JP5484664B2 - Image display apparatus and radiation CT apparatus - Google Patents

Description

  The present invention relates to an image processing apparatus and a radiation CT (Computed Tomography) apparatus, and more particularly to an image processing apparatus and a radiation CT apparatus that generate a radiation CT image of a chest of a subject.

  When a tomographic image (CT image) of a chest of a subject is generated using a radiation CT apparatus, the tomographic image reconstruction method is often changed according to the purpose. For example, when a cardiac region including a coronary artery or the like is an observation target, an electrocardiogram synchronous reconstruction method is used. When a non-cardiac region including a lung field or the like is an observation target, an electrocardiographic asynchronous reconstruction is performed. Law is used.

  The electrocardiogram synchronous reconstruction method is a method of reconstructing using only projection data collected when the subject's heart is in a specific cardiac phase period.

  According to the ECG-synchronous reconstruction method, when reconstructing a tomographic image, it is possible to use only projection data in the cardiac phase period in which the motion of the heart is small, and image distortion caused by the motion of the heart, so-called motion artifacts (motion A tomographic image in which artifacts are suppressed can be reconstructed. For this reason, the electrocardiogram synchronization reconstruction method is suitable when the heart region is the observation target.

  Examples of the electrocardiographic synchronization reconstruction method include a prospective ECG trigger (prospective Electrocardiogram trigger) method and a retrospective ECG gate (retrospective Electrocardiogram gate) method. The former is a method of performing reconstruction processing by exposing radiation in synchronization with a desired cardiac phase (cardiac time phase) based on electrocardiographic information obtained from an electrocardiograph attached to the subject. In the latter case, an electrocardiograph is attached to the subject, and the subject is continuously exposed to radiation to collect projection data (data) and electrocardiographic information at the same time. Is extracted and reconstructed (see Patent Document 1).

  On the other hand, the ECG asynchronous reconstruction method is a method of extracting and reconstructing projection data necessary for reconstructing a tomographic image regardless of the cardiac phase of the heart.

According to the electrocardiogram asynchronous reconstruction method, when reconstructing a plurality of tomographic images continuous in the slice direction (the body axis direction of the subject), discontinuous portions in the slice direction appear in stripes. Banding artifacts can be suppressed. This is because, in the ECG asynchronous reconstruction method, there is no restriction on the collection time of projection data used for reconstruction, so reconstruction is performed using projection data whose collection time is substantially continuous in tomographic images adjacent in the slice direction. Because it can. In addition, in the ECG asynchronous reconstruction method, so-called full recon. That requires 360 ° projection data in the view direction can be adopted for reconstruction. There is little noise. For this reason, the ECG asynchronous reconstruction method is suitable when a non-cardiac region is an observation target.
JP 2007-000408 A

  In the ECG synchronous reconstruction method, so-called half recon that can be reconstructed with projection data in the view direction for 180 ° + α (fan angle of the X-ray beam (beam)) instead of full recon. Is often used. In the ECG-synchronous reconstruction method, in order to suppress motion artifacts as much as possible, the projection data collection time allowed as the “specific cardiac phase period” is limited to a short time in one heartbeat. Accordingly, the imaging time tends to be long to prepare projection data necessary for reconstruction of one tomographic image, and in the case of a retrospective ECG gate method using a helical scan, exposure to the subject is performed. There is also concern about the increase. For these reasons, the ECG synchronization reconstruction method mainly uses a half recon that can be reconstructed with less projection data. Therefore, an image reconstructed by the electrocardiogram synchronous reconstruction method tends to have more image noise than that by the electrocardiogram asynchronous reconstruction method.

  In the electrocardiogram synchronous reconstruction method, image reconstruction is performed using only projection data collected in a specific cardiac phase period. Therefore, when reconstructing a plurality of tomographic images continuous in the slice direction by the electrocardiogram synchronous reconstruction method, a tomographic image or a group of tomographic images in which the collection time of projection data used for reconstruction is discontinuous is used. A plurality of strings are generated in the slice direction. In other words, the tomographic images of a plurality of consecutive slices have discontinuous boundaries in the body axis direction of the subject due to discontinuities in the projection data collection time. Therefore, in the electrocardiogram reconstruction method, banding artifacts are generated in an image obtained by projecting a three-dimensional image composed of a plurality of tomographic images continuous in the slice direction in a direction perpendicular to the body axis of the subject.

  As described above, the electrocardiogram synchronization reconstruction method can suppress motion artifacts, but also has a surface that reduces the image quality of a generated image due to noise and banding artifacts.

  By the way, when observing the chest of the subject, there are cases where it is desired to observe both the heart region and the non-cardiac region. In such a case, it may be possible to cope with only the chest image obtained by any reconstruction method, but in the chest image by the ECG synchronous reconstruction method, banding artifacts are observed in the non-cardiac region. In addition, in the chest image obtained by the ECG asynchronous reconstruction method, motion artifacts obstruct observation in the heart region.

  Therefore, for example, it is possible to prepare the above-mentioned two types of chest images with different reconstruction methods and interpret these images by switching them on the display surface or displaying them side by side on the same display surface. It is done.

  However, when two types of chest images with different reconstruction methods are switched and displayed on the display surface, this switching operation is complicated, and the observation target is smoothly switched between the heart region and the non-cardiac region. It is difficult to move to (smooth).

