JP4786306B2 - Method for creating correction data in X-ray sensitivity correction and X-ray CT apparatus - Google Patents

Description

  The present invention relates to a technique for creating correction data used for correcting the sensitivity of exposed X-rays.

  The X-ray CT apparatus is an apparatus that exposes X-rays, detects X-rays transmitted through the subject, and reconstructs an image in the subject from the detected X-rays. An image in the subject is created by faithfully converting the intensity of the X-rays transmitted through the subject into an electrical signal and processing the electrical signal by a back projection processing method.

  The conversion of the X-ray intensity into an electric signal is performed by an X-ray detector and a data acquisition unit. In the X-ray detector, X-ray detection elements each composed of a scintillator and a photoelectric conversion element are arranged in the slice direction and the channel direction. The X-ray detector captures and emits X-rays, captures the emitted light, and converts it into an electrical signal. The data collection unit includes a data collection element, a gain circuit, and an A / D converter. The data collection unit collects weak electrical signals for each channel, and amplifies and performs A / D conversion for each channel.

  The detection sensitivity of X-rays is determined by the characteristics of conversion of X-rays into light, photoelectric conversion characteristics, and amplification accuracy by detecting X-rays through an X-ray detector and a data acquisition unit. The conversion characteristics of X-rays into light, photoelectric conversion characteristics, and amplification accuracy drift for each channel depending on the atmosphere such as temperature and changes with time. Therefore, the detected X-ray is subjected to correction that excludes the influence of changes in sensitivity characteristics (see, for example, Patent Document 1).

  Correction of X-ray sensitivity is performed using correction data. However, since the change in sensitivity characteristics depends on the atmosphere such as temperature and changes over time, correction data is periodically created along with the change in sensitivity characteristics. . In principle, the correction data is obtained by photographing a phantom that is uniformly uniform with water, resin, or the like. However, due to the complexity of setting, etc., the phantom was photographed at the reference time to obtain correction data, and after a certain period of time, the data obtained by photographing the phantom at the reference time with data using air was corrected. Yes.

  Specifically, at the reference time point, that is, the time-change starting point, the phantom is photographed under various photographing conditions, the ring artifact removal process is performed, and the correction data Hs is obtained, and the photographing using the air is performed under various photographing conditions. To obtain the air projection data As. Further, at the time of correction, that is, after a change with time, imaging using air is performed again under various imaging conditions, and air projection data An is acquired.

  Then, new correction data Hn at the time of correction, that is, projection data obtained when the phantom is shot under various shooting conditions at the time of correction is calculated by a calculation formula represented by correction data Hn = Hs × (An / As). The change rate of the sensitivity characteristic from the reference time to the correction time is obtained from the air projection data As at the reference time and the air projection data An at the correction time, and this change rate is reflected in the correction data Hs at the reference time. Thus, the correction data Hn at the time of correction is acquired.

  For shooting using a phantom, each shooting area (FOV) included in the shooting conditions must be replaced with a phantom having the same size as the shooting area. In this correction data creation method, air is used. There is an advantage that data can be collected all at once regardless of the shooting area, phantom replacement time is saved, and collection time is shortened.

JP-A-9-24043

  However, the imaging conditions include a tube voltage (kV), a combination of slice thickness (mm) and the number of columns, an imaging area, a gain, an imaging mode, and the like. The shooting area has a head, a torso, etc., and is set according to the subject. A plurality of gains such as 1 ×, 3 ×, 5 ×, 10 ×, and 20 × are prepared. It should be noted that the gain and the shooting area have a one-to-one correspondence or one-to-N correspondence, and if the shooting area changes, the gain also changes accordingly.

  Then, in photographing using the phantom at the reference time point, it must be performed in accordance with a combination of all parameters included in the photographing conditions, four kinds of tube voltages, 25 kinds of combinations of slice thickness and number of columns, and photographing areas. If there are five types, a total of 500 shots must be taken. In shooting using air at the reference time point, the shooting area is constant, but the amplification accuracy drifts due to an atmosphere such as temperature or a change over time, and thus a total of 500 shootings must be performed. Similarly, even when shooting using air at the time of correction, if a common gain is not used between different shooting areas, similarly, a total of 500 shootings must be performed.

  Therefore, this correction data creation method can save the phantom replacement time, but in order to create correction data at the time of correction, if the common gain is not used between different shooting areas, the number of shooting is not reduced. In other words, it is necessary to perform air shooting 500 times at the reference time and further air shooting 500 times at the correction time.

  The present invention solves the above-described problem, and in the creation of correction data used for correcting the sensitivity of X-rays, correction data is created by reducing the number of times of imaging performed for creating correction data. The purpose is to further reduce the collection time of data collection.

