FR2672760A1 - Flat scanner equipped with an indirect lighting device and digitising suite using such a scanner - Google Patents

Abstract

The invention relates to a flat scanner equipped with an indirect lighting device and a digitising suite using such a scanner. It consists of a box (5) equipped with an upper window (6), the whole being covered by a box (10) containing at least one light source (13). The box (10) includes recesses (14, 15) making it possible to introduce a film (21) on the glazed window (6). Advantageously, the box will comprise a matt glass (11) and/or a reflecting wall of concave shape (12). The invention also relates to a digitising suite including a scanner according to this description. It is particularly intended for medical image processing, of the radiology or mammography type.

Description

 The present invention relates to a flatbed scanner provided with an indirect lighting device and a digitization chain using such a scanner.

 The invention more particularly finds applications in the field of medical imaging, and for example it facilitates the viewing and processing of images obtained by radiography, ultrasound or mammography.

 The digitization of images is of great interest, in the field of medical imaging where it makes it possible to obtain information of improved readability, to compare images with each other, and to highlight certain particularly significant details. Associated with image processing software, this technology also makes it possible to perform calculations on the shapes displayed and can therefore be used as a diagnostic aid.

 There is no doubt that the applications of direct digitization will become more widespread in the coming years. This method consists in directly capturing the information on a flat surface provided with a plurality of sensitive cells arranged in the form of a grid, each cell assigning a numerical value to the information it receives.

 However, this process has the drawback of imposing heavy investments for the time being, and its implementation has not yet been mastered by operators in medical imaging. It is important to emphasize that the "film" support remains predominant in medical imaging: it is the support on which most of the equipment currently in use works, whether in the field of radiology or mammography than, to a lesser extent , in the field of ultrasound.

 In addition, the knowledge bases currently available, consisting of medical records with history of illnesses, contain "image" information essentially in the form of films.

 For all of these reasons, it is interesting to use mammographic or ultrasound radiological films as sources for creating digitized files.

To this end, it has been proposed in particular to place a professional class video camera on a fixed base and to capture by means of this camera the light reflected by a film centered on the focal axis of this camera. To compensate for the fact that the films are generally not very contrasted and dark, we illuminate these supports with a particularly intense light. However, such a device has many drawbacks:
In the first place, the overall height is significant, because of the need to place the camera at a sufficient altitude relative to the surface of the film to view the entire film.

 In addition, the camera settings require long and meticulous operations. Furthermore, the presence of a large flow of unconfined light between the lighting device and the film can constitute a gene for the other workstations placed in the same examination room.

 Finally, whatever the quality of the optics used, the reduction of the information to the size of approximately 1 cm2 corresponding to the dimensions of the CCD sensors placed behind the lens inevitably results in a loss of information. Added to these problems are the effects of optical aberrations which inevitably occur for parts of the images distant from the focal axis of the lens.

 Furthermore, it is almost impossible to obtain a truly uniform illumination of the film, which risks causing the appearance of false information, especially after image processing by thresholding.

 To resolve all of the difficulties set out above and with the aim of producing a digitization device which is at the same time of a low cost price, of a reduced bulk and of an easy handling, while producing digitized files of a high degree of reliability, the invention proposes in particular to remove the camera and to replace this camera by a flat scanner of conventional design, to which a certain number of modifications and improvements, which form an integral part of the invention will have been brought.

 It is known per se to create a digitized file from an image using a specific computer peripheral, of the type known under the generic name of flatbed scanner. Such devices are generally in the form of rectangular parallelepipeds, the upper face of which is provided with a flat window covered by an articulated cover. The image, of a format generally less than or at most equal to 21 x 30 cm, is placed opposite the glass and under the cover. After triggering of the scanning operation, a mobile assembly whose axis is generally parallel to the short sides of the upper glazed window and whose useful width is at least equal to that of this window, moves from one end to the 'other of said window, so as to read the information contained in the image.

