Patent Application
20120020541
The present invention relates to a radiographic apparatus and a control method for the same.
With recent demands for the digitization of images, a digital imaging apparatus having a function of outputting digital images has begun to be used as a radiographic apparatus, which captures a radiation image transmitted through an object. A computed radiographic apparatus is used to perform general imaging by using an imaging plate which stores a radiation image as a latent image, in place of a screen-film system, and excites the latent image by laser-scanning the imaging plate. This apparatus reads the fluorescence produced by this operation via a photoelectron multiplier. An I.I.-DR imaging apparatus is also used to capture moving images, which uses a solid-state imaging device such as a CCD in place of an image pickup tube. Both the apparatuses have a function to output digital images. This is beginning to contribute to the digitization of medical images. There is also available a digital imaging apparatus which directly digitizes a radiation image without via an optical system and the like by using a so-called FPD (Flat Panel Detector), which is a radiation flat panel detector having a phosphor and a large-area amorphous silicon sensor arranged in tight contact with each other.
Conventionally, as disclosed in Japanese Patent Laid-Open No. 2005-006196 and Japanese Patent No. 4124915, a radiation flat panel detector (FPD) registers defect positions (defect coordinate map) in advance, and always corrects predetermined pixels based on the defect positions. According to Japanese Patent Laid-Open No. 2005-006196, the flat panel detector extracts first and second defective pixels. According to Japanese Patent No. 4124915, the flat panel detector segments an image into a plurality of areas, obtains a standard deviation, and extracts a defective pixel within each area.
There has not been available any means for, for example, changing abnormal pixel correction methods depending on whether an abnormal pixel is a permanently abnormal pixel or a temporarily abnormal pixel. This makes it impossible to correct abnormal pixels by proper methods.
The present invention provides a radiographic apparatus, which can choose between spatial correction and temporal correction in accordance with whether an abnormal pixel is a permanently abnormal pixel or a temporarily abnormal pixel.
According to one aspect of the present invention, there is provided a radiographic apparatus including X-ray irradiation means for irradiating X-rays and X-ray detection means for detecting an X-ray image of an object irradiated by the X-ray irradiation means, the apparatus comprising:
first defect detection means for detecting, as a position-dependent defect, a pixel, of a plurality of X-ray images detected by the X-ray detection means, whose pixel value is always abnormal, and acquiring position information of the defect in the X-ray image;
first defect correction means for correcting the pixel value of the pixel in which an abnormality is detected, based on the position information and a pixel value of a neighboring pixel of the pixel in which the abnormality of the pixel value is detected;
acquisition means for acquiring information indicating an imaging condition for the object when the X-ray detection means detects the X-ray image;
decision means for deciding, based on the information indicating the imaging condition acquired by the acquisition means, whether to further correct the X-ray image corrected by the first defect correction means;
second defect detection means for, when the decision means decides to further correct the X-ray image, detecting, as a defect, a pixel, of the plurality of X-ray images detected by the X-ray detection means, which temporarily becomes abnormal dependent on a lapse of time;
determination means for determining a correction method for correcting the pixel value of the pixel in which the abnormality is detected by the second defect detection means, based on the information indicating the imaging condition; and
second defect correction means for correcting the pixel value of the pixel detected by the second defect detection means in accordance with the correction method determined by the determination means.
The present invention can provide a radiographic apparatus, which can choose between spatial parameter correction and temporal parameter correction for a temporarily defective pixel.
In addition, it is possible to provide a radiographic apparatus, which can change to a suitable correction method for an abnormal pixel which does not always appear, like an X-ray shot noise pixel or an abnormal dot pixel, in accordance with imaging conditions.
Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings).
The preferred embodiments of the present invention will be exemplarily described in detail below with reference to the accompanying drawings.
The arrangement of a radiographic apparatus will be described with reference
The X-ray irradiation control unit 1005 and the data acquisition unit 1006 are connected to a CPU bus 1026. The main memory 1015, an image processing unit 1013, a CPU 1014, an operation panel 1016, and an image display unit 1017 are also connected to the CPU bus 1026. The main memory 1015 stores various kinds of data necessary for processing in the CPU 1014, and also functions as a working memory for the CPU 1014. The CPU 1014 functions as a control means for a radiographic apparatus 1000, and performs, for example, operation control of the overall apparatus in accordance with operation from the operation panel 1016 by using the main memory 1015. The preprocessing unit 1007 performs the gain correction processing of correcting variations in sensitivity of the X-ray detection unit 1004 for each pixel, and the dark current correction processing of correcting variations in dark current in the X-ray detection unit 1004 for each pixel. A gain correction image and a dark current correction image are stored in the main memory 1015 before radiography. The preprocessing unit 1007 can read out these images at the time of correction as needed. When the user inputs an imaging instruction via the operation panel 1016, the contents of the imaging instruction are stored in a storage unit 1012 and displayed on the operation panel 1016. Body parts are displayed via the operation panel 1016. A body part selection unit 1025 then selects a specific body part based on the instruction input by the user via the operation panel 1016. The imaging information acquisition unit 1024 acquires and stores information corresponding to the body part, for example, a frequency to be enhanced and an enhancement degree, stored in the storage unit 1012 in advance, based on the information of the body part selected by the body part selection unit 1025. When the user issues an instruction to generate X-rays by using the operation panel 1016 of the X-ray generator thereafter, the CPU 1014 controls the X-ray irradiation unit 1001 and the X-ray detection unit 1004 via the X-ray irradiation control unit 1005 to execute radiography.