According to the first aspect of the present invention, sensitivity correction is performed on X-ray data acquired by a detector that detects X-rays and a data acquisition unit that collects detected X-ray data and amplifies the data with a predetermined gain. A correction data creation method for obtaining phantom data amplified at various gains with a predetermined time as a reference time, creating correction data at the reference time based on the phantom data, and starting from the reference time After a predetermined time has elapsed, new correction data at the correction time is created, and at the correction time, the air amplified by the reference gain resulting from the change in sensitivity characteristics over time from the reference time to the correction time is created. a change in the data, causes reflected in phantom data amplified reference point in the various gains, the output of the air data amplified by the standards gain, in various gain At the output ratio of the output width is air data, the changes due to aging of the sensitivity characteristic, by reflecting the phantom data amplified reference point in the various gains, to create the new correction data It is characterized by this.

According to a second aspect of the present invention, sensitivity correction is performed on X-ray data acquired by a detector that detects X-rays and a data acquisition unit that collects detected X-ray data and amplifies the data with a predetermined gain. Correction data creation method for obtaining phantom data amplified at various gains with a predetermined time as a reference time, creating correction data at the reference time based on the phantom data, and generating a predetermined data from the reference time After the time has elapsed, new correction data at the correction time is created, and at the correction time, the air data at the reference time amplified by the reference gain is added to the air data at the reference time. calculating an output of, by reflecting the respective output ratio of the output of the air data amplified by the various gains, the reference air data amplified by the various gain at the reference point , The air data correction when it is amplified by the reference gain, and the output of the air data amplified by the reference gain in the modified time, by reflecting the respective output ratio of the output of the air data amplified by the various gains, Calculates corrected air data amplified at various gains at the time of correction, acquires sensitivity change rates for the various gains from the reference air data and the corrected air data, and phantom data at the reference time amplified by the various gains to, to reflect the rate of change in sensitivity of the various gains, creating the new correction data for various gain based on the reflected result, characterized by.

According to a third aspect of the present invention, sensitivity correction is performed on X-ray data acquired by a detector that detects X-rays and a data acquisition unit that collects detected X-ray data and amplifies the data with a predetermined gain. Correction data creation method for obtaining phantom data amplified at various gains with a predetermined time as a reference time, creating correction data at the reference time based on the phantom data, and generating a predetermined data from the reference time as a correction time point after a time lapse, to create the new correction data at the modified time, the Fixed point, the new correction data for the various gains (Gx) various photographing conditions can take under (Cy) next It creates based on the calculation result of a type | formula, It is characterized by the above-mentioned. (Formula) Ws (Gx, Cy) × {An (Gs, Cy) / As (Gs, Cy)} × {An (Gx, Cs) / An (Gs, Cs)} / {As (Gx, Cs) / As (Gs, Cs)} Ws (Gx, Cy): Phantom data acquired under various imaging conditions (Cy) that can be taken under various gains (Gx) at the reference time point As (Gs, Cy): At the reference time point Air data acquired under various imaging conditions (Cy) that can be taken under the reference gain (Gs) As (Gx, Cs): acquired under reference imaging conditions (Cs) that can be taken under various gains (Gx) at the reference time point Air data As (Gs, Cs): Air data An (Gs, Cy) acquired at reference photographing conditions (Cs) that can be taken under the reference gain (Gs) at the reference time point: Reference gain ( Gs) under Air data An (Gx, Cs) acquired under various photographing conditions (Cy) that can be taken: Air data An (Gs, Cs) obtained under reference photographing conditions (Cs) that can be taken under various gains (Gx) at the time of correction Cs): air data acquired under reference photographing conditions (Cs) that can be taken under the reference gain (Gs) at the time of correction

According to a fourth aspect of the present invention, there is provided an X-ray source that emits X-rays, a detector that detects X-rays transmitted through the subject, and data collection that collects and amplifies the detected X-ray data. A pre-processing unit that corrects the sensitivity of the collected X-ray data based on the correction data, and an image reconstruction unit that reconstructs an image in the subject based on the X-ray data. The processing unit creates correction data at the reference time based on the phantom data amplified with various gains acquired with the predetermined time as the reference time, and uses the correction time as a correction time after the predetermined time has elapsed. create a new correction data at the time, the Fixed time, due to aging of the sensitivity characteristics from a reference time point to modify the time, the change of the amplified air data were in reference gain, amplified by the various gain The reference point Together reflect the Tom data, and output of the air data amplified by the standards gain, the output ratio of the output of the air data amplified by the various gains, a change based on changes over time in the sensitivity characteristic, in the various gain by reflecting the phantom data amplified reference time, to create the new correction data, and wherein.

