JP2005143947A - X-ray computed tomograph - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an X-ray computed tomograph reducing the burden on an operator. <P>SOLUTION: This X-ray CT adds a slice number, a scan number, rotating board angle information, and the like, as a header to RAW data obtained from a detector and intermittently reconstructs and displays a tomogram based on the header. Especially in a volume scan, this X-ray CT uses a pseudo scanogram reconstructed using data of a predetermined angle and, when the operator specifies a region of interest and post-reconstruction on the pseudo scanogram, reads data related to the region and reconstructs and displays the image. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an X-ray CT apparatus for reconstructing a tomographic image or a scanogram image.

  In the X-ray CT apparatus, an X-ray tube and an X-ray detector are arranged to face each other, and an X-ray beam irradiated from the X-ray tube passes through the subject and enters the X-ray detector. The dose of X-rays incident on the detector is attenuated from the original X-rays according to the transmittance of the subject, and the attenuation amount is converted into a digital electric signal by a preamplifier. The subject can move in the body axis direction between the X-ray tube and the X-ray detector by a movable bed, and the amount of movement and the direction of travel can be changed by a control signal.

  The X-ray tube and the X-ray detector arranged opposite to each other are mounted on a turntable, and the subject is irradiated with X-rays at regular intervals while rotating around the subject by a control signal, and an electrical signal is output by a preamplifier. Then, the data is transmitted to the image processing apparatus by the data transmission system. A series of data necessary for image reconstruction consists of data for all projection angles detected during one rotation of the X-ray tube and detector, and is a three-dimensional image having channel direction components, projection angle components, and slice direction components. It is data.

  A data transmission system provided on the rotary plate and stationary side of the X-ray CT apparatus transmits data input from the detector to the image processing apparatus every several data on a transmission line using an electric signal or an optical signal. The image processing apparatus performs image reconstruction processing on the transmitted data and displays an image on the monitor of the console.

  A technique for displaying a pair of tomographic images having substantially the same anatomical tomographic position when there are a plurality of sets of images reconstructed in this manner is known (for example, see Patent Document 1).

  Furthermore, a continuous scan image can be obtained in the body axis direction by irradiating the subject with X-rays while moving the movable bed on which the subject is placed while the turntable is rotating. This scanning method is called volume scanning, and the moving distance of the movable bed per scan rotation with respect to the slice thickness is called a helical pitch.

In addition, a scanogram image, which is a simple X-ray fluoroscopic image, can be reconstructed by irradiating the subject with X-rays while moving only the movable bed on which the subject is placed with the rotating disk fixed at a fixed angle. Can do.
JP-A-8-294485

  In the conventional data processing method as described above, RAW data is sequentially reconstructed and all scanned images are displayed. However, since a large amount of RAW data is generated particularly in a multi-slice X-ray CT apparatus equipped with a detector divided into multi-slices, a large amount of time and effort is required to confirm all the images when all the scan images are displayed. This increases the burden on the operator, increases the amount of image data, and requires a large-capacity storage device for data storage.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an X-ray CT apparatus that reduces the burden on the operator.

  In order to achieve the above object, an X-ray CT apparatus according to the first feature of the present invention acquires transmission X-ray data by scanning the subject around the body axis in a designated body axis direction range of the subject. Based on transmission X-ray data corresponding to a predetermined time interval or a predetermined slice interval in the acquired transmission X-ray data, and storage means for temporarily storing the acquired transmission X-ray data Reconstructing means for intermittently reconstructing a tomographic image, and display means for displaying the reconstructed tomographic image.

  In the X-ray CT apparatus according to the first feature of the present invention, since the tomographic image is displayed intermittently, the number of images to be observed and confirmed by the operator is reduced, and the burden is reduced. The transmitted X-ray data obtained by scanning the subject is stored in the storage means, so that detailed image processing may be performed based on this data, or only necessary data may be stored.

  The X-ray CT apparatus according to the second feature of the present invention is the X-ray CT device according to the first feature of the present invention, wherein the storage means converts the acquired transmitted X-ray data into an angle around the body axis of the subject. Means for reconstructing a pseudo-scanogram image of the subject using transmission X-ray data corresponding to a specified angle among the stored transmission X-ray data, and a user in the pseudo-scanogram image Means for setting a region of interest based on the instruction input, and means for reconstructing a second tomographic image based on transmission X-ray data corresponding to the region of interest among the stored transmission X-ray data. The display means displays the pseudo-scanogram image and the second tomographic image.