In radiography, first of all, the X-ray irradiation unit 1001 irradiates the object 1003 with the X-ray beam 1002. The irradiated X-ray beam X is transmitted through the object 1003 while being attenuated, and then reaches the X-ray detection unit 1004 to be detected. The X-ray detection unit 1004 outputs the detected X-ray image signal. In this embodiment, the object 1003 can be a human body. In this case, the X-ray image output from the X-ray detection unit 1004 becomes an image (human body image) transmitted through the human body. The data acquisition unit 1006 performs A/D conversion and the like for the X-ray image (signal) output from the X-ray detection unit 1004 to convert the data into a predetermined digital signal, and supplies it as X-ray image data to the preprocessing unit 1007. The preprocessing unit 1007 performs preprocessing such as dark current correction processing and gain correction processing for the X-ray image data. The preprocessed X-ray image data is transferred as original image data to the main memory 1015 via the CPU bus 1026 under the control of the CPU 1014. The first defect correction unit 1009 performs defect correction by using the defective pixel position map in the first defective pixel position storage unit 1018 and the spatially neighboring pixels arranged near the defective pixel of the two-dimensionally arrayed pixels constituting the X-ray image data. The defect-corrected image data is transferred to the main memory 1015 via the CPU bus 1026 under the control of the CPU 1014.
A second defective pixel position detection unit 1010 detects a defect in each defect-corrected image data (second defect detection). The second defective pixel position detection unit 1010 extracts, for each image, a temporarily defective pixel such as an X-ray shot noise pixel produced when X-ray photons interact with each other or an abnormal dot pixel produced when noise accidentally mixes in the semiconductor X-ray detector. A second defective pixel position storage unit 1019 stores the extracted defect for each image. A second defect correction unit 1011 performs defect correction (second defect correction) of the detected temporarily defective pixels, and transfers them to the main memory 1015 via the CPU bus 1026 under the control of the CPU 1014.
By using the information stored in the imaging information acquisition unit 1024 and indicates dose information, a body part, and the like, a defect correction method decision unit 1020 decides which one of a plurality of correction methods is to be used to perform defect correction (second defect correction) of a defective pixel.
The second defect correction unit 1011 performs defect correction (second defect correction) of a defective pixel based on the decision result obtained by the defect correction method decision unit 1020. The second defect correction unit 1011 corrects the defective pixel (second defect correction) by using a spatial defect correction unit 1021 and a temporal defect correction unit 1022. The second defect correction unit 1011 further corrects the defective pixel (third defect correction) with respect to the X-ray image data having undergone the second defect correction by using the method controlled by a weighting control unit 1023 which performs weighting for spatial/temporal defect correction. The X-ray image data having undergone the second defect correction is transferred to the main memory 1015 and the image processing unit 1013 via the CPU bus 1026 under the control of the CPU 1014. The image processing unit 1013 performs noise reduction processing, frequency processing, and tone processing, and outputs the resultant X-ray image data to the image display unit 1017.
Space/time-dependent defect correction and defect correction based on weighting will be described with reference to
A processing procedure in the radiographic apparatus according to this embodiment will be described with reference to
In step S301, the radiographic apparatus 1000 starts radiography after the completion of preparation for the apparatus. The X-ray irradiation unit 1001 generates a predetermined dose of X-rays corresponding to a body part, and irradiates the object 1003 with the X-rays. The X-ray detection unit 1004 detects X-rays transmitted through the object 1003. After the lapse of a predetermined storage time, the data acquisition unit 1006 reads out an image of detected X-rays (X-ray image). The imaging information acquisition unit 1024 stores the information acquired at the time of radiography. The imaging information acquisition unit 1024 stores the body part information input via the operation panel 1016, a spatial frequency enhancement parameter corresponding to each body part, the dose of X-rays which have reached the X-ray image detection panel included in the X-ray detection unit 1004, and the like. The data acquisition unit 1006 performs, for example, A/D conversion, amplification, and X-ray image data rearrangement for the obtained X-ray image data. These processing results are sent to the main memory 1015.