The invention according to claim 5 is an X-ray source that emits X-rays, a detector that detects X-rays transmitted through the subject, and data collection that collects and amplifies data of the detected X-rays A pre-processing unit that corrects the sensitivity of the collected X-ray data based on the correction data, and an image reconstruction unit that reconstructs an image in the subject based on the X-ray data. The processing unit creates correction data at the reference time based on the phantom data amplified with various gains acquired with the predetermined time as the reference time, and uses the correction time as a correction time after the predetermined time has elapsed. New correction data at the time is created, and at the time of correction, the output of the air data amplified with the reference gain at the reference time and the air data amplified with various gains are added to the air data at the reference time amplified with the reference gain. each of the output of data By reflecting the force ratio, calculates a reference air data amplified by the various gain at the reference point, the air data amplified corrected time at the reference gain, the air data amplified by the reference gain in the modified time output The corrected air data amplified with various gains at the time of correction is calculated by reflecting each output ratio between the output of the air data amplified with various gains , and various values are calculated from the reference air data and the corrected air data. get the sensitivity change rate of the gain, created phantom data amplified reference time at various gains, reflecting the rate of change in sensitivity of the various gains, the new correction data for various gain based on the reflected result It is characterized by doing.

According to a sixth aspect of the present invention, there is provided an X-ray source for exposing X-rays, a detector for detecting X-rays transmitted through the subject, and data collection for collecting and amplifying detected X-ray data. A pre-processing unit that corrects the sensitivity of the collected X-ray data based on the correction data, and an image reconstruction unit that reconstructs an image in the subject based on the X-ray data. The processing unit creates correction data at the reference time based on the phantom data amplified with various gains acquired with the predetermined time as the reference time, and the correction time is determined after a predetermined time has elapsed from the reference time. create a new correction data in the Fixed point, it is created based the new correction data for the various gains (Gx) various photographing conditions can take under (Cy) to the result of the formula: X-ray CT apparatus characterized by this. (Formula) Ws (Gx, Cy) × {An (Gs, Cy) / As (Gs, Cy)} × {An (Gx, Cs) / An (Gs, Cs)} / {As (Gx, Cs) / As (Gs, Cs)} Ws (Gx, Cy): Phantom data acquired under various imaging conditions (Cy) that can be taken under various gains (Gx) at the reference time point As (Gs, Cy): At the reference time point Air data acquired under various imaging conditions (Cy) that can be taken under the reference gain (Gs) As (Gx, Cs): acquired under reference imaging conditions (Cs) that can be taken under various gains (Gx) at the reference time point Air data As (Gs, Cs): Air data An (Gs, Cy) acquired at reference photographing conditions (Cs) that can be taken under the reference gain (Gs) at the reference time point: Reference gain ( Gs) under Air data An (Gx, Cs) acquired under various photographing conditions (Cy) that can be taken: Air data An (Gs, Cs) obtained under reference photographing conditions (Cs) that can be taken under various gains (Gx) at the time of correction Cs): air data acquired under reference photographing conditions (Cs) that can be taken under the reference gain (Gs) at the time of correction

According to the present invention, the air data amplified with the reference gain and the output ratio between the output of the air data amplified with the reference gain and the output of the air data amplified with the various gains are obtained and amplified with the various gains. Since the correction data can be corrected, it is possible to reduce the number of times of photographing for generating correction data and shorten the data collection time for generating correction data.

  Hereinafter, an X-ray CT apparatus according to an embodiment of the present invention will be described with reference to FIGS. 1 to 4.

  A configuration of an X-ray CT apparatus according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a block diagram showing a schematic configuration of an X-ray CT apparatus according to an embodiment of the present invention. The X-ray CT apparatus is an apparatus that exposes an X-ray beam, detects an X-ray beam transmitted through the subject, and reconstructs the inside of the subject as an image.

  As shown in FIG. 1, the X-ray CT apparatus according to this embodiment includes a gantry device 10, a bed device 20, and a console unit 30.

  The gantry device 10 includes an X-ray source 12 and an X-ray detector 13 facing a rotating gantry 14 (gantry), and a high voltage generator 11, a gantry driver 16, an aperture driver 17, and a data collector 15. To do.

  The couch device 20 has a couch top plate 23 that is inserted into the opening of the rotating gantry 14 on a couch base 22, and a couch driving unit 21 is provided inside.

  The console unit 30 includes a scan control unit 31 that controls the gantry device 10 and the couch device 20, a preprocessing unit 32 that reconstructs and displays the inside of the subject as an image, a reconstruction processing unit 33, an image storage unit 34, an image A processing unit 35, a display device 36, and an input unit 37 for inputting photographing conditions are provided.

  The scan control unit 31 controls the high voltage generation unit 11, the gantry driving unit 16, the data collection unit 15, the aperture driving unit 17, and the bed driving unit 21 according to the imaging conditions. The control is performed by outputting a control signal reflecting the contents of the shooting conditions.

  An X-ray beam generation control signal for controlling X-ray beam generation is output to the high voltage generator 11. An instruction to start diagnosis and a gantry control signal for controlling the driving of the rotating gantry 14 are output to the gantry driving unit 16. A data collection control signal for controlling data collection drive is output to the data collection unit 15. An aperture control signal for controlling the aperture of the X-ray beam is output to the aperture drive unit 17. An instruction to start diagnosis and a bed movement control signal for controlling bed movement are output to the bed driving unit 21.