  When two types of chest images with different reconstruction methods are displayed side by side on the same display surface, it is necessary to shift the line of sight when switching the observation target between the heart region and the non-cardiac region. Since one image size is reduced, the resolution of the image is lowered and it is difficult to interpret.

  As described above, it is difficult for the image interpreter to comfortably observe both the heart region and the non-cardiac region.

  In view of the above circumstances, an object of the present invention is to provide an image processing apparatus and a radiation CT apparatus capable of comfortably observing both a heart region and a non-cardiac region.

  In a first aspect, the present invention relates to a tomographic image of an imaging space that is obtained by scanning a tomographic image of the imaging space based on projection data obtained by scanning an imaging space including a chest having a heart of a subject with radiation. ECG asynchronous reconstruction means for reconstructing by a configuration method, and ECG synchronous reconstruction for reconstructing a tomographic image of at least a portion of the imaging space including the heart based on the projection data by an electrocardiographic synchronization reconstruction method. An image representing a non-cardiac region based on a tomographic image reconstructed by the electrocardiographic asynchronous reconstruction unit, and the heart based on the tomographic image reconstructed by the electrocardiographic synchronous reconstruction unit An image processing apparatus is provided that includes display means for displaying a chest image including an image representing a heart region.

  In a second aspect, the present invention provides that the ECG asynchronous reconstruction means reconstructs a first tomographic image corresponding to a slice including the heart in the imaging space, and the ECG synchronous reconstruction means The second tomographic image corresponding to the slice is reconstructed, the non-cardiac region becomes the image of the non-cardiac region in the first tomographic image, and the heart region becomes the image of the heart region in the second tomographic image. As described above, the image processing means further includes image combining means for combining the first tomographic image and the second tomographic image to generate a tomographic combined image corresponding to the slice, and the display means is generated by the image combining means An image processing apparatus according to the first aspect of the present invention that displays the chest image based on the tomographic composite image that has been obtained.

  In a third aspect, the present invention provides the image processing apparatus according to the second aspect, wherein the display means displays the tomographic composite image as the chest image.

  In a fourth aspect, the present invention provides the image synthesizing unit that generates a plurality of tomographic composite images corresponding to a plurality of slices including the heart in the imaging space, and the display unit includes the plurality of tomographic composite images. An image processing apparatus according to the second aspect is provided that displays a projection image obtained by projecting a three-dimensional image constituted by a predetermined direction as at least a part of the chest image.

  In a fifth aspect, the present invention provides the method according to any one of the second to fourth aspects, wherein the heart region is a region constituted by the heart and the vicinity of the heart in the chest. An image processing apparatus is provided.

  In a sixth aspect, the present invention provides the image synthesizing unit, wherein the image synthesizing unit includes a pixel for each combination of pixels corresponding to each other between the first tomographic image and the second tomographic image. The image according to any one of the second to fifth aspects, which is synthesized by weighting and adding the values of each other at a ratio determined according to the distance from the boundary of the heart region to the pixel. A processing device is provided.

  In a seventh aspect, according to the present invention, the electrocardiogram asynchronous reconstruction means reconstructs a plurality of tomographic images corresponding to the same slice and having different cardiac phases of the heart based on the projection data, There is provided an image processing apparatus according to any one of the second to sixth aspects, further comprising a heart area specifying means for specifying the heart area based on a change in luminance in a tomographic image.

  In an eighth aspect, the present invention relates to the sixth to sixth aspects, wherein the electrocardiogram asynchronous reconstruction means further comprises heart region specifying means for specifying the heart region based on a region specified by an operator. An image processing apparatus according to any one of the above aspects is provided.

  In a ninth aspect, the present invention provides scanning means for collecting projection data by scanning an imaging space including a chest having a heart of a subject with radiation, and based on the acquired projection data, An electrocardiographic asynchronous reconstruction means for reconstructing a tomographic image by an electrocardiographic asynchronous reconstruction method, and a tomographic image of at least a portion including the heart in the imaging space based on the projection data by an electrocardiographic synchronous reconstruction method An electrocardiogram synchronous reconstruction means to reconstruct, an image representing a non-cardiac region based on a tomographic image reconstructed by the electrocardiogram asynchronous reconstruction means, and a tomographic image reconstructed by the electrocardiogram synchronous reconstruction means And a display means for displaying a chest composite image including an image representing a heart region including the heart based on the above.

  According to the present invention, the display means includes an image of the heart region based on the tomographic image reconstructed by the electrocardiogram synchronous reconstruction means and a non-cardiac region based on the tomographic image reconstructed by the electrocardiogram asynchronous reconstruction means. Since the chest image including the image is displayed, the heart region image with reduced distortion due to the heart beat is displayed in the heart region, and the temporal discontinuity of the projection data used for reconstruction in the non-cardiac region An image in which artifacts due to the above are reduced can be integrally displayed on the same display surface, and both the heart region and the non-cardiac region can be comfortably observed.

  FIG. 1 is a block diagram showing an overall configuration of an X-ray CT apparatus (radiation CT apparatus) 1 according to an embodiment of the present invention.

  The X-ray CT apparatus 1 is configured as a CT apparatus that collects projection data of a subject 9 from a plurality of view directions by so-called helical scanning and performs image reconstruction based on the projection data. Note that the present invention is also applicable to a non-helical scan X-ray CT apparatus.