In step S302, this apparatus performs the first defect correction. The apparatus corrects spatial-position-dependent defective pixel by using the position information of permanently defective pixels (first defective pixel positions (defective pixel position map)) stored in the first defective pixel position storage unit 1018.
In step S303, the defect correction method decision unit 1020 decides whether to execute a correction method for the correction of a defective pixel (second defect correction). By using the information acquired at the time of radiography and stored in the imaging information acquisition unit 1024, the defect correction method decision unit 1020 decides whether to execute the second defect correction. The information acquired at the time of imaging (information acquired at imaging) includes, for example, an X-ray dose, body part information, frequency enhancement information, a moving amount in an image, an imaging frame rate, a pixel pitch, execution/non-execution of pixel binning, and an X-ray random noise amount. It is possible to decide, by using at least one of these pieces of information, whether to execute the second defect correction. If, for example, the X-ray dose stored in the imaging information acquisition unit 1024 is larger than a predetermined dose, the X-ray image data is input to the image processing unit 1013 without execution of the second defect detection for the execution of the second defect correction in order to correct X-ray shot noise. If the X-ray dose stored in the imaging information acquisition unit 1024 is smaller than the predetermined dose, the defect correction method decision unit 1020 decides to execute the second defect detection for the execution of the second defect correction. The process then advances to step S304.
In step S304, the second defective pixel position detection unit 1010 performs defect detection for the image having undergone the first defect correction in step S302 described above. In the second defect detection, this apparatus performs defect correction for the defective pixel or output abnormal pixel which has not been corrected by the first defect correction. In the first defect detection, the apparatus has mainly detected output abnormal pixels dependent on spatial positions as defective pixels. A cause of a defective pixel or the like can be mixing of a foreign component in a pixel when it is manufactured in a semiconductor process. The first defective pixel position detection unit 1008 also detects an abnormal output pixel originating from each signal line through which an output signal value passes or an amplifier IC, instead of each pixel as a cause, as a spatial-position-dependent defective pixel.
The pixels detected in this step mainly include time-dependent output abnormal pixels. For example, X-ray shot noise and abnormal dots are assumed as such abnormal pixels. As described later, X-ray shot noise is not a defective pixel originating from a pixel, signal line, amplifier IC, or the like. X-ray shot noise occurs when an X-ray photon transmitted through a phosphor is accidentally converted into an electrical signal due to a photoelectric effect inside a photoelectric conversion element. That is, such noise always occurs in every pixel at a predetermined probability. In addition, an abnormal dot can sometimes become a defective pixel if there is a contact failure or an unstable portion in a corresponding pixel, signal line, amplifier IC, or the like. If such pixels which are not always defective pixels are detected as permanently defective pixels in the first defect detection, there is a possibility that they will be excessively registered as defective pixels. In the present invention, in order to perform defect correction for proper pixels, the first defect detection is performed to detect abnormal pixels which always appear, whereas the second defect detection is performed to detect abnormal pixels which appear at some probability (temporarily) for each image. The purpose of this step is to detect abnormal pixels which cannot be captured as defective pixels which appear steadily.
In step S305, the defect correction method decision unit 1020 selects a correction method (second defect correction) for the correction of the defective pixel detected in step S304. In the present invention, the defect correction method decision unit 1020 can select (i) defect correction using spatially neighboring pixels, (ii) defect correction using temporally neighboring pixels, (iii) weighting defect correction using both spatially neighboring pixels and temporally neighboring pixels upon weighting, and (iv) no defect correction. Note that the pixel detected in the first defect detection is a pixel in a permanently defective state (permanently defective pixel), and hence is generally subjected to (i) defect correction using spatially neighboring pixels described above. The defect correction method decision unit 1020 decides a defect correction method using the information acquired at the time of imaging. When the number of second defective pixels detected is small, the step of detecting second defective pixels and performing the second defect correction takes much calculation time when displaying a moving image in real time. This may lead to a delay time before display. It is therefore preferable to select (iv) no defect correction described above. If, however, the above image is to be repeatedly seen afterward or used for diagnosis or the like instead of being displayed in real time, any accidental defective pixel may spoil the displayed image or exhibit an abnormal value. In this case, therefore, defect correction is performed by using one of the correction methods (i) to (iii).