  The high voltage generator 11 supplies a high voltage according to the imaging conditions to the X-ray source 12 based on a control signal from the scan controller 31. The X-ray source 12 exposes an X-ray beam such as a fan shape or a cone shape by the high voltage supplied from the high voltage generator 11. The aperture drive unit 17 moves the X-ray shielding plate according to the imaging conditions, and adjusts the exposure range in the X-ray slice direction.

  The X-ray detector 13 detects an X-ray beam that is exposed from the X-ray source 12 and transmitted through the subject. In the case of a single slice CT apparatus, the X-ray detector 13 is configured by arranging, for example, 1000 channels of X-ray detection elements in a row in a fan shape or a linear shape. In the case of a multi-slice CT apparatus, the X-ray detector 13 has a plurality of X-ray detection elements arranged in an array in two directions (slice direction and channel direction) orthogonal to each other.

  The rotary mount 14 holds the X-ray source 12 and the X-ray detector 13 inside. Further, the rotating gantry 14 is rotated by a gantry driving unit 16 around a rotation axis passing through an intermediate point between the X-ray source 12 and the X-ray detector 13. The gantry driving unit 16 rotates the rotating gantry 14 based on the gantry control signal output by the scan control unit 31.

  The data collection unit 15 (DAS) includes a data collection element, a gain circuit corresponding to each channel, and an A / D converter.

  The data acquisition elements are arranged in an array similar to the X-ray detection elements of the X-ray detector 13, and the X-ray beam (X-ray beam (X) output from the X-ray detector 13 in synchronization with the output timing of the data acquisition control signal) Actually, the detection signal) is collected. The gain circuit amplifies the X-ray beam with a predetermined gain for each channel. The A / D converter converts the amplified X-ray beam into a digital signal. The X-ray beam collected and digitally converted by the data collection unit 15 is output to the console unit 30 as projection data (raw data).

  Based on the bed movement control signal output from the scan control unit 31, the bed driving unit 21 calculates the amount of movement of the bed top plate 23 per rotation of the rotating base 14, and uses the amount of movement during scanning to set the bed top plate. 23 is moved. The bed base 22 moves the bed top plate 23 in the vertical direction by the bed driving unit 21. The couch top 23 carries a subject and is movable in the body axis direction (Z-axis direction: slice direction) of the subject.

  The preprocessing unit 32 performs sensitivity correction for correcting the X-ray intensity on the projection data output from the data collection unit 15. Sensitivity characteristics change for each channel depending on the atmosphere such as temperature and changes with time. This sensitivity characteristic has the detection sensitivity, collection sensitivity, and amplification accuracy of the X-ray beam as parameters. This change in sensitivity characteristic does not have a simple correlation with the amount of change in the atmosphere such as temperature, the amount of change with time, and the gain, but is seemingly nonlinear. In the sensitivity correction process, correction data is created by the pre-processing unit 32, and the correction data is used to correct the change in sensitivity characteristic for the projection data. The correction data is corrected every predetermined period by observing changes in sensitivity characteristics over time.

  The reconstruction processing unit 33 reconstructs the image in the subject from the projection data output from the preprocessing unit 32 by a known back projection processing method, and creates tomographic image data. The tomographic image data is temporarily stored in the image storage unit 34. The back projection processing method is a reconstruction method such as fan beam reconstruction assuming that the X-ray paths in the slice direction are parallel, cone beam reconstruction in consideration of the X-ray exposure angle (cone angle) in the slice direction. .

  The image processing unit 35 performs various kinds of image processing on the tomographic image data stored in the image storage unit 34 to generate display image data. Various setting conditions for generating display image data, setting of a region of interest, and the like are performed based on an input by the operator using the input unit 37. The display unit 37 displays an image corresponding to the display image data generated by the image processing unit 35.

  The sensitivity correction in the preprocessing unit 32 will be described in more detail with reference to FIGS. FIG. 2 is a functional block diagram of the preprocessing unit 32 related to sensitivity correction, and FIG. 3 is a diagram illustrating correction data used for sensitivity correction. As shown in FIG. 2, the preprocessing unit 32 includes a sensitivity correction unit 321, a correction data storage unit 322, and a correction data creation unit 323.

  The sensitivity correction unit 321 performs sensitivity correction on the projection data. The correction data is read from the correction data storage unit 322, and the projection data is corrected using the correction data. The correction data corresponding to the shooting condition and channel of the obtained projection data is acquired from the correction data sheet 322a prepared for each shooting condition. The correction data creation unit 323 creates correction data from various projection data obtained by scanning for creating correction data.

  The correction data sheet 322a is prepared for each imaging condition of the projection data and is stored in the correction data storage unit 322. The imaging conditions include a tube voltage (kV), a combination of slice thickness (mm) and the number of columns, an imaging area, a gain, an imaging mode, and the like. The shooting area has a head, a torso, etc., and is set according to the subject. A plurality of gains such as 1 ×, 3 ×, 5 ×, 10 ×, and 20 × are prepared. The shooting area and the gain usually correspond one-to-one. When a certain shooting area is set, the gain is uniquely determined. The relationship between the shooting area and the gain can be set separately. There may be a case where a plurality of gains are prepared for a certain photographing region.

