METHOD FOR DETERMINING THE QUALITY OF AN IMAGING PLATE AND IMAGING PLATE SCANNER THEREFOR

Abstract

The invention relates to a method for determining the quality of an imaging plate, comprising the steps of carrying out an exposure of the imaging plate, carrying out a scan of the imaging plate in order to determine an image, determining a signal-to-noise ratio of the image or/and carrying out edge recognition on the image and calculating a quality value of the imaging plate on the basis of the signal-to-noise ratio of the image or/and on the basis of the recognized edge structure. Furthermore, the invention relates to an imaging plate scanner for carrying out such a method.

Claims

1-10. (canceled)

11. A method for determining quality of an imaging plate, the method comprising: carrying out an exposure of the imaging plate; carrying out a scan of the imaging plate in order to determine an image; removing markings from the image to generate a preprocessed image; adding an unsharpness to the preprocessed image to form an unsharpness preprocessed image; carrying out an edge recognition on the unsharpness preprocessed image to form an edge recognition preprocessed image; converting the edge recognition preprocessed image into a binary image by means of a threshold value operation; and calculating a quality value of the imaging plate on the basis of the binary image.

12. The method of claim 11, further comprising: after the removing markings from the image to generate the preprocessed image step, determining a local signal-to-noise ratio for each pixel of a plurality of pixels of the preprocessed image using an associated averaging array comprising a local subset of the plurality of pixels; marking a first subset of the plurality of pixels for which their local signal-to-noise ratios are below a threshold value marking; marking a second subset of the plurality of pixels corresponding to recognized edges; and calculating a quality value of the imaging plate on the basis of the binary image and by using a ratio of the first and second subsets of marked pixels to the plurality of pixels of the preprocessed image.

13. The method of claim 11, wherein the carrying out the exposure comprises setting a specific distance between the imaging plate and a recording device.

14. The method of claim 12, further comprising: generating a first image mask that marks the first subset of the pixels; and generating a second image mask that marks the second subset of the pixels.

15. The method of claim 12, further comprising: ascertaining a number and/or a size of instances of damage of the imaging plate on the basis of a local signal-to-noise ratio for one or more segments of the image.

16. The method of claim 11, further comprising: ascertaining damage of the imaging plate on the basis of a recognized edge.

17. The method of claim 11, wherein the carrying out the edge recognition comprises using a Canny algorithm.

18. The method of claim 11, further comprising: after carrying out the edge recognition, performing a morphological dilatation and/or a closing operation.

19. The method of claim 14, wherein the calculating comprises performing a logic OR operation on the first subset and the second subset of marked pixels to provide a combined set of the first subset and the second subset of marked pixels used to determine the ratio.

20. The method of claim 12, wherein the determining the local signal-to-noise ratio for each pixel of the preprocessed image comprises: defining the associated averaging array; determining the local signal-to-noise ratio using all of the pixels contained in the associated averaging array; and assigning the local signal-to-noise ratio to one of the pixels contained int eh associated averaging array.

21. An imaging plate scanner configured to perform steps, the steps comprising: carrying out an exposure of the imaging plate; carrying out a scan of the imaging plate in order to determine an image; removing markings from the image to generate a preprocessed image; adding an unsharpness to the preprocessed image to form an unsharpness preprocessed image; carrying out an edge recognition on the unsharpness preprocessed image to form an edge recognition preprocessed image; converting the edge recognition preprocessed image into a binary image by means of a threshold value operation; and calculating a quality value of the imaging plate on the basis of the binary image.

22. The imaging plate scanner of claim 21, wherein the scanner is further configured to perform: after the removing markings from the image to generate the preprocessed image step, determining a local signal-to-noise ratio for each pixel of a plurality of pixels of the preprocessed image using an associated averaging array comprising a local subset of the plurality of pixels; marking a first subset of the plurality of pixels for which their local signal-to-noise ratios are below a threshold value marking; marking a second subset of the plurality of pixels corresponding to recognized edges; and calculating a quality value of the imaging plate on the basis of the binary image and by using a ratio of the first and second subsets of marked pixels to the plurality of pixels of the preprocessed image.