(i) Defect correction using spatially neighboring pixels needs to be performed when, for example, still images are captured or the moving image frame rate is low. In this case, since there exists some time interval between adjacent frames, the object or the like may have greatly moved. In such a case, defect correction using adjacent frames results in defect correction using considerably different pixel values. The methods (ii) and (iii) are defect correction methods using temporally neighboring pixels. At the time of imaging at a high moving image frame rate, the pixel values of temporally neighboring pixels sometimes are higher in accuracy than those of spatially neighboring pixels. For example, this is the case when the object hardly moves. In such a case, (ii) defect correction using temporally neighboring pixels is used. At the time of imaging at a high frame rate, settings are often made on the radiographic apparatus side so as to read out pixels upon binning. This is because, it takes much time to read out many pixels, and hence it is difficult to read out an image at a high frame rate. In addition, the larger the image size, the more difficult it is to perform image processing such as preprocessing. Performing pixel binning will increase the distances to spatially neighboring pixels, and hence will increase the necessity to perform defect correction using temporally neighboring pixels. When, for example, a high frame rate is to be set, and this apparatus performs, for example, 2×2 pixel binning or 4×4 pixel binning instead of reading out all the pixels, a pixel size with a pitch of 160 μm is virtually regarded as a pixel size with a pitch of 320 μm or 640 μm. At this time, performing defect correction using spatially neighboring pixels will lead to the necessity to perform defect correction using pixels at distant positions and will reduce the accuracy of defect correction. That is, when imaging is performed at a high frame rate, spatially neighboring pixels are located at more spatially distant positions while temporally neighboring pixels are located temporally closer to each other. Owing to such synergistic effect, the apparatus selects the method of performing defect correction using temporally neighboring pixels.
When this apparatus does not perform the second defect correction, the process advances to step S309 to perform image processing for display. When the apparatus does not perform the second defect correction, there is a demerit that pixels exhibiting abnormal outputs are dispersed and displayed as noise on an image. On the other hand, there is a merit that since the computation processing amount decreases, it is possible to quickly display an image.
If spatial defect correction is selected in step S305, the process advances to step S306. A merit of spatial defect correction as the second defect correction is that even if the user feels a low image quality of an image having undergone the first defect correction using spatial defect correction, using spatially neighboring pixels will help him or her comprehend the contents of the image look degree. In addition, the spatial defect correction method has been repeatedly improved to make images look more naturally. For example, this method can effectively correct defects such as a continuous defect and a line defect.
If temporal defect correction is selected in step S305, the process advances to step S307. Temporal defect correction is defect correction performed based on the pixel values of pixels which are identical to a pixel exhibiting an abnormal output and obtained from temporally adjacent frames. When displaying an image in real time, it is desirable to use pixels identical to those in the immediately preceding frame. When playing back an image repeatedly or performing display processing for diagnosis, it is desirable to perform this temporal defect correction by using adjacent frames at the same proportions.
If defect correction using both temporal defect correction and spatial defect correction is selected in step S305, the process advances to step S308. In step S308, the apparatus executes defect correction by temporal defect correction and spatial defect correction upon weighting. In step S309, the apparatus performs image processing for display. Image processing for display is divided into tone processing, frequency processing, and pixel count processing. Tone processing is processing for adjusting the density of interest of a captured image to match the display tone of a monitor or the like. Frequency processing is frequency enhancement processing for properly expressing the frequency of interest of a captured image. Pixel count processing includes binning processing and cutting processing. In general, since a 1024-pixel image or 2048-pixel image is often displayed on a monitor or the like, the apparatus performs processing for changing the number of pixels to that suitable for display. If it is decided in step S310 that imaging is to be continued (YES in step S310), the process returns to step S310 to repeat the same processing as described above. If it is decided in step S310 that imaging is not continued (NO in step S310), the process advances to step S311 to execute display (output) processing for the image having undergone the image processing executed in step S309. The processing is then terminated.
A statistic distribution obtained when X-ray photons mix with visible light photons and interact with each other will be exemplified with reference to
When the amount of noise in the radiation flat panel detector (FPD) is very small, since the X-ray dose increases as a higher sensitivity is set, the number of pixels recognized in an image upon direct photoelectric conversion of X-rays increases. This is because, if the quantity of X-ray photons directly photoelectrically converted in the radiation flat panel detector (FPD) is small, for example, one or less, a pixel in which photoelectric conversion has accidentally occurred appears as shot-like noise like a pixel whose pixel value has abruptly increased. As the X-ray dose increases, one or more X-ray photons are photoelectrically converted in every pixel. Finally, the distribution approaches a Gaussian distribution. Such X-ray shot noise is the result of visualization of photoelectric conversion when X-rays accidentally strike a pixel which is not a defective pixel by itself but is a normal pixel.
An abnormal pixel correction method will be conceptually described with reference to
Reference numeral 502 denotes an example in which a temporarily defective pixel is generated in an image captured at a high moving image frame rate. The defect correction method decision unit 1020 decides to perform temporal defect correction using the pixel values of identical pixels in adjacent frames. In this case, for example, the defect correction method decision unit 1020 can also decide to perform defect correction using the pixel values of identical pixels in adjacent frames upon increasing the temporal defect correction weight. Reference numeral 503 denotes an example in which a temporarily defective pixel is generated in an image captured at an intermediate/low moving image frame rate. The defect correction method decision unit 1020 corrects a defective pixel by executing a correction method as a combination of a spatial defect correction method and a temporal defect correction method using spatially neighboring pixel values in the same image and pixel values in adjacent frame images. For example, the weighting control unit 1023 sets weights for spatial defect correction and temporal defect correction based on the decision result obtained by the defect correction method decision unit 1020. This apparatus executes a correction method as a combination of a spatial defect correction method and a temporal defect correction method based on the set weights.
