JP2009082250A - X-ray ct apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an X-ray CT apparatus which displays a tomographic image by performing image reconstruction on the tomographic image with sufficient density resolution and high spatial resolution. <P>SOLUTION: The X-ray CT apparatus (100) is equipped with an X-ray generating device (21), a first multi-row X-ray detecting device (KD) which is provided to face the X-ray generating device (21) and has first spatial resolution in a prescribed direction, a second multi-row X-ray detecting device (MD) which is provided to face the X-ray generating device and has second spatial resolution, that is different from the first spatial resolution, in a prescribed direction, and an image reconstruction part (33) which performs the image reconstruction on the tomographic image having the sufficient density resolution and the sufficient spatial resolution in accordance with output data of the first and second multi-row X-ray detecting devices. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to medical X-ray CT (Computed
(Tomography) X-ray CT apparatus technology.

  As shown in FIG. 3, the conventional multi-row X-ray detector X-ray CT apparatus uses a multi-row X-ray detector having a structure of a scintillator SD and a photodiode PD. The scintillator captures almost 100% of X-rays and emits light. However, the efficiency of conversion into light from the photodiode is said to be about 60% because of the efficiency with which the light from the scintillator reaches the photodiode. In addition, to increase the resolution of tomographic images, it is necessary to miniaturize the multi-row X-ray detector. For example, assume that a multi-row X-ray detector having a pitch of 0.3 mm in the channel direction and the row direction is made. Crosstalk between the multi-row X-ray detector channels is suppressed between the multi-row X-ray detector channels by a light reflector called a reflector. The X-ray detector efficiency of the multi-row X-ray detector is 0.1 mm / 0.3 mm = 1/3, that is, 1/3 becomes a reflector because the width of the reflector is about 0.1 mm. Inefficiency. In this respect, the multi-row X-ray detector using the scintillator / photodiode has a problem that it is not suitable for high resolution.

JP 2002-330955 A

However, in a multi-row X-ray detector X-ray CT apparatus or an X-ray CT apparatus using a two-dimensional X-ray area detector typified by a flat panel, there is a great demand for high spatial resolution. Evaluation of stenosis of coronary arteries (Stenosis)
Evaluation) requires a high spatial resolution on the order of 0.2 mm. Further, in the examination of the lung field, high spatial resolution at a level where the alveoli can be seen is required. Furthermore, high spatial resolution is also required for examinations of the ossicles of the head.
However, the high resolution of the prior art has a problem in diagnostic applications because even if a tomographic image with a high spatial resolution can be displayed, a sufficient density resolution at the current level cannot be maintained. For this reason, it is desired that the CT apparatus of the new technology can reconstruct and display a tomographic image with higher spatial resolution while maintaining at least the current level of density resolution.

  Accordingly, an object of the present invention is to provide an X-ray for reconstructing and displaying a high spatial resolution tomographic image having a sufficient density resolution in various scans of an X-ray CT apparatus having a two-dimensional X-ray area detector. It is to provide a CT apparatus.

  The present invention uses a multi-row X-ray detector capable of providing sufficient spatial resolution and a multi-row X-ray detector capable of providing sufficient density resolution, and acquires X-ray projection data with each multi-row X-ray detector. When image reconstruction is performed from projection data based on a multi-row X-ray detector that can provide sufficient spatial resolution, a high spatial resolution tomographic image with high resolution can be obtained even in the details of the tomographic image. On the other hand, if image reconstruction is performed from projection data based on a multi-row X-ray detector that can provide sufficient density resolution, a tomographic image that can detect subtle changes in CT values such as lesions can be obtained. For this reason, by combining both of these projection data by weighted calculation processing, etc., by combining both tomographic images obtained by image reconstruction of the projection data by weighted calculation processing, etc., or overlapping and displaying them, It is possible to obtain a tomographic image with a high density resolution capable of expressing a lesion or the like on a tomographic image having a high spatial resolution to the details.

An X-ray CT apparatus according to a first aspect includes an X-ray generator, a first multi-row X-ray detector provided opposite to the X-ray generator and having a first spatial resolution in a predetermined direction, and an X-ray generator A second multi-row X-ray detector provided in a predetermined direction and having a second spatial resolution different from the first spatial resolution in a predetermined direction, a first multi-row X-ray detector and a second multi-row X-ray detector; And an image reconstruction unit that reconstructs a tomographic image based on the output data.
In the X-ray CT apparatus according to the first aspect, X-ray projection data from the first multi-row X-ray detector having high spatial resolution and X-ray projection from the second multi-row X-ray detector having different spatial resolutions. A tomographic image can be obtained based on the data.

In the X-ray CT apparatus according to the second aspect, the second multi-row X-ray detector is a detector having a density resolution higher than that of the first multi-row X-ray detector, and the first multi-row X-ray detector and the second multi-row X-ray detector. A row X-ray detector is provided in an overlapping manner.
In the X-ray CT apparatus according to the second aspect, for example, as shown in FIG. 4A or FIG. 10A, a plurality of multi-row X-ray detectors having different spatial resolutions are overlapped in the X-ray irradiation direction. X-ray projection data of a multi-row X-ray detector having a high spatial resolution and X-ray projection data of a multi-row X-ray detector having a high density resolution can be obtained simultaneously for the same region and the same range of the subject. Therefore, based on the X-ray projection data of the multi-row X-ray detector having a high spatial resolution and the X-ray projection data of the multi-row X-ray detector having a high density resolution simultaneously for the same part and the same range of the subject, A tomographic image with good spatial resolution and a tomographic image with good density resolution can be obtained.

In the X-ray CT apparatus of the third aspect, the first multi-row X-ray detector and the second multi-row X-ray detector are in close contact with each other. The row X-ray detector is provided in contact therewith.
In the X-ray CT apparatus according to the third aspect, when a plurality of multi-row X-ray detectors having different spatial resolutions are provided closely as shown in FIG. 4A or FIG. Since the positional relationship between the X-ray detector and the second multi-row X-ray detector in the channel direction or the column direction can be easily grasped, a process for synthesizing or overlapping each X-ray projection data or tomographic image Becomes easier.

In the X-ray CT apparatus of the fourth aspect, the first multi-row X-ray detector is made of a material having a low X-ray absorption coefficient, and the second multi-row X-ray detector is made of a material having a high X-ray absorption coefficient. X-rays configured and not absorbed by the first multi-row X-ray detector are detected.
In the X-ray CT apparatus according to the fourth aspect, when a plurality of multi-row X-ray detectors having different spatial resolutions are stacked, the multi-row X-ray detector on the X-ray focal side in the X-ray irradiation direction is X If the material does not have a small linear absorption coefficient, the multi-row X-ray detector on the X-ray detector side will not be sufficiently irradiated with X-rays. For this reason, the first multi-row X-ray detector needs to be a substance having a small X-ray absorption coefficient. Thereby, it is possible to sufficiently irradiate both the first multi-row X-ray detector and the second multi-row X-ray detector with X-rays.

In the X-ray CT apparatus of the fifth aspect, in the fourth aspect, the first multi-row X-ray detector is composed of a semiconductor detector, and the second multi-row X-ray detector is composed of a scintillator and a photodiode. .
In the fifth aspect, since the first multi-row X-ray detector is composed of a semiconductor detector, the detector has a high spatial resolution and has a low X-ray absorption coefficient. Thereby, even if the second multi-row X-ray detector exists on the rear surface in the X-ray irradiation direction, X-rays transmitted through the first multi-row X-ray detector are incident on the second multi-row X-ray detector. Become. When the second multi-row X-ray detector is composed of a scintillator and a photodiode, the scintillator having a large X-ray absorption coefficient receives X-rays and emits light, and the photodiode detects the emitted light. As a result, a plurality of multi-row X-ray detectors having a balanced X-ray absorption coefficient between the front surface and the rear surface in the X-ray irradiation direction and having a balanced spatial resolution between the X-ray spatial resolution and the X-ray density resolution are different. Can be realized.

The X-ray CT apparatus according to the sixth aspect further includes an image configuration unit that performs weighting processing on the output data of the first multi-row X-ray detector and the output data of the second multi-row X-ray detector.
The X-ray CT apparatus according to the sixth aspect provides the X-ray projection data of the first multi-row X-ray detector with high spatial resolution and the second multi-row X-ray with good density resolution for the same part and the same range of the subject. By combining the X-ray projection data of the detector with the X-ray projection data of the multi-row X-ray detector having a good density resolution, the S / N is further improved. Further, by adding the X-ray projection data of the second multi-row X-ray detector to the X-ray projection data of the first multi-row X-ray detector, the X-ray projection data of the multi-row X-ray detector having a good spatial resolution. Improves S / N.

