Backlight unit for liquid crystal display (LCD) apparatus

The present invention relates to a backlight unit for a liquid crystal display (LCD) apparatus and relates particularly, but not exclusively, to a backlight unit for a colour or greyscale LCD display apparatus for use in medical imaging. The invention also relates to an LCD display apparatus incorporating such a backlight unit. In medical imaging applications, high illumination LCD displays are used. In certain applications, a group of displays may be arranged next to each other in order to display different aspects of part of a patient. However, because of manufacturing tolerances between the constituent components of different displays, the colour tone of different displays, even displays of the same model, can vary. This is often disturbing to a viewer of the display.

JP2002-072982 discloses a backlit LCD display apparatus having a backlight unit comprising fluorescent lamps of different colours for illuminating an LCD panel on which an image is displayed. The individual fluorescent lamps of different colours are alternately arranged, and the colour tone of the display image is tuned by altering the respective signal levels of the colour components in the video signal received by the display. This arrangement suffers from a number of significant drawbacks. Firstly, the arrangement of fluorescent lamps of different colours in an alternating manner can lead to the occurrence of coloured stripes or bands in the displayed images. In order to overcome this problem, a diffuser screen is used. However, this leads to the disadvantage of reducing the brightness of the displayed image, as a result of which the backlight is required to operate at a higher light intensity. It is also undesirable to tune the colour point by adjusting the relative signal levels of the colour components in the video signal, since this creates the risk of inadvertent altering of the information contained in the video signal. For example, alteration of the colour components of the video signal could result in alteration of the contrast between parts of an image, which can lead to incorrect interpretations such as false positives in medical imaging applications.

The present invention seeks to overcome the above disadvantages of the prior art.

According to an aspect of the present invention, there is provided an illumination apparatus for illuminating an LCD panel of an LCD display, the illumination apparatus comprising:

- at least one illumination unit for illuminating an LCD panel of an LCD display and adapted to be mounted to a housing of the LCD display, wherein each said illumination unit comprises (a) at least one first fluorescent light source for emitting light of a first peak wavelength, (b) at least one second fluorescent light source for emitting light of a second peak wavelength, and (c) at least one third fluorescent light source for emitting light of a third peak wavelength, wherein said light sources of at least one said illumination unit are arranged adjacent to each other, and said first, second and third LCD panel in use can be adjusted by adjusting the intensity of light emitted by said light sources; and

- at least one controller for controlling supply of electrical power to at least one said first, second and third light source of at least one said illumination unit to enable independent adjustment of the intensity of light emitted by said first, second and third light sources. By providing at least one illumination unit including light sources of different colours such that the colour components can be independently adjusted, this provides the advantage of enabling the colour tone of each illumination unit to be individually tuned, while avoiding the occurrence of coloured stripes or bands in the image. At the same time, the necessity to carry out any adjustment of the colour components of the video signal of the display apparatus is avoided, which in turn provides the advantage of minimising the occurrence of errors in the video signal information.

The apparatus may comprise at least one waveguide, wherein at least one said illumination unit is adapted to be mounted adjacent to a respective edge region of said waveguide.

This provides the advantage of maximising the area of irradiation achieved by the illumination unit.

At least one said waveguide may be adapted to diffuse light passing therethrough.

This provides the advantage of maximising uniformity of light intensity and colour of light illuminating the LCD panel.

The apparatus may comprise a plurality of said illumination units adapted to be mounted opposite the LCD panel.

By suitable choice of the first, second and third peak wavelengths of the light sources, for example, red, blue and green light sources, this provides the advantage of avoiding the necessity of white fluorescent lamps. This permits colour tuning over a wider range. According to another aspect of the present invention, there is provided an LCD display apparatus comprising a housing, an LCD display panel including a plurality of pixels adapted to transmit light therethrough in dependence upon electrical signals applied to said pixels, and an illumination apparatus as defined above for illuminating said LCD display panel. According to a further aspect of the present invention, there is provided a medical imaging apparatus including at least one imaging device for receiving image data from a patient, at least one processor for forming image model data of a patient, and an LCD display apparatus as defined above.

According to a further aspect of the present invention, there is provided a data structure executable by a computer for controlling illumination of an LCD display panel of an LCD display apparatus as defined above, the data structure comprising first computer code executable to control supply of electrical power to at least one said first, second and third light source of at least one said illumination unit to enable independent adjustment of the intensity of light emitted by said first, second and third light sources. According to a further aspect of the present invention, there is provided a data carrier having a data structure as defined above stored thereon.