This embodiment can provide a radiographic apparatus which can choose between a spatial parameter and a temporal parameter for correcting a temporarily defective pixel. The embodiment can also provide a radiographic apparatus which can change to a suitable correction method for an abnormal pixel which does not always appear, like an X-ray shot noise pixel or an abnormal dot pixel, in accordance with imaging conditions.
This embodiment will exemplify an arrangement for changing the second defect correction method by using an X-ray dose as information acquired at the time of imaging. The influences of X-ray shot noise corresponding to an X-ray dose on image quality will be exemplarily described with reference to
Reference numeral 6c in
An X-ray dose threshold will be described next. Whether one pixel value is visually recognized in random noise depends on whether the value falls within the range of about 1/7 to about 1/10 the X-ray dose. In the case of the penetration dose of an X-ray dose, in which if the pixel value of X-ray shot noise is 100 LSB (Least Significant Bit), the pixel value of random noise is about 15 LSB or less, which is 1/7 that of the X-ray shot noise, a defect correction method decision unit 1020 decides to perform the second defect correction. In the case of a dose equal to or more than the entrance dose, the corresponding pixel is unnoticeable and is not completely a defective pixel. This pixel includes some correct pixel value, to which only a pixel value of as small as about 100 LSB is added. In this case, therefore, the defect correction method decision unit 1020 does not regard the pixel as a defective pixel. That is, the defect correction method decision unit 1020 decides not to perform the second defect correction.
A processing procedure in the radiographic apparatus according to the second embodiment will be described with reference to
In step S702, the apparatus captures an X-ray image. This processing is the same as that in step S301 in
In step S704, the apparatus analyzes the X-ray image captured in step S702 to calculate a penetration X-ray dose. It is possible to calculate this penetration X-ray dose based on each pixel value detected by an X-ray detection unit 1004. The pixel value decreases in a thick region of an object, in the X-ray irradiation direction, through which X-rays are transmitted for a large distance, and increases in a thin region of the object through which X-rays are transmitted for a small distance.
In step S705, the apparatus calculates the statistic amount of X-ray quantum noise with respect to the entrance X-ray dose. Since random noise amounts are obtained in advance as indicated by the ordinate and abscissa denoted by reference numeral 6c, the apparatus executes conversion processing by using them as a conversion table.
In step S706, the apparatus calculates the ratio between the pixel value of X-ray shot noise and the statistic amount of random noise amounts. In general, as denoted by reference numerals 6a and 6b, since the visual recognition limit falls within the range of 1/7 to 1/10 the random noise amount, the apparatus calculates and outputs the ratio of the two values.
In step S707, the defect correction method decision unit 1020 decides, based on the ratio calculated in step S706, whether to execute the second defect correction. When a temporarily defective pixel occurs at neighboring pixel values at which the doses are larger than, for example, 1/7 the random noise amount, there is a possibility that the corresponding pixel cannot be visually recognized. For this reason, the defect correction method decision unit 1020 decides not to perform the second defect correction. In this case, the process advances to step S709. If a temporarily defective pixel occurs at neighboring pixel values at which the doses are smaller than the dose (threshold) at which the ratio of the X-ray dose to the random noise is, for example, 1/7, the defect correction method decision unit 1020 decides to execute the second defect correction.
In step S707, a second defect correction unit 1011 executes the second defect correction. In step S709, the apparatus executes image processing for display, and displays (outputs) the captured X-ray image on a film, monitor, or the like. The processing is then terminated. Note that the numerical values 1/7 and 1/10 described as the thresholds in this embodiment are merely examples indicating visual recognition limits. Obviously, the gist of the present invention is not limited to these examples of numerical values.
According to this embodiment, it is possible to change the second defect correction method by using an X-ray dose as information acquired at the time of imaging.
This embodiment will exemplify an arrangement for controlling the contents of the second defect correction by using body part information input or detected by a radiographic apparatus, which is information acquired at the time of imaging (information acquired at imaging). Reference numeral 7a in
Reference numeral 7b denotes a graph showing the relationship (distribution) between enhancement frequencies and enhancement degrees in a bone region and soft tissue region as body parts. In a diagnosis image, a soft tissue region is often subjected to weak enhancement amount processing with a low enhancement frequency. In contrast, a bone region is often subjected to enhancement processing with a high enhancement degree and a high enhancement frequency. Enhancement parameters for frequency processing for other body parts generally fall between parameters for the above body parts. Checking image processing parameters for frequency enhancement in this manner allows to grasp a specific spatial frequency of interest in accordance with each body part of each captured image. In this embodiment, the defect correction method decision unit 1020 decides, in accordance with whether the spatial frequency of interest is a high spatial frequency or a low spatial frequency, whether to place importance on spatial defect correction or temporal defect correction in the second defect correction method.