In the X-ray CT apparatus according to the seventh aspect, the X-ray CT apparatus further includes only the first tomographic image based on only the output data of the first multi-row X-ray detector and the output data of the second multi-row X-ray detector. And a second tomographic image based on the display unit.
In the X-ray CT apparatus according to the seventh aspect, the X-ray projection data of the multi-row X-ray detector having a high spatial resolution and the X-ray projection of the multi-row X-ray detector having a good density resolution for the same part and the same range of the subject. Reconstruct the image separately from the data. Then, a tomographic image with good spatial resolution and a tomographic image with good density resolution can be reconstructed and displayed in an overlapping manner, and a tomographic image with good spatial resolution and density resolution can be displayed.

In the X-ray CT apparatus according to the eighth aspect, the imaging field of view of the first multi-row X-ray detector and the imaging field of view of the second multi-row X-ray detector are different from each other.
In the X-ray CT apparatus according to the eighth aspect, for example, the first multi-row X-ray detector is arranged at the center so that the center of the field of view becomes a field region with high spatial resolution, and the entire field of view of the image is large. A multi-row X-ray detector with a good density resolution can be arranged over the entire imaging field so that the imaging field region has a good density resolution.

In the X-ray CT apparatus according to the ninth aspect, in the first to eighth aspects, the X-ray generator and the second multi-row X-ray detector rotate around the rotation axis of the gantry, The line detector is formed in an annular shape with respect to the gantry rotation axis.
In the X-ray CT apparatus according to the ninth aspect, for example, as shown in FIG. 12 (a), the second multi-row X-ray detector includes an X-ray generator and a second multi-row X-ray detector, and a gantry rotation axis. It is configured as a third generation system that rotates around the center. The first multi-row X-ray detector is arranged as an annular fourth generation system. At this time, since the X-ray focal point of the third generation method rotates outside the imaging region of the third generation method, the multi-row X-ray detection for the fourth generation method which is the first multi-row X-ray detector. The X-ray focal point is rotating outside the instrument. The X-ray focal point of the X-ray generator of the third generation X-ray data acquisition system can also be used as the X-ray focal point of the X-ray generator of the fourth-generation multi-row X-ray detector. In this way, the X-ray tube and the first and second multi-row X-ray detectors can be configured in common.

According to a tenth aspect, in the X-ray CT apparatus according to the ninth aspect, the first multi-row X-ray detector is based on a tomographic image reconstructed with X-ray projection data from the second multi-row X-ray detector. The image reconstruction unit reconstructs X-ray projection data from the first multi-row X-ray detector based on the position information.
In the X-ray CT apparatus according to the tenth aspect, since the first multi-row X-ray detector is present in the imaging region of the second multi-row X-ray detector, the tomographic image of the second multi-row X-ray detector is used. Since the position of the first multi-row X-ray detector can be recognized and the X-ray focal point position is known, the geometric system of the X-ray projection data by the first multi-row X-ray detector, the imaging region and its image reconstruction Can be predicted. Thereby, the X-ray projection data of the first multi-row X-ray detector and the X-ray projection data of the second multi-row X-ray detector can be matched at the same position for the same part and the same range of the subject. .

In an eleventh aspect, in the X-ray CT apparatus according to any one of the first to tenth aspects, the X-ray CT apparatus further includes the first multi-row X-ray detector and the second multi-row X-ray detection. A dual energy image reconstruction unit that reconstructs a quantitative distribution tomographic image of a desired substance using an X-ray energy difference received by the device.
In the X-ray CT apparatus according to the eleventh aspect, as shown in FIG. 4 (a), FIG. 10 (a), FIG. 12 (a) or FIG. 16, multi-row X-ray detection with different spatial resolution in the X-ray irradiation direction. Since there are a plurality of detectors, the X-ray energy received by the first and second multi-row X-ray detectors varies. For example, a semiconductor X-ray detector on the front surface in the X-ray irradiation direction and a multi-row X-ray detector composed of a scintillator and a photodiode on the rear surface receive only the amount of X-ray energy absorbed by the semiconductor X-ray detector. X-ray energy is different. Dual energy imaging can be performed using the difference in X-ray energy. As a result, a tomographic image with a good spatial resolution, a tomographic image with a good density resolution, and a tomographic image showing the distribution of the composition of the substance can be reconstructed and displayed for the same part and the same range of the subject. At this time, since X-ray projection data with low X-ray energy and X-ray projection data with high X-ray energy can be collected simultaneously, a tomographic image with good S / N with little S / N artifact is obtained. be able to.

  According to the X-ray tomography apparatus of the present invention, it is possible to realize an X-ray CT apparatus that displays a tomographic image having sufficient spatial resolution and sufficient density resolution in various scans of the X-ray CT apparatus.

<Overall configuration of X-ray CT apparatus>
FIG. 1 is a configuration block diagram of an X-ray CT apparatus 100 according to an embodiment of the present invention. The X-ray CT apparatus 100 includes an operation console 1, an imaging table 10, and a scanning gantry 20.

  The operation console 1 includes an input device 2 such as a keyboard or a mouse that receives input from an operator, a central processing unit 3 that executes preprocessing, image reconstruction processing, postprocessing, and the like, and an X-ray projection collected by the scanning gantry 20. And a data collection buffer 5 for collecting data. Furthermore, the operation console 1 includes a monitor 6 that displays a tomographic image reconstructed from projection data, and a storage device 7 that stores a program, X-ray projection data, or X-ray tomographic image. The photographing condition input is input from the input device 2 and stored in the storage device 7. The imaging table 10 includes a cradle 12 on which the subject HB is placed and taken in and out of the opening of the scanning gantry 20. The cradle 12 is moved up and down and moved linearly by a motor built in the imaging table 10.

  The gantry rotating unit 15 of the scanning gantry 20 includes an X-ray tube 21, an X-ray controller 22, a collimator 23, a beam forming X-ray filter 28, a multi-row X-ray detector 24, and a data acquisition device (DAS: Data Acquisition System) 25. The multi-row X-ray detector 24 includes a multi-row X-ray detector KD having a high spatial resolution and a multi-row X-ray detector MD having a high density resolution. The data acquisition device 25 also includes a DAS 25K for the multi-row X-ray detector KD having a high spatial resolution and a DAS 25M for the multi-row X-ray detector MD having a high density resolution.

  The gantry rotating part 15 is rotatable via a bearing. When a rotation motor (not shown) rotates, the rotation is transmitted to the gantry rotation unit 15 via a belt (not shown), and the gantry rotation unit 15 rotates. Further, the scanning gantry 20 includes a rotating unit controller 26 that controls the gantry rotating unit 15 rotating around the body axis of the subject HB, and a control controller 29 that exchanges control signals and the like with the operation console 1 and the imaging table 10. It is equipped with. The beam forming X-ray filter 28 has the thinnest filter thickness in the X-ray direction toward the center of rotation, which is the imaging center, and the filter thickness increases toward the periphery so that X-rays can be absorbed more. X-ray filter.

  The central processing unit 3 includes a preprocessing unit 31, an image reconstruction unit 33, a projection data synthesis unit 35, a tomographic image synthesis unit 37, an X-ray detector fan conversion unit 38, and a dual energy image reconstruction unit 39. Yes.

  The preprocessing unit 31 performs offset correction logarithmic conversion and X dose correction inter-channel sensitivity correction on the X-ray projection data collected by the data collection device 25.

The image reconstruction unit 33 receives the projection data preprocessed by the preprocessing unit 31, and reconstructs an image based on the projection data. The projection data is converted into a frequency domain by a fast Fourier transform (FFT).
Transform) is performed, and the reconstruction function Kernel (j) is superimposed on it, and inverse Fourier transform is performed. Then, the image reconstruction unit 33 performs three-dimensional backprojection processing on the projection data obtained by superimposing the reconstruction function Kernel (j), and obtains a tomographic image (for each body axis direction (Z direction) of the subject HB. xy plane). The image reconstruction unit 33 stores the tomographic image in the storage device 7.

The projection data synthesizer 35 is configured to project the X-ray projection data D1 from the multi-row X-ray detector KD having a high spatial resolution of the multi-row X-ray detector 24 and the X-ray projection from the multi-row X-ray detector MD having a high density resolution. The data D2 is synthesized.
The tomographic image synthesis unit 37 detects a tomographic image Gh (x, y) reconstructed from only the X-ray projection data D1 of the multi-row X-ray detector KD with high spatial resolution, and multi-row X-ray detection with high density resolution. The tomographic image Gl (x, y) reconstructed from only the X-ray projection data of the device MD is synthesized.
That is, in order to process projection data from the multi-row X-ray detector KD having a high spatial resolution and the multi-row X-ray detector MD having a high density resolution, the synthesizing unit includes a projection data synthesizing unit 35 and a tomographic image synthesizing unit 37. And have.

The X-ray detector fan conversion unit 38 performs calculation related to collection of X-ray projection data related to a fourth generation (N-R method) X-ray detector in a 360 degree direction shown in FIG. That is, the projection data is converted in consideration of a virtual X-ray fan beam in which each view position of the X-ray focal point is a virtual X-ray detector.
The dual energy image reconstruction unit 39 uses an X-ray tube related to the distribution of atoms from projection data having a wide spectral range from low to high X-ray energy spectrum and projection data of a high X-ray energy spectrum. A two-dimensional distribution tomogram of voltage-dependent information, that is, a so-called dual energy imaging tomogram is reconstructed.

