Classifications

• • G—PHYSICS
  • G06—COMPUTING OR CALCULATING; COUNTING
  • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
  • G06T5/00—Image enhancement or restoration
  • G06T5/50—Image enhancement or restoration using two or more images, e.g. averaging or subtraction

Definitions

• the present invention relates to an X-ray image diagnostic apparatus that detects an X-ray transmitted through a subject with a flat panel detector and obtains an X-ray image of a diagnostic portion of the subject, and in particular, removes an afterimage of the flat panel detector.
• the present invention relates to an X-ray diagnostic imaging apparatus capable of obtaining an image without motion artifacts.
• an X-ray diagnostic imaging apparatus irradiates a subject with X-rays, and detects X-rays transmitted through a diagnostic site of the subject using a flat detector (reference: Paul R. Granfors; Performance Characteristics of an Amorphous Silicon Flat panel X-ray Imaging Detector. Proc. SPIE Medical Imaging, Feb. 1999. pp. 480-488 ”) and receive the X-ray image output from this X-ray receiving system to CRT (cathode- ray tube) It is configured to display on a monitor or the like.
• Flat detectors used in X-ray diagnostic imaging systems consist of a scintillator that converts X-rays that have passed through the subject into light, and a photodiode that converts the light output from this scintillator into electric charges (for example, amorphous silicon An X-ray image is obtained by reading out the charge of the photodiode via a switching element (eg, TFT (Thin Film Transistor)).
• TFT Thin Film Transistor
• Fig. 5 shows an example of how the unread charge in the photodiode, that is, the afterimage, decreases with time (for details, see RL Weisfield; High Performance Amorphous Silicon Image Sensor for X-ray Diagnostics). Medical Imaging Applications. Proc. SPIE Medical Imaging, Feb. 1999. pp. 307-317. As is evident from Fig.
• the charge remaining after reading hardly changes during a short time of 1 second or less, in which images of X-ray fluoroscopy and X-ray imaging are captured one after another, and affects the next image in the form of 'afterimage of the previous image'. This causes motion artifacts in the image, which hinders diagnosis.
• the charge remaining after reading in the photodiode of the flat panel detector is stored in the image storage unit. Without this, reading (hereinafter referred to as blank reading) is performed.
• Fig. 6 is a diagram for explaining the example, and Fig. 6 (a) shows an example (X-ray image) of the distribution of charges accumulated in the photodiode of the flat panel detector that received the X-ray image It is.
• Fig. 6 (a) shows an example (X-ray image) of the distribution of charges accumulated in the photodiode of the flat panel detector that received the X-ray image It is.
• Fig. 6 (b) shows the distribution of charges accumulated in the photodiode of the flat panel detector after one blank reading of the X-ray image of Fig. 6 (a).
• the present invention has been made in view of the above circumstances, and an object of the present invention is to reduce the time required for blank reading by skipping only pixels having many afterimages of a previous image, and to generate the image by the afterimage.
• An object of the present invention is to provide an X-ray diagnostic imaging apparatus capable of removing a motion artifact and obtaining a high-quality image. Disclosure of the invention
• the X-ray diagnostic imaging apparatus of the present invention provides: An X-ray source, a flat X-ray detector which is arranged opposite to the X-ray source, receives transmitted X-rays of the subject, and outputs X-ray image data, and stores the output X-ray image as image data Image display means for displaying the stored image data as an image, operating means for outputting an image read start signal, and receiving the output read start signal and receiving X-rays from the planar X-ray detector.
• An X-ray diagnostic imaging apparatus comprising: readout control means for controlling readout of image data; wherein the operating means detects the X-ray image data obtained in a time phase immediately before a predetermined time phase by the plane X-ray detection. Means for determining the readout range based on the distribution of readout data after reading out from the detector to the image storage means, and the readout control means controls the plane X-ray detector based on the determined readout range. Read unread data It is provided with means for controlling the delivery.