The relationship between spatial frequencies and MTFs (Modulation Transfer Functions) will be exemplarily described with reference to
In contrast, when the frequency of interest is a low spatial frequency, the apparatus controls the contents of the second defect correction method so as to decrease the temporal defect correction weight and increase the spatial defect correction weight. Controlling the contents of the second defect correction method in this manner can execute the second defect correction method whose contents are suitable to the characteristics of a designated body part.
Although this embodiment has exemplified the case in which the operator designates a body part on the operation window, the gist of the present invention is not limited to this. Obviously, for example, the present invention can also be applied to a case in which an image is analyzed on software by using a support vector machine to recognize a body part, and the obtained body part is input. In addition, this embodiment allows the present invention to be applied to obtaining a frequency of interest based on a body part. However, the gist of the present invention is not limited to this. Obviously, it is also possible to input a frequency of interest and spatial defect correction and temporal defect correction weights in advance via an operation window or the like.
According to this embodiment, it is possible to control the contents of the second defect correction by using body part information input or detected by a radiographic apparatus, which is information acquired at the time of imaging (information acquired at imaging).
This embodiment will exemplify an arrangement for controlling the contents of the second defect correction by using an imaging frame rate of the information acquired at the time of imaging (information acquired at imaging). The relationship between maximum frame rates and the total numbers of pixels (pixel binning) will be exemplarily described with reference to
The arrangement of a weight calculation unit for the information acquired at the time of imaging (information acquired at imaging) will be described with reference to
According to this embodiment, it is possible to control the contents of the second defect correction by using an imaging frame rate of the information acquired at the time of imaging (information acquired at imaging).
This embodiment will exemplify an arrangement for controlling the contents of the second defect correction by detecting the moving amount of a pixel position in an image, of the information acquired at the time of imaging (information acquired at imaging).
Assume that a temporally abnormal pixel value is generated in a pixel in a region of the object with a large moving amount denoted by reference numeral 13a. In this case, if this apparatus performs defect correction with the average value of identical pixels which are temporally neighboring pixels in adjacent frames ((n−1)th and (n+1)th frames), the output after defect correction of the nth frame becomes a pixel value greatly different from those of spatially neighboring pixels. This result indicates that spatial defect correction cannot be properly performed by using temporally neighboring pixels.
This embodiment therefore controls the defect correction method so as to select the non-execution of temporal defect correction or decrease the corresponding weight when a moving amount is detected in a region spatially surrounding a detected temporarily defective pixel, and an object with a large moving amount like that denoted by reference numeral 13a is detected near the temporarily defective pixel.
A processing procedure in the radiographic apparatus according to the fifth embodiment will be described with reference to
In step S1404, the apparatus evaluates the result of the second defect correction. The evaluation step (S1404) includes steps S1405 and S1406. In step S1405, the apparatus compares the pixel values of neighboring pixels (the values of spatially neighboring pixels) of the pixel in which a pixel value abnormality is detected, and outputs the deviation amount calculation result. In this case, a CPU 1014 functions as the first deviation amount calculation means for calculating the deviation amount of spatial defect correction.
In step S1406, the apparatus compares the pixel values (the values of temporally neighboring pixels) of pixels which are identical to the pixel in which the pixel value abnormality is detected and are obtained from frames temporally located before and after the frame including the pixel in which the abnormality is detected, and outputs the deviation amount calculation result. The CPU 1014 functions as the second deviation amount calculation means for calculating the deviation amount of temporal defect correction.
In step S1407, the apparatus compares the moving amount of the pixel of interest as a correction target with each deviation amount, and decides whether each deviation amount falls within a predetermined error range (error decision). If the deviation amount falls outside the error range, the process returns to step S1402 to execute the same processing as described above. In step S1403, the apparatus resets at least one of the weighting information for spatial defect correction and weighting information for temporal defect correction so as to make the deviation amount fall within the error range. If it is decided by error decision that the deviation amount of spatial defect correction exceeds the error range, weight calculation units 901 to 907 and an addition unit 910, which function as calculation means, reset the weighting information for spatial defect correction. If it is decided by error decision that the deviation amount of temporal defect correction exceeds the error range, the weight calculation units 901 to 907 and the addition unit 910 reset the weighting information for temporal defect correction. A second defect correction unit 1011 then executes the correction method as a combination of spatial defect correction and the temporal defect correction based on the reset weighting information.
If it is decided in step S1407 that the deviation amount falls within the error range, the process advances to step S1408 to execute image processing for display. The processing is terminated.