<Operation flowchart of X-ray CT apparatus>
FIG. 2 is a flowchart showing an outline of the operation of the X-ray CT apparatus of the present embodiment.
In step P1, the subject HB is placed on the cradle 12 and aligned. Here, the subject HB placed on the cradle 12 aligns the slice light center position of the scanning gantry 20 with the reference point of each part. Then, scout image collection is performed. In scout imaging, the X-ray tube 21 and the multi-row X-ray detector 24 are fixed, and X-ray projection data is collected while the cradle 12 is moved linearly. Here, the scout image is usually photographed at view angle positions of 0 degrees and 90 degrees. The right side in FIG. 2 is an example of a scout image 41 obtained by photographing the vicinity of the chest at 0 degrees. From this scout image 41, it is possible to plan a tomographic image capturing position.

  In step P2, the photographing condition is set while displaying the position and size of the tomographic image to be photographed on the scout image 41. The dotted line shown in the scout image 41 is the position of the tomographic image. In the present embodiment, a plurality of scan patterns such as a conventional scan, a helical scan, a variable pitch helical scan, and a helical shuttle scan are provided. The conventional scan is a scan method in which the X-ray tube 21 and the multi-row X-ray detector 24 are rotated to acquire X-ray projection data every time the cradle 12 is moved at a predetermined interval in the z-axis direction. The helical scan is an imaging method for collecting X-ray projection data by moving the cradle 12 at a constant speed while the X-ray tube 21 and the multi-row X-ray detector 24 rotate. The variable pitch helical scan is an imaging method for collecting X-ray projection data by changing the speed of the cradle 12 while rotating the X-ray tube 21 and the multi-row X-ray detector 24 as in the helical scan. In the helical shuttle scan, the cradle 12 is accelerated and decelerated while rotating the X-ray tube 21 and the multi-row X-ray detector 24 as in the helical scan, and reciprocally moves in the positive direction of the z-axis or the negative direction of the z-axis. In this scanning method, X-ray projection data is collected while collecting position information of z-direction coordinates. When these plural radiographs are set, X-ray dose information as a whole is displayed.

  In setting the tomographic image capturing conditions, the exposure of the subject HB can be optimized by using the X-ray automatic exposure mechanism of the X-ray CT apparatus 100. Further, in this tomographic imaging condition setting, for the so-called dual energy imaging tomographic imaging, the imaging condition of the X-ray tube 21 with a low X-ray tube voltage, for example, 80 kV, and the high X-ray tube voltage, for example, 140 kV, Shooting conditions can be set.

  In step P3 to step P9, tomographic imaging is performed. In step P3, X-ray data collection is performed. Here, when collecting data by helical scanning, the data collection operation of X-ray projection data is performed while rotating the gantry rotating unit 15 around the subject HB and moving the cradle 12 on the imaging table 10 linearly. I do. Then, the z-direction coordinates of the X-ray projection data DA (view, j, i) (j = 1 to ROW, i = 1 to CH) represented by the view angle view, the detector row number j, and the channel number i. A position Ztable (view) is added. As described above, in the helical scan, X-ray projection data collection within a constant speed range is performed.

In step P4, the preprocessing unit 31 performs preprocessing on the X-ray projection data DA (view, j, i) and converts it into projection data. Specifically, offset correction is performed, logarithmic conversion is performed, X-ray dose correction is performed, and sensitivity correction is performed.
In Step P5, beam hardening correction is performed. Here, beam hardening correction is performed on the preprocessed projection data DB (view, j, i). At this time, since independent beam hardening correction can be performed for each j column of the detector, if the tube voltage of the X-ray tube 21 varies depending on the imaging conditions, the difference in the X-ray energy characteristics of the detector for each column can be obtained. Can be corrected.

  In step P6, the image reconstruction unit 33 performs z filter convolution processing. Here, a z-filter convolution process for applying a filter in the z direction (column direction) is performed on the projection data DC (view, j, i) subjected to beam hardening correction.

In step P7, the image reconstruction unit 33 performs reconstruction function superimposition processing. That is, the Fourier transform (Fourier Transform) for transforming the X-ray projection data into the frequency domain is performed, the reconstruction function is multiplied in the frequency space, and the inverse Fourier transform is performed.
In step P8, the image reconstruction unit 33 performs a three-dimensional backprojection process. Here, three-dimensional backprojection processing is performed on the projection data DD (view, j, i) subjected to the reconstruction function superimposition processing to obtain backprojection data DE (x, y, z). The image to be reconstructed is a plane perpendicular to the z axis. A three-dimensional image is reconstructed on the xy plane. The following reconstruction area P is assumed to be parallel to the xy plane.

In step P9, the image reconstruction unit 33 performs post-processing. Post-processing such as image filter convolution, processed image space z-filter convolution processing, and CT value conversion is performed on the backprojection data DE (x, y, z) to obtain a tomographic image 42.
In step P10, the tomographic image reconstructed is displayed. As an example of the tomographic image 42, the tomographic image 42 is shown on the right side of FIG.

Next, the X-ray detector according to this embodiment will be described.

Here, the semiconductor detector includes a compound semiconductor detector such as a silicon semiconductor detector, a GZT (cadmium zinc tetramide) detector, and a CdTe detector. In either case, a detector with high spatial resolution can be realized, but in the following, description will be made using an example of a silicon semiconductor.
In FIG. 4A, a multi-row X-ray detector KD having a small X-ray absorption coefficient and a high spatial resolution is arranged upstream of the X-ray incident direction, and a large X-ray absorption coefficient and a high density resolution are provided downstream. This is an example in which a row X-ray detector MD is arranged. The acquisition area KA of the multi-row X-ray detector KD with high spatial resolution and the acquisition area MA of the multi-row X-ray detector MD with high density resolution are the same size.
FIG. 4B is a diagram showing a detector module in which detectors having different resolutions are combined.
FIG. 4C is a diagram showing a detector configured in the order of a silicon semiconductor X-ray detector SiD, a scintillator SD, and a photodiode PD in the X-ray irradiation direction.
FIG. 4D is a diagram showing a detector configured in the order of a silicon semiconductor X-ray detector SiD, a photodiode PD, and a scintillator SD in the X-ray irradiation direction.
FIG. 4 (e) is a diagram showing a detector in which a silicon semiconductor X-ray detector SiD is multilayered in the X-ray irradiation direction and is configured in the order of a scintillator SD and a photodiode PD.
FIG. 4F is a diagram showing a detector configured in the order of the scintillator SD, the photodiode PD, and the silicon semiconductor X-ray detector SiD in the X-ray irradiation direction.

Since the silicon semiconductor X-ray detector SiD is made of silicon, the X-ray absorption coefficient in the X-ray incident direction (X-ray linear
The absorption coefficient is small. Moreover, the conversion efficiency for converting X-rays into electrical signals may be large. FIG. 4B is an X-ray detector that combines the silicon semiconductor X-ray detector SiD shown in FIG. The silicon semiconductor X-ray detector SiD can manufacture a detector with high spatial resolution relatively easily.

In the configuration shown in FIG. 4C, a silicon semiconductor X-ray detector SiD having a high spatial resolution, a scintillator SD having a high density resolution, and a photodiode PD are stacked in order from the X-ray incident direction.
The silicon semiconductor X-ray detector SiD does not absorb much X-rays, but can detect X-ray signals with sufficient X-ray utilization efficiency. The scintillator / photodiode X-ray detector in the next layer absorbs X-rays with a large X-ray absorption coefficient. First, the scintillator SD emits light, and the emitted light passes through the scintillator SD to the photodiode PD. The photodiode PD converts the emitted light into an electrical signal.

In FIG. 4 (b), the area of one channel of the silicon semiconductor detector SiD corresponds to a quarter of the channel of the scintillator / photodiode X-ray detector, so that the openings in the channel direction and the column direction are ½. It consists of a width and is a high spatial resolution X-ray detector.
On the other hand, in the scintillator / photodiode X-ray detector, the X-ray light receiving area is four times that of the silicon semiconductor detector SiD, so the spatial resolution is slightly reduced, but X-rays are absorbed and converted into electrical signals with good density resolution. ing.
Since the scintillator SD has a large X-ray absorption coefficient, X-rays are absorbed almost 100% in the scintillator SD after passing through the silicon semiconductor detector SiD. For this reason, the photodiode PD is not damaged by X-rays, and the lifetime of the photodiode PD can be sufficiently secured.

