WO2003043499A1

WO2003043499A1 - X-ray ct device, and method for preparing tomographic image thereof

Info

Publication number: WO2003043499A1
Application number: PCT/JP2002/012063
Authority: WO
Inventors: Taiga Goto; Osamu Miyazaki
Original assignee: Hitachi Medical Corporation
Priority date: 2001-11-21
Filing date: 2002-11-19
Publication date: 2003-05-30
Also published as: JP2003153893A

Abstract

An X-ray CT device comprises a scanner including an X-ray source and an X-ray detector for detecting the X-ray irradiated on a body to be detected from the X-ray source and transmitted through the body and performing scanning by rotating the X-ray source and the X-ray detector around the axis of rotation relatively to the body an image processor for processing the data measured by the scanner and preparing a tomographic image, and a display device for displaying the tomographic image. The image processor comprises a plurality of re-configuration image preparing means of different re-configuration algorithms and a re-configuration selecting means for selecting the re-configuration image preparing means according to a preset condition, and prepares the tomographic image by the selected re-configuration image preparing means. Since there are provided the plurality of re-configuration image preparing means and the re-configuration selecting means, the tomographic image of a desired condition can be obtained by adequately selecting the re-configuration image preparing means corresponding to the purpose of the inspection, and preparing the tomographic image.

Description

Specification

X-ray CT apparatus and method for creating tomographic image thereof

The present invention relates to a computer tomography apparatus (X-ray CT apparatus) that obtains a tomographic image by performing image processing by a computer on measurement data obtained by detecting transmitted X-rays from a subject irradiated with X-rays. The present invention relates to an X-ray CT apparatus having a feature in reconstructing calculation of measurement data and a method of creating a tomographic image thereof. Background art

In the X-ray CT apparatus, an X-ray source and an arc-shaped detector pointing at the focal point of the X-ray source are arranged at positions facing each other with the subject interposed therebetween.

The X-rays from the X-ray source are collimated to form a fan-shaped X-ray beam, and this X-ray beam is applied to the imaging section of the subject to rotate the transmitted X-rays attenuated by the subject. The photographing operation is performed by measuring.

The measurement operation during the rotation of the scanner is performed at angular intervals of about 0.1 to 0.5 degrees, for example, to acquire projection data of about 600 to 1200 angles in total.

The detector is composed of a large number of detection elements, and the output of each element is collected as digital data by a measurement circuit, and data (views) for the number of elements is formed for each measurement angle (hereinafter, as described below). The configured measurement system for acquiring view data is called a scanner).

The view data measured by the scanner is transferred to an image processing device, subjected to pre-processing such as characteristic correction of a detection element, radiation quality correction and log conversion, and then reconstructed as tomographic image data by a reconstruction algorithm. You. Then, post-processing such as filtering is performed on the reconstructed image data to create a tomographic image, and the tomographic image is displayed on a display device.

The method of acquiring view data by the scanner includes fixing an object table on which an object is placed at the time of rotation of an X-ray source and a detector at an imaging position. There are known a normal scan in which scanning is performed while standing still, and a spiral scan in which the subject table is moved at the same time as the rotation of the X-ray source and the detector, that is, scanning is performed while moving the subject (Japanese Patent Laid-Open No. 2001-346794). No. gazette).

In addition, the detector has a single-row detector, and a single-slice X-ray CT apparatus that obtains a tomographic image by capturing one cross section (one slice plane) in one scan, 2. Description of the Related Art A multi-slice type X-ray CT apparatus having a row of detectors and capturing a large number of slice planes in one scan is known (Japanese Patent Application Laid-Open No. 2001-346794). As described above, there are various types of X-ray CT systems depending on the scanning method and the number of rows of detectors, and each type is applied according to the diagnostic application by taking advantage of the respective advantages. Then, a single reconstruction algorithm is used for the reconstruction operation for reconstructing the tomographic image data of these X-ray CT apparatuses. The reconstruction algorithm includes a filter-corrected backprojection method (described in pl07, pl26-pl27 of "Kindai Kagakusha: Image Processing Algorithm, First Edition, March 10, 1993") and a Fourier reconstruction method ("Kindai Kagakusha" : Image processing algorithm, described in pl07 of "March 10, 1993, first edition", 3D back projection method ("Modern Science Inc .: Image processing algorithm, first edition of March 10, 1993," described in pl55 to pl60 ), And a known reconstruction method such as a weighted spiral correction reconstruction method (Japanese Patent Laid-Open No. 2001-346794).

In particular, multi-slice X-ray CT systems, which are expected to become mainstream in the future, use the weighted spiral correction reconstruction method and the three-dimensional backprojection method, but these have advantages and disadvantages. is there.

In other words, the weighted spiral correction reconstruction method has a high calculation speed and a high measurement throughput, but has a large error. On the other hand, the three-dimensional backprojection method has a small error but a long calculation time, so that the measurement throughput is low. In X-ray CT imaging, high-speed imaging and high-speed calculation are required for examination patients and emergency patients, and high image quality is especially required for close-up inspection patients, so only a single reconstruction algorithm is used. In some cases, it was not possible to obtain a tomographic image under desired conditions.