  In the X-ray CT apparatus according to the second feature of the present invention, the operator can observe and confirm a tomographic image of a necessary portion in detail by referring to the pseudo-scanogram image and setting a region of interest. Further, such setting of the region of interest and confirmation of the tomographic image can be freely and repeatedly performed. Further, since such processing is performed based on already acquired transmission X-ray data, it is not necessary to perform a new scan for reconstruction of the pseudoscanogram image or tomographic image reconstruction of the region of interest. The exposure dose of the specimen does not increase.

  The X-ray CT apparatus according to the third feature of the present invention is the X-ray CT device according to the first feature of the present invention or the second feature of the present invention, wherein data is recorded in the pseudo-scanogram image based on a user's instruction input. The apparatus further comprises means for setting an area, and means for recording transmission X-ray data corresponding to the data recording area in the stored transmission X-ray data.

  In the X-ray CT apparatus according to the third feature of the present invention, since only the necessary portion of the transmitted X-ray data stored in the storage means can be stored, the storage capacity required for data storage is reduced. be able to.

  In the X-ray CT apparatus according to the present invention, the burden on the operator is reduced.

  Hereinafter, preferred embodiments of an X-ray CT apparatus according to the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 shows a configuration of an X-ray CT apparatus 100 according to the present embodiment. The X-ray CT apparatus 100 includes a detection unit on which an X-ray tube 2 and an X-ray detector 3 disposed opposite to the X-ray tube 2 are mounted, and the X-ray tube 2 and the X-ray detector 3 fixed on the same plane. A turntable 5 that rotates around the specimen, a movable bed 7 that can move the subject 6 in the body axis direction, a preamplifier 4 that converts output data of the X-ray detector 3 into a digital signal, and an image processing apparatus Data transmission systems 8 and 9 for transmitting to the image processing apparatus 10, an image processing apparatus 10 that performs image processing based on detection data, and a monitor 11 that displays an image.

  The X-ray CT apparatus 100 irradiates X-rays while rotating the X-ray tube 2 and the X-ray detector 3 around the subject 6, collects X-rays transmitted through the subject 6 with the detector 3, Based on the detected data, the image processing apparatus 10 performs a reconstruction calculation to display a tomographic image, a 3D image, and the like.

  First, an outline of the X-ray CT apparatus 100 according to the present embodiment will be described. FIG. 2 is a block diagram showing the data flow of the present invention. Reference numeral 14 denotes a large-capacity memory which can be mounted so that memory addresses can be divided and stored in a matrix for each slice and scan and can be freely accessed from the image processing apparatus 10. As a mounting method, a memory arranged in parallel so as to have a storage capacity determined from the number of scans, the number of slices of the detector, and the number of patients, or another mass storage device in place thereof is used.

  Reference numerals 8 and 9 denote data transmission systems. The RAW data obtained from the detector 3 is the rotation disk angle information obtained from the rotation disk angle detector 15 (FIG. 8), and the projection number / slice obtained from the X-ray scanner control circuit 16. A header including a number / scan number is added, and data is transmitted to the image processing apparatus 10. The format of the transmission data is shown in FIG.

  The image processing apparatus 10 stores the raw data in the large-capacity memory 14 by dividing the memory address into a matrix using the projection number, slice number, and scan number of the header of the transmitted data. The storage in this large capacity memory is shown in FIG. Subsequently, the image processing apparatus 10 reads out the image data from the memory only when the slice number / scan number corresponds to the number determined in advance in the imaging condition, performs the reconstruction calculation, and monitors 11 while thinning the image. To display. FIG. 5 shows reading from a large-capacity memory.

  At the same time, based on the rotating disk angle information, RAW data at an arbitrary fixed angle specified by the operator under the shooting conditions, such as 90 ° for the head protocol and 0 ° for the chest protocol, is read and moved. A reconstruction calculation is performed from information such as the amount of movement of the bed 7 and the traveling direction, and a pseudo scanogram image is displayed.

  After scanning, when the operator designates the region of interest and slice thickness, 2D / 3D display, and post-reconstruction processing on the pseudo scanogram image, the image processing device determines the necessary slice number and scan number, and the large capacity The RAW data stored in the memory is freely read out, and a necessary reconstruction calculation is performed to display a detailed image.

  In addition, when the examination is completed or the next patient examination is started, the operator designates a necessary range on the pseudo scanogram image, so that a specific scan number and RAW data stored in the large-capacity memory are selected. Only the data corresponding to the slice number can be stored in the storage device 13 such as a hard disk or an optical disk, and the data can be read again later to observe the image. Since all data is not saved, the storage area of the storage device 13 can be saved. FIG. 6 shows a block diagram of the image processing apparatus, and FIG. 7 shows a flowchart of the operation.