23. The imaging plate scanner of claim 21, wherein the carrying out the exposure comprises setting a specific distance between the imaging plate and a recording device.

24. The imaging plate scanner of claim 22, wherein the scanner is further configured to perform: generating a first image mask that marks the first subset of the pixels; and generating a second image mask that marks the second subset of the pixels.

25. The imaging plate scanner of claim 22, wherein the scanner is further configured to perform: ascertaining a number and/or a size of instances of damage of the imaging plate on the basis of a local signal-to-noise ratio for one or more segments of the image.

26. The imaging plate scanner of claim 21, wherein the scanner is further configured to perform: ascertaining damage of the imaging plate on the basis of a recognized edge.

27. The imaging plate scanner of claim 21, wherein the carrying out the edge recognition comprises using a Canny algorithm.

28. The imaging plate scanner of claim 21, wherein the scanner is further configured to perform: after carrying out the edge recognition, performing a morphological dilatation and/or a closing operation.

29. The imaging plate scanner of claim 24, wherein the calculating comprises performing a logic OR operation on the first subset and the second subset of marked pixels to provide a combined set of the first subset and the second subset of marked pixels used to determine the ratio.

30. The imaging plate scanner of claim 22, wherein the determining the local signal-to-noise ratio for each pixel of the preprocessed image comprises: defining the associated averaging array; determining the local signal-to-noise ratio using all of the pixels contained in the associated averaging array; and assigning the local signal-to-noise ratio to one of the pixels contained int eh associated averaging array.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Exemplary embodiments of the invention are explained in greater detail below with reference to the drawings, in which:

[0024] FIG. 1 shows a first embodiment of a method according to the invention in a flow diagram;

[0025] FIG. 2 shows a first development of the method from FIG. 1 in a flow diagram;

[0026] FIG. 3 shows a second embodiment of the method from FIG. 1 in a flow diagram;

[0027] FIG. 4 shows a second alternative or additional embodiment of the method from FIG. 3 in a flow diagram; and

[0028] FIG. 5 shows an imaging plate scanner according to the invention in a schematic illustration.

DESCRIPTION OF PREFERRED EXEMPLARY EMBODIMENTS

[0029] FIG. 1 illustrates one exemplary embodiment of a method according to the invention in a simplified schematic flow diagram. The method comprises the step of exposing an imaging plate S1. When exposing the imaging plate, it is advantageous if the imaging plate is exposed with a specific dose. It has proved to be advantageous if the imaging plate is positioned within a predefined distance from the recording device. 12 cm has proved to be worthwhile in practice, which can be set as a diameter of a CD. By way of example, the setting for modular teeth can be used as a setting for the X-ray apparatus.

[0030] In the next step, the imaging plate is read and a digital image is generated (S2). The dose with which the imaging plate was exposed can be determined after or during the reading. An output to the operator can be effected regarding whether the dose was chosen to be too high or too low. If appropriate, the operator must expose the imaging plate once again since the signal-to-noise ratio can change with the dose.

[0031] The next step involves preprocessing the image for ascertaining the quality of the imaging plate (S3). The step of preprocessing (S3) is explained in detail below.

[0032] After preprocessing (S3), two method blocks can be processed simultaneously in parallel, successively or/and as an alternative to one another.

[0033] The preprocessed image can be transformed into a mask in which pixels are marked for which a signal-to-noise ratio lies below a specific threshold value (S4). Alternatively or additionally, an edge recognition can be carried out on the preprocessed image (S5), on the basis of which edge recognition a mask can be generated in which the pixels thus recognized are marked.

[0034] By means of these two masks, a total number of marked pixels can be ascertained (S6). If this number of marked pixels is related to the total number of all pixels (reduced by the number of pixels of the exclusion mask) by a ratio, the quality of the imaging plate can be ascertained on the basis of this ratio (S7).