The present invention has been made in view of such circumstances, and has as its object to provide an X-ray CT apparatus that can obtain a tomographic image under desired conditions. Disclosure of the invention

In order to achieve the above object, an X-ray CT apparatus according to the present invention comprises: an X-ray source; and an X-ray source. An X-ray detector for detecting X-rays transmitted through the subject, and scanning the X-ray source and the X-ray detector around the subject relative to the subject. An X-ray CT apparatus, comprising: a scanner that processes the data measured by the scanner to create a tomographic image; and a display device that displays the tomographic image, wherein the image processing apparatus includes: A plurality of reconstructed image creating means having different reconstruction algorithms; and a reconstructing selecting means for selecting the reconstructed image creating means in accordance with preset conditions. Is created. The preset condition is at least one of a scan condition of the scanner and / or a measurement parameter. Specifically, there are an imaging region, a measurement mode determined by a moving speed of the object table and an effective slice thickness, a region of interest, an exposure dose, and a reconstruction mode.

Preferably, the plurality of reconstructed image creating means are a first reconstructed image creating means having a high-speed reconstructing operation algorithm, and a high-precision reconstruction operation having higher accuracy than the first reconstructed image creating means. A second reconstructed image creating unit having an algorithm, and a reconstructed image creating unit having at least two different reconstructing algorithms. Create an image.

As one use mode of the X-ray CT apparatus, a region of interest is set in an image created by the first reconstructed image creating unit, and the set region of interest is locally set by the second reconstructed image creating unit. By creating an image and replacing the region of interest of the image created by the first reconstructed image creating unit with the local image, only the region of interest can be a high-definition image, and diagnostic performance can be enhanced. Can be.

Also, a region of interest can be set in the image created by the first reconstructed image creating unit, and a reconstructed image can be created from the set region of interest by the second reconstructed image creating unit. Further, a third reconstructed image creating means having a reconstructing algorithm whose reconstruction operation is faster than the first reconstructed image creating means is provided. The reconstructed image created by the reconstructed image creating means can be displayed on the display device as a preview image.

Furthermore, the plurality of reconstructed image creating means assigns priorities to a plurality of images having different effective fields of view and image sizes according to reconstruction accuracy, and replaces or assigns weights according to the priorities. It is also possible to set a local region of the set tomographic image on the display image and create a reconstructed image with the set local region as an effective field of view. In addition, the tomographic image creating method of the present invention includes: an X-ray source; and an X-ray source that faces the subject with the X-ray source sandwiching the X-ray source. A scanner for scanning the X-ray source and the X-ray detector by rotating the X-ray source and the X-ray detector around a rotation axis relative to the subject; and data measured by the scanner. And a tomographic image creating method of displaying a tomographic image created by the image processing device on a display device, wherein the image processing device has a plurality of different reconstruction algorithms. A reconstructed image creating means, and a reconstructing selecting means for selecting the reconstructed image creating means according to a preset condition, wherein a step of taking a scanogram image; and taking a subject from the scanogram image. Setting a range, setting scan conditions and measurement parameters for creating a tomographic image, obtaining projection data with the scanner, and selecting the reconstruction based on the scan conditions and / or measurement parameters. Means for selecting one or more reconstructed image creating means from among the plurality of reconstructed image creating means; creating a tomographic image with the selected reconstructed image creating means; and displaying the tomographic image on the display device. And the step of displaying the information. As one use form of the tomographic image creating method, a step of setting a region of interest in a cross-sectional image displayed on the display device, and creating the set region of interest as a local image by the selected reconstruction selecting means Replacing the region of interest of the tomographic image with the local image, and synthesizing the replaced local image with the tomographic image. Replacing the region of interest with the local image, Can be used as high-definition images to enhance diagnostic performance. The selected reconstructed image creating means is a reconstructed image creating means having a high-speed reconstruction operation algorithm, and the another reconstructed image creating means is a reconstructed image having the high-speed reconstruction operation algorithm. This is a reconstructed image creating means having a high-precision reconstruction operation algorithm with higher accuracy than the composed image creating means.

As still another use form, a step of setting at least two or more regions of interest in the tomographic image displayed on the display device, and the setting performed by the reconstructed image creating means different from the selected reconstruction selecting means A step of creating a region of interest as a local image; and a step of replacing the region of interest in the tomographic image with the local image, and combining the replaced local image with the tomographic image. The selected reconstructed image creating unit is a reconstructed image creating unit having a fast reconstruction operation algorithm, and the another reconstructed image creating unit is more than a reconstructed image creating unit having the fast reconstruction operation algorithm. This is a reconstructed image creating means having a highly accurate high-precision reconstruction operation algorithm.

As another usage form, a step of setting at least two or more regions of interest in the tomographic image displayed on the display device, and the step of setting the reconstructed image by a reconstructed image creating means different from the selected reconstruction selecting means Creating a region of interest as a local image; and displaying the created local image on the display device. The selected reconstructed image creating means is a reconstructed image creating means having a fast reconstruction operation algorithm, and the another reconstructed image creating means is a reconstructed image creating means having the high speed reconstruction operation algorithm The local image is created by a reconstructed image creating unit having a high-precision reconstruction operation algorithm having higher accuracy than the reconstructed image creation unit having the high-accuracy reconstruction operation algorithm. The plurality of reconstructed image creating means have higher accuracy than a reconstructed image creating means having at least one or more high-speed reconstruction arithmetic algorithm, and a reconstructed image creating means having the high-speed reconstruction arithmetic algorithm. And a reconstructed image creating means having at least one high-precision reconstruction operation algorithm.