  The correction data is based on projection data obtained when a phantom is photographed (hereinafter referred to as “phantom data”), and is obtained by subjecting the phantom data to image quality improvement processing such as ring artifact removal processing. The phantom data reflects changes in sensitivity characteristics. The phantom is a water bag or a resin having a uniform internal density, and a phantom having a specific size for each imaging region such as the head and torso of the subject.

  In the sensitivity correction unit 321, as projection data correction processing, the correction data optimum for the imaging condition and channel is read, and the correction data is reflected in the projection data in the subject imaging, thereby obtaining the projection data obtained in the subject imaging. To remove the influence of the change in sensitivity characteristics.

  That is, calculation of corrected projection data Tc (Cy, CHz) = projection data Tb (Cy, CHz) / correction data (Cy, CHz) is performed. Cy represents a predetermined shooting condition, and CHz represents a predetermined channel.

  The correction data creation unit 323 creates correction data serving as a reference, and corrects the correction data to reflect a change in sensitivity characteristics from the reference time to the correction time. In the correction process, the change in sensitivity characteristics from the reference time to the correction time is obtained from the projection data of the both air acquired at the reference time and the correction time (hereinafter referred to as “air data”), and the phantom data acquired at the reference time (hereinafter referred to as “air data”). , The phantom data at the time of correction is calculated.

  Specifically, new correction data = Ws (Gx, Cy) × {An (Gx, Cy) / As (Gx, Cy)} is calculated, and a new correction corrected thereby is calculated. Create data. Here, for convenience of explanation, the gain is extracted from the shooting conditions, and the shooting conditions and the gain are handled as parallel parameters.

  Ws (Gx, Cy) indicates reference phantom data under the shooting conditions Cy and gain Gx, and An (Gx, Cy) indicates air data at the time of correction in the shooting conditions Cy and gain Gx (hereinafter, “corrected air data”). As (Gx, Cy) indicates air data at the reference time point (hereinafter referred to as “reference air data”) in the imaging condition Cy and the gain Gx.

  As shown in this calculation formula, the rate of change in sensitivity characteristics from the correction point to the reference point is calculated based on the ratio between the corrected air data and the reference air data, and this change rate is applied to the reference phantom data. Phantom data (hereinafter referred to as “corrected phantom data”).

  Here, in the present embodiment, the reference air data As (Gx, Cy) is the reference air data As (Gx, Cy) = As (Gs, Cy) × {As (Gx, Cs) / As (Gs, Cs). )}.

  As (Gs, Cy) is air data acquired with the imaging condition Cy and the reference gain Gs at the reference time point. The reference gain Gs is obtained by selecting a predetermined one of the gains Gx that can be taken by the gain circuit as a reference. As (Gx, Cs) is air data acquired at the reference time point with the reference imaging condition Cs and the gain Gx. The reference photographing condition Cs is obtained by selecting a predetermined one of the photographing conditions as a reference. As (Gs, Cs) is air data acquired at the reference time point with the reference imaging condition Cs and the reference gain Gs.

  As shown in this calculation formula, the reference air data As (Gx, Cy) amplified with various gains Gx is the air data As (Gs, Cy) obtained by amplification with the reference gain Gs and the data of the reference gain Gs. And As (Gx, Cs) / As (Gs, Cs), which is an output ratio of the output of the other gain Gx.

  The output ratio represents the difference in the change in amplification accuracy between gains. In the correction data creation unit 323, the reference air data As (Gx, Cy) amplified with various gains Gx is not acquired by direct imaging, but is obtained with the air data As (Gs, Cy) obtained by amplification with the reference gain Gs. It is calculated by multiplying the output ratio As (Gx, Cs) / As (Gs, Cs) between the data of the reference gain Gs and the output of the other gain Gx.

  Further, the corrected air data An (Gx, Cy) under the photographing condition Cy and gain Gx is corrected air data An (Gx, Cy) = An (Gs, Cy) × An (Gx, Cs) / An (Gs, Cs). Is calculated by

  An (Gs, Cy) is air data acquired with the imaging condition Cy and the reference gain Gs at the time of correction. As (Gx, Cs) is air data acquired with the reference imaging condition Cs and the gain Gx at the time of correction. As (Gs, Cs) is air data acquired with the reference imaging condition Cs and the reference gain Gs at the time of correction.

  As shown by this calculation formula, in the correction data creation unit 323, the corrected air data As (Gx, Cy) of each gain Gx is converted into air data An (Gs, Cy) obtained by amplification with the reference gain Gs. It is calculated by multiplying An (Gx, Cs) / An (Gs, Cs), which is the output ratio between the data of the reference gain Gs and the output of the other gain Gx.