 Thus, all of the points appearing on the image are identified by its abscissa (the distance traveled by the moving equipment from the starting point to the point studied) and by its ordinate (the distance between the edge of the mobile equipment and the position of the point studied on the generator of said mobile equipment). A numerical value is associated with each image point, this value being either "zero" or "one" for the simplest systems. In reality, the scanners currently sold are designed to assign a value between "zero" and "16" or between "zero" and "250" or more at each point of the image. The number of values that can be assigned to a given point represents the number of colors or gray levels read and restored by the scanner. The higher the number, the better the definition of the scanned image. In the same way the definition obtained will be all the better the tighter the grid pattern, that is to say that the number of points defining a given portion of the image will be higher. This point density criterion is measured in "dpi" (density per square inche) value which commonly reaches 300 and can reach 400 or 600 for high-performance devices. It is understood that such systems make it possible to create files usable by computerized systems, since to each point of the image corresponds a numerical value. It is also understood that it is particularly easy to store and process these files by conventional computer means, for example by subjecting them to modifications which improve the readability of the images studied.

 It turns out that, in their current design, scanning devices are incompatible with the processing of radiographic or mammographic film. In fact, these devices contain an internal light source, which source is most often attached to the mobile equipment, which is not able to produce sufficient light, quantitatively as well as qualitatively, to allow the Reading the information contained on the film: placed on a flat scanner, an X-ray or mammographic film will most of the time produce a scanned image containing no other usable information than that of the contours of the shapes observed.

 One of the objectives of the invention is to enable operators in medical imaging to benefit from the comfort of using a flatbed scanner for digitizing the images contained on radiographic or mammographic films, while retaining a sufficient definition for the information obtained, this objective will be achieved in particular by making improvements to the design and production of flatbed scanners, and more particularly in terms of the image lighting devices intended to be scanned.

 Another objective is to improve the quality and readability of the digitized images, in particular by eliminating the defects introduced by the use of a camera.

 An additional object of the present invention is to reduce the cost price of a medical image scanning installation, and thus allow the acquisition of such channels by many hospitals, or even by private practices.

 An additional objective is to offer a complete image scanning installation which is both compact and particularly easy to handle.

 These objectives, as well as others which will appear subsequently, are achieved by means of a digitization installation comprising a flatbed scanner provided with specific arrangements. This flatbed scanner is characterized in that it comprises an upper part arranged so as to allow on the one hand the placement of an X-ray film on the upper window of the scanner and on the other hand the indirect illumination of the crew mobile of the scanner through the said film by a light source located in a box placed above the upper glass of the scanner. To allow good performance, the film illumination device must produce both intense and diffuse light: it is indeed important not to introduce a preferential illumination zone in any place whatsoever: on the one hand the over-illuminated zone could appear abnormally clear to the observer and on the other hand, during a treatment by thresholding the scanned file, treatment which consists in favoring certain colors (or grayscale) over others, there is a risk of revealing false information. In an advantageous embodiment, the lighting device may have one or more masks, removable or not. These masks will have the function of compensating for the very large difference existing on the films between the exposed areas and the unexposed areas, this so as to limit the sensitivity values on which the receiving cells placed on the moving part must operate. According to an advantageous characteristic of the invention, these masks may be constituted by one or more panes having the property of having a variable transparency depending on the flow to which they are exposed.

 Furthermore, the lighting device according to the invention should be particularly compact and will have a shape such that it can be easily placed above a flatbed scanner of conventional shape, with the upper cover of which it has for vocation to replace.

Other characteristics and advantages of the invention will appear on the following reading of a preferred embodiment of the invention, given by simple illustrative title and the appended drawings in which:
- Figure 1 shows a conventional digitization chain.

 - Figure 2 shows a flat type conventional scanner.

 - Figure 3 shows a flatbed scanner equipped with an illumination device according to the invention.

 - Figure 4 shows a digitization chain comprising a device according to the invention.

 Recall that a conventional digitization chain as shown in Figure 1, includes a camera (1) on the focal axis of which is placed the film (21). The information captured by the camera is transmitted to the central unit (2), which makes it possible to view it, preferably on a large screen (3). The images after scanning and processing can also be printed on a suitable peripheral (4).