According to the present invention, a plurality of reconstructed image creating means having different reconstruction algorithms and a reconstructing selecting means for selecting the reconstructed image creating means according to a preset condition are provided. A corresponding tomographic image under desired conditions can be obtained. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a diagram showing the overall configuration of an X-ray CT apparatus including a tomographic image creating apparatus according to an embodiment of the present invention, and FIG. 2 is a diagram showing the configuration of a tomographic image creating apparatus of the X-ray CT apparatus shown in FIG. Fig. 3, Fig. 3 is a flowchart of tomographic image creation by the tomographic image creating apparatus shown in Fig. 2, Fig. 4 is an explanatory diagram showing a specific example of tomographic image creation by the flowchart of Fig. 3, and Fig. 5 is shown in Fig. 2. Flow chart of another tomographic image creation by the tomographic image creating apparatus, FIG. 6 is an explanatory diagram showing a specific example of tomographic image creating by the flowchart of FIG. 5, and FIG. 7 is another tomographic image creating by the tomographic image creating apparatus shown in FIG. FIG. BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following embodiments, the force s for describing the case where the present invention is applied to a helical scan type X-ray CT apparatus equipped with a multi-row (multi-slice) detector, and the present invention is not limited to this. However, the present invention can be applied to a spiral scan type X-ray CT device equipped with a single slice detector and a normal scan type X-ray CT device equipped with a single slice detector.

"System configuration"

FIG. 1 is a diagram showing an overall configuration of a spiral scan type X-ray CT apparatus including a multi-row detector to which an embodiment of the present invention is applied. The X-ray CT apparatus shown in FIG. 1 includes an X-ray generator 1 that generates X-rays, a collimator 2 that collimates the X-rays generated by the X-ray generator 1 and irradiates the object 4 with an X-ray. The scanner 13 includes an X-ray detector 5 for detecting X-rays transmitted through the subject 4. The scanner 13 is rotated around the subject 4 by the scanner driving device 6, and the subject 4 is placed on the subject table 3 such that the body axis of the subject substantially matches the center axis of the rotation. . The subject table 3 can be moved along the scanner rotation axis by a subject table moving mechanism (not shown), and is moved based on a control signal from a table controller (see FIG. 2). Operation signals such as scan conditions and measurement parameters set by the input device 11 are input to a system control device 23 for controlling the entire system, and generate operation signals of the scanner 13, and these signals are transmitted to the scanner controller 7 and an image to be described later. Input to the image processing device 9. The input device 11 includes input devices such as a keyboard, a mouse, and a touch panel (not shown). Further, input scan conditions and measurement parameters are stored in a memory provided in the input device 11 (FIG. 2). Parameter table).

The X-ray generator 1 is supplied with a high voltage for generating X-rays from a high-voltage generator 10. The scanner driving device 6, the object table moving mechanism (not shown) and the high voltage generator 10 are controlled by the scanner controller 7, and the collimator 2 is controlled by the collimator controller 8 included in the scanner controller 7. .

The detector 5 has a plurality of detection element rows arranged in the body axis direction of the subject 4 (the rotation center axis direction of the scanner 13). The detectors 5 arranged in a two-dimensional manner have a number of columns of, for example, 4 to 16 rows, and each of the detection element rows is composed of a plurality of detection elements.

Each of the detection elements generates an electric signal indicating the intensity of the incident X-ray beam and outputs the signal to the image processing device 9. These electric signals are data representing the attenuation of the X-ray beam transmitted through the subject 4 (hereinafter, referred to as projection data). The image processing device 9 includes a pre-processing arithmetic unit 91 that performs pre-processing such as characteristic correction of a detection element, line quality correction, and log conversion on the projection data, and a pre-processing data by a reconstruction algorithm. It is composed of a reconstruction operation device 92 for reconstructing as tomographic image data, and a post-processing operation device 93 for performing post-processing such as a filter on the reconstructed image data. The tomographic image reconstructed by the image processing device 9 is displayed on the display device 12.

《Configuration and operation of tomographic image creation device》

FIG. 2 is a diagram showing a configuration of a tomographic image creating apparatus of the X-ray CT apparatus shown in FIG. Measurement parameters (slice thickness, helical pitch, scan speed, scan range, effective field of view, voltage of X-ray tube of X-ray generator 1) during imaging and post-processing after imaging (Tube voltage), current (tube current), etc. and reconstruction parameters

(Reconstruction filter function, reconstruction slice interval, effective field of view, reconstruction algorithm, etc.) are stored in the parameter table 22. The measurement and reconstruction parameters from the parameter table 22 are transmitted to the subject tape via the system controller 23. Input to the table controller 25 that controls the scanner 3 and the scanner controller 7 that controls the scanner 13, the position and movement speed of the object table 3, the rotation speed (scan time) of the scanner 13, and the tube of the X-ray generator 1. It controls scan parameters such as current, tube voltage, and collimator 2 collimation width.

The scanner 13 and the sample tape holder 3 are controlled under the scanning conditions output from the input device 11 to perform a spiral scan. The data detected by the multi-row detector 6 of the scanner 13 by the spiral scan is stored in the projection data buffer memory 31 of the data collection device 30. This stored data is input to the pre-processing arithmetic unit 91 when there is no addition signal from the system control unit 23, and is added by the addition unit 32 when there is an addition signal from the system control unit 23, and It is input to the processing operation unit 91.

The addition signal means, for example, an addition command signal in a case where the number of rows of the multi-row detector is 16, and four rows are added to each other to obtain a 4-slice tomographic image. The preprocessing arithmetic unit 91 includes a logarithmic conversion unit 34 and a ring artifact correction unit 35, and the projection data output from the data collection unit 30 is used for various types of correction such as characteristic correction of a detection element and line quality correction. After performing the above correction processing, the data subjected to logarithmic conversion by the logarithmic conversion means 34 and the logarithmically converted data by the ring artifat correction means 35 are subjected to ring artifact correction processing to create preprocessed projection data, and Is input to the reconstruction processor 92 and stored in the pre-processing projection data memory 36. The reconstruction operation device 92 includes two reconstruction algorithms, a high-speed reconstruction means 37 having a high-speed reconstruction algorithm and a high-precision reconstruction means 61 having a high-precision reconstruction algorithm. These reconstructing means are configured by a reconfiguration switch A48 and a reconfiguration switch B49 based on conditions (such as measurement parameters) preset in the input device 11 by a switching signal generated by the system controller 23. Switch the selector switch to select.