[0035] The preprocessing (S3) of the image obtained from the reading process is discussed in greater detail below. FIG. 2 shows one possible embodiment of the process of preprocessing (S3). An edge mask is provided for the image read out (S31). The edge mask can involve for example a distance which extends peripherally around the edge of the image and outside which the image data are discarded or not used for processing. In the case of the conventional sizes for imaging plates for the oral region (from 2x3 cm to approximately 6x8 cm), for example, one to two millimeters that should remain free as a peripheral edge suffice. Said distance can be fixedly set or freely selectable by the operator.

[0036] A further step involves detecting possible markings which are applied on the imaging plate and do not belong to the actual image content (S32). The detecting can be carried out by means of a morphological operation, for example, and can search for known structures in the image content, for example. Recognized markings or similar structures are added to the edge mask, which thus becomes an exclusion mask (S33).

[0037] Optionally, the edge or exclusion mask thus created can be displayed to an operator for control or/and for information purposes (S34).

[0038] The exclusion mask or edge mask thus created is applied to the image read out (S35), thus resulting in a preprocessed image. The latter is taken as a basis for one of the next steps (S4, S5).

[0039] FIG. 3 illustrates, in a flow diagram, some aspects of one embodiment of a method for determining a number of no longer operable pixels of an imaging plate by means of a calculation of a signal-to-noise ratio (S4). The method (S4) comprises firstly carrying out (S41) a local signal-to-noise ratio (SNR). In this case, an averaging array is defined, within which the SNR is determined as a value for all pixels contained therein. The value thus determined is correspondingly assigned to one of the pixels contained therein. This calculation step is carried out at all positions that are possible in the image. The averaging array is advanced as it were pixel by pixel and a local SNR is calculated in each case at the new location. An SNR thus results for virtually every pixel in the image (with the exception of an edge strip corresponding to the chosen size of the averaging array). These values can be interpreted and represented as an SNR image of the preprocessed image (S42). In practice, in the case of the imaging plate sizes mentioned and the corresponding image sizes, an averaging array of 21?21 pixels has proved to be expedient. Other averaging array sizes are also conceivable, having for example only half the magnitude or double the magnitude.

[0040] In a further step (S43), an SNR range is determined as an additional variable (S43). In this case, the local SNR values can be used for the calculation of the SNR range. By way of example, a minimum value and a maximum value can be determined. Alternatively, a global SNR value can be calculated from the local SNR values or solely on the basis of the preprocessed image.

[0041] A further step (S44) involves determining an SNR threshold value. The latter can be oriented toward the SNR range. Alternatively or additionally, a local SNR values can influence the ascertainment of the SNR threshold value. The SNR threshold value can be calculated for example as follows:

[00002]$\frac{SN{R}_{local}\left(x,y\right)-SN{R}_{\min }}{SN{R}_{\max }-SN{R}_{\min }},$

wherein SNR.sub.local(x, y) represents the local SNR value, SNR.sub.min represents the minimum SNR value and SNR.sub.max represents the maximum SNR value. If this value is 20% or less, the corresponding pixel is marked as defective. However, other percentage values such as 10% or 30%, for example, are also conceivable.

[0042] By means of the SNR threshold value thus ascertained, it is then possible to determine the pixels in the SNR image whose SNR lies below the SNR threshold value (S45).

[0043] In a further step (S46), the pixels thus marked are combined to form a mask which marks the no longer operable region of the imaging platedetermined on the basis of the SNR.

[0044] FIG. 4 illustrates, in a flow diagram, an alternative embodiment of a method (S5) for ascertaining no longer functional regions of an imaging plate on the basis of an edge recognition method. This embodiment can be used simultaneously with or as an alternative to the method which provides for determining the signal-to-noise ratio.

[0045] A first step involves adding an unsharpness to the preprocessed image (S51). Adding the unsharpness serves the purpose of avoiding an excessively great reaction of the edge recognition algorithm to individual greatly noisy pixels.

[0046] An edge recognition is then carried out (S52) on the image that has been preprocessed in this way. By way of example, the Canny algorithm can be used in this case. However, other edge recognition algorithms are also conceivable. The result of the edge recognition algorithm is once again an image, which is converted into a binary image (only 0 or 1 exist as image values) by means of a threshold value operation (S53). The choice of the threshold value depends for example on the general image quality, the noise level, the quality of the reading process, etc.

[0047] On the edge recognition image that has been converted in this way, for better visibility of the detected structures, a morphological dilatation and a closing operation can be carried out in order to fill small gaps or holes in the edges (S54). This results in a second mask, which likewise marks regions in the image and thus indirectly the imaging plate which no longer function properly.

[0048] The image masks thus generated in two different ways can be combined with one another by means of a logic OR operation, for example. The obtained number of instances of damage in the form of no longer functional pixels can be convertedas has already been explained thoroughly further aboveinto a rating of the imaging plate in accordance with the formulae

[00003]$f_{\mathrm{marked}}=-\ln \frac{N_{\mathrm{marked}}}{N_{total}-N_{\mathrm{Mask}}}$$\mathrm{and}{f}_{\mathrm{final}}=w_0+w_1{f}_{\mathrm{marked}}$

[0049] The weighting factors wo and wi can be used for adapting the quality checking method to the desired scaling of the quality classification of the respective imaging plate and can be determined for example by means of a linear regression on a training dataset such that the resulting final value corresponds to an expert rating of the plate quality as well as possible.

[0050] In a comparison of the quality classification by means of the method presented above and the classification results of experts (dentists, technicians), an extensive correlation of the two classifications was found.

[0051] FIG. 5 shows a scanning device 10 for reading an imaging plate 12 carrying a latent X-ray image in the form of metastable storage centers excited by X-ray radiation. The scanning device 10 comprises a supporting device 14 for the imaging plate 12. By way of example, the imaging plate 12 can be secured on the supporting device 14 by means of reduced pressure such that the imaging plate 12, which is generally flexible, nestles against the supporting surface 14 in a planar manner. The scanning device 10 furthermore comprises a laser 16 as read-out light source, said laser generating a read-out light beam 18 having a wavelength in the red, by means of which beam the metastable storage centers of the imaging plate 12 can be excited to produce fluorescent light. Said fluorescent light 20 is typically in the blue.

[0052] In the present embodiment of the scanning device 10, the laser 16 is arranged such that it directs the read-out light bean? 18 onto a controllable deflection unit. The controllable deflection unit is embodied as a mirror 22 in the present case. Other deflection units such as, for instance, optical units or the like are also conceivable. The mirror 22 can be embodied as a micromirror, in particular as a MEMS component, and thus enable the surface of the imaging plate 12 to be scanned without or with only little relative movement between mirror 22 and supporting device 14. Alternatively, the mirror 22 can also be provided as a rotary mirror for a drum scanner. In this case, a relative movement between the supporting device 14 and the mirror 22 is realized by means of a transport device (not depicted). A further technique for reading the imaging plate 12 comprises the use of a rotary pentaprism.

[0053] The scanning device 10 can furthermore comprise a reflector 24, which is indicated by dashed lines in the drawing and which encloses the entire measurement space around the imaging plate 12 in a light-tight fashion, such that the fluorescent light 20 emanating from the imaging plate 12 is reflected to a photodetector 26. In order to prevent stray read-out light 18 from passing into the detector 26, suitable measures such as a dichroic filter material, for instance, can be provided. For controlling the reading process, the scanning device 10 comprises a control unit 28, which can also perform evaluation or correction functions besides the control function. in the embodiment shown in the present case, the control unit 28 is configured to carry out one of the abovementioned methods for determining the quality of an imaging plate.