In FIG. 4D, the silicon semiconductor detector SiD, the photodiode PD, and the scintillator SD are stacked in order from the X-ray incident direction.
When X-rays are incident, the scintillator SD emits more light on the front side in the X-ray incident direction. Therefore, in the configuration of FIG. 4D, more light emission can be efficiently converted into an electric signal by arranging the photodiode PD on the front side of the scintillator SD. That is, the configuration of FIG. 4D can reduce the light transmission loss due to light emission in the scintillator SD and can receive more light with the photodiode PD, compared to the structure of FIG.
However, the configuration of FIG. 4D is disadvantageous compared to the configuration of FIG. 4C in terms of performance degradation of the photodiode PD due to X-ray damage, that is, life.
In the case of FIGS. 4C and 4D as well, the order of X-ray data collection is that X-rays are absorbed by the silicon semiconductor X-ray detector SiD from the X-ray incident direction, and then X-rays are absorbed by the scintillator SD. Then, it is converted into an electric signal by the photodiode PD.

The next multi-row X-ray detector shows a case where the configuration order of the silicon semiconductor X-ray detector SiD and the scintillator SD is reversed as shown in FIG.
In FIG. 4F, X-rays enter the scintillator SD and the photodiode PD in order from the X-ray incident direction, and then the X-rays reach the silicon semiconductor X-ray detector SiD.

  In this case, since the scintillator SD section absorbs most of the X-rays because of the large X-ray absorption coefficient, the X-rays do not reach the silicon semiconductor X-ray detector SiD sufficiently, and the X / N ratio is good. Line data cannot be collected. Further, the incident X-ray causes X-ray scattering when passing through the scintillator / photodiode X-ray detector, and then reaches the silicon semiconductor X-ray detector SiD. This silicon semiconductor X-ray detector SiD cannot collect data with high spatial resolution due to scattered X-rays.

  In other words, a plurality of X-ray detectors having different spatial resolutions are arranged in such a manner that a multi-row X-ray detector KD having a small X-ray absorption coefficient and a high spatial resolution is arranged in front of the X-ray incident direction, and X-rays in the subsequent stage. It is preferable to arrange a multi-row X-ray detector MD having a large absorption coefficient and good density resolution. Further, since the multi-row X-ray detector KD with high spatial resolution has a small X-ray absorption coefficient, a plurality of layers may be arranged in the X-ray incident direction as shown in FIG.

Hereinafter, image reconstruction according to the present embodiment will be described using an example.
<Example 1>
In the first embodiment, X-ray projection data collected from each X-ray detector is an image reconstructed. That is, the X-ray CT apparatus 100 simultaneously collects X-ray data of the X-ray projection data of the multi-row X-ray detector KD having a high spatial resolution and the X-ray projection data of the multi-row X-ray detector MD having a high density resolution. . The image reconstruction unit 33 performs image reconstruction on each X-ray projection data separately, and displays a tomographic image with a high spatial resolution and a tomographic image with a high density resolution that have been reconstructed. At the same time, these tomographic images can be overlapped.

FIG. 5 is a flowchart of overlap display.
In step H1, a scan such as a conventional scan or a helical scan is started.
In step H2, the data acquisition buffer 5 collects two types of X-ray data by the multi-row X-ray detector KD having a high spatial resolution and the multi-row X-ray detector MD having a high density resolution. A dedicated data acquisition device (DAS) 25 is used for each of the multi-row X-ray detector KD having a high spatial resolution and the multi-row X-ray detector MD having a high density resolution. This is because a multi-row X-ray detector may have different numbers of channels, columns, and in some cases depending on the purpose and specifications. The data acquisition buffer 5 can be shared by the multi-row X-ray detector KD having a high spatial resolution and the multi-row X-ray detector MD having a high density resolution.
In step H3, the image reconstruction unit 33 reconstructs X-ray projection data D1 having a high spatial resolution. The X-ray projection data D1 having a high spatial resolution is preprocessed using the correction data for high spatial resolution, and image reconstruction suitable for the frequency domain is performed.
In step H4, the image reconstruction unit 33 reconstructs X-ray projection data D2 having a good density resolution. Since X-ray projection data with good density resolution has low spatial resolution, pre-processing is performed using correction data for low spatial resolution, and image reconstruction suitable for the frequency domain is performed.
In step H5, a tomographic image Gh (x, y) having a high spatial resolution is displayed on the monitor 6.
In step H6, a tomographic image Gl (x, y) with good density resolution is displayed on the monitor 6.
In step H7, the tomographic image Gh (x, y) having a high spatial resolution and the tomographic image Gl (x, y) having a good density resolution are displayed in an overlapping manner on the monitor 6. Each tomographic image may be displayed with weighted addition.

As shown in the enlarged view of FIG. 4B, the opening pc in the channel direction of the X-ray detector KD having a high spatial resolution is ½ smaller than the opening of the normal multi-row X-ray detector 24. Further, the opening pr in the column direction is also ½ smaller than the opening of the normal multi-row X-ray detector 24.
The spatial filter processing unit (not shown) applies a (1, 1) spatial filter in the channel direction as shown in FIG. 6A to the channel direction aperture pc in the normal multi-row X-ray detector 24. Perform noise improvement processing. Similarly, the (1, 1) spatial filter is applied in the column direction to perform noise improvement processing.
The spatial filter processing unit optimizes the S / N of the X-ray projection data based on the sampling theorem that the optimum data sampling pitch for the opening 2p is p.

If the data before the spatial filter processing at this time is D (view, ch, row), the data after the spatial filter processing is Df (view, ch, row), and the spatial filter is Filter (ch), (Formula 1)
... (Formula 1)
The tomographic image Gc (x, y) displayed in the overlap in step H7 is obtained by adding the tomographic image Gh (x, y) having a high spatial resolution and the tomographic image Gl (x, y) having a high density resolution (Formula 2). become that way. However, k is a constant of 0 ≦ k ≦ 1.
... (Formula 2)
At this time, it is preferable that the operator can freely set the constant k by the photographing condition setting means.

In this way, the X-ray CT apparatus 100 superimposes two multi-row X-ray detectors having different spatial resolutions in the channel direction and the column direction in the X-ray incident direction, and in the same range of the same part of the subject. Collect line data. Then, X-ray projection data D1 and D2 of two multi-row X-ray detectors are obtained and image reconstruction is performed, and a tomographic image Gh (x, y) having a high spatial resolution and a spatial resolution is reduced but a density resolution is good. A tomographic image Gl (x, y) can be displayed, and a tomographic image Gc (x, y) in which the two are overlapped can be displayed. By inputting the tomographic image Gh (x, y) having a high spatial resolution and the tomographic image Gl (x, y) having a high density resolution to the two memory screens, the two memory screens are expressed as (Equation 2). An overlap display may be displayed. Or you may display the tomographic image which carried out the weighted addition process like (Formula 2).
<Example 2>

  In the second embodiment, in the multi-row X-ray detector having the configuration shown in FIG. 4B, the X-ray projection data D1 of the multi-row X-ray detector KD having a high spatial resolution and the multi-row X-ray having a high density resolution. X-ray projection data D2 of the detector MD is collected. Example 2 shows an example in which two X-ray projection data D1 and D2 are synthesized before image reconstruction processing or in the middle of image reconstruction, and a tomographic image with good spatial resolution and density resolution is displayed.

<Composition of X-ray projection data before image reconstruction>
The flowchart of FIG. 7 shows image reconstruction after collecting X-ray projection data D1 of the multi-row X-ray detector KD with high spatial resolution and X-ray projection data D2 of the multi-row X-ray detector MD with high density resolution. Combining before processing into one X-ray projection data D3. Thereafter, the synthesized X-ray projection data D3 is reconstructed to obtain a tomographic image with good spatial resolution and density resolution.
In step H11, a scan such as a conventional scan or a helical scan is started.
In step H12, the data collection buffer 5 collects X-ray projection data D1 (view, ch, row) with high spatial resolution. In step H13, the data collection buffer 5 collects X-ray projection data D2 (high density resolution). (view, ch, row) is collected In step H14, the projection data synthesis unit 35 synthesizes X-ray projection data D1 with high spatial resolution and X-ray projection data D2 with high density resolution.
In step H15, the image reconstruction unit 33 performs image reconstruction of the combined X-ray projection data D3 (view, ch, row).
In step H16, the tomographic image is displayed on the monitor 6.

<Pre-synthesis 1: Channel area ratio>
There are several image composition methods in step H15, examples of which are shown below.
First, as one image synthesis method, the channel area ratio of X-ray projection data D1 (view, ch, row) with high spatial resolution and X-ray projection data D2 (view, ch, row) with high density resolution is set. Used to synthesize X-ray projection data D3 (view, ch, row).

However, X-ray projection data D1 (view, ch, row) having a high spatial resolution and X-ray projection data D2 (view, ch, row) having a high density resolution are preliminarily per unit area of the multi-row X-ray detector. Are already adjusted to the same scale.
S1 is the area for one channel of the multi-row X-ray detector KD with high spatial resolution, and S2 is the area for one channel of the multi-row X-ray detector MD with high density resolution.
... (Formula 3)
However, in this (Formula 3), it is assumed that viewε [1, K], chε [1,2N], rowε [1,2M].