When the high-speed reconfiguration means 37 is selected, the reconfiguration switch A48 is connected to the a side, and the reconfiguration switch 49B is connected to the c side. On the other hand, when the high-precision reconfiguration means 61 is selected, the reconfiguration switch A48 is connected to the b side, and the reconfiguration switch 49B is connected to the d side. In the case of normal scan, spiral correction is not necessary, The configuration switch A48 is connected to the b side and executes the following processing.

The high-speed reconstruction means 37 includes a spiral correction means 39 for performing a spiral correction using a weighted addition memory 38 in which a weighting function is stored, a rearrangement processing means 27, a reconstruction filter processing means 40, a two-dimensional reconstruction means 62, The high-precision reconstruction means 61 is composed of a rearrangement processing means 27, a reconstruction filter processing means 40, a cone angle correction means 41, a three-dimensional reconstruction means 42, and an image data memory 43.

The reason why the high-precision reconstruction means 61 does not perform the spiral correction is that the spiral correction is a process for interpolating the data obtained by the spiral scan into circular data by the normal scan. This is for dimensional reconstruction. In high-precision reconstruction such as three-dimensional reconstruction, a high-quality reconstructed image can be created without performing interpolation processing or correction processing by the helical correction.

The rearrangement processing means 27, the reconstruction filter processing means 40, and the image data memory 43 are common to the high-speed reconstruction means 37 and the high-precision reconstruction means 61.

The rearrangement processing means 27 is means for performing rearrangement from fan beam data to parallel beam data, and the reconstruction filter processing means 40 performs filter processing on the rearranged parallel beam data to reduce blur. It is a means to reduce it.

The image data memory 43 is a memory for storing reconstructed tomographic image data. When the high-speed reconstruction unit 37 is selected, the projection data from the pre-processing unit 91 is input to the spiral correction unit 39, and the spiral correction is performed using the weighting function stored in the weighted addition memory 38. The projection data corrected by the helical correction unit 39 rearranges the fan beam into a parallel beam by the rearrangement processing unit 27 and performs a filtering process on the next reconstruction filter processing unit 40 to reduce blur.

Then, two-dimensional reconstructed image data is created by the two-dimensional reconstructing means 62 using the projection data subjected to the blurring process, and stored in the image data memory 43.

On the other hand, when the high-precision reconstruction means 61 is selected, the projection data from the preprocessing arithmetic unit 91 is processed by the rearrangement processing means 27 and the reconstruction filter processing means 40 to rearrange the fan beams into parallel beams, respectively. Perform filter processing. The projection data subjected to this filter processing is used to correct the error due to the X-ray tilt angle The corrected projection data is used to generate three-dimensional reconstructed image data by the three-dimensional reconstruction means 42, and this is stored in the image data memory 43.

The two-dimensional or three-dimensional reconstructed image data created and stored in this way is used to create a two-dimensional or three-dimensional image by the post-processing operation device 93 and display the image on the display device 12.

The post-processing arithmetic unit 93 includes various processing means such as three-dimensional image processing, image analysis, and image filter processing, and performs processing in accordance with an operation command from the input device 11. The three-dimensional image processing means 45 described above uses a volume rendering method, a maximum intensity projection method, or the like to display a pseudo three-dimensional image. In order to perform the processing, the image filter processing means 47 performs processing for reducing noise and artifacts when they are large.

Note that the process of replacing the high-precision reconstructed image of the local portion of the reconstructed image obtained by the high-speed reconstructing means 37 described later with the reconstructed image obtained by the high-speed reconstructing means 37 includes post-processing operations. Performed by device 93.

In the X-ray CT apparatus having such a configuration, the scanner 13 is stopped, and the X-ray beam from the X-ray generator 1 is irradiated onto the imaging section of the object while moving the object table to capture a scanogram image. The imaging region of the subject is determined from the scanogram image, and the subject 4 is moved linearly with respect to the rotation axis while rotating the scanner 13 around the subject 4 with respect to the determined region. The X-ray tube 1 irradiates the subject 4 with X-rays having a three-dimensional spread from the X-ray tube 1 and detects X-rays transmitted through the subject 4 using the X-ray detectors 5 arranged two-dimensionally. . The detected data is subjected to various corrections to obtain projection data, and the projection data is used to create a tomographic image by the image processing device and display the tomographic image on a display device.

《Selection of reconstruction algorithm》

The reconstruction algorithm of the reconstruction processor of the image processing apparatus is selected by the following scan conditions, measurement parameters, and reconstruction modes set by the input device 11 in (1) to (5).

(1) Imaging site (2) Bed moving speed and effective slice thickness

(3) Designation of region of interest or non-region of interest

(4) Exposure dose

(5) Specifying the reconfiguration mode

(High-speed reconstruction mode, high-precision reconstruction mode, other modes)

The imaging conditions (scanning conditions, measurement parameters) and reconstruction modes described in (1) to (5) above and the reconstruction mode When input from the input device 11 before the start of imaging, the reconstruction used by the system controller 23 according to these input signals The mode is determined. In the case of FIG. 2, it is determined whether the mode is the high-speed reconstruction mode or the high-precision reconstruction mode. When the high-speed reconfiguration mode is selected, the reconfiguration switches # 48 and # 49 are switched to the high-speed reconfiguration means 37 (a side, c side). Switch A48 and reconstruction switch B49 are switched to the high-precision reconstruction means 61 side and d side).