  The X-ray CT apparatus 1 includes a scanning gantry (scanning means) 2, an operation console (console) (image display device) 3, an imaging table (table) 4, and an electrocardiograph 5.

  The scanning gantry 2 detects the X-rays emitted from the X-ray tube 20, the collimator 22 that shapes the X-rays emitted from the X-ray tube 20, and the X-rays emitted from the X-ray tube 20, Drive control of the X-ray detector 23 that outputs an electrical signal corresponding to the detected X-ray dose, a data collection unit 24 that collects projection data based on the electrical signal output from the X-ray detector 23, and the X-ray tube 20 An X-ray tube controller 25 and a collimator controller 26 for driving and controlling the collimator 22.

  The scanning gantry 2 includes an X-ray tube 20 and an X-ray detector 23, and includes a rotating unit 27 that rotates integrally therewith, and a rotation controller 28 that drives and controls the rotating unit 27. The scanning gantry 2 includes a bore 29 that is a hollow portion into which a subject is carried, and an X-ray tube 20 and an X-ray detector 23 are disposed to face each other with the bore 29 interposed therebetween.

  The operation console 3 converts the projection data collected by the data collection unit 24 based on signals from the input device 31 that outputs a signal according to the input operation of the operator and various devices such as the input device 31 and the scanning gantry 2. A central processing unit 30 that executes various processes such as an image reconstruction process based on it, a display device 32 that displays a CT image or the like reconstructed by the central processing unit 30, and a program ( program), storage device 33 for storing data and X-ray CT images.

The imaging table 4 includes a cradle 41 on which the subject 9 is placed and taken in and out of the bore 29 of the scanning gantry 2. The cradle 41 is driven by, for example, a servo motor (servo motor) (not shown) built in the imaging table 4, and the servo motor is not shown.
It is controlled based on a control signal from the central processing unit 30 via an amplifier).

  The electrocardiograph 5 is attached to the subject 9 and outputs electrocardiographic data representing the electrocardiographic waveform of the heart of the subject 9 to the central processing unit 30.

  FIG. 2 is a schematic diagram showing an imaging state by the X-ray CT apparatus 1. In the present embodiment, the body axis direction of the subject 9 is described as the z-axis direction, the vertical direction is defined as the y-axis direction, and the direction perpendicular to the y-axis and the z-axis is described as the x-axis direction. FIG. 3 is a perspective view showing details of the collimator 22 and the X-ray detector 23.

  As shown in FIG. 2, the X-ray tube 20 and the X-ray detector 23 rotate around the body axis (z axis) of the subject 9 as the rotating unit 27 rotates. On the other hand, the cradle 41 conveys the subject 9 in the z-axis direction. Thereby, the X-ray tube 20 and the X-ray detector 23 relatively move around the subject 9 in a spiral shape.

  As shown in FIGS. 2 and 3, the X-ray tube 20 and the X-ray detector 23 are arranged to face each other with the bore 29 interposed therebetween. The collimator 22 is located between the X-ray tube 20 and the X-ray detector 23 and in the vicinity of the X-ray tube 20, and an X-ray beam 201 irradiated from the X-ray tube 20 toward the subject 9. The X-ray beam is shaped by shielding a part of the X-ray beam.

  The collimator 22 includes a plurality of collimator plates 221 that define an aperture ap, a plurality of shafts (not shown) fixed to the plurality of collimator plates 221, and a shaft (not shown) that drives the plurality of shafts, respectively. And a plurality of motors. Each collimator plate 221 moves when a shaft is driven by a motor. The motor is controlled by a collimator controller 26.

  The collimator plate 221 is made of a material capable of blocking X-rays, for example, lead or tungsten.

  The collimator 22 is merely an example, and any collimator 22 may be used as long as the mechanism can adjust the shape of the aperture ap.

  The X-ray detector 23 is a so-called multi-row detector. That is, a plurality of detection elements 231 are arranged in the channel direction, and the detection elements 231 are also arranged in the z-axis direction. The number in the channel direction and the number of columns in the z-axis direction may be set as appropriate. For example, the number in the channel direction is 1024, and the number of columns in the z-axis direction is 4 to 128 columns.

  The detection element 231 includes a scintillator and a photoelectric conversion element such as a photodiode, and can output an electrical signal corresponding to the incident X-ray dose. The data collection unit 24 collects information on the X-ray dose incident on the plurality of detection elements 231 and outputs the collected information to the central processing unit 30.

  The central processing unit 30 of the operation console 3 includes a control unit 30a, a projection data acquisition unit 30b, an electrocardiogram waveform specifying unit 30c, an electrocardiogram asynchronous reconfiguration unit (electrocardiogram asynchronous reconfiguration means) 30d, and an electrocardiogram synchronization. A reconstruction unit (electrocardiogram synchronization reconstruction unit) 30e, an image composition unit (image composition unit) 30f, a display control unit 30g, and a heart region identification unit (heart region identification unit) 30h are provided. These units constituting the central processing unit 30 are constructed, for example, by the central processing unit 30 executing a program recorded in the storage device 33 or the like.

  The display control unit 30g and the display device 32 in the present invention function as display means in the present invention.