  Next, a method for reconstructing a pseudoscanogram image will be described. As shown in FIG. 10, when a pseudo-scanogram image is reconstructed from RAW data of volume scan, a gap is generated in a series of RAW data depending on the relationship between the number of slices and a helical pitch. Therefore, an interpolation operation corresponding to each pitch is required. The helical pitch is a movable couch travel distance per scan rotation with respect to the slice thickness. In the following description, for the sake of simplicity, the case of representative helical pitches 3, 5, and 7 will be described as an example for an X-ray CT apparatus having four slices.

First, it is assumed that the moving bed traveling direction and the helical pitch information have been acquired as pre-processing of the calculation, and the image inversion processing is completed so that the image display direction is constant vertically and horizontally regardless of the traveling direction of the movable bed. It shall be. Hereinafter, each pitch will be described with reference to FIG. Here, φ is the rotation disk angle (constant), j is the channel number (1 count), m is the scan number (1 count) to be added for each rotation, n is the slice number (1 count), and the raw data is four-dimensional. This is expressed as a matrix Dφ _{, j, m, n} . Further, the raw data after the interpolation array is expressed as a two-dimensional matrix G _{j, z where z} is the position in the body axis direction (1 addition).
(1) Case of Helical Pitch 3 Since RAW data for one pitch overlaps, RAW data at a fixed angle is extracted from the slices excluding the fourth slice and arranged.

と書き表される。
（２）ヘリカルピッチ５の場合
一定角度のＲＡＷデータにおいて４ピッチごとに1ピッチ分の間隙が生じてしまうため、一定角度のＲＡＷデータのみでは画像を再構成できない。そこで、１８０°反対側からの投影データである対向データを利用して補間演算を行う。図１１に示すように、間隙部分を補間するためにスライス２、３の対向データを用いる。
補間データG_{i j,z}は、

ここで、Gi j,zは対向データから導出したことにより鏡像になっているので、画像反転処理を加える。 RAW data G _{j, z} after interpolation array is

Is written.
(2) Case of Helical Pitch 5 A gap corresponding to one pitch is generated for every four pitches in the RAW data at a constant angle, so that an image cannot be reconstructed only with the RAW data at a constant angle. Therefore, the interpolation calculation is performed using the opposing data that is the projection data from the opposite side of 180 °. As shown in FIG. 11, the opposing data of slices 2 and 3 are used to interpolate the gap portion.
The interpolation data G _{ij, z} is

Here, Gi j, z is a mirror image obtained by being derived from the opposing data, and therefore image inversion processing is added.

と書き表される。 Interpolated data G _i ′ _{j, z} after image inversion processing is expressed as follows:

Is written.

と書き表される。
（３）ヘリカルピッチ７の場合
（２）の場合と同様に、４ピッチごとに３ピッチ分の間隙が生じてしまうため、対向データを利用して補正処理を行う。 RAW data G _{j, z} after interpolation array is

Is written.
(3) Case of Helical Pitch 7 As in the case of (2), a gap corresponding to 3 pitches occurs every 4 pitches, so that correction processing is performed using the facing data.

ここで、（２）の場合と同様にG_{i j,z}は対向データから導出したことにより鏡像になっているので、画像反転処理を加える。 The interpolation data G _{ij, z} is

Here, as in the case of (2), G _{ij, z} is a mirror image by being derived from the opposing data, and therefore image inversion processing is added.

と書き表される。 Interpolated data G _i ′ _{j, z} after image inversion processing is expressed as follows:

Is written.

と書き表される。 RAW data G _{j, z} after interpolation array is

Is written.

  By performing the back projection operation on the RAW data after the interpolation array obtained as described above, pseudo scanogram images can be obtained for the helical pitches 3, 5, and 7 in the X-ray CT apparatus having four slices. Furthermore, if this calculation method is applied, a pseudo scanogram image can be reconstructed with respect to an arbitrary number of slices and a helical pitch.

この関数は一意的な関係にあるので、m,nはzによって特定することができ、

と書き表すことができる。 Finally, a method for designating a region of interest in a pseudoscanogram image will be described. This is because the position z in the body axis direction of the RAW data G _{j, z} after interpolation array, the scan number m, and the slice number n are related in the reconstruction operation of the pseudo scanogram image described above. It can be realized using. In the interpolation array process, z is expressed as a function of m and n as shown in the following equation.