Here, the selection of the reconstruction algorithm will be described with an example.

(a) Selection by reconstruction mode

When a high-precision reconstruction mode (high-quality mode) is input from the input device 11 as one of the reconstruction algorithm selection conditions, the high-precision reconstruction means 61 is selected via the system controller 23.

(b) Selection based on bed moving speed

Since the processing range of the high-precision reconstruction means 61 is narrower than that of the high-speed reconstruction means 37, the high-precision reconstruction means 61 can perform reconstruction even when performing a spiral scan at the set bed moving speed. In this case, a signal for selecting the high-precision reconfiguration means 61 is transmitted from the system controller 23 to the reconfiguration switch A48 and the reconfiguration switch B49.

(c) Selection by imaging site

The reconstruction algorithm is changed according to the area to be photographed. To be more specific, using the existing modes such as the head and abdomen, the high-precision reconstruction means 61 is used for the head, and the high-speed reconstruction is performed for the abdomen, using the existing modes such as the head and abdomen. Select means 37. As described above, the reconfiguration algorithm is selected by the system controller 23 according to the part, and a signal is sent to the reconfiguration switch A48 and the reconfiguration switch B49. Note that the high-speed reconstruction means 37 shown in FIG. 2 performs a weighted spiral correction re-run at a higher operation speed for a system with a relatively small X-ray beam inclination of about 4 or 8 rows in a multi-slice CT. A construction algorithm (spiral correction means 39, weighted addition memory 38) is used.

This weighted spiral correction reconstruction algorithm is based on the X-ray generator 1 shown in FIG.

Focus of X-ray tube (not shown) Force ^ Beam tilted in the irradiated _Z direction (direction of relative movement of the subject; also known as: body axis direction, slice direction, couch movement direction), and a beam parallel to the reconstructed image As a result, the reconstructed image data is created by interpolation, and reconstructed by the two-dimensional reconstruction algorithm (two-dimensional reconstruction means 62) used in the single-row X-ray detector CT (single-slice CT). .

The feature of the weighted spiral correction reconstruction algorithm is that interpolation can be performed using a weight function (weight function), so reconstruction can be performed in the same time as image reconstruction time in single-slice CT, and multi-slice CT The operation is the fastest among the reconstruction algorithms in. However, when the accuracy in the z direction is poor and the relative movement speed of the subject is high, the error increases.

In addition, the weighted spiral correction reconstruction algorithm allows the spiral pitch (the ratio of the distance the subject moves during one rotation of the scanner 13 to the distance between the detector rows) to be twice as large as the number of X-ray detector rows. (Japanese Unexamined Patent Publication No. 2001-346794), which is the fastest among the reconstruction algorithms in multi-slice CT and has a high throughput. If the above weighted spiral correction reconstruction algorithm is applied to a multi-slice CT using a 4-row X-ray detector, the number of rows is small and the effect of X-ray beam tilt is small, so there is little effect on image quality. Calculation and high throughput are possible.

Further, in a system in which the influence of the X-ray beam inclination of 16 rows or more is remarkable, a three-dimensional reconstruction algorithm, which is a high-precision reconstruction algorithm of the high-precision reconstruction means 61 shown in FIG. Note that the above three-dimensional reconstruction algorithm reconstructs each reconstruction point using only data that passes through or reappears at each reconstruction point. The calculation takes a lot of time. The reconstruction algorithm in multi-slice CT requires computation time and throughput is low, but image quality is good. In addition, when the imaging site is the heart, the change in the reconstructed image is larger than in other imaging sites due to the movement accompanying the pulse. Apply the configuration algorithm (cardiac synchronous reconstruction means). Therefore, the ECG-gated reconstructing means may be incorporated in the reconstruction calculation device shown in FIG.

As described above, the imaging region, the bed moving speed, the effective slice thickness, the region of interest, and the reconstruction mode are set by the input device 11 of FIG. 2, and the set measurement parameters are input to the system controller 23 and used. By appropriately selecting the reconstruction means to be performed, an optimal tomographic image corresponding to the purpose of the inspection can be obtained.

<< Example of creating a tomographic image >>

(1) Example of setting a region of interest in an image reconstructed by high-speed reconstruction means and reconstructing this region of interest by high-precision reconstruction means

Figure 3 shows a flowchart. The scanner 13 is stopped, and the X-ray beam from the X-ray generator 1 is applied to the imaging section of the object while moving the object table 3 to capture a scanogram image (step 51). The imaging range of the subject is set from the scanogram image. (Step 52). Then, measurement parameters for creating a tomographic image are set (step 53). The setting of the photographing range and the setting of the measurement parameters are performed by the input device 11. After these settings, a spiral scan is performed, projection data is collected by the data collection device 91, and various correction processes are performed by the preprocessing arithmetic device 91 to obtain preprocessed projection data. (Step 54).

Next, the system controller 23 determines whether to use the high-speed reconstruction means 37 or the high-precision reconstruction means 61 as the reconstruction means of the reconstruction operation device 92 based on the imaging region set before the imaging and the measurement parameters. to decide. In this example, since the high-speed reconstruction means 37 is used, tomographic image data is created by a high-speed reconstruction algorithm, and this tomographic image data is stored in the image data memory 43 and is processed by the post-processing arithmetic unit 93 as desired. The processed image is displayed on the display device 12 as a tomographic image (step 55).