  The control unit 30a controls the rotating unit 27, the imaging table 4, and the like so as to scan the subject and obtain projection data of the subject. More specifically, the control unit 30a includes the X-ray tube controller 25, the collimator controller 26, the rotation controller 28, and the servo amplifier built in the imaging table 4, and the X-ray tube 20, the collimator 22, the rotation unit 27, The cradle 41 is driven and controlled.

  The projection data acquisition unit 30b acquires projection data obtained by scanning an imaging space including a chest having a subject's heart with X-rays. Here, the projection data obtained by the helical scan is acquired from the data collection unit 24 of the scanning gantry 2.

  The electrocardiogram waveform specifying unit 30c specifies the electrocardiogram waveform of the subject during scanning. Here, the electrocardiogram waveform specifying unit 30 c specifies the electrocardiogram waveform of the subject during the scanning period based on the electrocardiogram data sent from the electrocardiograph 5.

  The electrocardiogram asynchronous reconstruction unit 30d reconstructs a tomographic image of the imaging space including the chest of the subject based on the projection data acquired by the projection data acquisition unit 30b by an electrocardiogram asynchronous reconstruction method. Here, the ECG asynchronous reconstruction method means a general reconstruction method in which the collection time of projection data used for reconstruction is not limited to a specific cardiac phase. When reconstructing one tomographic image, the electrocardiogram asynchronous reconstruction unit 30d extracts projection data necessary for reconstruction of one tomographic image from the projection data acquired by the projection data acquisition unit 30b. A tomographic image of the imaging space including the chest of the subject is reconstructed based on the projection data. Projection data required for reconstruction of one tomographic image is, for example, projection data in a plurality of view directions obtained by rotating the rotation unit 27 by 360 °, or projection in a plurality of view directions obtained by rotating the rotation unit 27 by 180 ° + α. You can think of data. Here, the electrocardiogram asynchronous reconstruction unit 30d reconstructs a tomographic image using projection data in a plurality of view directions for 360 ° so that the image quality of the reconstructed image is improved. The electrocardiogram asynchronous reconstruction unit 30d reconstructs tomographic images for a plurality of slices in the imaging space including the chest of the subject by the above-described electrocardiogram asynchronous reconstruction method. The projection data used for reconstruction is calculated from the projection data obtained by the helical scan by weighted calculation processing (interpolation processing).

  The electrocardiogram synchronization reconstruction unit 30e reconstructs a tomographic image of a portion including at least the heart in the imaging space including the chest of the subject by the electrocardiogram synchronization reconstruction method. In the ECG synchronization reconstruction method, reconstruction is performed by referring to the electrocardiographic waveform of the subject as information for specifying the cardiac phase of the subject. When reconstructing one tomographic image, the electrocardiogram reconstructing unit 30e projects projection data required for reconstruction of one tomographic image in a specific cardiac phase period of the subject from the projection data input by the projection data input unit 30b. And a tomographic image in a specific cardiac phase period of the portion including the heart is reconstructed based on the extracted projection data. A specific cardiac phase is generally considered to be end systole or end diastole, where the heart moves most slowly. The specific cardiac phase period is, for example, by referring to the electrocardiographic waveform of the subject during the scanning period, which is specified by the electrocardiographic waveform specifying unit 30c and displayed on the display surface of the display device 32 by the operator. It is determined by designating a period corresponding to a specific cardiac phase period during the scanning period. Further, for example, the electrocardiogram waveform specified by the electrocardiogram waveform specifying unit 30c or the projection data acquired by the projection data acquiring unit 30b is analyzed, and the scan corresponds to a specific cardiac phase period. Determine by finding the period. The electrocardiogram synchronization reconstruction unit 30e reconstructs a tomographic image for a plurality of slices of a portion including at least the heart in the imaging space including the chest of the subject. The projection data used for reconstruction is calculated from the projection data obtained by the helical scan by weighted arithmetic processing.

  The image compositing unit 30f has a non-cardiac region in the tomographic image (first tomographic image) corresponding to the slice in which the non-cardiac region is reconstructed by the electrocardiogram asynchronous reconstruction unit 30d in the imaging space. The first tomographic image is an image of the heart region, and the heart region is an image of the heart region in the tomographic image (second tomographic image) corresponding to the slice reconstructed by the electrocardiogram synchronization reconstruction unit 30e. The image and the second tomographic image are combined to generate a tomographic combined image corresponding to the slice. Here, the heart region is, for example, a region composed of the heart and the vicinity of the heart in the chest. Further, the non-cardiac region is a region excluding the heart region from the entire region of the tomographic image or the region corresponding to the chest.

  Here, the image compositing unit 30f generates a tomographic composite image for a plurality of slices of the portion including the heart in the imaging space including the chest of the subject.

  Further, the image compositing unit 30f determines the value of each pixel according to the distance from the boundary of the heart region to the pixel for each combination of pixels corresponding to each other between the first tomographic image and the second tomographic image. Are synthesized by weighting and adding at a predetermined ratio. This makes it possible to generate a tomographic composite image in which the boundary between the heart region and the non-cardiac region is smoother and easier to observe.

  The display control unit 30g is based on an image representing a heart region including the heart based on the tomographic image reconstructed by the electrocardiogram synchronous reconstruction unit 30e, and on the tomographic image reconstructed by the electrocardiogram asynchronous reconstruction unit 30d. The display device 32 is controlled to display a chest composite image in which an image representing a non-cardiac region is combined.