• a console for outputting an image reading start signal; a flat panel detector for receiving X-rays transmitted through the subject and outputting an X-ray image; and an X-ray image output from the flat panel detector as image data.
• Image display means for storing image data stored in the image storage means as an X-ray image; receiving an image reading start signal from the console to receive X-rays from the flat panel detector;
• An X-ray diagnostic imaging apparatus comprising: a readout control unit that performs control for reading out image data.
• image data of an X-ray image output from the plane detector is stored, and the plane detector Before outputting the image data of the predetermined position, the specific pixel of the flat panel detector is read in an empty manner, and the pre-image storage means for overwriting and storing the empty-read image data, and the image data stored in the preceding image storage means are overwritten.
• a readout address determining unit that extracts a specific pixel from the data, calculates an address corresponding to the position of the specific pixel, and outputs the address to the readout control unit, wherein the specific pixel is based on a luminance value of image data.
• the read-out control means performs control for performing blank reading of only the specific pixels of the flat panel detector in accordance with the address of the specific pixels input from the read-out address determination means.
• the previous image storage unit and the read address determination unit are added to the conventional X-ray image diagnostic apparatus, so that the previous image storage unit can perform blank reading based on the brightness value of the image data. Because it is possible to extract specific pixels to be read and to overwrite with image data that has been blank-read from specific pixels, It is possible to grasp the unread state of the electric charge at each pixel in the detector, and further, it is possible to determine the address of the specific pixel to be read by the read address determination means. However, it is possible to execute the blank reading of only a specific pixel of the flat panel detector. As a result, blank reading is limited to only specific pixels, and blank reading time is reduced.
• the specific pixel in the previous image storage unit is a pixel having a luminance value equal to or more than a specific value (hereinafter, referred to as a threshold).
• a specific value hereinafter, referred to as a threshold.
• the X-ray image diagnostic apparatus of the present invention extraction of a specific pixel in the previous image storage means and blank reading of a specific pixel in the flat panel detector are performed a plurality of times. In this configuration, if only one blank reading is performed and the remaining charge remaining in the flat detector is not sufficiently removed, the specific pixel to be blank-read by the flat detector is extracted and blank reading is performed twice or more. As a result, the flat-panel detector can sufficiently and efficiently remove the unread charges. '
• the threshold used as a reference for extracting the second and subsequent specific pixels for the second and subsequent blank readings from the image data of the previous image storage unit is determined based on the previous threshold.
• the threshold of the extraction reference for the specific pixel of the blank reading can be determined in association with the previous threshold, so that the threshold is easily determined, for example, by keeping the ratio of the two constant.
• the threshold value is determined in association with the luminance value of the pixel of the flat panel detector, the state of the charge left unread on the flat panel detector can be easily grasped, and the charge left unread on the flat panel detector can be reliably determined. Can be reduced.
• the specific pixels of the second and subsequent blank readings from the image data of the previous image storage unit are determined from the number of pixels in one frame to the pixels of the specific pixels of the first blank reading.
• the number shall be deducted.
• two blank readings can be performed during the reading time of one frame of image data. For example, in the first blank reading, a pixel having a luminance value greater than or equal to the threshold value is read out, and the second blank reading is performed. By reading out the image data in the order of the luminance value in the reading, the blank reading can be performed efficiently.
• FIG. 1 is a block diagram showing the configuration of an embodiment of an X-ray image diagnostic apparatus according to the present invention.
• FIG. 2 shows a read address determining means 17 which selects a threshold value from image data stored in a previous image storing means 16.
• FIG. 3 is a flowchart for explaining a flow of a process of searching for a pixel having the above-described luminance value as a specific pixel to be blank-read, and FIG. 3 shows a threshold for blank-reading and image data stored in the previous image storage unit 16.
• FIG. 4 is a flow chart for explaining a flow of a process for searching for an address of a specific pixel for performing a second blank reading in the read address determining means 17, and FIG. FIG.
• FIG. 6 is a diagram showing an example of how the afterimage of the detector decreases with time
• FIG. 6 is a diagram showing an example of a change of the afterimage of the flat panel detector before and after the idle reading.
• FIG. 1 is a block diagram showing the configuration of an embodiment of the X-ray image diagnostic apparatus of the present invention.
• the X-ray image diagnostic apparatus of the present embodiment includes a plane detector (two-dimensional detector) 11 that receives transmitted X-rays transmitted through a subject (not shown) and outputs an X-ray image.
• Image storage means 12 for storing the X-ray image output from the plane detector 11 as image data, and display for displaying the image data stored in the image storage means 12 on a monitor or the like as an X-ray image Means 13, an operator 14 for sending a signal for the operator to start reading an image from the flat panel detector 11 to the read controller 15, and an image read start signal from the operator 14
• Readout control means 15 for controlling readout of image data of the plane detector 11, and after image data output from the plane detector 11 is stored in the image storage means 12 by a control signal from the readout control means 15.
• the stored image data is stored, and the image data of only the specific pixels that have been read in blank are placed on the stored image data.
• the characteristic part in the present invention relates to the method of reading the image data of the plane detector 11 without reading.
• the elements related to the reading of the image data of the plane detector 11 are the following.
• the plane detector 11 is composed of a plate-shaped scintillator and a photodiode array as described in the section of the prior art, and the charge of the photodiode is read out via a switching element.
• the plane detector 11 charges corresponding to the X-ray dose distribution of the X-ray image are accumulated in each element of the photodiode array of the plane detector 11. Therefore, each element of the photodiode array corresponds to each pixel of the X-ray image, and the charge stored in each element of the photodiode array corresponds to image data (pixel value).
• the readout control means 15 receives the image readout start signal from the console 14 and performs the first readout control of the image data of the flat panel detector 11.
• the readout first image data is stored in the image storage means 12. Is output to the previous image storage means 16.
• the image data output to the image storage unit 12 is stored there, displayed on the display unit 13, and used for medical diagnosis.
• the first image data output to the previous image storage means 16 is stored there and used for extracting a specific pixel.
• the readout control unit 16 further performs the second readout of image data, that is, a blank readout, for only the specific pixel of the flat panel detector 11 based on the address information of the specific pixel determined by the readout address determination unit 17. Is output to the previous image storage means 16. At this time, the second image data is output to the image storage unit 12. Absent.
• the previous image storage means 16 stores the second image data over the first image data for the specific pixel.
• the previous image storage means 16 is used for extracting specific pixels to be subjected to blank reading after storing the first image data under the control of the read control means 15. After the specific pixel is extracted, the previous image storage means 16 stores the second image data for the specific pixel. Each time of the image data stored in the previous image storage means 16 is used for the extraction of the specific pixel in the next time.
• the read address determining means 17 extracts a specific pixel based on the image data stored in the previous image storage means 16, determines the read address of the extracted specific pixel, and outputs the read address to the read control means 15. is there.
• the extraction of the specific pixel is usually performed based on image data corresponding to the electric charge accumulated in the photodiode of the plane inspection device 11, that is, a luminance value. Since the afterimage increases as the luminance value increases, a predetermined luminance value is set as a luminance threshold (hereinafter, referred to as a threshold), and a pixel having a luminance value larger than the threshold is extracted as a specific pixel.
• a threshold luminance threshold
• the threshold may be set directly at the console 14 as shown by the solid line in FIG. 1 or by separately providing a threshold setting means 18 as shown by the broken line in FIG. May be set.
• the threshold value can be set by giving the threshold value setting means 18 a threshold table and selecting a threshold value from the table, or by giving the threshold value setting means 18 a formula and selecting a variable.
• the function of setting the threshold value may be provided to the read address determining means 17 for extracting a specific pixel using the threshold value.
• the extraction of a specific pixel may be performed once or sometimes more than once.
• the threshold value is usually set with a luminance value.
• the threshold value is not necessarily set only with the luminance value, but may be set with other items, such as the number of pixels.