The region of interest of the displayed image is set with the mouse or the like of the input device 11 (step 56), and the set region of interest is input to the reconstruction arithmetic unit 92 via the system controller 23. Since the reconstruction means in this case is reconstruction of the region of interest, high-precision reconstruction is performed. The configuration means 61 is selected. Then, the set region of interest is reconstructed using a high-precision reconstruction algorithm to create a high-quality local image. (Step 57). Finally, the region of interest in the tomographic image created by the high-speed reconstruction means is replaced by the local image by the post-processing arithmetic unit 93 (step 58).

Note that in order to set the region of interest, it is necessary to calculate the entire tomographic image (preview image) at high speed and display it on the display device 12. As a construction algorithm, there is a successive approximation method or a two-dimensional Fourier transform method.

Also, in the three-dimensional reconstruction algorithm, an algorithm speeded up by approximation or thinning may be used.

Thus, by using a high-speed algorithm to grasp the whole picture and a high-precision algorithm to grasp the details, compared with the case where the whole area is reconstructed by the high-precision algorithm, The processing speed becomes faster. In a high-speed algorithm, the helical pitch can be larger than that in the high-precision algorithm, so that a wider range of images can be generated with the same dose, and the effective dose is reduced. That is, according to the embodiment shown in FIG. 3, a high-accuracy tomographic image of the region of interest can be obtained, and a portion other than the region of interest is tomographic image corresponding to the purpose of the inspection at a high speed with a low exposure dose. An image can be obtained, and a tomographic image under desired conditions can be obtained.

FIG. 4 is an explanatory diagram of creating a tomographic image according to the flowchart of FIG. 3 described above. A region of interest is set in an image reconstructed by the high-speed reconstruction means, and a local image in the region of interest is precisely reconstructed by the high-precision reconstruction means. FIG. 8 is an explanatory diagram of a case where the local image reconstructed is replaced with a region of interest of the image reconstructed by the high-speed reconstruction means. The high-speed reconstruction algorithm 101 (the spiral correction means 39 including the weighted addition memory 38 in FIG. 2), the rearrangement processing means 27, the reconstruction filter processing means 40, and the two-dimensional reconstruction means 62) in the reconstruction arithmetic unit 92 provide: Reconstruct and create a tomographic image. Further, for the region of interest 103 where the artifact 102 occurs, the high-precision reconstruction algorithm 104 of the reconstruction operation device 92 (the rearrangement processing means 27, the reconstruction filter processing means 40, the cone angle correction means 41 and Artifacts using three-dimensional reconstruction A local image 106 in which 102 does not occur is created. Then, the region of interest 103 is replaced with the local image 106 by the post-processing arithmetic unit 93, and a high-quality tomographic image with few artifacts 102 can be created as the composite image 105 in the region of interest 103 at high speed.

Here, the local image is an image obtained by reconstructing a part of the preview image created first, and is reconstructed by reducing the image size and the effective visual field size.

In this case, if one of the image size and the effective visual field size (the vertical and horizontal sizes of the image) is determined, the other is also determined. The method of determination can be determined from the selected local area using an input device such as a mouse in the preview image displayed on the screen, or entered manually using a touch panel or keyboard. Good. Since the algorithm used needs to reconstruct the local image with higher accuracy, it is necessary to use a higher-precision reconstruction algorithm than the single preview image. At present, a three-dimensional reconstruction algorithm is equivalent.

As described above, according to the embodiments of FIGS. 3 and 4, the input device 11 and the display device 12 shown in FIG. , That is, a tomographic image having a highly accurate local image can be obtained.

In this case, even if the calculation time of the high-precision reconstruction algorithm is enormous, it is limited to a narrow region such as a local region, so that it is possible to achieve a higher speed than when reconstructing the entire image. Become.

(2) Example of determining a region of interest based on measurement parameters, and simultaneously performing parallel reconstruction for high-speed reconstruction and high-precision reconstruction

Figure 5 shows the flowchart. The reconstruction algorithm of the tomographic image creation method according to the flowchart of FIG. 5 is determined based on the set measurement parameters. Here, the scanning of the scanogram (step 71), the determination of the imaging range (step 72), the setting of the measurement parameters (step 73), and the spiral scan (step 75) are performed in accordance with the embodiment shown in FIG. Is the same.

The determination of the reconstruction algorithm is performed based on the measurement parameters (step 74). Here, the reconstruction algorithm is used for the moving speed of the object table 3, which is one of the measurement parameters. The algorithm shall be determined. Since a high-speed algorithm such as the weighted spiral correction method can increase the moving speed of the subject table 3, when the moving speed of the subject table is set to high, the moving speed of the subject table 3 is applied by the system controller 23. The range is wide, the high-speed reconstruction means 37 is selected (step 76), and a high-precision algorithm such as three-dimensional reconstruction can reduce the moving speed of the object table 3, so that the moving speed of the object table 3 can be reduced. If the speed is low, the application range of the moving speed of the object table 3 is narrow, but the high-precision reconstruction means 61 having higher image quality is selected and reconstruction is performed (step 77), and a tomographic image is created. You.

Then, the obtained local images are combined by the post-processing arithmetic unit 93 to create a tomographic image (step 78). In addition, a high-speed and high-precision reconstructed algorithm is simultaneously processed in parallel, so that a high-speed and high-precision tomographic image suitable for preset conditions can be obtained.

Next, FIG. 6 is a diagram showing a specific application example in which a tomographic image is created according to the flow of FIG. 5, which is an embodiment of the present invention. In the application example shown in FIG. 6, it is an explanatory diagram of a method of setting a plurality of regions of interest and obtaining a plurality of local images by a plurality of high-precision reconstruction operations.