According to a further aspect of the present invention, there is provided a method of controlling illumination of an LCD display panel of an LCD display apparatus as defined above, the method comprising controlling supply of electrical power to at least one said first, second and third light source of at least one said illumination unit to enable independent adjustment of the intensity of light emitted by said first, second and third light sources.

Preferred embodiments of the invention will now be described, by way of example and not in any limitative sense, with reference to the accompanying drawings, in which:

Figure 1 is a schematic diagram of a medical imaging apparatus embodying the present invention;

Figure 2 is a cross-sectional view of a backlight unit of a first embodiment of the present invention for use in the LCD display apparatus of Figure 1 ; and

Figure 3 is a backlight unit of a second embodiment of the present invention for use with the LCD display apparatus of Figure 1.

Referring to Figure 1 , a medical imaging apparatus 2 has a circular frame 4 supporting a circular arrangement of opposed pairs (only one such pair being shown in Figure 1) of X-ray sources 6 and X-ray detectors 8 for forming image data in a plane 10 passing through a patient 12. The patient 12 is scanned by moving a platform 14 supporting the patient 12 in the direction of arrow A in Figure 1.

The X-ray sources 6 and detectors 8 are controlled by means of a processor 16 which also receives image data from the detectors 8. The processor 16 forms 3D model data of the region of the patient 12 (for example the patient's colon) being scanned, and one or more images are displayed on a liquid crystal display (LCD) display device 18. The LCD display device 18 has a housing 20 containing a backlight unit 22, a light diffuser screen 24 and an LCD display panel 26 for transmitting light in dependence upon electrical signals received by the individual pixels of the display panel 26. The functioning of this aspect of the display device 18 will be familiar to persons skilled in the art and will therefore not be described in further detail.

Referring to Figure 2, the backlight unit 22 of Figure 1 has a housing 28 in which a series of white fluorescent lamps 30 for illuminating the LCD panel 26 of the display 18 (Figure 1) are arranged in a spaced apart parallel manner. The backlight unit also includes a waveguide 32, and a pair of clusters 34 of coloured fluorescent lamps arranged along opposed edges of the waveguide 32. The light emitted by the clusters 34 penetrates inside the waveguide 32. After multiple reflections/diffusions from the edges of the waveguide, the light is emitted from a surface of the waveguide 32, mainly in the direction of LCD panel 26. In this way, a relatively small irradiating area of the illumination unit is converted to a bigger one. The waveguide 32 is also provided with a special pattern distributed over the edges and/or inside of waveguide so that the waveguide diffuses light passing through it. Each of the clusters 34 includes a blue fluorescent lamp 36, a green fluorescent lamp 38 and a red fluorescent lamp 40 and are separately controllable by means of a controller (not shown) incorporated into the processor 16 (Figure 1) so that the blue, green and red colour intensities can be separately adjusted to adjust the overall colour tone of

light emitted by the cluster 34. In this manner, the overall colour tone of the light passing through the diffuser panel 24 (Figure 1) can be adjusted by suitable adjustment of the intensity of the individual lamps of the clusters 34.

Because a conventional LCD display would include a backlight unit having white fluorescent lamps 30, it is envisaged that the backlight unit 22 of Figure 2 could be installed as an upgrade of an existing LCD display. However, it will also be appreciated by persons skilled in the art that the backlight unit 22 could also be manufactured as an integral component of an LCD display.

Referring to Figure 3, in which parts common to the embodiment of Figure 2 are denoted by like reference numerals but increased by 100, a second embodiment of a backlight unit 122 for use in the apparatus of Figure 1 is shown. The backlight unit 122 includes an array of fluorescent lamp clusters 134, each cluster being identical in construction to the clusters of the backlight unit of Figure 2. The lamp clusters 134 are arranged in a parallel and spaced apart manner and the individual intensities of the red, green and blue components of light emitted by each cluster can be independently adjusted by means of a controller (not shown) to enable the overall colour tone of the light emitted by each cluster 134 to be adjusted.

By using an array of lamp clusters 134 across the entire width of the backlight unit 122, this enables the white fluorescent lamps 30 of the embodiment of Figure 2 to be replaced, since the white phosphor of a white lamp is a generally a mixture of red, green and blue phosphors. By replacing white lamps by colour lamps, this therefore enables colour tuning over a wider range than in the backlight unit 22 of Figure 3.

It will be appreciated by persons skilled in the art that the above embodiments have been described by way of example only, and not in any limitative sense, and that various alterations and modifications are possible without departure from the scope of the invention as defined by the appended claims. For example, although the embodiments of Figures 1 to 3 have been described in the context of X-ray imaging, it will be appreciated by persons skilled in the art that the invention is equally applicable to other methods of imaging, such as magnetic resonance imaging.