  Here, the display control unit 30g controls to display the chest image or the chest composite image based on the tomographic image reconstructed by the electrocardiogram asynchronous reconstruction unit 30d and the tomographic composite image generated by the image composition unit 30f. To do. For example, a tomographic image or tomographic composite image corresponding to an arbitrary slice, or a projection image obtained by projecting a three-dimensional image composed of a tomographic image or tomographic composite image corresponding to a plurality of slices in an imaging space in a predetermined direction Control to display.

  The heart region specifying unit 30h specifies a heart region three-dimensionally in an image space corresponding to an imaging space including the chest of the subject, or two-dimensionally specifies a heart region in a tomographic image corresponding to an arbitrary slice. Or

  Here, the electrocardiogram asynchronous reconstruction unit 30d reconstructs a plurality of tomographic images corresponding to a plurality of slices of the imaging space including the chest of the subject based on the projection data, and the display control unit 30g A three-dimensional image composed of tomographic images, a projection image obtained by projecting the three-dimensional image in a predetermined direction (for example, the x-axis direction, the y-axis direction, etc.), a tomographic image corresponding to an arbitrary slice, etc. are automatically or It displays on the display surface of the display apparatus 32 according to operation by the operator. Then, the heart region specifying unit 30h specifies a heart region based on the region specified by the operator on the image displayed on the display surface. For example, the heart region is formed into a rotating body shape (so-called spindle shape) when a predetermined ellipse having a major axis or a minor axis in the z-axis direction is rotated about the major axis or minor axis in the image space. Suppose that the source is specified by approximation. The operator refers to the first projection image obtained by projecting the three-dimensional image in the y-axis direction and the second projection image obtained by projecting the three-dimensional image in the x-axis direction on these projection images. An area and a position for specifying the shape of the rotating body are specified. For example, the operator designates a desired elliptical region including the heart on the first projection image as an elliptical region when the rotating body is projected in the y-axis direction, and y on the second projection image. A desired position in the axial direction is designated as the position of the axis of the rotating body.

  For example, the operator designates an elliptical region including the heart on the tomographic image while referring to the tomographic image corresponding to an arbitrary slice. The heart region specifying unit 30h specifies the elliptic region as a heart region in the tomographic image of the slice.

  Based on the heart region specified by the heart region specifying unit 30h, the electrocardiogram synchronization reconstructing unit 30e specifies a portion including the heart in the imaging space including the chest, and reconstructs a tomographic image of each slice of the portion. Configure. Further, the image compositing unit 30f reconstructs each slice of the portion including the heart in the imaging space including the chest based on the heart region specified by the heart region specifying unit 30h by the electrocardiogram asynchronous reconstruction unit 30d. The heart region is specified on the tomographic image and the tomographic image reconstructed by the electrocardiogram synchronization reconstruction unit 30e, and the heart region image and the non-cardiac region image are synthesized.

  From this, the workflow in the X-ray CT apparatus 1 in this embodiment is demonstrated.

  FIG. 4 is a diagram showing a workflow in the X-ray CT apparatus 1 in the present embodiment.

  In step S1, a helical scan is performed on the imaging space including the chest of the subject. At this time, projection data is collected, and electrocardiographic data of the subject during the scan execution period is collected. The projection data and the electrocardiographic waveform can be correlated in time, and the relationship between the data in each view direction constituting the projection data and the cardiac phase of the subject when the data is collected is specified. .

  Specifically, the control unit 40a sends control signals to the X-ray tube controller 25, the collimator controller 26, the rotation controller 28, and the imaging table 4, and the X-ray tube 20, the collimator 22, the rotation unit 27, and the cradle 41 are driven. A controlled helical scan is performed. The projection data acquisition unit 40 b acquires projection data from the data collection unit 24 of the scanning gantry 2, sends it to the storage device 33, and stores it. The projection data is, for example, data in which data in each view direction is associated with the time when the data is collected. The electrocardiogram waveform specifying unit 30 c acquires electrocardiographic data from the electrocardiograph 5 and sends it to the storage device 33 for storage. The electrocardiographic data is, for example, data in which each electrocardiographic signal is associated with the time when the signal is obtained.

When performing a helical scan, the helical pitch (helical
(pitch) may be constant, but the helical pitch is variable, and the helical pitch when scanning a predetermined area including the heart in the imaging space may be smaller than the helical pitch when scanning other areas. . In this way, the projection data for the heart necessary for reconstructing a tomographic image by the electrocardiogram synchronous reconstruction method can be sufficiently collected, and the exposure dose to the part other than the heart in the chest can be kept low. . The predetermined region including the heart may be designated with reference to a scout image obtained by a scout scan performed in advance by the operator, for example.

  In step S2, based on the projection data obtained in step S1, a tomographic image corresponding to each slice when the imaging space including the chest of the subject is divided into a plurality of slices is reconstructed by an electrocardiographic asynchronous reconstruction method. To do.

  FIG. 5 is a diagram illustrating a correspondence relationship between the imaging space including the chest of the subject and the reconstructed tomographic image.