  In the correction data creation unit 323, the reference air data An (Gx, Cy) amplified with various gains Gx is not acquired by direct imaging, but is converted into air data An (Gs, Cy) obtained by amplification with the reference gain Gs. The calculation is performed by multiplying An (Gx, Cs) / An (Gs, Cs), which is the output ratio between the output of the reference gain Gs and the output of the other gain Gx.

  The correction data correction operation will be described with reference to FIG. FIG. 4 is a flowchart showing an operation of creating correction data processed by the preprocessing unit 32. The creation operation is divided into creation of reference correction data and correction of correction data. The creation of reference correction data is performed once every several months, and new correction data is corrected daily.

  First, a phantom that matches each imaging area is placed on the couch top plate 23, an X-ray beam is exposed to the phantom under imaging conditions Cy, and the detected X-ray beam is amplified with a gain Gx to obtain reference phantom data Ws ( Gx, Cy) is acquired (S01).

  Next, the bed top plate 23 is pulled back to expose the X-ray beam to the air under the imaging condition Cy, and the detected X-ray beam is amplified by the reference gain Gs to acquire the reference air data As (Gs, Cy) (S02). ).

  When data is acquired by photographing with another photographing condition Cy (S03, Yes), S01 to S02 are repeated until photographing is finished with each photographing condition Cy and each gain Gx. The reference phantom data Ws (Gx, Cy) and the respective reference air data As (Gs, Cy) are alternately photographed for photographing at the same time.

  Since the reference air data is collected at the same time, the photographing of the reference phantom data Ws (Gx, Cy) and the reference air data As (Gs, Cy) has four types of tube voltages and 25 combinations of slice thickness and number of columns. If there are 5 types and shooting areas, 500 times each is performed.

  When the reference phantom data Ws (Gx, Cy) and the reference air data As (Gs, Cy) are acquired, the X-ray beam is exposed to the air under the reference imaging condition Cs for each imaging region, and the detected X-ray beam is Each reference air data As (Gx, Cs) is acquired by amplification with each gain Gx (S04).

  This imaging is performed when collecting the reference phantom data Ws (Gx, Cy) and the reference air data As (Gs, Cy) for each imaging area. Therefore, if there are five types of shooting areas, there are also five types of gains Gx, which are performed 25 times in total.

  Shooting at this reference time (S01 to S04) is repeated 1025 times if there are 100 types of shooting conditions, 5 types of shooting regions, and 5 types of gains, as described above.

  After this shooting, the reference phantom data Ws (Gx, Cy) is subjected to image quality improvement processing to obtain correction data. During a certain period, the projection data is corrected with this correction data (S05). When a certain period elapses, the correction data is corrected and new correction data is created.

  In correction data correction, an X-ray beam is exposed to air under each imaging condition in a single imaging region, and the detected X-ray beam is amplified by a reference gain Gs to obtain corrected air data An (Gs, Cy). (S06). This photographing is performed 100 times in total if there are four types of tube voltages and 25 types of combinations of slice thickness and number of rows.

  When the corrected air data An (Gs, Cy) is acquired, the X-ray beam is exposed to the air under a combination of the reference imaging condition Cs and each gain Gx for a single imaging region, and each corrected air data An (Gx , Cs) is acquired (S07). In this photographing, a total of five times for each gain Gx is obtained, and a total of five corrected air data An (Gx, Cs) is acquired.

  In the photographing at the time of correction (S06 to S07), as described above, if there are 100 kinds of photographing conditions and five kinds of gains, the photographing is repeated a total of 105 times.

  By acquiring the projection data at the reference time and the projection data at the correction time, the pre-processing unit 323 has the reference phantom data Ws (Gx, Cy), the reference air data As (Gs, Cy), and the reference air data As. (Gx, Cs), corrected air data An (Gs, Cy), and corrected air data An (Gx, Cs) are stored.

Next, the pre-processing unit 323 creates new correction data for each shooting condition by calculating the following calculation formula and performing image quality improvement processing (S08).
New correction data = Ws (Gx, Cy) × {An (Gs, Cy) × An (Gx, Cs) / An (Gs, Cs)} / {As (Gs, Cy) × As (Gx, Cs) / As (Gs, Cs)}

  The new correction data is collected in the correction data sheet 322a for each shooting condition corresponding to the channel, and stored in the correction data storage unit 322 (S09).

  As described above, when creating correction data, if there are 100 shooting conditions, 5 shooting areas, and 5 gains, a total of 1025 shooting operations including the phantom data and the air data are performed at the reference time point. At the time of correction, a total of 105 photographing operations are sufficient.

  The number of times of photographing is suppressed to less than half of the number of conventional photographing operations at the time of correction. This halving of the number of times of photographing is brought about by adopting a method in which the air data is acquired only for the reference gain Gs and the air data at each gain Gx is derived from the output ratio between the reference gain Gs and the other gains Gx. It is. Therefore, in the present embodiment, the number of times of photographing for creating correction data is halved, and the collection time can be shortened.

Here, new correction data = Ws (Gx, Cy) × {An (Gs, Cy) × An (Gx, Cs) / An (Gs, Cs)} / {As (Gs, Cy) × As (Gx, Cs) / As (Gs, Cs)}
= Ws (Gx, Cy) × {An (Gs, Cy) / As (Gs, Cy)} × {An (Gx, Cs) / An (Gs, Cs)} / {As (Gx, Cs) / As ( Gs, Cs)}.

  That is, this calculation formula reflects the change in sensitivity {An (Gs, Cy) / As (Gs, Cy)} over time in the reference gain Gs in the reference phantom data Ws (Gx, Cy) at the reference time. The reference phantom data Wn (Gx, Cy) amplified by the reference gain Gs at the time of correction is calculated. Further, the change in the output ratio between gains over time {An (Gx, Cs) / An (Gs, Cs)} / {As (Gx, Cs) / As (Gs, Cs)} The reference phantom data Wn (Gx, Cy) amplified by the gain Gx is calculated. Therefore, in this embodiment, it can be said that the correction data is corrected with respect to the detection sensitivity and collection sensitivity of the X-ray beam with two items, and the amplification accuracy is corrected with three items.

1 is a block diagram showing a schematic configuration of an X-ray CT apparatus according to an embodiment of the present invention. It is a functional block diagram which shows the pre-processing part with which the X-ray CT apparatus which concerns on embodiment of this invention is provided. It is a figure which shows the correction data storage part with which a pre-processing part is provided. It is a flowchart figure which shows the correction data creation operation | movement of the X-ray CT apparatus concerning embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Stand apparatus 11 High voltage generation part 12 X-ray source 13 X-ray detector 14 Rotating mount 15 Data collection part 16 Mount drive part 17 Diaphragm drive part 20 Sleeper apparatus 21 Sleeper drive part 22 Sleeper base 23 Sleeper table top 30 Console part 31 Scan Control Unit 32 Preprocessing Unit 321 Sensitivity Correction Unit 322 Correction Data Storage Unit 323 Correction Data Creation Unit 33 Reconstruction Processing Unit 34 Image Storage Unit 35 Image Processing Unit 36 Display Device 37 Input Unit

Claims (6)