• setting a high luminance value reduces the readout time because the number of specific pixels decreases, but increases afterimages and increases the number of empty readings, resulting in low luminance.
• Setting by value increases the number of specific pixels and The reading time becomes longer and the efficiency of blank reading becomes worse. Therefore, how to set the threshold is important.
• a value obtained by multiplying the highest luminance value of the previous image data by a certain ratio is set as the threshold value.
• a fluoroscopy mode and an imaging mode as imaging modes of an X-ray image.
• the fluoroscopy mode the subject is imaged with a small amount of X-ray to determine the imaging position of the subject, and the X-ray images are continuously read from the flat panel detector 11 and displayed on the display means 13 such as a monitor as a moving image.
• the imaging mode at the imaging position of the subject determined in the fluoroscopic mode, a clear image with a small noise component is captured with a relatively large amount of X-ray, and the X-ray image is obtained from the plane detector 11. read out.
• the above-mentioned perspective mode for example, 30 X-ray images per second are read out from the flat panel detector 11 and displayed on the display means 13.
• the operator After irradiating the subject with the X-rays, the operator inputs a signal to start reading out the X-ray image from the console 14 to the readout control means 15 to detect the plane receiving the X-rays transmitted through the subject.
• An X-ray image is output from the device 11 and stored in the image storage means 12.
• the mode is shifted from the photographing mode to the fluoroscopic mode.
• the imaging mode after the image data of the X-ray image output from the plane detector 11 is stored in the image storage means 12, the same image data is also stored in the previous image storage means 16.
• the luminance value of the image data (image data of the X-ray image in the imaging mode) stored in the previous image storage means 16 increases, the X displayed on the display means 13 when the mode shifts to the fluoroscopy mode.
• the afterimage appearing in the line image becomes large.
• the read address determining means 17 searches the image data stored in the previous image storing means 16 for pixels having a brightness value equal to or higher than the brightness threshold value, and assigns an address as a specific pixel to which these pixels are to be blank-read. The address is determined, and the determined address is sent to the read control means 15.
• the threshold value is determined in advance by the operator (or the threshold setting means 18) in consideration of the afterimage characteristics in FIG. 5 or the time required for switching from the imaging mode to the fluoroscopic mode, and the operation console 14 (or It is sent from the threshold setting means 18) to the read address determination means 17.
• the read-out control means 15 reads out (empty-reads) the image data from the flat panel detector 11 based on the address of the specific pixel to be read-out-free sent from the read-out address determination means 17 and precedes the read-out image data. It is overwritten and stored in the image storage means 16.
• the above idle reading process is repeated until a signal for starting the reading of the X-ray image in the fluoroscopic mode is input from the console 14.
• FIG. 2 illustrates a flow of a process in which the read address determining means 17 searches for a pixel having a luminance value equal to or larger than a threshold value from the image data stored in the previous image storage means 16 as a specific pixel to be read as a blank. It is a flowchart for the.
• the image data stored in the previous image storage means 16 is read out one pixel at a time to the judgment block 21 of the read address determination means 17.
• the read image data of the pixel is compared with a predetermined threshold value. If the image data of the pixel read from the previous image storage unit 16 is larger than the threshold value, the address of this pixel is determined by the processing block 22 as the address of the specific pixel to perform the blank reading, and is sent to the read control unit 15.
• the read address determining means 17 repeats the above-described processing by the number of pixels of the image data stored in the previous image storing means 16. Next, an example of a method of determining a threshold value for the second blank reading will be described.
• the threshold T1 at the time of the second blank reading is set by the console 13 or the threshold setting means 18 as a new threshold based on the threshold used at the first blank reading, and sent to the read address determining means 17. If the threshold value for the first blank reading is T and the ratio of the unread charge after reading the charge to the accumulated charge in the photodiode of the flat panel detector 11 is / 0 , a new blank reading is set for the second time. In this case, the threshold T1 is expressed by the following equation.