<Pre-synthesis 2: Projection data ratio>
As another image synthesis method, as shown in the following (Equation 4), X-ray projection data D1 of an X-ray detector channel with good density resolution is converted into four X-ray detectors with high spatial resolution corresponding to the same position. This is a method of dividing and adding by the X-ray projection data ratio in the channel.
... (Formula 4)
However, in this (Formula 4), it is assumed that viewε [1, K], chε [1,2N], rowε [1,2M].
The projection data synthesis unit 35 performs adaptive processing (adaptive processing) when dividing the X-ray projection data D2 with high density resolution using the X-ray projection data D1 with high spatial resolution. S / N can also be improved.
Two examples of the synthesis method have been described above, but the image synthesis method may be other methods.

<Composition after pretreatment>
Here, the data collection buffer 5 collects X-ray projection data D1 (view, ch, row) and X-ray projection data D2 (view, ch, row), and the projection data synthesis unit 35 performs pre-processing or image processing. One X-ray projection data D3 is obtained by combining during the reconstruction process. Then, the image reconstruction unit 33 reconstructs the combined X-ray projection data D3 and displays a tomographic image with good spatial resolution and density resolution on the monitor 6.

FIG. 8 is a flowchart showing a flow of processing for synthesizing X-ray projection data of two multi-row X-ray detectors having different spatial resolutions during image reconstruction and reconstructing the image.
In step H21, a scan such as a conventional scan or a helical scan is started.
In step H22, the data collection buffer 5 collects two types of X-ray data D1 and D2 by the multi-row X-ray detector KD having a high spatial resolution and the multi-row X-ray detector MD having a high density resolution.
In step H23, the preprocessing unit 31 preprocesses the X-ray projection data D1 (view, ch, row) with high spatial resolution.
In step H24, the preprocessing unit 31 performs preprocessing of the X-ray projection data D2 (view, ch, row) with good density resolution.
In step H25, the projection data synthesis unit 35 synthesizes X-ray projection data with high spatial resolution and X-ray projection data Da (view, ch, row) with high density resolution. The projection data combining unit 35 has high spatial resolution X-ray projection data D1 (view, ch, row) processed in step H23 and high density resolution X-ray projection data D2 (view, ch, row) processed in step H24. ) To obtain a tomographic image with good spatial resolution and density resolution.
In step H26, the image reconstruction unit 33 performs image reconstruction of the synthesized X-ray projection data Da (view, ch, row).
In step H27, the tomographic image reconstructed is displayed on the monitor 6.

  In steps H23 and H24, the preprocessing unit 31 performs preprocessing, beam hardening correction, and z filter convolution processing. The z filter convolution process is effective when the width in the z direction of one channel of the X-ray detector with good spatial resolution and the X-ray detector with good density resolution is different. In addition, since X-ray dose correction is performed in the preprocessing, it is assumed that each X-ray projection data value has been normalized by an X-ray dose comparison detector (Reference Channel).

<Synthesis after pretreatment: Method 1>
The projection data synthesizing unit 35 has the following method (Equation 5) as an example of the synthesis method, as in (Equation 3).
... (Formula 5)
However, in this (Formula 5), it is assumed that viewε [1, K], chε [1,2N], rowε [1,2M].

<Synthesis after pretreatment: Method 2>
Further, the projection data synthesis unit 35 may improve the S / N ratio of the X-ray projection data having a high spatial resolution by using the same method as the above <Pre-synthesis 2: Projection data ratio>.
The processing method in this case is shown in the following (Formula 6).
... (Formula 6)
However, in this (Formula 6), it is assumed that viewε [1, K], chε [1,2N], rowε [1,2M].
Similarly to <pre-synthesis 2: projection data ratio>, the projection data synthesis unit 35 can also improve the S / N by adaptive processing, and can use other synthesis methods.

In step H26, if the correction processing in steps H23 and H24 has been performed up to the pre-processing, the image reconstruction unit 33 performs the image reconstruction processing from the beam hardening correction, and if the beam hardening correction has been performed, The image reconstruction unit 33 performs image reconstruction processing from z filter superimposition processing. If the correction process has been performed up to the z filter superimposition process, the image reconstruction process may be performed from the reconstruction function superimposition process.
In this way, the projection data synthesis unit 35 synthesizes two types of X-ray projection data into one X-ray projection data before the image reconstruction process or during the image reconstruction process to obtain a spatial resolution. In addition, a tomographic image with good density resolution can be obtained.
<Example 3>

<Compositing after image reconstruction>
The third embodiment shows a method of combining after image reconstruction.
FIG. 9 is a flowchart for synthesizing a tomographic image with high spatial resolution and a tomographic image with good density resolution in an image space to obtain a tomographic image with good spatial resolution and density resolution.
In step H31, a scan such as a conventional scan or a helical scan is started.
In step H32, the data collection buffer 5 collects two types of X-ray data D1 and D2 by the multi-row X-ray detector KD having a high spatial resolution and the multi-row X-ray detector MD having a high density resolution.
In step H33, the image reconstruction unit 33 performs image reconstruction of the X-ray projection data Gh (x, y) having a high spatial resolution.
In step H34, the image reconstruction unit 33 performs image reconstruction of the X-ray projection data Gl (x, y) with good density resolution.
In step H35, the tomographic image synthesis unit 37 synthesizes a tomographic image Gh (x, y) with high spatial resolution and a tomographic image Gl (x, y) with high density resolution.
In step H36, the synthesized tomographic image Ga (x, y) is displayed on the monitor 6.

In step H33 and step H34, the image reconstruction unit 33 reconstructs a tomographic image with a high spatial resolution with a matrix of 1024 × 1024 pixels, and reconstructs a tomographic image with a high density resolution with a matrix of 512 × 512 pixels. Constitute.

<Post-reconstruction synthesis: Method 1>
The tomographic image synthesizing unit 37 in step H35 has a method of the following (Equation 7) as an example of the synthesis method as in (Equation 3) and (Equation 5).
... (Formula 7)
However, in this (Equation 7), x∈ [1,1024], y∈ [1,1024], and w1 is a weighted addition coefficient.

<Synthesis after reconstruction: Method 2>
Further, the tomographic image synthesis unit 37 divides each pixel value of the tomographic image with high density resolution using each pixel value of the tomographic image with high spatial resolution using the same method as <pre-combining 2: projection data ratio>. Then, it may be added to each pixel value of a tomographic image with high spatial resolution.
The processing in this case is shown in (Formula 8) below.
... (Formula 8)
However, also in this (Formula 8), it is set as x (epsilon) [1,1024], y (epsilon) [1,1024].
Further, the adaptive noise filter is Fa (x, y), and a tomographic adaptive noise filter having a high spatial resolution is superimposed as shown in the following (Equation 9) and (Equation 10) to obtain density resolution. If each pixel of a good tomographic image is divided, an improvement in S / N can be expected.
... (Formula 9)
(Equation 10)
In this way, the tomographic image synthesis unit 37 can synthesize two tomographic images in the image space even after image reconstruction, and obtain one tomographic image with good spatial resolution and density resolution.
<Example 4>

In the fourth embodiment, an example in which multi-row X-ray detectors having different imaging regions are combined will be described.
FIG. 10A shows an X-ray in which a multi-row X-ray detector KD having a different spatial resolution and a good resolution and a multi-row X-ray detector MD having a good density resolution include two types of X-ray detectors. It is a figure which shows a data collection system.

  FIG. 10B is a diagram showing the X-ray projection data D1 of the multi-row X-ray detector KD with good spatial resolution. FIG. 10C shows X-ray projection data D2 of the multi-row X-ray detector MD with good density resolution. FIG. 10D is a diagram showing X-ray projection data obtained by combining X-ray projection data D1 with good spatial resolution and X-ray projection data D2 with good density resolution. FIG. 10E is a diagram showing X-ray projection data obtained by performing weighted addition processing on X-ray projection data D1 with good spatial resolution and X-ray projection data D2 with good density resolution.

  In this embodiment, the imaging area between the imaging area KA of the multi-row X-ray detector KD having a high spatial resolution and the imaging area MA of the multi-row X-ray detector MD having a high density resolution as shown in FIG. The synthesis method in different cases is shown. The synthesis method can be processed in the same manner as the flowchart shown in FIG.

  The difference here is that the multi-row X-ray detector KD with a high spatial resolution can cover only the imaging area KA, so that the X-ray projection data D1 with a high spatial resolution can be backprojected only in the imaging area KA. In addition, when the subject protrudes from the imaging area KA, an artifact is generated in the peripheral portion of the imaging area KA. For this reason, the projection data synthesis unit 35 synthesizes two X-ray projection data in the detector portion where the imaging areas KA and MA overlap, and the density of the imaging area outside the imaging area KA Only X-ray projection data D2 with good resolution is used.