  Specifically, as shown in FIG. 5, the electrocardiogram asynchronous reconstruction unit 30 d is based on the projection data stored in the storage device 33, and the image space corresponding to the imaging space including the chest 9 b of the subject 9. The tomographic images P11, P12,..., P1n corresponding to the slices when B is divided into n slices B1,..., Bn are reconstructed by the electrocardiographic asynchronous reconstruction method. The chest 9b has a heart 9h and a lung field 9L. A three-dimensional image P1 is constituted by the tomographic images P11, P12,.

  In step S3, the heart region H is specified three-dimensionally in the image space B with reference to the three-dimensional image P1 obtained in step S2.

  FIG. 6 is a diagram illustrating an example of a three-dimensional image P1 based on a tomographic image reconstructed by an electrocardiogram asynchronous reconstruction method and a projection image thereof.

  Specifically, as shown in FIG. 6, the display control unit 30g projects the first projection image J1y obtained by projecting the three-dimensional image P1 in the y-axis direction and the three-dimensional image P1 in the x-axis direction. The display device 32 is controlled to display the second projection image J1x formed on the display surface of the display device 32. Then, the heart region specifying unit 30h specifies the heart region H on the image displayed on the display surface based on the region specified by the operator via the input device 31.

  For example, it is assumed that the heart region H is specified in the image space B by approximating the spindle shape. The operator designates a region and a position for specifying the spindle-shaped body on these projection images while referring to the first projection image J1y and the second projection image J1x. Here, as shown in FIG. 6, the operator sets a desired elliptical region including the heart 9h on the first projection image J1y as an elliptical region Hy obtained by projecting the spindle-shaped body in the y-axis direction. At the same time, a predetermined position in the y-axis direction on the second projection image J1x is specified as a position Hg in the y-axis direction of the axis of the spindle-shaped body. The heart region H is, for example, an ellipse having the same shape as the ellipse region Hy drawn on the xz plane whose position in the y-axis direction is the position Hg, and rotated around the axis in the z-axis direction that is the major axis or the minor axis. It is specified as a spindle-shaped body.

  In step S4, based on the projection data obtained in step S1, the slice Ba,... Including the heart region H identified in step S3 among the plurality of slices B1,. , Bb (1 ≦ a <b ≦ n) respectively, the tomographic images P2a,..., P2b are reconstructed by the electrocardiographic synchronization reconstruction method.

  Specifically, the display control unit 30g reads the electrocardiographic waveform data from the storage device 33, and controls the display device 32 to display the electrocardiographic waveform represented by the electrocardiographic waveform data on the display surface. The ECG synchronization reconstructing unit 30e determines the end systole or the end diastole on the electrocardiogram waveform displayed on the display surface based on the region designated by the operator via the input device 31. Determine as phase phase. As shown in FIG. 5, the electrocardiogram synchronization reconstructing unit 30e sequentially sets the slices Ba,..., Bb as the target slices based on the projection data stored in the storage device 33. Projection data required for reconstruction of the tomographic image in the specific cardiac phase period corresponding to the slice of interest is extracted from the image, and the tomographic image is reconstructed based on the extracted projection data, and the tomographic image P2a,. .. Reconfigure P2b.

  In step S5, a tomographic composite image corresponding to each of the plurality of slices Ba,..., Bb including the heart region H among the plurality of slices B1,. Specifically, the image composition unit 30f performs the following processing.

  FIG. 7 is a diagram illustrating a state in which a tomographic composite image corresponding to a target slice is generated.

  First, a target slice Bi (i = a,..., B) is set. And the heart cross-sectional area | region Hi corresponding to attention slice Bi is specified. Here, the heart cross-sectional area Hi is an area that appears when the heart area H is cut along a plane corresponding to the slice Bi.

  Next, the tomographic image P1i corresponding to the target slice Bi reconstructed by the electrocardiographic asynchronous reconstruction method in step S2 and the target slice Bi reconstructed by the electrocardiographic synchronous reconstruction method in step S4. The tomographic image P2i is synthesized. Specifically, the weighting amount is changed in accordance with the distance from the boundary between the two pixels, that is, for each combination of pixels corresponding to each other, the pixel value of each pixel is changed from the boundary of the heart cross-sectional area Hi to Composition is performed by weighting and adding at a ratio determined according to the distance to the pixel. Such a synthesis process is expressed by the following equation.

P3i (x, y) = W * P1i (x, y) + (1-W) * P2i (x, y) (1)
Here, P1i (x, y) is the pixel value of the pixel located at the coordinate (x, y) in the tomographic image P1i, and P2i (x, y) is located at the coordinate (x, y) in the tomographic image P2i. The pixel value P3i (x, y) of the pixel is the pixel value of the pixel located at the coordinate (x, y) in the tomographic composite image P3i. W is a weighting variable that changes in the range of 0 ≦ W ≦ 1, and takes, for example, 0.5 when the pixel p (x, y) is on the boundary of the heart cross-sectional area Hi, and the pixel p ( When x, y) is outside the heart cross-sectional area Hi, it becomes larger as the shortest distance from the boundary to the pixel becomes larger (fixed to 1 when the predetermined distance is exceeded), and the pixel p (x, y) becomes the heart cross-section. The variable is such that when it is inside the region Hi, it becomes smaller as the shortest distance from the boundary to the pixel becomes larger (fixed to 0 when a predetermined distance is exceeded). By such a synthesis process, the non-cardiac region becomes an image of the non-cardiac region in the tomographic image reconstructed by the electrocardiogram asynchronous reconstruction method, and the heart region is reconstructed by the electrocardiogram synchronous reconstruction method. A tomographic composite image that is an image of the heart region at is generated. Then, the tomographic composite image is an image having no sense of incongruity in which the images are smoothly connected in the vicinity of the boundary between the heart region and the non-cardiac region.

