FI86228C - A method for reading an image disc containing information includes a stimulating beam - Google Patents

Description

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Method for reading an image disc containing information with a stimulating beam - Method for reading an image plate with a stimulating beam 5

The present invention relates to a method for reading an image disc containing stored image information with a stimulating beam, wherein the stimulating beam is made to wipe the disc in streaks, the light emitted from the image plate caused by the stimulating beam is measured and converted into a signal corresponding to the image information.

Such a method is used in particular in connection with X-ray imaging 15 to read a so-called RIM (radiation image) plate. One such method and apparatus is disclosed, for example, in U.S. Patent 4,527,060.

The reading of the RIM board is performed by directing a very small laser dot 20 to the surface of the RIM board and collecting the generated radiation with a light guide to a photomultiplier tube, from which the signal ... is further processed to propagate the image information. The laser beam is made to sweep the surface of the RIM plate using a galvanometer using a rotatable mirror that moves 25 laser dots back and forth across the RIM plate while moving the plate linearly.

However, the fluorescent materials on the RIM board have an afterglow property that degrades image contrasts, especially for pixels after highly irradiated areas.

The object of the following invention is now to reduce this disadvantage and at the same time thus improve the contrasts of the read image. To achieve this object, the invention is characterized by what is set out in the appended claim 1.

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It is therefore essential in the invention that the stimulating beam, which is usually a laser beam, is interrupted at a certain frequency and, accordingly, the light emitted from the RIM board is also measured and analyzed with a synchronized stimulating beam interruption, the light always being measured between pixels, that is, when the laser beam is off.

In this connection, it can also be stated that it is known to switch off the laser beam always during the return line, in a manner similar to e.g. the reception of a television signal, but this interruption does not, of course, eliminate the above-mentioned problem of afterglow.

The invention will now be described in more detail by way of example with reference to the accompanying drawing, in which Figure 1 schematically shows a device for reading a RIM disk and Figure 2 shows the functions related to the description of the method according to the invention.

In Figure 1, reference numeral 1 denotes a laser source which transmits a laser beam L to a RIM disk 3 readable via a rotatable mirror 2.

The light emitted from the surface of the RIM disk is collected by a light guide 5 and directed through a filter 6 to a photomultiplier tube 7, the signal of which is fed to the system processor 8.

According to the invention, the laser beam L is interrupted under the control of the processor 8 at a certain frequency, e.g. about 1000 times for each line, i.e. for each revolution cycle of the mirror 2. Also, the galvanometer 10 rotating the mirror 2, as well as the linearly movable holder 4 of the RIM plate 3, are controlled 35 from the processor 8.

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The digital information generated by the processor 8, corresponding to the image information of the RIM disk 3, is transferred to the memory 9, from which it can be further printed in a suitable manner.

It is clear that the system may include other components, such as amplifiers, additional optical elements, etc., which, however, are omitted from Figure 1 as irrelevant to the invention.

10 Figure 2 (a) shows, in principle, the image content of a RIM disc in a single line. Point b shows the state of the laser beam L, i.e. the beam is switched on and off several hundred times in one line.

15 c shows the measured signal, i.e. the signal of the photomultiplier tube 7, when the signal is always measured once per the state of the laser beam, i.e. once when the laser beam is on and once when the laser beam is switched off. Point d shows the signal of the photomultiplier tube 7, respectively, when two measurements are made for each state of the laser beam.

t · - The proportion of afterglow in the signal coming to the photomultiplier tube can be compensated by subtracting the proportion of afterglow 25 of the previous pixels from the measured signal when the laser is on, which in turn can be deduced from the measured signal when the laser is switched off. As the afterglow gradually attenuates, the compensation accuracy naturally improves by increasing the number of measurements during the state of each laser beam.

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Claims (5)

A method for reading an image disc containing stored image information with a stimulating beam, wherein the stimulating beam is made to scan the disc in streaks, the light emitted from the image plate caused by the stimulating beam is measured and changed to match the image information and that the emitted light is measured periodically, respectively, synchronously with the interruption to reduce or eliminate afterglow. A method according to claim 1, characterized in that the extinction period of the scanning beam is dimensioned so long that a considerable part of the after-light of the light emission caused by the previous period of action of the stimulating beam has time to disappear during the extinction period. A method according to claim 1 or 2, characterized in that the on and off periods of the scanning beam are approximately the same length. Method according to one of the preceding claims, characterized in that the emitted light is received and measured at least once also during the extinction period. 4 86228 Method according to one of the preceding claims, characterized in that the scanning beam is cut off at least 100 times, e.g. about 1000 times, in one line. 5 86228