls the optical sensor  25  to capture an image of the number sleeve  19 . The processor  24  discards the left half  604  of this image and keeps the right half  606  of the image. This is illustrated in  FIG. 6 a    by the cross hatching in the right half  606  of the field of view  600 . The next step is illustrated in  FIG. 6 b   , in which the processor  24  deactivates the left LEDs  608  and activates the right LEDs  610 . This causes reflections  611  to appear in the right half  606  of the field of view sensor. The processor  24  again controls the optical sensor  25  to capture an image of the number sleeve  19 . The processor  24  discards the right half  606  of this second image and keeps the left half  604  of the image (this is again illustrated by cross hatching in the left half  604 ). The processor  24  then takes the right half  606  of the first image and left half  604  of the second image and combines them into a final image which is free of reflections. 
         [0073]    Having a greater number of LEDs  29  increases the quality and evenness of the illumination. Positioning the LEDs  29  closer to the dose window  13  also improves the illumination of the number sleeve  19  and increases the amount of light reaching the dose window  13  and optical sensor  25  for a given LED light output. In general, it is desirable to position the LEDs  29  such that minimal reflections appear in the illuminated area, while at the same time producing an illumination which is bright and homogeneous. Thus the LEDs  29  are positioned such that the reflections produced appear in a section of the field of view and captured image which is subsequently discarded. Dividing the field of view vertically into left and right halves, rather than upper and lower halves also increases the quality of the illumination as the part of the image which the processor  24  keeps is closer to a source of illumination. Another advantage of certain aspects of the disclosure is that they require no modification of existing injection pen designs to implement. 
         [0074]      FIGS. 7 a  and 7 b    show a third embodiment of the disclosure. In this embodiment there are again four LEDs  29  arranged linearly along a center line of the dose window  13 . The lens position  702  is again illustrated with a dashed circle. In this embodiment the LEDs are grouped into an inner pair  704  and an outer pair  706 . The inner pair  704  are located approximately one third of the dose window  13  height from the top and bottom edges of the dose window  13 . The outer LEDs  706  are located at the dose window  13  edges. 
         [0075]    In this embodiment the processor  24  divides the field of view  700  into a central section  708  and two peripheral sections  710 . The central section  708  may occupy approximately half of the field of view  700 , while the peripheral section  710  each occupy approximately one quarter of the field of view. However these ratios may be adjusted depending on the expected positions of the reflections. 
         [0076]    The processor  24  first activates the inner LEDs  704 . This produces inner reflections  712  in the central section  708  of the field of view  700  of the optical sensor  25 . The processor  24  controls the optical sensor  25  to capture an image of the number sleeve  19 . The processor  24  keeps the upper and lower peripheral sections  710  of this image and discards the central section  708  of the image. The processor  24  then deactivates inner LEDs  704  and activates outer LEDs  706 . These LEDs cause outer reflections  714  to appear in the upper and lower peripheral section  710  of the field of view  700 . The processor  24  again controls the optical sensor  25  to capture an image of the number sleeve  19 . The processor  24  keeps the central section  708  of this second image and discards the upper and lower peripheral section  710  of the image. The processor  24  then combines the upper and lower peripheral sections  710  from the first image with the central section  708  from the second image to create a final image which is free of reflections. An OCR process can then be performed on this final image to determine the numbers which are visible. 
         [0077]    In some embodiments of the disclosure only even numbers are printed, in ascending order, on the number sleeve  19 . In this case each of the arrangements shown in FIGS.  5   a  to  7   b  represents a situation in which an odd number of units are dialed into the injection device  1 . This is because the number of dialed units would normally be displayed centrally within the dose window  13 . 
         [0078]      FIG. 8  illustrates an embodiment in which only even numbers are printed on the number sleeve  19  and where a dose of 26 units has been dialed into the injection device  1 . Thus the number  26  appears centrally in the dose window  13 . The position of the LEDs  29  in  FIG. 8  is the same as in  FIGS. 6 a  and 6 b   , with a pair of LEDs located at either end of the dose window  13 . The optical sensor lens is again located centrally above the dose window  13 . This arrangement of LEDs therefore leads to the same pattern of reflections in the field of view  800  of the optical sensor  25 . However since these reflections occur in the upper and lower thirds of the field of view  800 , none of the reflections directly overlap with the centrally displayed number. Thus no division of the field of view  800  by the processor  24  is necessary in this situation. Alternatively, the processor  24  may continue to divide the image as previously described, even if the reflections do not obscure any areas of interest. The processor  24  may additionally be configured to detect the white spaces between the printed numbers in order to determine whether a number is displayed centrally within the window or not.