For example, the projection data combining unit 35 generates the X-ray projection data D1 of the imaging area KA shown in FIG. 10B and the X-ray projection data D2 of the imaging area MA shown in FIG. Synthesize like this.
The collection of X-ray projection data with high spatial resolution starts at the N / 4 + 1 channel of X-ray projection data with good density resolution and ends at 3N / 4 channel.
In this case, the processing corresponding to (Equation 5) is the following (Equation 11) and (Equation 12).
In the range of ch∈ [1, N / 2] or ch∈ [3N / 2, 2N],
... (Formula 11)
In the range of ch∈ (N / 2, 3N / 2),
... (Formula 12)
However, the number of views is view ∈ [1, K], the number of channels is ch ∈ [1, 2N], and the number of columns is row ∈ [1, 2M].
Alternatively, the processing corresponding to (Formula 6) is represented by the following (Formula 13) and (Formula 14).
In the range of ch∈ [1, N / 2] or ch∈ [3N / 2, 2N],
... (Formula 13)
In the range of ch∈ (N / 2, 3N / 2),
... (Formula 14)
However, the number of views is view ∈ [1, K], the number of channels is ch ∈ [1, 2N], and the number of columns is row ∈ [1, 2M].

<Reconstruction outside the shooting area KA>
As shown in FIG. 10E, only the X-ray projection data D1 having a high spatial resolution is used in the imaging area KA, and the X-ray projection data D2 having a good density resolution is used outside the imaging area KA in the imaging area MA. You may do it. Since the image processing in this case may be discontinuous at the boundary between the imaging area KA and the imaging area MA, the weighted addition processing is performed on the two X-ray projection data D1 and D2 to continuously smooth the image processing. Can be connected.
As described above, when the multi-row X-ray detector KD having a high spatial resolution is used for the imaging area KA and the multi-row X-ray detector MD having a high density resolution is used for the imaging area MA, the projection data synthesizing unit 35 Inside the area KA, spatial resolution and density resolution are improved.

  Also in the imaging region MA, as shown in FIG. 11, the X-ray tube 21, the multi-row X-ray detector KD with high spatial resolution, and the multi-row X-ray detector MD with high density resolution are in the y direction (0 degree direction). ), The shaded area A1 is covered by the multi-row X-ray detector KD having a high spatial resolution. Further, when the X-ray tube 21, the multi-row X-ray detector KD having a high spatial resolution, the multi-row X-ray detector MD having a high density resolution and the system are in the x direction (90-degree direction), the area of the hatched portion A2 is The multi-row X-ray detector KD with high spatial resolution covers it. That is, the spatial resolution can be expected to improve somewhat even in the area outside the imaging area KA.

In this way, the projection data synthesis unit 35 not only improves the spatial resolution and density resolution in the imaging region covered by the multi-row X-ray detector KD with high spatial resolution, but also multi-row X-rays with high spatial resolution. Even in an imaging region that is not covered by the detector KD, the spatial resolution can be slightly improved.
<Example 5>

In Example 5, an example using a 360 ° detector will be described.
In the X-ray CT apparatus 100, as shown in FIG. 12A, a multi-row X-ray detector KD having a high spatial resolution is fixedly arranged in a 360 ° direction as a fourth generation (X-ray detector. Density resolution. A good multi-row X-ray detector MD rotates with the X-ray tube 21 as a third generation X-ray detector.
The fourth-generation multi-row X-ray detector KD and the multi-row X-ray detector MD with good density resolution overlap with each other in the X-ray incident direction, but they are separated from each other. In addition, the data collection buffer 5 includes the X-ray projection data D1 of the multi-row X-ray detector KD having a high spatial resolution in the same part and the same range of the subject, and the X-ray of the multi-row X-ray detector MD having a high density resolution. The line projection data D2 is collected, and a tomographic image with good spatial resolution and density resolution can be obtained.

FIG. 12B is a flowchart using the fourth generation multi-row X-ray detector KD.
In step H51, a scan such as a conventional scan or a helical scan is started.
In step H52, the data collection buffer 5 performs X-ray data collection D1 of the fourth generation multi-row X-ray detector KD with high spatial resolution.
In step H53, the data collection buffer 5 performs X-ray data collection D2 of the third generation multi-row X-ray detector MD with good density resolution.

  In step H54, the tomographic image synthesizer 37 reconstructs an image of the X-ray projection data D1 of the fourth generation multi-row X-ray detector KD having a high spatial resolution. Rather than performing image reconstruction with X-ray projection data by an X-ray fan (Source Fan) in a normal third-generation X-ray detector, it is once converted into X-ray projection data by an X-ray detector fan (Detector Fan) After that, image reconstruction is performed. The X-ray detector fan conversion principle will be described later. Further, before the X-ray detector fan conversion by the X-ray detector fan conversion unit 38, the preprocessing unit 31 performs preprocessing and beam hardening correction. After the fan conversion, the image reconstruction unit 33 continues the z-filter convolution process, the reconstruction function convolution process, the three-dimensional backprojection process, and the post-process.

In step H55, the tomographic image synthesizer 37 reconstructs the X-ray projection data D2 of the third-generation multi-row X-ray detector MD with good density resolution. The preprocessing unit 31 performs preprocessing and beam hardening correction on the X-ray projection data D2 of the multi-row X-ray detector MD with good density resolution using the collected correction data, and the image reconstruction unit 33 The z filter convolution process, the reconstruction function convolution process, and the three-dimensional backprojection process are performed according to the photographing conditions. Since the multi-row X-ray detector KD is arranged in the imaging region of the multi-row X-ray detector MD with good density resolution, the multi-row X-ray detector KD is obtained from the tomogram of the multi-row X-ray detector MD. The position can be recognized. For this reason, it is possible to perform image reconstruction of the multi-row X-ray detector KD with good density resolution in accordance with the position of the multi-row X-ray detector KD.
In step H56, the tomographic image synthesis unit 37 synthesizes a tomographic image with a high spatial resolution and a tomographic image with a high density resolution.
In step H57, the tomographic image is displayed on the monitor 6.

<X-ray detector fan conversion principle>
X-ray detector fan conversion is: “X-ray direction is incident from the X-ray focal point to the X-ray detector, but the X-ray direction is changed and the X-ray direction is changed from the X-ray detector to the X-ray focal point. Even so, the X-ray projection data value does not change ".
FIG. 13A shows an X-ray data acquisition method of the fourth generation X-ray data acquisition system, and FIG. 13B shows an X-ray data acquisition system in which two types of X-ray detectors with a resolution exist apart from each other. Indicates.
In the X-ray detector fan conversion, as shown in FIG. 13A, each X-ray detector is viewed as if X-rays are transmitted from each X-ray detector channel to each view position of the X-ray focal point. Consider a virtual X-ray fan beam using a virtual X-ray focus and a view position of each X-ray focus as a virtual X-ray detector. In other words, X-ray detector fan conversion refers to a process of converting an X-ray fan beam that exits from a normal X-ray focal point and enters the X-ray detector into a virtual X-ray detector fan beam.

  FIG. 13B shows the collection of X-ray projection data from the X-ray focus position of the i view to the X-ray focus position of the 2N + i + 2 view when the X-ray focus is rotated in the fourth generation multi-row X-ray detector. Yes. The X-ray detector fan conversion unit 38 at this time can obtain the following X-ray projection data of the X-ray detector fan by performing X-ray detector fan conversion.

  The X-ray detector fan conversion in FIG. 13B obtains X-ray projection data from the X-ray focal position i view to the X-ray focal position 2N + i view in the X-ray detector n channel, and converts the X-ray detector n channel into the X-ray detector n channel. A virtual X-ray fan beam, that is, a virtual X-ray fan beam, that is, an X-ray detector fan beam is obtained in which each view position of the X-ray focus is a virtual X-ray detector channel position.

Similarly, in the X-ray detector n + 1 channel, the X-ray detector n + 1 channel is used as a virtual X-ray focal point, and a virtual X-ray fan beam from the X-ray focal point position i + 1 view to the X-ray focal point position 2N + i + 1 view is obtained. Similarly, in the X-ray detector n + 2 channel, the X-ray detector n + 2 channel is used as a virtual X-ray focal point, and a virtual X-ray fan beam from the X-ray focal point position i + 2 view to the X-ray focal point position 2N + i + 2 view is obtained.
In this way, the X-ray detector fan converter 38 performs X-ray detector fan conversion in each X-ray detector channel.

<X-ray detector fan conversion schematic diagram>
X-ray data collection at this time is performed by collecting X-ray data for 2N views corresponding to the number of virtual X-ray detectors within an X-ray detector fan angle corresponding to a predetermined X-ray fan angle, It is assumed that the number of X-ray detector channels in the 360 degree direction, which is the line focus, is arranged for K channels, which is the number of virtual X-ray views. FIG. 14 is a schematic diagram showing this conversion processing in an X-ray projection data space.
In the X-ray projection data of the multi-row X-ray detector KD having a high spatial resolution, the X-ray detector fan data indicates that each X-ray detector channel FD1, FD2, FD3 is in the view direction as shown before conversion in FIG. Stretch and place. The X-ray detector fan conversion unit 38 can convert a virtual channel in the horizontal axis direction and a virtual view in the vertical axis direction as shown in FIG. Therefore, FD1, FD2, and FD3 can be aligned.