  By performing such synthesis processing by sequentially updating the target slice from Ba to Bb, tomographic composite images P3a,..., P3b corresponding to a plurality of slices including the heart region H are generated.

  When the tomographic composite images P3a, ..., P3b are generated, the tomographic images P11, ..., P1 (a-1), the tomographic composite images P3a, ..., P3b, and the tomographic image P1 (b + 1),..., P1n constitute a three-dimensional image P3 for display. Various images are generated based on the three-dimensional image P3 and displayed on the display surface of the display device 32 (step S6).

  FIG. 8 is a diagram illustrating how various images are generated based on the three-dimensional image P3 for display.

  The display control unit 30g displays a projection image J3y obtained by projecting the three-dimensional image P3 in a predetermined direction, for example, the y-axis direction, or the three-dimensional image P3, as shown in FIG. The display device 32 is controlled such that a tomographic image P3k corresponding to an arbitrary slice Bk of the cross-sectional image M3t and the three-dimensional image P3 when cut along an arbitrary plane is displayed on the display surface of the display device 32.

  According to the above embodiment, the display control unit 30g has an image of the heart region based on the tomographic image reconstructed by the electrocardiogram synchronous reconstruction unit 30e and the tomographic image reconstructed by the electrocardiogram asynchronous reconstruction unit 30d. Since the display device 32 is controlled to display a chest image including an image of a non-cardiac region based on the heart region, an image of a heart region in which distortion due to heartbeat is reduced is displayed in the heart region. Images with reduced artifacts due to temporal discontinuities in the projection data used for reconstruction can be displayed integrally on the same display surface, allowing comfortable observation of both cardiac and non-cardiac regions It becomes possible to do.

  In the present embodiment, the image composition unit 30f generates a plurality of tomographic composite images corresponding to a plurality of slices including the heart region H in advance and prepares a three-dimensional image P3 for display. A tomographic image corresponding to a slice, a projection image of a three-dimensional image P3, an MPR (Multi Planar Reconstruction) image, and the like can be displayed on the display surface in a short time.

  The present invention is not limited to the above embodiment, and may be implemented in various aspects.

  For example, in the above-described embodiment, the image composition unit 30f previously generates a plurality of tomographic composite images corresponding to a plurality of slices including the heart region H, prepares a three-dimensional image P3 for display, and displays it. The control unit 30g displays a desired projection image or tomographic image based on the three-dimensional image P3. When only the tomographic image is displayed, a slice corresponding to the tomographic image to be displayed is displayed. After the designation, the image composition unit 30f may generate a tomographic composite image corresponding to the designated slice as necessary.

  Further, for example, in the above embodiment, the display control unit 30g displays the tomographic composite image generated by the image composition unit 30f on the display surface, but the tomographic image reconstructed by the electrocardiogram asynchronous reconstruction unit 30d is displayed. After being displayed on the display surface of the display device 32, only the heart region portion of the tomographic image reconstructed by the electrocardiogram synchronization reconstructing unit 30e is displayed on the tomographic image so as to be superimposed and displayed. It may be displayed.

  Further, for example, in the above embodiment, the heart region specifying unit 30h specifies the region specified by the operator as the heart region, but the electrocardiogram asynchronous reconstruction unit 30d uses the projection data for the subject. For each slice of the imaging space including the chest, a plurality of tomographic images representing the same slice and having different heart phases are reconstructed, and the heart region specifying unit 30h has a large change in luminance between the plurality of tomographic images. A region may be extracted, and the extracted region itself or a region having a predetermined positional relationship with the region may be specified as a heart region.

  Further, for example, in the above-described embodiment, the image composition unit 30f includes the first tomographic image reconstructed by the electrocardiogram asynchronous reconstruction unit 30d and the second tomographic image reconstructed by the electrocardiogram synchronous reconstruction unit 30e. Is generated by projecting a three-dimensional image P1 constituted by the first tomographic image reconstructed by the electrocardiogram asynchronous reconstruction unit 30d in the y-axis direction. J1y and a projection image J2y obtained by projecting the three-dimensional image P2 constituted by the second tomographic image reconstructed by the electrocardiogram synchronization reconstruction unit 30e in the y-axis direction are combined to generate a projection composite image You may make it do. In this case, synthesis may be performed by changing the weighting amount according to the distance from the boundary of the cardiac projection region Hy obtained by projecting the cardiac region H in the y-axis direction.

It is a block diagram which shows the structure of the X-ray CT apparatus which is embodiment of this invention. It is the schematic which shows the imaging state by the X-ray CT apparatus which is embodiment of this invention. It is a perspective view which shows the detail of the collimator and detector of the X-ray CT apparatus which are embodiment of this invention. It is a flowchart which shows the work procedure in the X-ray CT apparatus which is embodiment of this invention. It is a figure which shows the correspondence of the imaging space containing the chest of a subject, and the tomographic image reconstructed. It is a figure which shows the example of the three-dimensional image by the tomographic image reconstructed by the electrocardiogram asynchronous reconstruction method, and its projection image. It is a figure which shows a mode that the tomographic composite image corresponding to an attention slice is produced | generated. It is a figure which shows a mode that a various image is displayed based on the three-dimensional image for a display.