• T 1 T X (W / 100)... (1)
• FIG. 3 is a schematic diagram for explaining the relationship between the threshold value at the time of blank reading and the image data stored in the previous image storage unit 16.
• FIG. 3A shows the luminance distribution of an arbitrary line of the image data before blank reading stored in the previous image storage means 16.
• the address of a specific pixel corresponding to a luminance area ⁇ (areas S2 and S4) that is equal to or greater than a predetermined threshold T is determined by the readout address determination means 17, and each specific pixel is determined according to the address.
• the idle reading is performed by the read control means 15.
• FIG. 3B shows the luminance distribution of an arbitrary line of the image data stored in the previous image storage means 16 after the blank reading. Since the specific pixels for which the blank reading has been performed are overwritten and stored in the previous image storing means 16, the image data after the blank reading stored in the previous image storing means 16 is as shown in FIG. 3 (b).
• the image data for the specific pixels in the blank-read areas S2 and S4 has a brightness value distribution of W ° / 0 of the initial brightness value, and the brightness data for the pixels in the blank areas S1, S3, and S5 that are not blank-read.
• the image data has a luminance distribution with the initial luminance value (below the threshold T).
• the address of the specific pixel corresponding to ⁇ ⁇ is determined, and the second blank reading is performed by the read control unit 15 according to the address.
• the first blank reading and the second blank reading are to be completed within the same time as one image is read from the flat panel detector 11. From this fact, for example, the total number of image data read out from the plane detector 11, that is, the number of pixels of one image is set to N, and the image data overwritten and stored in the previous image storage means 16 in the first blank reading.
• the number is nl
• the number n2 of image data to be subjected to the second blank reading is
• n 2 N- n l... (2)
• the threshold value T1 for the second blank reading is the brightness value of the ⁇ 2th pixel when the pixels of the image data stored in the previous image storage unit 16 are arranged in descending order of the brightness value at the end of the first blank reading. Become. Therefore, the threshold value T1 is not automatically determined as in Expression (1), and must be searched from the image data stored in the previous image storage means 16.
• FIG. 4 is a flowchart for explaining the flow of the process in which the read address determining means 17 searches for the address of a specific pixel to be subjected to the second blank read.
• the previous image storage means 16 stores image data obtained by overwriting and storing the blank reading image data after the first blank reading.
• the maximum luminance value Tmax is detected from the image data of the previous image storage means 16.
• the judgment block 42 the image data read from the previous image storage means 16 is compared with the maximum luminance value Tmax, and if they are the same value, this image data is sent to the next judgment block 43. . If the image data read from the previous image storage means 16 is different from the maximum luminance value Tmax, the value of the maximum luminance value Tmax is changed in the processing block 44.
• the decision block 43 determines whether or not the transmitted image data is included in the number n2 of image data to be subjected to the second blank reading, and determines whether or not the transmitted image data is included in the number n2 of the number of stroke data to be subjected to the blank reading.
• the image data is Is determined as the address of a specific pixel to be read as an empty read, and sent to the read control unit 15.
• the processing for finding the address of the specific pixel to be blank-read by the processing block 46 is terminated. The above processing is repeated in processing block 47 until the number of blank-read pixels reaches n2.
• the blank reading is performed only for the time to read one image of the flat panel detector 11 . If the time is known in advance, conditions such as repeating the blank reading a certain number of times or setting all image data stored in the previous image storage means 16 to a desired value Tmax or less are set. Then, the above processing may be repeated.
• the desired value Tmax is a value determined as a luminance value at which the afterimage does not affect the next image.
• the present invention relates to the case where two or more X-ray images are transferred from the fluoroscopic mode to the imaging mode or in the imaging mode. It goes without saying that the present invention can be applied to the time until the image data of the next image at the time of reading is read or between the fluoroscopic modes.
• the image storage means and the previous image storage means are described as being provided as separate storage means. However, a part of the image storage means is used as the previous image storage means. Needless to say, this may be done.
• an X-ray image diagnostic apparatus capable of shortening the time required for blank reading. Can be provided.

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