  As described above, the X-ray detector fan conversion unit 38 can handle the same as normal X-ray projection data by performing the X-ray detector fan conversion, and the subsequent z filter convolution processing and reconstruction function convolution processing. 3D back projection processing and post processing can be performed.

The X-ray detector fan conversion unit 38 can also perform fan-para conversion in the X-ray detector fan conversion. Thereby, X-ray detector fan conversion and fan para conversion can be performed at a time, which is efficient. Further, the X-ray detector fan conversion can be performed in the same manner before the beam hardening correction, before the preprocessing, after the z filter convolution process, and after the reconstruction function convolution process.
The tomographic image synthesizer 37 can synthesize the tomographic image KD with a high spatial resolution and the tomographic image MD with a high density resolution, which are converted by the X-ray detector fan, in the same manner as in Step H35 of FIG. One tomographic image with good spatial resolution and density resolution can be obtained.
<Example 6>

In the sixth embodiment, application to dual energy imaging will be described.
Conventional dual energy imaging has been performed by switching the X-ray tube voltage, and thus there has been a case where misregistration artifacts due to body movement of the subject occur.

  In the embodiments described so far, when X-ray data is collected by two multi-row X-ray detectors having different resolutions, the X-ray projection data D1 of the multi-row X-ray detector KD having a high spatial resolution, and the density resolution The X-ray energy when receiving X-rays is different from the X-ray projection data D2 of the good multi-row X-ray detector MD. That is, the incident X-ray energy is first absorbed and attenuated by the multi-row X-ray detector KD having a high spatial resolution, and reaches the multi-row X-ray detector MD having a good density resolution as X-ray energy having a different spectrum. In this case, the multi-row X-ray detector KD with good spatial resolution may be a silicon semiconductor detector, but the multi-row X-ray detector using a CdTe (cadmium telluride) semiconductor detector having an energy discrimination function. Is better.

  FIG. 15A is a diagram showing a difference in X-ray energy distribution incident on a multi-row X-ray detector having good spatial resolution and X-ray energy distribution incident on a multi-row X-ray detector having good spatial resolution. As shown in FIG. 15, the incident X-ray energy of the multi-row X-ray detector KD having a higher spatial resolution receives a wider X-ray energy spectrum range than the multi-row X-ray detector MD having a higher density resolution. The composition information of the subject can be collected. The dual energy image reconstruction unit 39 can reconstruct a quantitative distribution tomographic image of a desired substance, so-called dual energy tomographic image, using the X-ray energy difference received by the two multi-row X-ray detectors.

FIG. 15B is a flowchart of dual energy imaging that obtains a quantitative distribution tomographic image of a desired substance using X-ray projection data D1 with high spatial resolution and X-ray projection data D2 with high density resolution. .
In step D71, a scan such as a conventional scan or a helical scan is started.
In step D72, the data collection buffer 5 collects two types of X-ray data D1 and D2 by the multi-row X-ray detector KD having a high spatial resolution and the multi-row X-ray detector MD having a high density resolution.

In step D73, the dual energy image reconstruction unit 39 has a wide spectrum range from low to high X-ray energy spectrum of the X-ray projection data D1 of the multi-row X-ray detector having high spatial resolution. Therefore, it is handled as X-ray projection data with a low X-ray tube voltage.
In step D74, the dual energy image reconstruction unit 39 has already absorbed a portion of the low X-ray energy spectrum by the multi-row X-ray detector KD having a high spatial resolution, so that the multi-row X-ray detector having a good density resolution. X-rays of the X-ray energy spectrum with higher MD will be detected. For this reason, the dual energy image reconstruction unit 39 handles the X-ray projection data D2 of the multi-row X-ray detector MD having a good density resolution as X-ray projection data of a high X-ray tube voltage.

In step D75, the dual energy image reconstruction unit 39 performs weighted addition processing and weighted addition processing on the X-ray projection data handled as a low X-ray tube voltage and the X-ray projection data handled as a high X-ray tube voltage. A dual energy tomographic image is reconstructed by reconstructing the projection data. Or, by performing weighted addition processing (or weighted subtraction processing) on a tomographic image treated as a low X-ray tube voltage after image reconstruction and a tomographic image treated as a high X-ray tube voltage after image reconstruction, Create an energy tomogram.
In step D76, a dual energy tomogram is displayed on the monitor 6.

<Dual energy tomographic noise reduction>
Note that the dual energy image reconstruction unit 39, in order to improve the image quality of the dual energy tomographic image, each X-ray projection data noise of the two multi-row X-ray detectors KD and MD, or each tomographic image reconstructed. Can be further optimized by making the image noises equal to or equal to a certain ratio.
The dual energy image reconstruction unit 39 is designed by changing the channel thickness of the two multi-row X-ray detectors in order to control the noise of the X-ray projection data or the image noise of the tomographic image reconstructed. In the case of a scintillator / photodiode X-ray detector, it can be designed by changing the characteristics of the photodiode PD.

  Further, in this embodiment, the coefficients of the column direction (z direction) filters having different coefficients are superimposed on the columns in the column direction of the preprocessed or beam hardening corrected X-ray projection data of each channel. Thus, by adjusting the variation in image quality, noise can be reduced by suppressing artifacts with a uniform slice thickness in each column. For this, various z-direction filter coefficients can be considered, and in any case, the same effect can be obtained.

  Another aspect of the X-ray CT apparatus is that in a plurality of multi-row X-ray detectors having different spatial resolutions in the channel direction or the column direction, after the X-rays are first incident on the semiconductor detector in the X-ray irradiation direction, A multi-row X-ray detector having a structure in which X-rays are incident on a multi-row X-ray detector composed of diodes in the order of a scintillator and a photodiode.

  Yet another aspect of the X-ray CT apparatus is that in a plurality of multi-row X-ray detectors having different spatial resolutions in the channel direction or the column direction, after the X-rays are first incident on the semiconductor detector in the X-ray irradiation direction, A multi-row X-ray detector having a structure in which X-rays are incident on a multi-row X-ray detector composed of a photodiode in the order of a photodiode and a scintillator.

  Another aspect of the X-ray CT apparatus includes a multi-row X-ray detector composed of a plurality of multi-row X-ray detectors having different spatial resolutions in the channel direction or the column direction, and the spatial resolution is in the channel direction or the column direction. The high multi-row X-ray detector has a structure separated from the multi-row X-ray detector having a low spatial resolution in the channel direction or the column direction. The multi-row X-ray detector having a high spatial resolution in the channel direction or the column direction includes an unfixed multi-row X-ray detector.

  In addition, a plurality of multi-row X-ray detectors having different spatial resolutions in the channel direction or the column direction are different from the tomographic image in which the X-ray projection data obtained by at least one type of multi-row X-ray detector is reconstructed. The position of one type of multi-row X-ray detector having a spatial resolution is detected, and X-ray projection data obtained by another type of multi-row X-ray detector having another spatial resolution is reconstructed based on the position information.

  In addition, a plurality of multi-row X-ray detectors having different spatial resolutions in the channel direction or the column direction have different X-ray data collection methods of at least one kind of multi-row X-ray detectors having a spatial resolution, or image reconstruction methods. Are different.

  A plurality of multi-row X-ray detectors having different spatial resolutions in the channel direction or the column direction are at least one type of multi-row X-ray detector having a spatial resolution. Data collection is performed, or third-generation or fourth-generation image reconstruction is performed.

  In addition, among a plurality of multi-row X-ray detectors having different spatial resolutions in the channel direction or the column direction, a multi-row X-ray detector having a high spatial resolution in the channel direction or the column direction has a plurality of hierarchical structures in the X-ray irradiation direction. Is a multi-row X-ray detector having a three-dimensional structure.

  Another aspect of the X-ray CT apparatus is dual energy imaging between X-ray projection data or tomographic images of a plurality of multi-row X-ray detectors having different spatial resolutions in a channel direction or a column direction aligned in the X-ray irradiation direction. Optimizing the thickness in the X-ray transmission direction of the multi-row X-ray detector with two types of spatial resolution so that the tomographic images can be reconstructed and optimized in terms of image quality including image noise in dual energy imaging X-ray data collection means is included.

  In the present embodiment, the helical scan, the variable pitch helical scan, and the helical shuttle scan are realized by moving the cradle 12 of the imaging table 10 in the z direction. Further, the movement between the z-direction scan positions of the conventional scan or the cine scan is realized. However, relatively similar effects can also be obtained by moving the scanning gantry 20 or the rotating unit 15 in the scanning gantry 20 with respect to the cradle 12 of the imaging table 10.