According to this embodiment, it is possible to control the contents of the second defect correction by detecting the moving amount of a pixel position in an image of the information acquired at the time of imaging (information acquired at imaging).
The arrangement of a radiographic apparatus according to the sixth embodiment will be described with reference to
A defective pixel position detection unit 1608 stores, in a defective pixel position storage unit 1609, the position information of the permanently defective pixel detected by an X-ray detection unit 1004, together with a defective pixel extraction mode. A spatial defect correction unit 1021 corrects a defective pixel in each image stored in a memory 1015 by using the pixel values of spatially neighboring pixels, and stores each defect position in a storage unit 1012.
When the user inputs an imaging instruction via an operation panel 1016, the contents of the imaging instruction are stored in the storage unit 1012 and displayed on the operation panel 1016. When the imaging instruction is issued, a specific body part is selected by a body part selection unit 1025 via the operation panel 1016.
An imaging information acquisition unit 1024 stores body part information 1628 selected by the body part selection unit 1025. The imaging information acquisition unit 1024 stores image processing information 1632 such as enhancement frequencies and enhancement degrees in spatial frequency processing which are adjusted for each body part in accordance with the body part information selected by the body part selection unit 1025.
The preprocessed X-ray image data is transferred as original image data to the main memory 1015 via a CPU bus 1026 under the control of a CPU 1014. The spatial defect correction unit 1021 performs defect correction by using spatially neighboring pixels and the defective pixel position map stored in the defective pixel position storage unit 1609 at the time of shipment. The obtained image data is transferred to the main memory 1015 via the CPU bus 1026 under the control of the CPU 1014. The main memory 1015 stores a program for causing a computer to execute a control method for the radiographic apparatus.
The apparatus then extracts a defect from each obtained image data by using a defective pixel position detection unit 1608. The defective pixel position storage unit 1609 stores the obtained defective pixel position together with the defective pixel extraction mode. The defective pixel position detection unit 1608 extracts a temporarily defective pixel for each image such as an X-ray shot noise pixel generated by interaction between X-ray photons or an abnormal dot pixel generated when, for example, noise accidentally mixes in the semiconductor X-ray detector.
The spatial defect correction unit 1021 and a temporal defect correction unit 1022 perform defect correction for the detected defective pixel in accordance with weighting controlled by a weighting control unit 1023 for spatial/temporal defect correction.
The weighting control unit 1023 sets weighting information based on any one of the information in the defective pixel position storage unit 1609, the information in the imaging information acquisition unit 1024, the information from a weighting input unit 1611, and a weighting table 1610. The weighting control unit 1023 can control settings so as to change each of the set values of weighting information for spatial defective pixel correction and weighting information for temporarily defective pixel correction based on, for example, the information acquired at the time of imaging the object.
The defective pixel position storage unit 1609 stores, for example, for each pixel, a defective pixel extraction mode indicating the mode of extracting a permanently defective pixel or the mode of extracting temporarily defective pixel which appears temporarily or in accordance with a dose. The imaging information acquisition unit 1024 stores X-ray dose information 1627 obtained from the pixel value detected by the X-ray detection unit 1004, the body part information 1628, pixel binning amount information 1629, image acquisition frame rate information 1630, object moving amount information 1631, and the like. The weighting control unit 1023 performs control to decide by which weight spatially/temporarily defective pixel correction is performed by using the defective pixel extraction mode stored in the imaging information acquisition unit 1024 and the defective pixel position storage unit 1609. The X-ray image data having undergone defective pixel correction processing is transferred as original image data to the main memory 1015 and an image processing unit 1013 via the CPU bus 1026 under the control of the CPU 1014. The image processing unit 1013 performs noise reduction processing, frequency processing, and tone processing, and outputs the resultant X-ray image data to an image display unit 1017.
A processing procedure in the radiographic apparatus according to this embodiment will be described with reference to
In step S1702, the apparatus performs defective pixel correction (first defect correction) dependent on spatial positions. The defective pixel position storage unit 1609 stores, at the time of shipment, permanently defective pixel positions existing in the radiographic apparatus together with the defective pixel extraction mode. The apparatus performs defective pixel correction dependent on spatial positions by using a defective pixel position map indicating permanently defective pixel positions.
In step S1705, the apparatus calculates weights for temporal defect correction and spatial defect correction. The pixel detected by the first defect detection is a permanently defective pixel, and hence the temporal defect correction weight is set to 0 to perform defect correction using only spatially neighboring pixels. The apparatus also determines a defect correction method by using the information acquired at imaging. When the number of second defective pixels is very small, the step of detecting second defective pixels and performing the second defect correction takes much calculation time when displaying a moving image in real time. This may lead to a delay time before display. At this time, it is desirable to set both the temporal defect correction weight and the spatial defect correction weight to 0 so as not to perform defect correction.
If, however, a given image is to be repeatedly seen afterward or used for diagnosis or the like instead of being displayed in real time, any accidental defective pixel may spoil the displayed image or an analysis function for indicating tones can indicate an abnormal value. For this reason, the apparatus performs defective pixel correction by controlling temporal defect correction/spatial defect correction weights. It is when, for example, still image capturing is performed or the moving image frame rate is low that it is proper to perform defect correction upon increasing the weight for defect correction using spatially neighboring pixels. At this time, since there exists some time interval between adjacent frames, the object or the like may have greatly moved. In such a case, defect correction using adjacent frames results in defect correction using considerably different pixel values.
The following is a case in which it is proper to perform defect correction upon increasing the weight for defect correction using temporally neighboring pixels. At the time of imaging at a high frame rate, the pixel values of temporally neighboring pixels are sometimes higher in accuracy than those of spatially neighboring pixels. For example, this is the case when the object hardly moves. In such a case, the weight for defect correction using temporally neighboring pixels is increased. In addition, at the time of imaging at a high frame rate, settings are often made on the radiographic apparatus side so as to read out pixels upon binning. This is because, it takes much time to read out many pixels, and hence it is difficult to read out an image at a high frame rate. This is also because that image processing such as preprocessing becomes more difficult as the image size increases. Performing pixel binning will increase the distances to spatially neighboring pixels, and hence will further increase the necessity to perform defect correction using temporally neighboring pixels. When, for example, a high frame rate is to be set, and this apparatus performs, for example, 2×2 pixel binning or 4×4 pixel binning instead of reading out all the pixels, a pixel size with a pitch of 160 μm is virtually regarded as a pixel size with a pitch of 320 μm or 640 μm. At this time, performing defect correction using spatially neighboring pixels will lead to the necessity to perform defect correction using pixels at distant positions and will reduce the accuracy of defect correction. That is, when imaging is performed at a high frame rate, spatially neighboring pixels are located at more spatially distant positions while temporally neighboring pixels are located temporally closer to each other. Owing to such synergistic effect, the apparatus performs defect correction upon increasing the weight for defect correction using temporally neighboring pixels.
In step S1706, the apparatus performs spatial/temporal defect correction by using the weighting settings calculated and controlled in the previous step. In a broad sense, when either of the weights is set to 0, the apparatus performs only spatial defect correction or temporal defect correction. A merit of defect correction upon increasing the weight for spatial defect correction is that even if the user feels a low image quality of an image having undergone the defect correction, using spatially neighboring pixels will help him or her comprehend the contents of the image to some degree because he/she is used to the previous spatial defect correction. In addition, the spatial defect correction method has been repeatedly improved to make images look more natural. For example, since some contrivance is made to correct a continuous defect and a line defect, the maturity of a defect correction algorithm is the highest merit.
This embodiment can provide a radiographic apparatus which can choose between spatial parameter correction and temporal parameter correction for a temporarily defective pixel. The embodiment can also provide a radiographic apparatus which can change to a suitable correction method for an abnormal pixel which does not always appear, like an X-ray shot noise pixel or an abnormal dot pixel, in accordance with imaging conditions.
This embodiment will exemplify an arrangement for controlling spatial/temporal defect correction weighting by using an X-ray dose as information acquired at the time of imaging. A processing procedure in the radiographic apparatus according to the embodiment will be described with reference to
In step S1807, the apparatus controls spatial/temporal defect correction weighting based on the ratio obtained in step S706. If a temporarily defective pixel is generated at neighboring pixel values at which the ratio obtained in step S706 is higher than that of the X-ray dose which is, fore example, 1/7, since there is a possibility that the pixel will not be seen, both the spatial defect correction weight and the temporal defect correction weight are set to 0. That is, the apparatus performs control not to perform defect correction. If, for example, a temporarily defective pixel is generated at neighboring pixel values at which the ratio is lower than that of the dose which is, for example, 1/7, the apparatus controls spatial/temporal defect correction weighting so as to increase the temporal defect correction weight.
In step S1808, the apparatus performs defect correction using spatial/temporally neighboring pixels in accordance with the weights obtained in the previous step.
According to this embodiment, it is possible to control spatial/temporal defect correction weighting by using an X-ray dose as information acquired at the time of imaging.
Aspects of the present invention can also be realized by a computer of a system or apparatus (or devices such as a CPU or MPU) that reads out and executes a program recorded on a memory device to perform the functions of the above-described embodiment(s), and by a method, the steps of which are performed by a computer of a system or apparatus by, for example, reading out and executing a program recorded on a memory device to perform the functions of the above-described embodiment(s). For this purpose, the program is provided to the computer for example via a network or from a recording medium of various types serving as the memory device (for example, computer-readable medium).
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2009-115918, filed May 12, 2009, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-115918 | May 2009 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2010/056893 | 4/13/2010 | WO | 00 | 9/30/2011 |