Explanation of symbols

1 X-ray CT system (radiation CT system)
2 Scanning gantry (scanning means)
3 Operation console (image processing device)
4 imaging table 5 electrocardiograph 9 subject 9b chest 9h heart 9L lung field 20 X-ray tube 21 X-ray tube moving unit 22 collimator 23 X-ray detector 24 data collecting unit 25 X-ray tube controller 26 collimator controller 27 rotating unit 28 Rotation controller 29 Bore 30 Central processing unit 30a Control unit 30b Projection data acquisition unit 30c ECG waveform identification unit 30d ECG asynchronous reconfiguration unit (ECG asynchronous reconfiguration unit)
30e ECG synchronization reconstruction unit (ECG synchronization reconstruction means)
30f Image composition unit (image composition means)
30g Display control unit (display means)
30h Heart region specifying unit (heart region specifying means)
31 Input device 32 Display device (display means)
33 Storage device 41 Cradle 231 Detection element

Claims (9)

To imaging space including a chest with heart and lung of the subject by radiation, a scan region including the heart and lung, than other scan region including the lung field does not include the adjacent to the scan area heart Based on projection data obtained by performing helical scan with a small helical pitch, tomographic images in the scan region including the heart and lung fields and the other scan regions were used with projection data of multiple views for 360 °. An ECG asynchronous reconstruction means for reconfiguration by an ECG asynchronous reconstruction method;

An electrocardiographic reconstruction means for reconstructing a tomographic image of a scan region including the heart and lung fields by an electrocardiographic reconstruction method based on the projection data;

And an image representing the cardiac region is a part of the tomographic image of the scanned area including the heart and lung field reconstructed by the ECG gated reconstruction means, said cardiac reconstructed by the electrocardiogram asynchronous reconstruction means And a display means for displaying a chest image synthesized with an image representing a non-cardiac region composed of regions other than the heart region in a tomographic image of a scan region including a lung field .
The electrocardiogram asynchronous reconstruction means reconstructs a first tomographic image corresponding to a slice of a scan region including the heart and lung fields in the imaging space;

The electrocardiogram synchronous reconstruction means reconstructs a second tomographic image corresponding to the slice,
Image synthesizing means for synthesizing the first tomographic image and the second tomographic image to generate a tomographic synthesized image corresponding to the slice, wherein a non-cardiac region in the tomographic synthesized image is the first tomographic image. The first tomographic image and the second tomographic image are synthesized so that a non-cardiac region image in the tomographic image is obtained, and the heart region in the tomographic composite image is the heart region image in the second tomographic image. , Further comprising image composition means for generating a tomographic composite image corresponding to the slice,

The image processing apparatus according to claim 1, wherein the display unit displays the chest image based on a tomographic composite image generated by the image combining unit.
The image processing apparatus according to claim 2, wherein the display unit displays the tomographic composite image as the chest image. The image synthesis means generates a plurality of tomographic composite images corresponding to a plurality of slices of a scan region including the heart and lung fields in the imaging space,

The image processing apparatus according to claim 2, wherein the display unit displays a projection image obtained by projecting a three-dimensional image composed of the plurality of tomographic composite images in a predetermined direction as at least a part of the chest image. .
The image processing apparatus according to any one of claims 2 to 4, wherein the heart region is a region formed by the heart and a vicinity of the heart in the chest.
The image synthesizing unit sets the value of each pixel to the distance from the boundary of the heart region to the pixel for each combination of pixels corresponding to each other between the first tomographic image and the second tomographic image. 6. The image processing apparatus according to claim 2, wherein the image processing apparatus performs synthesis by weighting and adding at a ratio determined according to the ratio.
The electrocardiogram asynchronous reconstruction means reconstructs a plurality of tomographic images corresponding to the same slice based on the projection data and having different cardiac phases of the heart,

The image processing apparatus according to any one of claims 2 to 6, further comprising a heart region specifying unit that specifies the heart region based on a change in luminance in the plurality of tomographic images.
The image processing apparatus according to claim 2, wherein the electrocardiogram asynchronous reconstruction unit further includes a heart region specifying unit that specifies the heart region based on a region specified by an operator. .
To imaging space including a chest with heart and lung of the subject by radiation, a scan region including the heart and lung, than other scan region including the lung field does not include the adjacent to the scan area heart Scanning means for collecting projection data by performing helical scanning with a small helical pitch ; and

Electrocardiographic asynchronization for reconstructing the acquired tomographic images in the scan region including the heart and lung fields and the other scan regions by an electrocardiographic asynchronous reconstruction method using projection data of a plurality of views for 360 °. Reconstruction means;

An electrocardiographic reconstruction means for reconstructing a tomographic image of a scan region including the heart and lung fields by an electrocardiographic reconstruction method based on the projection data;

And an image representing the cardiac region is a part of the tomographic image of the scanned area including the heart and lung field reconstructed by the ECG gated reconstruction means, said cardiac reconstructed by the electrocardiogram asynchronous reconstruction means And a display means for displaying a chest composite image in which a tomographic image of a scan region including a lung field is combined with an image representing a non-cardiac region composed of regions other than the heart region.

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