A method for generating correction data for correcting the sensitivity of X-ray data acquired by a detector that detects X-rays, a data collection unit that collects detected X-ray data and amplifies the data with a predetermined gain There,
Obtain phantom data amplified at various gains with a predetermined time as a reference time, create correction data at the reference time based on the phantom data,
Create a new correction data at the correction time, with a predetermined time after the reference time as the correction time,
At the time of the correction,
Due to aging of the sensitivity characteristics from a reference time point to modify the time, the change of the amplified air data were in reference gain, causes reflected in phantom data amplified reference point in the various gains,
The output of the air data amplified by the standards gain, the output ratio of the output of the air data amplified by the various gains, the changes due to aging of the sensitivity characteristic, the amplified reference point at the various gain by reflecting the phantom data, to create the new correction data,
X-ray sensitivity correction data creation method characterized by the above. A correction data generation method for correcting the sensitivity of X-ray data acquired by a detector that detects X-rays and a data acquisition unit that collects detected X-ray data and amplifies the data with a predetermined gain. And
Obtain phantom data amplified at various gains with a predetermined time as a reference time, create correction data at the reference time based on the phantom data,
Create a new correction data at the correction time, with a predetermined time after the reference time as the correction time,
At the time of the correction,
By reflecting each output ratio between the output of air data amplified with the reference gain at the reference time and the output of air data amplified with the various gains to the air data at the reference time amplified with the reference gain , Calculate reference air data amplified with various gains at the time,
The air data amplified corrected time at the reference gain, and the output of the air data amplified by the reference gain in the modified time, by reflecting the respective output ratio of the output of the air data amplified by the various gains, modified Calculate corrected air data amplified with various gains at the time,
Obtain sensitivity change rates for various gains from the reference air data and the corrected air data,
The phantom data amplified reference time at various gains, reflecting the rate of change in sensitivity of the various gains, creating the new correction data for various gain based on the reflected result,
X-ray sensitivity correction data creation method characterized by the above. A correction data generation method for correcting the sensitivity of X-ray data acquired by a detector that detects X-rays and a data acquisition unit that collects detected X-ray data and amplifies the data with a predetermined gain. And
Obtain phantom data amplified at various gains with a predetermined time as a reference time, create correction data at the reference time based on the phantom data,
Create a new correction data at the correction time, with a predetermined time after the reference time as the correction time,
At the time of the correction,
It is created based the new correction data for the various gains (Gx) various photographing conditions can take under (Cy) to the result of the formula:
X-ray sensitivity correction data creation method characterized by the above.
(Formula) Ws (Gx, Cy) × {An (Gs, Cy) / As (Gs, Cy)} × {An (Gx, Cs) / An (Gs, Cs)} / {As (Gx, Cs) / As (Gs, Cs)}
Ws (Gx, Cy): Phantom data acquired under various imaging conditions (Cy) that can be taken under various gains (Gx) at the reference time point As (Gs, Cy): Under the reference gain (Gs) at the reference time point Air data As (Gx, Cs) acquired under various imaging conditions (Cy) that can be taken: Air data As (Gs, Cs) acquired under standard imaging conditions (Cs) that can be taken under various gains (Gx) at the reference time point Cs): Air data acquired under the reference shooting conditions (Cs) that can be taken under the reference gain (Gs) at the reference time point An (Gs, Cy): Various shootings that can be taken under the reference gain (Gs) at the time of correction Air data acquired under condition (Cy) An (Gx, Cs): Air data acquired under reference photographing conditions (Cs) that can be taken under various gains (Gx) at the time of correction. Data An (Gs, Cs): in the modified time, air data acquired by the reference gain (Gs) standard photography condition can take under (Cs) An X-ray source that emits X-rays;
A detector for detecting X-rays transmitted through the subject;
A data collection unit for collecting and amplifying detected X-ray data;
A pre-processing unit for correcting the sensitivity of the collected X-ray data based on the correction data;
An image reconstruction unit that reconstructs an image in a subject based on X-ray data;
With
The pre-processing unit is
Create correction data at the reference time based on the phantom data amplified with various gains acquired with the predetermined time as the reference time,
Create a new correction data at the correction time, with a predetermined time after the reference time as the correction time,
At the time of the correction ,
Due to aging of the sensitivity characteristics from a reference time point to modify the time, the change of the amplified air data were in reference gain, causes reflected in phantom data amplified reference point in the various gains,
The output of the air data amplified by the standards gain, the output ratio of the output of the air data amplified by the various gains, the changes due to aging of the sensitivity characteristic, the amplified reference point at the various gain by reflecting the phantom data, to create the new correction data,
X-ray CT apparatus characterized by this. An X-ray source that emits X-rays;
A detector for detecting X-rays transmitted through the subject;
A data collection unit for collecting and amplifying detected X-ray data;
A pre-processing unit for correcting the sensitivity of the collected X-ray data based on the correction data;
An image reconstruction unit that reconstructs an image in a subject based on X-ray data;
With
The pre-processing unit is
Create correction data at the reference time based on the phantom data amplified with various gains acquired with the predetermined time as the reference time,
Create a new correction data at the correction time, with a predetermined time after the reference time as the correction time,
At the time of the correction,
By reflecting each output ratio between the output of air data amplified with the reference gain at the reference time and the output of air data amplified with the various gains to the air data at the reference time amplified with the reference gain , Calculate the reference air data amplified at various gains in
By reflecting each output ratio between the output of air data amplified with the reference gain at the time of correction and the output of air data amplified with various gains to the air data at the time of correction amplified with the reference gain , Calculate the corrected air data amplified with various gains in
Obtain sensitivity change rates for various gains from the reference air data and the corrected air data,
The phantom data amplified reference time at various gains, reflecting the rate of change in sensitivity of the various gains, creating the new correction data for various gain based on the reflected result,
X-ray CT apparatus characterized by this. An X-ray source that emits X-rays;
A detector for detecting X-rays transmitted through the subject;
A data collection unit for collecting and amplifying detected X-ray data;
A pre-processing unit for correcting the sensitivity of the collected X-ray data based on the correction data;
An image reconstruction unit that reconstructs an image in a subject based on X-ray data;
With
The pre-processing unit is
Based on the phantom data amplified with various gains acquired with the predetermined time as the reference time, create correction data at the reference time,
Create a new correction data at the correction time, with a predetermined time after the reference time as the correction time,
Wherein the modified time, be created based on the new correction data for the various gains (Gx) various photographing conditions can take under (Cy) to the result of the formula:
X-ray CT apparatus characterized by this.
(Formula) Ws (Gx, Cy) × {An (Gs, Cy) / As (Gs, Cy)} × {An (Gx, Cs) / An (Gs, Cs)} / {As (Gx, Cs) / As (Gs, Cs)}
Ws (Gx, Cy): Phantom data acquired under various imaging conditions (Cy) that can be taken under various gains (Gx) at the reference time point As (Gs, Cy): Under the reference gain (Gs) at the reference time point Air data As (Gx, Cs) acquired under various imaging conditions (Cy) that can be taken: Air data As (Gs, Cs) acquired under standard imaging conditions (Cs) that can be taken under various gains (Gx) at the reference time point Cs): Air data acquired under the reference shooting conditions (Cs) that can be taken under the reference gain (Gs) at the reference time point An (Gs, Cy): Various shootings that can be taken under the reference gain (Gs) at the time of correction Air data acquired under condition (Cy) An (Gx, Cs): Air data acquired under reference photographing conditions (Cs) that can be taken under various gains (Gx) at the time of correction. Data An (Gs, Cs): in the modified time, air data acquired by the reference gain (Gs) standard photography condition can take under (Cs)

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