Since this function has a unique relationship, m and n can be specified by z,

Can be written as:

  However, since the scan number / slice number associated with the position in the body axis direction is different at each pitch, a reference table is created so that information associated with each pitch can be referred to. By doing in this way, the number of channels and the position in the body axis direction are calculated by inversely converting the coordinate data of the part and slice thickness specified on the pseudo-scanogram image into the coordinates on the raw data after the interpolation arrangement, From there, the associated scan number and slice number can be determined.

  By performing arbitrary 2D / 3D processing instructed by the operator, post-reconstruction processing, and the like on the RAW data specified in this way, an image can be observed freely. This process itself can be applied to RAW data stored in a storage device such as a hard disk, and can also be applied to a device that does not have a large-capacity memory.

  The specification of the RAW data is not limited to use for image processing, and can be used for storing only specific RAW data in a storage device. FIG. 12 is an explanatory diagram for designating the region of interest in the pseudoscanogram image.

  As described above, with the X-ray CT apparatus 100 according to the present embodiment, it is possible to easily perform image operations in volume scanning in which a large amount of data is generated. Since the images can be observed at regular intervals during the volume scan, the same diagnosis as before can be performed while reducing the burden on the operator.

  In addition, ineffective exposure of the subject can be reduced if planning and imaging are performed simultaneously using a pseudoscanogram by volume scanning instead of planning by scanogram.

  Furthermore, when the region of interest and slice thickness, 2D / 3D display, and post-reconstruction processing are specified in the pseudo-scanogram image after the scan is completed, an image reconstructing the region is displayed and can be observed in detail. In this way, a large amount of scanned images obtained by volume scanning etc. can be observed and stored only by the operator's need, so there is no need to be aware of the operation of a large amount of image data, and there is no burden on the operator. .

  Further, since specific RAW data can be designated from the pseudo scanogram image and stored in the storage device, the storage area can be saved.

1 is a configuration diagram of an X-ray CT apparatus according to an embodiment of the present invention. FIG. 6 is a block diagram illustrating a data flow according to an embodiment of the present invention. It is a figure which shows data transmission format concerning one Embodiment of this invention. FIG. 5 is a diagram illustrating data storage in a large-capacity memory according to an embodiment of the present invention. FIG. 6 is a diagram illustrating data reading from a large-capacity memory according to an embodiment of the present invention. 1 is a block diagram showing an X-ray CT apparatus according to an embodiment of the present invention. It is a flowchart which shows operation | movement concerning one Embodiment of this invention. It is a figure which concerns on one Embodiment of this invention and shows turntable angle information. It is a figure which shows the data of 1 image concerning one Embodiment of this invention. It is a figure which concerns on one Embodiment of this invention and shows RAW data and a helical pitch. It is a figure which shows the interpolation calculation of a pseudo scanogram concerning one Embodiment of this invention. It is a figure which shows designation | designated of the region of interest in a pseudo scanogram image concerning one Embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 100 ... X-ray CT apparatus, 1 ... X-ray scanner, 2 ... X-ray tube, 3 ... X-ray detector, 4 ... Preamplifier, 5 ... Turntable, 6 ... -Subject, 7 ... movable bed, 8 ... data transmission system (transmitting device), 9 ... data transmission system (receiving device), 10 ... image processing device, 11 ... monitor, 12 ... Operation console, 13 ... Storage device, 14 ... Large capacity memory, 15 ... Rotary disk angle detector, 16 ... X-ray scanner control circuit

Claims (3)

Means for scanning the subject around the body axis in a designated body axis direction range of the subject and acquiring transmission X-ray data;
Storage means for temporarily storing the acquired transmission X-ray data;
Reconstruction means for intermittently reconstructing a tomogram based on transmission X-ray data corresponding to a predetermined time interval or a predetermined slice interval in the acquired transmission X-ray data;
Display means for displaying the reconstructed tomographic image;
An X-ray CT apparatus comprising: The storage means stores the acquired transmitted X-ray data in association with an angle around the body axis of the subject,
Means for reconstructing a pseudo-scanogram image of the subject using transmission X-ray data corresponding to a specified angle among the stored transmission X-ray data, and based on a user instruction input to the pseudo-scanogram image; Means for setting a region of interest; and means for reconstructing a second tomogram based on transmission X-ray data corresponding to the region of interest among the stored transmission X-ray data,
The X-ray CT apparatus according to claim 1, wherein the display unit displays the pseudo-scanogram image and the second tomographic image.   Means for setting a data recording area in the pseudo-scanogram image based on a user's instruction input; and means for recording transmission X-ray data corresponding to the data recording area in the stored transmission X-ray data. The X-ray CT apparatus according to claim 1 or 2, characterized by the above.

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