The image reconstruction method in the present embodiment may be a three-dimensional image reconstruction method by a conventionally known Feldkamp method. Furthermore, other three-dimensional image reconstruction methods may be used. Alternatively, two-dimensional image reconstruction may be used.
Although the present embodiment describes the case where the scanning gantry 20 is not tilted, the same effect can be obtained even in the case of so-called tilt scanning in which the scanning gantry 20 is tilted. Although this embodiment describes the case where X-ray data acquisition is not synchronized with a biological signal, the same effect can be obtained even when synchronized with a biological signal, particularly a heartbeat signal.

In the present embodiment, the medical X-ray CT apparatus is described based on the original, but also in an industrial X-ray CT apparatus or an X-ray CT-PET apparatus, an X-ray CT-SPECT apparatus combined with other apparatuses, etc. Available.
In this embodiment, a silicon semiconductor X-ray detector SiD is used as a multi-row X-ray detector with high spatial resolution, and a scintillator / photodiode X-ray detector is used as a multi-row X-ray detector MD with good density resolution. However, an X-ray detector using other materials may be used.

  In the fifth embodiment, as shown in FIG. 12A, a fourth-generation multi-row X-ray detector is used as a multi-row X-ray detector with high spatial resolution, and the multi-row X-ray detector MD with good density resolution is used. A third generation multi-row X-ray detector was used. However, as shown in FIG. 16, the multi-row X-ray detector with high spatial resolution is also the third-generation multi-row X-ray detector, and the multi-row X-ray detector MD with high density resolution is also of the third generation. A multi-row X-ray detector may be used. Even if a plurality of multi-row X-ray detectors having different spatial resolutions are separated in the X-ray irradiation direction, if the scintillator / photodiode X-ray detector MD on the rear surface in the X-ray irradiation direction is fixed, the scintillator Image reconstruction can be performed based on the position of the semiconductor X-ray detector KD in which the photodiode X-ray detector MD is in front of the X-ray irradiation direction.

1 is a block diagram showing an X-ray CT apparatus 100 according to an embodiment. 3 is a general operation flowchart of the X-ray CT apparatus 100. (A) is a figure which shows the conventional X-ray detector module, (b) is a figure which shows the block diagram of the conventional X-ray detector module. (C) is a figure which shows the ratio of the reflector of a X-ray detector. (A) It is a figure which shows the detector module which combined the detector from which resolution differs. (B) shows a detector configured in the order of silicon semiconductor X-ray detector SiD, scintillator SD, and photodiode PD, and (c) shows an order of silicon semiconductor X-ray detector SiD, scintillator PD, and photodiode SD. It is a figure which shows the detector comprised by. (D) is a figure which shows the detector which made silicon semiconductor X-ray detector SiD multilayer. (E) is a figure which shows the detector comprised in order of the scintillator SD, the photodiode PD, and the silicon semiconductor X-ray detector SiD. It is a flowchart which shows the flow of the process which overlap-displays the tomogram of two multi-row X-ray detectors from which spatial resolution differs. It is an example of a spatial filter. It is a flowchart which shows the flow of a process which synthesize | combines the X-ray projection data of two multi-row X-ray detectors with different spatial resolution before image reconstruction, and reconstructs an image. It is a flowchart which shows the flow of the process which synthesize | combines X-ray projection data of two multi-row X-ray detectors with different spatial resolutions during image reconstruction, and reconstructs an image. It is a flowchart which synthesize | combines a tomogram with high spatial resolution and a tomogram with good density resolution in an image space, and calculates | requires a tomogram with good spatial resolution and density resolution. (A) is a figure which shows the state in which the X-ray detector of two types of resolutions from which a magnitude | size differs exists. (B) is a diagram showing X-ray projection data D1 of the multi-row X-ray detector KD with good spatial resolution. (C) is a diagram showing the X-ray projection data D2 of the multi-row X-ray detector MD with good density resolution. (D) is a diagram showing X-ray projection data D3 obtained by synthesizing X-ray projection data D1 with good spatial resolution and X-ray projection data D2 with good density resolution. (E) It is a figure which shows the X-ray projection data which carried out the weighted addition process of the X-ray projection data D1 with favorable spatial resolution, and the X-ray projection data D2 with favorable density resolution. It is a figure which shows the change of an area | region with a sufficient spatial resolution in an imaging | photography area | region. (A) is a figure which shows the X-ray data collection system in which the 3rd generation and the 4th generation X-ray detector exist. (B) is a flowchart for reconstructing images of X-ray projection data of a fourth-generation multi-row X-ray detector with good spatial resolution and a third-generation multi-row X-ray detector with good density resolution. (A) is a figure which shows the X-ray data collection method of a 4th generation X-ray data collection system. (B) is a figure which shows the positional relationship of the X-ray detector fan from each channel of a 4th generation X-ray data acquisition system. It is a figure which shows X-ray detector fan conversion in a multi-row X-ray detector. It is a figure which shows the difference in the X-ray energy distribution which injects into the multi-row X-ray detector which has good X-ray energy distribution density resolution which is incident on the multi-row X-ray detector with good spatial resolution. It is a figure which shows the state in which the X-ray detector of two types of resolution exists away from each other.

Explanation of symbols

PD ... Photodiode SD ... Scintillator SiD ... Silicon semiconductor detector MA ... Imaging region KA of density resolution X-ray CT apparatus ... Imaging region MD of spatial resolution X-ray CT apparatus ... Multi-row X-ray detector KD for density resolution Multi-row X-ray detector 1 for spatial resolution ... Operation console 2 ... Input device 3 ... Central processing unit 5 ... Data collection buffer 6 ... Monitor 7 ... Storage device 10 ... Imaging table 12 ... Cradle 15 ... Gantry rotating unit 20 ... Scanning gantry 21 ... X-ray tube 22 ... X-ray controller 23 ... Collimator 24 ... Multi-row X-ray detector or two-dimensional X-ray area detector 25 ... Data acquisition device (DAS)
DESCRIPTION OF SYMBOLS 26 ... Rotation part controller 27 ... Scanning gantry inclination controller 28 ... Beam forming X-ray filter 29 ... Control controller 31 ... Processing part 33 ... Image reconstruction part 35 ... Projection data composition part 37 ... Tomographic image composition part 38 ... X-ray detector Fan converter 39 ... Dual energy image reconstruction unit

Claims (11)

An X-ray generator;
A first multi-row X-ray detector provided opposite to the X-ray generator and having a first spatial resolution in a predetermined direction;
A second multi-row X-ray detector provided opposite to the X-ray generator and having a second spatial resolution different from the first spatial resolution in the predetermined direction;
An image reconstruction unit configured to reconstruct a tomographic image based on output data of the first multi-row X-ray detector and the second multi-row X-ray detector;
An X-ray CT apparatus comprising:   The second multi-row X-ray detector is a detector having a density resolution higher than that of the first multi-row X-ray detector, and the first multi-row X-ray detector and the second multi-row X-ray detector are The X-ray CT apparatus according to claim 1, wherein the X-ray CT apparatus is overlapped.     The second multi-row X-ray detector is a detector having a density resolution, and the first multi-row X-ray detector and the second multi-row X-ray detector are provided in contact with each other. The X-ray CT apparatus according to claim 1. The first multi-row X-ray detector is made of a material having a low X-ray absorption coefficient,
4. The X-ray CT apparatus according to claim 1, wherein the second multi-row X-ray detector is made of a material having a high X-ray absorption coefficient. 5. The first multi-row X-ray detector is a detector composed of a semiconductor.
The X-ray CT apparatus according to claim 4, wherein the second multi-row X-ray detector is a detector including a scintillator and a photodiode. The X-ray CT apparatus further includes an image construction unit that performs weight processing on output data of the first multi-row X-ray detector and output data of the second multi-row X-ray detector. The X-ray CT apparatus according to any one of claims 1 to 6. The X-ray CT apparatus further includes a first tomographic image based only on output data of the first multi-row X-ray detector and a second tomographic image based only on output data of the second multi-row X-ray detector. The X-ray CT apparatus according to any one of claims 1 to 6, further comprising a display unit that performs overlap display.   9. The imaging field of view of the first multi-row X-ray detector and the imaging field of view of the second multi-row X-ray detector are different from each other. The X-ray CT apparatus described. The X-ray generator and the second multi-row X-ray detector rotate around a gantry rotation axis,
The X-ray CT apparatus according to any one of claims 1 to 8, wherein the first multi-row X-ray detector is formed in an annular shape with respect to the gantry rotation axis.   Based on the tomographic image reconstructed with the X-ray projection data from the second multi-row X-ray detector, position information of the first multi-row X-ray detector is detected, and the image reconstruction unit includes the The X-ray CT apparatus according to claim 9, wherein X-ray projection data obtained by the first multi-row X-ray detector is reconstructed based on position information.   The X-ray CT apparatus further uses the X-ray energy difference received by the first multi-row X-ray detector and the second multi-row X-ray detector to generate a quantitative distribution tomographic image of a desired substance. The X-ray CT apparatus according to claim 1, further comprising a dual energy image reconstruction unit configured to perform image reconstruction.