 It is also recalled that a conventional flatbed scanner, such as shown in FIG. 2, is constituted by a box (5) of parallelepiped shape, provided with a transparent window (6) on its upper face, which window is covered by a hinged cover (7).

 The essential characteristic of the invention, characteristic illustrated in FIG. 3, resides in the fact that the cover (7) of a flat scanner is replaced by a housing (10) whose walls include two recesses (14,15) placed on two opposite faces of said housing (10), said recesses having a shape such that they allow the housing (10) to be placed on the same plane as the scanner (5) while covering most of the latter .

 The housing (10) is provided with at least one light source (13). This light source (13) emits a beam of light which, after one or more reflections on the walls (12) of the housing (10) reaches the film (21) placed on the upper window (6) of the housing (5). It is important that the light flux reaching the moving part of the scanner (5) after having undergone reflections and having passed through the film (21) then the window (6) is intense and is as regular as possible. Indeed the image of the source (13) on the film can cause the appearance of false information completely detrimental to the accuracy of the diagnosis. In order to avoid this major drawback, at least one glass (11) made of frosted glass will advantageously be placed between the source (13) and the film (21). walls (12) on which the rays are reflected a non-planar shape in at least one of its dimensions and, preferably, a concave shape. Thus the luminous flux illuminating the film will be particularly homogeneous and the "images" of the light source or sources (13) will be practically eliminated. This point is essential to allow processing of the information contained in a radiographic or mammographic film by using the many possibilities offered by image processing software.

 Note that one of the recesses (14) in the side walls of the housing (10) is slightly higher than the housing (5) of the flatbed scanner. This in order to provide a slot through which it is possible to slide the film (21) in order to place it against the glass window (6).

 The film studied (21) may have on the one hand a very dark area (23) and on the other hand a very clear area, we will advantageously place a mask (16) between the film (21) and the window (6). This mask (16) may be constituted by a plate of transparent material having the property of having a variable transparency as a function of the quantity of light which it receives.

Finally, to avoid any heating of the air contained in the housing (10), an air renewal system (17) will advantageously be placed on one of the walls of said housing. ~
As shown in Figure 4, a flatbed scanner whose cover (7) has been replaced by a housing (10) as described above constitutes the first element of a scanning chain. Comparative studies made by applicants have shown that such a chain is on the one hand much cheaper and on the other hand more precise and more efficient than scanning chains using cameras. In addition, the handling of a digitization chain integrating the components described above is particularly easy and quick.

 Of course, the above descriptive elements are given only by way of illustration, and one can imagine other embodiments without departing from the scope of the present invention.

Claims (8)

-1- Flatbed scanner, of the type comprising a housing (5) of parallelepiped shape and a transparent window (6) on its upper face, characterized in that it is covered for the most part by a housing (10) provided at least one light source (13). -2- flatbed scanner according to claim 1 characterized in that the boot (10) comprises two recesses (14,15) formed in the side walls of said housing, recesses one of which comprises a slot through which it is possible to slide a film (21). -3- Scanner according to claim 1 characterized in that the housing (10) comprises a frosted glass pane (11) placed between the source (13) and the film (21). -4- Scanner according to claim 1, characterized in that the housing (10) comprises at least one wall (12) reflecting the rays from the source (13). -5- Scanner according to claims 1 and 4, characterized in that the wall (12) has a non-planar shape in at least one of its dimensions and, preferably, a concave shape.  -6- Scanner according to claim 1, characterized in that it is provided with a mask (16) placed between the film (21) and the transparent window (6). -7- Scanner according to claims 1 and 6 characterized in that the mask (16) consists of a plate made of a material having the property of having a variable transparency depending on the amount of light it receives. -8- Scanner according to claim 1, characterized in that the housing (10) is provided with a renewal system (17) of the air contained in said housing; -9- Digitization chain, in particular intended for the treatment of medical images, characterized in that it comprises a scanner according to at least one of the preceding claims.