FIG. 6 shows an example in which a region of interest (local region) is known before reconstruction. If the region of interest (the region reconstructed with high image quality) is known in advance, the region is input in advance, and the region is divided into the region of interest and other regions. Then, the region of interest is created as a new image by a high-precision reconstruction algorithm. The other regions are reconstructed by the fast reconstruction algorithm, and after this reconstruction, the reconstructed images are combined (replace the region of interest) to create the final reconstructed image.

Then, for the preset region of interest A113 and other non-interest regions, the region of interest A113 uses the high-precision reconstruction algorithm A111 to create a high-accuracy image A116 with few artifacts, Is used to create a high-speed image 119 using a high-speed reconstruction algorithm 117. By combining the obtained local images, a high-quality composite image 115 with little artifact in the region of interest is created at high speed. Furthermore, the region of interest A113 and the different region of interest B114 shown in FIG. A high-precision image B118 is obtained by the construction algorithm B112. As a result, it is possible to obtain a composite image 115 which is a tomographic image under desired conditions, that is, a tomographic image including a plurality of high-precision images A116 and B118, and a high-speed image 119 of the other non-interest area. Can be.

Here, the high-speed reconstruction algorithm 117, the high-precision reconstruction algorithm Alll, and the high-precision reconstruction algorithm B112 are executed by the reconstruction operation device 92 shown in FIGS. The region of interest A113 and the region of interest B114 are set by the input device 11 shown in FIGS.

Then, the composite image 115 is obtained by the post-processing operation device 93 shown in FIG. 1 and FIG.

In the embodiment shown in FIG. 6 as well, high-speed processing can be performed by performing reconfiguration simultaneously using a plurality of CPUs and ending the reconfiguration at the same time. In addition, priorities are assigned to images having different effective fields of view and image sizes created by a plurality of reconstruction algorithms according to reconstruction accuracy, and replaced or weighted and added according to the priorities. As a result, diagnosis can be performed with an optimal image corresponding to the purpose of the inspection.

(3) Example of obtaining multiple local images by performing high-precision reconstruction operation on multiple set regions of interest

Figure 7 shows the flowchart.

In the tomographic image creation method shown in FIG. 7, a plurality of reconstructions are performed by the system controller 23 according to the conditions input in advance for the preset conditions, that is, the region divided into the region of interest and the other region. The algorithm is selected simultaneously (step 84) and executes a plurality of fast and high precision reconstruction algorithms of the reconstruction unit 92 (steps 86 and 87). Then, a tomographic image is created by combining a plurality of local images obtained at the same time by the post-processing arithmetic unit 93 (step 88).

Here, the scanning of the scanogram (step 81), the determination of the shooting range (step 82), and the spiral scan (step 85) are the same as those in the flowchart of FIG. That is, determining the shooting range (step 82) and setting the measurement parameters (step 83) The plurality of regions of interest are determined by the input device 11, and the corresponding reconstruction algorithm is selected and executed by the system controller 23 (step 84). As shown in FIG. 7, a plurality of local images can be simultaneously created by a plurality of reconstruction algorithms, so that tomographic images under desired conditions, that is, a plurality of highly accurate tomographic images corresponding to the purpose of the inspection, can be obtained. A tomographic image can be obtained at high speed.

Although the embodiments of the present invention have been described and illustrated in detail, they are intended only for explanation and illustration, and are not intended to limit the scope of the present invention. For example, in the above embodiment, the reconstruction algorithm is determined according to the bed moving speed in the measurement parameters, but there is a method of determining the reconstruction algorithm according to the slice thickness.

Further, in the embodiment, an example using two types of the high-speed reconstruction algorithm and the high-precision reconstruction algorithm has been described. However, the present invention is not limited to the combination of these, and the high-speed high-speed Three or more types of reconstruction algorithms such as a reconstruction algorithm, a high-precision high-precision reconstruction algorithm, and a reconstruction algorithm effective for reducing exposure may be combined. Further, the X-ray tube used in the X-ray CT apparatus including the tomographic image creation device of the present invention is one embodiment of the X-ray source, and is not limited to the X-ray tube, but may be a radiation source (radioisotope) or the like. However, it is clear that a similar effect can be obtained. Industrial applicability

As described above, according to the X-ray CT apparatus and the tomographic image creating method thereof according to the present invention, the image processing apparatus for creating the tomographic image includes a plurality of reconstructed image creating means having different reconstruction algorithms, A reconstructing selection means for selecting a reconstructed image creating means in accordance with the set conditions, so that a reconstructing algorithm suitable for creating a required image from among the plurality of reconstructed image creating means is provided. Since the constituent image creating means can be selected, an optimal tomographic image corresponding to the purpose of the inspection can be obtained.

Claims

The scope of the claims

1. an X-ray source; and an X-ray detector that detects the X-rays that are emitted from the X-ray source onto the subject and transmitted through the subject, A scanner for rotating the X-ray source and the X-ray detector around the orbit relative to the subject for scanning, and processing data measured by the scanner to form a tomographic image. An X-ray CT apparatus, comprising: an image processing device to be created; and a display device to display the tomographic image.

The image processing apparatus further includes: a plurality of reconstructed image creation units having different reconstruction algorithms; and a reconstruction selection unit that selects a reconstructed image creation unit according to a preset condition. An X-ray CT apparatus, wherein a tomographic image is created by creating means.

2. The X-ray CT apparatus according to claim 1, wherein the preset condition is at least one of a scan condition of the scanner and Z or a measurement parameter.

3. The X-ray CT apparatus according to claim 1, wherein the preset condition is an imaging part.

4. The X-ray CT according to claim 1, wherein the preset condition is a measurement mode determined by a moving speed of the object table and an effective slice thickness.

5. The X-ray CT apparatus according to claim 1, wherein the preset condition is a region of interest.

6. The X-ray CT apparatus according to claim 1, wherein the preset condition is an exposure X-ray dose.

7. The X-ray CT apparatus according to claim 1, wherein the preset condition is a reconstruction mode.

8. The plurality of reconstructed image creating means includes a first reconstructed image creating means having a high-speed reconstruction operation algorithm, and a high-precision reconstruction operation algorithm having higher accuracy than the first reconstructed image creating means. With the second reconstructed image creating means 2. The X-ray CT apparatus according to claim 1, further comprising means for creating reconstructed images of at least two or more different reconstruction algorithms.

9. A region of interest is set in the image created by the first reconstructed image creating means, and a local image is created from the set area of interest by the second reconstructed image creating means. 9. The X-ray CT apparatus according to claim 8, wherein a region of interest of the image created by the constituent image creating means is replaced with the local image.

10. A region of interest is set in the image created by the first reconstructed image creating means, and the set region of interest is created by the second reconstructed image creating means to create a reconstructed image. X-ray CT apparatus according to claim 8.

11. A third reconstructed image creating means having a reconstructing algorithm whose reconstructing operation is faster than the first reconstructed image creating means is provided, and the reconstructed image created by the third reconstructed image creating means is provided. 9. The X-ray CT apparatus according to claim 8, wherein an image is displayed on the display device as a preview image.

12. A means for prioritizing a plurality of images having different effective visual fields and image sizes in the plurality of reconstructed image creating means according to reconstruction accuracy, replacing the images according to the priority order, or adding weights is provided. X-ray CT according to claim 1, characterized in that:

13. The method according to claim 1, further comprising means for selecting a local area of the reconstructed tomographic image, and means for creating a reconstructed image using the selected local area as an effective field of view. X-ray CT device.

14. The X-ray CT apparatus according to claim 1, further comprising means for selecting a local image on a display image displayed on the display device.

15. An X-ray source, and an X-ray detector that detects an X-ray that has been irradiated from the X-ray source onto the subject and transmitted through the subject, facing the X-ray source with the subject sandwiched therebetween. A scanner for rotating the X-ray source and the X-ray detector relative to the subject around an orbital axis and scanning, and processing data measured by the scanner to create a tomographic image And a tomographic image creating method for displaying a cross-sectional image created by the image processing device on a display device, comprising:

The image processing apparatus may generate a plurality of reconstructed images having different reconstruction algorithms. Means, and a reconstruction selecting means for selecting a reconstructed image creating means according to a preset condition,

Taking a scanogram image;

A step of setting an imaging range of the subject from the scanogram image; a step of setting scan conditions and measurement parameters for creating a tomographic image;

Obtaining projection data with the scanner;

Selecting one or more reconstructed image creating means from the plurality of reconstructed image creating means by the reconstruction selecting means according to the scan conditions and / or measurement parameters;

Creating a tomographic image with the selected reconstructed image creating means, and displaying the tomographic image on the display device;

A tomographic image creation method characterized by comprising:

16. setting a region of interest in the tomographic image displayed on the display device; and creating the set region of interest as a local image by the selected reconstruction selecting means;

Replacing the region of interest of the tomographic image with the local image, and combining the replaced local image with the tomographic image;

16. The tomographic image creation method according to claim 15, comprising:

17. The selected reconstructed image creating means is a reconstructed image creating means having a fast reconstructing operation algorithm, and the another reconstructed image creating means is a reconstructed image creating means having the fast reconstructing operation algorithm Reconstructed image creation means having a high-precision reconstruction operation algorithm with higher accuracy than means

17. The tomographic image creation method according to claim 16, wherein:

18. setting at least two or more regions of interest on the tomographic image displayed on the display device;

Creating the set region of interest as a local image by a reconstructed image creating means different from the selected reconstruction selecting means,

Replacing the region of interest of the tomographic image with the local image; Synthesizing an image and the tomographic image;

16. The tomographic image creation method according to claim 15, comprising:

19. The selected reconstructed image creating unit is a reconstructed image creating unit having a fast reconstruction operation algorithm, and the another reconstructed image creating unit is a reconstructed image creation unit having the fast reconstruction operation algorithm. Reconstructed image creation means having a high-precision reconstruction operation algorithm with higher accuracy than means

19. The tomographic image creation method according to claim 18, wherein:

20. setting at least two or more regions of interest in the tomographic image displayed on the display device;

Displaying the created local image on the display device;

16. The tomographic image creation method according to claim 15, comprising:

21. The selected reconstructed image creating unit is a reconstructed image creating unit having a fast reconstruction operation algorithm, and the another reconstructed image creating unit is a reconstructed image creation unit having the fast reconstruction operation algorithm. Reconstructed image creating means having a high-precision reconstruction operation algorithm higher in accuracy than the means, wherein the reconstructed image creation means having the high-accuracy reconstruction operation algorithm creates the local image. 21. The tomographic image creation method according to claim 20, wherein:

22. The plurality of reconstructed image creating units have a higher accuracy than a reconstructed image creating unit having at least one or more fast reconstruction algorithm, and a reconstructed image creating unit having the fast reconstruction algorithm. Reconstructed image creating means having at least one or more high-precision reconstruction algorithm,

16. The tomographic image creating method according to claim 15, comprising: