JP2009082632A - N-dimensional image display device and x-ray tomographic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To display variations within a time range of a prescribed region with respect to a time-series three-dimensional image. <P>SOLUTION: An X-ray CT apparatus (100) photographs a tomographic image G by acquiring projection data D of X rays transmitted through a subject (HB) while rotating an X-ray generating device (21) and a multi-row X-ray detector (24) provided to face the X-ray generating device (21) for detecting the X ray around the center of rotation found between the X-ray generating device and the multi-row X-ray detector. The X-ray CT apparatus includes an image input part (5) for inputting the tomographic image as a four-dimensional image arranged in a time-series manner, a projection processing part (35) for performing projection processing on the four-dimensional image in a time direction, and an image display part (6) for displaying the four-dimensional image subjected to the projection processing by the projection processing part as a three-dimensional image. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an N-dimensional image display device that displays an image as a four-dimensional image made up of, for example, three-dimensional images arranged in time series, and an X-ray tomographic imaging apparatus using the same.

For example, a method for displaying a three-dimensional image by performing image processing after obtaining a tomographic image of a subject in order to diagnose a lesion in the subject using an X-ray CT apparatus which is one of X-ray tomographic imaging apparatuses It has been known. However, an effective image display method for a four-dimensional image that is a time-series three-dimensional image has not been known. Re-projection display and MIP display (Maximum) are techniques for displaying a 3D image as a 2D image.
Intensity Projection (maximum intensity projection) is known.
JP 2006-320631 A

  When applied to a four-dimensional image using the above-described reprojection display or MIP display, two dimensions must be dropped to make the four-dimensional image a two-dimensional image that can be displayed on a two-dimensional monitor. There wasn't.

The present invention is for addressing such a problem, and an object of the present invention is to display a change in a certain time range of a certain pixel value range with respect to a four-dimensional image which is a time-series three-dimensional image. An object of the present invention is to realize a method capable of displaying and a device capable of displaying.
Another object of the present invention is to make it possible to display a change in a time range of a predetermined region with respect to a time-series three-dimensional image of an X-ray tomographic imaging apparatus.

  In order to realize the object of the present invention, in a four-dimensional image that is a time-series three-dimensional image, a projection process in a time axis direction is performed on a predetermined region, and the three-dimensional image is displayed by converting the three-dimensional image. It is possible to display a temporal change of a region of a certain pixel value range.

A four-dimensional image display device according to a first aspect uses an N-1D image arranged in this time series as an N-dimensional image, an image input unit that inputs the image, and performs a projection process on the N-dimensional image in the time direction. A projection processing unit and an image display unit that displays an N-dimensional image projected by the projection processing unit as an N-1D image are provided.
In the N-dimensional image display device according to the first aspect, an N-dimensional image that is a time-series N-1 dimensional image can be converted to an N-1 dimensional order by projecting in the time axis direction, and can be displayed even in the prior art. At the same time, due to degeneracy in the time axis direction, a change in a certain time range can be made an N-1 dimensional continuous region.

In the N-dimensional image display device according to the second aspect, the projection processing means performs a time-direction projection process for a time-series N-1D image on a limited range of CT values on the N-dimensional image. It is characterized by.
By performing the projection processing in the time axis direction on a certain pixel value range of the N-dimensional image, a change in the time range in a certain defined pixel value range can be made a continuous region in the N−1-dimensional space.

The projection processing unit according to the third aspect performs reprojection processing in the time direction or MIP processing in the time direction using N-1D images arranged in time series as N-dimensional images.
In the N-dimensional image display device according to the third aspect, a certain time range is obtained by performing degeneracy in the time axis direction with respect to a certain pixel value range of the N-dimensional image which is a time-series N-1D image. The change can be made a continuous area in the N-1 dimensional space, and the display can be easily displayed as the order is lowered. In the reprojection process in the time axis direction, an image can be displayed as an average pixel value or a sum of pixel values in a certain time range, and a change in a certain time range can be easily seen. The MIP processing in the time axis direction can display an image of the maximum pixel value in a certain time range, and can display changes in a certain time range with good contrast.

In the N-dimensional image display device according to the fourth aspect, the projection processing unit performs reprojection processing or MIP processing in which a color is changed at each time.
In the N-dimensional image display device according to the fourth aspect, when reprojecting in the time axis direction by changing the color of the N-1 dimensional image at each time when projecting in the time axis direction and degenerating, Since the trajectory of a moving object within the range of pixel values of interest can be changed by a color change, a display that makes it easy to recognize the direction and speed of movement can be achieved. In addition, when the maximum value is projected in the time axis direction and degenerated, the color of the N-dimensional image at each time is changed. It is possible to easily recognize a change in the movement of a moving object within a certain pixel value range.

In the N-dimensional image display device according to the fifth aspect, the projection processing unit performs adaptive reprojection processing.
By performing adaptive reprojection processing in the time axis direction, an image can be displayed as an average pixel value or a sum of pixel values in a predetermined time range, and a change in a time range can be easily seen.

In the N-dimensional image display device according to the sixth aspect, the projection processing unit performs adaptive MIP processing.
By performing adaptive MIP processing in the time axis direction, the maximum pixel value in a certain time range can be displayed as an image, and changes in a certain time range can be displayed with good contrast.

An X-ray tomographic imaging apparatus according to a seventh aspect includes an X-ray generator and a multi-row X-ray detector that detects X-rays relative to each other between the X-ray generator and the multi-row X-ray detector. While rotating around a certain center of rotation, X-ray projection data transmitted through the subject is collected and a tomographic image is taken. Then, an image input unit that inputs the tomographic image as a time-series N-dimensional image, a projection processing unit that performs projection processing on the N-dimensional image in the time direction, and an N-dimensional image that is projected by the projection processing unit And an image display unit that displays an image as an N−1-dimensional image.
The X-ray tomographic imaging apparatus according to the seventh aspect can convert an N-dimensional image, which is a time-series N-1 dimensional image, into an N-1 dimensional image by performing projection processing in the time axis direction. With a one-dimensional image display technique, changes in a certain time range can be displayed in N-1 dimensions. In particular, the X-ray tomographic imaging apparatus can visualize the movement / trajectory of the contrast agent to make it easy to see.

The X-ray tomographic imaging apparatus according to the eighth aspect performs time-series N-dimensional spatial filter processing on a pixel of interest at a certain time in an N-dimensional image.
The X-ray tomographic imaging apparatus according to the eighth aspect can adjust the time-axis characteristic or the spatial-axis characteristic of the target pixel by performing an N-dimensional spatial filter process on the target pixel. Therefore, the trajectory of the contrast agent can be imaged with an image with good image quality and S / N.

In the ninth aspect, the scan for collecting X-ray projection data is a cine scan or a helical scan.
Especially in cine scan by N-1 dimensional image reconstruction, it is an imaging method for observing temporal changes in a range spread in the z direction, and sees changes in contrasted blood vessels, contrast agent movement, and reprojection display. -It is an imaging method suitable for viewing the shape of a blood vessel indicated by the contrast agent trajectory by MIP display. In particular, when the helical pitch is slow, it is possible to perform N−1-dimensional display by continuous tomographic images at each time overlapping in the z direction.

In a tenth aspect of the X-ray tomographic imaging apparatus, the projection processing unit performs a time-direction projection process on a time-series N-1D image and a limited range of CT values on the ND image.
A change in a time range can be made a continuous region in the N-1 dimensional space.

In the X-ray tomographic imaging apparatus according to the eleventh aspect, the projection processing unit performs reprojection processing in the time direction or MIP processing in the time direction as an N-1D image N-dimensional image arranged in time series.
The X-ray tomographic imaging apparatus according to the eleventh aspect can display the temporal change of the CT value of the tomographic image in an N−1-dimensional manner with good S / N by performing reprojection processing in the time axis direction. By performing reprojection processing when projecting in the time axis direction and degenerating, the information at each time is degenerated with an equal weight, and the region with a high CT value or the trajectory of the contrast agent or moving object can be correctly displayed. it can. In particular, X-ray quantum noise (noise) corresponding to the X-ray dose exists in the tomographic image of the X-ray CT apparatus. By the reprojection processing in the time axis direction, each pixel of the N−1-dimensional image that is a continuous tomographic image is added in the time axis direction, so that the S / N of each pixel is improved. In addition, by performing MIP processing in the time axis direction, temporal changes can be displayed in N-1D with good contrast.

In the twelfth aspect, the projection processing unit performs reprojection processing or MIP processing in which a color is changed at each time, and the N-dimensional image display device according to claim 7.
In the X-ray tomographic imaging apparatus according to the twelfth aspect, when reprojecting in the time axis direction by changing the color of the N-1D image at each time when projecting in the time axis direction and degenerating, The change is a region having a high CT value or a change in the movement of a contrast medium or an object. When the color of the N-1D image at each time is changed, the image addition is performed in the time axis direction, and the reprojection process is performed, if the N-1D images at each time overlap, the N-1 at each time The color of the dimensional image is mixed and the intermediate color is also displayed. The movement of the contrast agent at each time can be recognized in detail from the subtle color change including the intermediate color. When MIP processing is performed by performing image addition in the time axis direction, the maximum value projection is performed in the time axis direction by changing the color of the N-1D image at each time, and when the degeneration in the time axis direction is performed, in particular, the contrast agent Since the maximum value is displayed preferentially, it becomes easier to recognize the movement of the maximum value that is the peak of the contrast agent.

An image input unit according to a thirteenth aspect determines a scan interval for collecting X-ray projection data in consideration of temporal changes in CT values of a predetermined region in an N-dimensional image.
When projecting an N-dimensional image in the time axis direction and reducing it to N-1 dimensional data to form a continuous N-1 dimensional region, the sampling interval in the time axis direction of the time-series N-1 dimensional image is sufficient. Need to be closely spaced. For this reason, the sampling interval of the time-axis direction of the time-sequential N-1 dimensional image suitable for the time change of a predetermined area is needed. By sufficiently considering the sampling interval in the time axis direction, a predetermined range of CT values can be made into a continuous N-1 dimensional region by projection in the time axis direction. Once the X-ray projection data is captured, the sampling interval of the N-1D image at each time in the time axis direction can be shortened.

  In the X-ray tomographic imaging apparatus according to the fourteenth aspect, the projection processing unit is adaptive reprojection processing in the time axis direction.

  In the X-ray tomographic imaging apparatus according to the fifteenth aspect, the projection processing unit is adaptive MIP processing in the time axis direction.

  An X-ray tomographic imaging apparatus according to a sixteenth aspect includes image reconstruction means for determining a time series interval of each tomographic image and performing image reconstruction in consideration of temporal changes in a region of a certain CT value range.

  The X-ray tomographic imaging apparatus according to the seventeenth aspect determines the time series interval of each tomographic image in consideration of the temporal change of the region of a certain CT value range and the expanded size of the region, and performs image reconstruction. Image reconstruction means to perform.

As an effect of the present invention, a four-dimensional image that is a time-series three-dimensional image is subjected to projection processing in a time axis direction for a predetermined area, converted into a three-dimensional image, and displayed as a three-dimensional image. There is an effect that it is possible to display a temporal change in a region of a certain pixel value range.
In addition, as another effect of the present invention, a projection process in the time axis direction is performed on a region of a certain CT value range for a four-dimensional image that is a time-series three-dimensional image in an X-ray CT apparatus, There is an effect that it is possible to display a temporal change in the region of the CT value range which is a three-dimensional image display by converting into a three-dimensional image.

<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 the operator, a central processing unit 3 that executes preprocessing, image reconstruction processing, postprocessing, and the like, and X-ray detection collected by the scanning gantry 20 And an image input unit 5 (data collection buffer) for collecting instrument data. Further, the operation console 1 includes a monitor 6 that displays a tomographic image reconstructed from projection data obtained by preprocessing X-ray detector data, a program, X-ray detector data, projection data, and X-ray tomography. And a storage device 7 for storing an image. The storage device 7 stores a tomographic image for each time. The photographing condition is input from the input device 2 and stored in the storage device 7. The imaging table 10 includes a cradle 12 on which a subject is placed and taken in and out of the opening of the scanning gantry 20. The cradle 12 is moved up and down and linearly moved by the motor built in the imaging table 10.

  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. It has. Further, the scanning gantry 20 includes a rotating unit controller 26 that controls the X-ray tube 21 rotating around the body axis of the subject, 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. For this reason, exposure of the body surface of the subject having a cross-sectional shape close to a circle or an ellipse can be reduced.

The central processing unit 3 includes a preprocessing unit 31, a beam hardening processing unit 33, an image reconstruction unit 34, and a projection processing unit 35.
The preprocessing unit 31 performs preprocessing including offset correction, logarithmic conversion, X-ray dose correction, and interchannel sensitivity correction on the raw data collected by the data collection device 25.

  The beam hardening processing unit 33 corrects the beam hardening of the projection data. Beam hardening is a phenomenon in which the X-ray absorption changes depending on the transmission thickness even if the same material is used, and the CT value (luminance) on the tomographic image changes. In particular, the energy distribution of the radiation that has passed through the subject is on the high energy side. It is biased to. For this reason, beam hardening is corrected with respect to the column direction and the channel direction of the projection data.

The image reconstruction unit 34 receives the X-ray projection data preprocessed by the preprocessing unit 31, and reconstructs an image based on the X-ray projection data. X-ray projection data is converted into a frequency domain by a fast Fourier transform (FFT).
Transform) is performed, the reconstruction function Kernel (j) is superimposed on it, and inverse Fourier transform is performed. Then, the image reconstruction unit 34 performs a three-dimensional backprojection process on the projection data on which the reconstruction function Kernel (j) is superimposed, and obtains a tomographic image (for each body axis direction (Z direction) of the subject HB). xy plane). The image reconstruction unit 34 stores this tomographic image in the storage device 7.
The projection processing unit 35 performs three-dimensional reprojection processing in the time direction or three-dimensional MIP processing in the time direction from the projection data, tomographic image, or three-dimensional or four-dimensional image stored in the storage device 7.

<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 is placed on the cradle 12 and aligned. Here, the subject placed on the cradle 12 aligns the slice light center position of the scanning gantry 20 with the reference point of each part. Then, a scout image (also called a scanogram or an X-ray fluoroscopic image) is collected. In scout imaging, the X-ray tube 21 and the multi-row X-ray detector 24 are fixed, and the data collection operation of X-ray detector data is performed while the cradle 12 is moved linearly. Here, the scout image is usually photographed at view angle positions of 0 degrees and 90 degrees. Depending on the part, for example, the head may be a 90-degree scout image only. 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 an axial scan, a cine 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 an X-ray data collection system including the X-ray tube 21 and the multi-row X-ray detector 24 rotates. The variable pitch helical scan collects X-ray projection data by changing the speed of the cradle 12 while rotating the X-ray data acquisition system including the X-ray tube 21 and the multi-row X-ray detector 24 as in the helical scan. It is a shooting method. In the helical shuttle scan, the cradle 12 is accelerated and decelerated while rotating the X-ray data acquisition system including the X-ray tube 21 and the multi-row X-ray detector 24 as in the helical scan, and the positive direction of the z axis or z This is a scanning method for collecting X-ray projection data by reciprocating in the negative direction of the axis. When these plural imagings are set, the X-ray dose information of each imaging is displayed.

  In setting the tomographic image capturing conditions, the exposure of the subject can be optimized by using the automatic exposure mechanism of the X-ray CT apparatus 100. Further, in this tomographic imaging condition setting, the range of the subject HB in the body axis direction (Z direction) and the imaging time are set. That is, settings for confirming tomographic images at different times are performed.

  In step P3 to step P9, tomographic imaging is performed. In step P3, X-ray data collection is performed. Here, in the case of collecting data by helical scan, variable pitch helical scan, or helical shuttle scan, the X-ray tube 21 and the multi-row X-ray detector 24 are rotated around the subject, and on the imaging table 10. The X-ray data collection operation is performed while moving the cradle 12 in a straight line. Then, the X-ray detector data D0 (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 is z-direction. A coordinate position Ztable (view) is added. As described above, in the helical scan, the variable pitch helical scan, or the helical shuttle scan, the data of the z-direction coordinate position information of each view is also collected together with the X-ray projection data. This z-direction coordinate position may be added to the X-ray projection data (X-ray detector data), or may be used in association with the X-ray projection data as a separate file. When reconstructing a three-dimensional image of X-ray projection data at the time of helical shuttle scan or variable pitch helical scan, it is preferable to use this z-direction coordinate position information. Further, by using the helical scan, the conventional scan, or the cine scan, it is possible to improve the accuracy and the image quality of the tomographic image reconstructed.

  As the z-direction coordinate position, the position control data of the cradle 12 of the imaging table 10 may be used, or the z-direction coordinate position predicted at each time predicted from the imaging operation set when the imaging condition is set. When X-ray data acquisition is performed by conventional scan or cine scan, the X-ray data acquisition system is rotated once or a plurality of times while the cradle 12 on the imaging table 10 is fixed at a certain z-direction position. Collect X-ray data. Then, if necessary, after moving to the next position in the z direction, the X-ray data acquisition system is again rotated once or a plurality of times to acquire X-ray data.

In step P4, the preprocessing unit 31 performs preprocessing. Here, pre-processing is performed on the X-ray detector data D0 (view, j, i) to convert 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, the beam hardening processing unit 33 performs beam hardening correction. Here, beam hardening correction is performed on the preprocessed projection data D1 (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 each X-ray data acquisition system differs depending on the imaging conditions, the X-ray energy characteristic of the detector for each column Differences can be corrected.

  In step P6, the image reconstruction unit 34 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 D11 (view, j, i) subjected to beam hardening correction. That is, the multi-row X-ray detector D11 (view, j, i) (i = 1 to CH, j = 1 to ROW) subjected to beam hardening correction after pre-processing in each view angle and each X-ray data acquisition system. For example, a filter with a column direction filter size of 5 columns is applied in the column direction.

  In step P7, the image reconstruction unit 34 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, and the inverse Fourier transform is performed.

  In step P8, the image reconstruction unit 34 performs a three-dimensional backprojection process. Here, three-dimensional backprojection processing is performed on the projection data D13 (view, j, i) subjected to reconstruction function superimposition processing to obtain backprojection data D3 (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 34 performs post-processing. Post-processing such as image filter superimposition and CT value conversion is performed on the backprojection data D3 (x, y, z) to obtain a tomographic image G (x, y, z). In this post-processing image filter convolution process, the tomographic image after three-dimensional backprojection is set to G (x, y, z), and data after image filter convolution is obtained. By repeating this tomographic image reconstruction on a tomographic image continuous in the z direction, a three-dimensional image as a tomographic image continuous in the z direction is obtained.

In step P10, the projection processing unit 35 performs a projection process in the time axis direction of the time-series three-dimensional image. This time-series three-dimensional image will be described later.
In step P11, the monitor 6 displays a three-dimensional image. Here, a three-dimensional MIP image 43 at a certain point in time among four-dimensional MIP (Maximum Intensity Projection) images arranged in time series from tomographic images continuously taken in the z direction is shown. Although there are various other image display methods, the operator uses different image display methods appropriately for diagnosis purposes.

<Time series of tomographic images>
3A and 3B show time-series cine scan and helical scan images obtained up to step P9. FIG. 3A is a diagram showing time series tomographic images of cine scan, and FIG. 3B is a diagram showing time series tomographic images of helical scan.

In the cine scan time-series tomographic image shown in FIG. 3A, the tomographic image corresponding to the z-direction coordinate range [z1, zN] of the multi-row X-ray detector 24 irradiated with the X-ray beam in the z direction is the time. It is obtained in the range of [t _n , t _{n + 2} ] in the direction.
In the cine scan of FIG. 3A, data of a plurality of rotations are collected at a certain coordinate position in the z direction, and the following time series three-dimensional image is obtained. However, in FIG. 3 (a), a tomographic image from the tomographic image at time t _{n + 2} at time t _n is is drawn offset, which is actually tomograms time different be those aid understanding overlaps.
Tomographic image _Gc of time _{t n (t n, z1)} , Gc (t n, z2), ... Gc (t n, zN-1), Gc (t n, zN),
Time _{t n + 1} of tomographic image _{Gc (t n + 1, z1} ), Gc (t n + 1, z2), ... Gc (t n + 1, zN-1), Gc (t n + 1, zN),
Time _{t n + 2} of the tomographic image _{Gc (t n + 2, z1} ), Gc (t n + 2, z2), ... Gc (t n + 2, zN-1), Gc (t n + 2, zN)

  As shown in FIG. 3A, there is a common three-dimensional region g (x, y, z, t) during a certain time interval tn−1 ≦ tn ≦ tn + 1. That is, this common three-dimensional region is a region in which the three-dimensional image changes in time series.

In the X-ray CT apparatus 100 using the multi-row X-ray detector 24, not only one Gh (t _n , z) tomographic image but also a plurality of tomographic images are obtained by performing three-dimensional image reconstruction in the helical scan. N tomographic images Gh (t _n , z1), Gh (t _n , z2),... Gh (t _n , zN−1), Gh (t _n , zN) can also be obtained. FIG. 3B shows a case of a low helical pitch (for example, a helical pitch of 0.2). In this case, image reconstruction can be performed so that Gh (ti, zj) and Gh (tk, zl) overlap. That is, a plurality of tomographic images having the same z coordinate can be reconstructed even if the tomographic images have different times.

In the time-series tomographic image of the helical scan shown in FIG.
At time t _n , a tomographic image in the z-direction coordinate range [z _n 1, z _n N] is obtained,
At time t _{n + 1} , a tomographic image in the z-direction coordinate range [z _{n + 1} 1, z _{n + 1} N] is obtained,
At time t _{n + 2} , a tomographic image in the z-direction coordinate range [z _{n + 2} 1, z _{n + 2} N] is obtained.

Tomographic image _Gc at time _{t n (t n, z1)} , Gc (t n, z2), ... Gc (t n, zN-1), Gc (t n, zN) to combine in the z-direction, at a certain time A three-dimensional image Cine 3D (t) is obtained. Therefore, when a three-dimensional image in the range up to [t _n , t _{n + m} ] is extracted in time series, a time series three-dimensional image is obtained. In addition, in order to obtain a temporal change in a tomographic image at a certain z-direction position, Gc (t _n , zi), Gc (t _{n + 1} , zi), Gc (t _{n + 2} , zi),... Gc (t _{n + m} , zi) Select. Then, a time-series tomogram is obtained.

In FIG. 3B, when the scan pitch overlaps with adjacent tomographic images in time series, that is, when there is a relationship such as z11 = z1, z12 = z21 = z2, z13 = z22 = z31 = z3. The helical scan in FIG. 3B is as follows.
Tomographic image _Gh of time _{t n (t n, z1)} , Gh (t n, z2), ... Gh (t n, zN-1), Gh (t n, zN),
Time _{t n + 1} of tomographic image _{Gh (t n + 1, z2} ), Gh (t n + 1, z3), ... Gh (t n + 1, zN), Gh (t n + 1, zN + 1),
Time _{t n + 2} of the tomographic image _{Gh (t n + 2, z3} ), Gh (t n + 2, z4), ... Gh (t n + 2, z
N + 1), Gh (t _{n + 2} , z N + 2)
Tomogram _Gh time _{t n + m (t n +} m, zm), Gh (t n + m, zm + 1), ... Gh (t n + m, z
N + m−2), Gh (t _{n + m} , z N + m−1)

A time-series change of a tomographic image at a certain z-direction position is selected by selecting Gh (t _n , zN), Gh (t _{n + 1} , zN), Gh (t _{n + 2} , zN),. Obtainable.
When M <N and tomographic images Gh (t, zM), Gh (t, zM + 1),... Gh (t, zN) are combined in the z direction, a three-dimensional range from zM to zN in the z direction coordinates. An image Helical 3D (t) can be obtained, and a time-series three-dimensional image in the range from time t1 to tM can be obtained.
Gh (t1, zM), Gh (t1, zM + 1),... Gh (t1, zN),
Gh (t2, zM), Gh (t2, zM + 1), ... Gh (t2, zN),
......
Gh (tM, zM), Gh (tM, zM + 1), ... Gh (tM, zN)

  When the helical pitch is made smaller than 1, the overlapping range becomes large in the range of tomographic images taken in the z direction at each time as shown in FIG. 3B, and between certain time intervals tn−1 ≦ tn ≦ tn + 1. There is a common three-dimensional region g (x, y, z, t) in FIG. That is, this common three-dimensional region is a region where the three-dimensional image changes in time series. When the helical pitch is 0, it corresponds to a cine scan.

  In addition to the cine scan and the helical scan described above, there are an axial shuttle scan and a helical shuttle scan that can continuously capture z-direction tomographic images in the same z-direction range in the time direction. FIG. 4 shows the operation of the axial shuttle scan, and FIG. 5 shows the operation of the helical shuttle scan. The hatched area on the left side of FIGS. 4 and 5 indicates the period during which the projection data Dwo is acquired.

  In the axial shuttle scan shown in FIG. 4, the cradle 12 of the imaging table 10 is moved, and the axial scan is alternately and continuously performed at the z-direction coordinate positions z0 and z1. It should be noted that the tomographic images at this time can be taken at continuous intervals in the z direction. Gz0 (1), Gz0 (2),... Gz0 (N) are axial scan tomograms at the z-direction coordinate position z0, and Gz1 (1), Gz1 (2), Gz0 (N) are axial scan tomograms at the z-direction coordinate position z1. ... Gz1 (N). However, N is the number of slices to be shot in one rotation in the axial scan. At this time, the interval between the tomographic images of the respective axial scans at the respective coordinate positions in the z direction is set to Δz as shown in (Formula 1).

However, zo (i) is the z-direction coordinate position of the tomographic image Gz0 (i), z1 (i) is the z-direction coordinate position of the tomographic image Gz1 (i), and i = 0,. The z-direction coordinate positions z0 and z1 are determined so that (N) −z1 (1) = Δz.
... (Formula 1)

In this way, the photographing of the z-direction coordinate positions z0 and z1 is repeated alternately. In the time direction, as shown in the timing chart of FIG. 4, X-ray data collection of the axial scan imaging at the z-direction coordinate position z0 is performed at the time of [t0, t1], and the z-direction coordinates at the time of [t1, t2]. Move from position z0 to z1.
In addition, the X-ray data of the axial scan imaging at the z-direction coordinate position z1 is collected at the time [t2, t3], and moved from the z-direction coordinate position z1 to z0 at the time [t3, t4].
Further, X-ray data collection of the axial scan imaging at the z-direction coordinate position z0 is performed at the time [t4, t5], and it is moved again from the z-direction coordinate position z0 to z1 at the time [t5, t6].

  By repeating this, if the X-ray aperture width of one axial scan is d as shown in FIG. 4, continuous tomographic images with z-direction intervals Δz in the range of 2d in the z direction can be obtained. This imaging method is particularly effective for perfusion scanning of the head. For example, d = 40 mm, one shooting is 0.5 seconds, that is, t1−t0 = 0.5 (seconds), and the moving time of the cradle 12 of one shooting table 10 is 1 second, that is, t2−t1. When = 1 (second), the tomographic image in the z-direction range of 2d = 80 mm is updated at intervals of 3 seconds. For this reason, in perfusion imaging, changes in contrast medium can be imaged at intervals of 3 seconds, and changes in each pixel at intervals of 3 seconds can be measured. As a result, the conventional cine scan can only perform perfusion imaging with a width of 40 mm in the z-direction range determined by the width of the X-ray detector at one time in the cine scan. A wide range of perfusion inspections can be performed in the z direction. Note that the tomogram slice thickness of the axial scan in the z-direction ranges z0 and z1 at this time may be Δz without overlap, or the tomogram slice thickness may be 2 · Δz with overlap.

In the helical shuttle scan shown in FIG. 5, the cradle 12 of the imaging table 10 is moved to relatively move the X-ray data collection system from the z-direction coordinate position z0 to the z-direction coordinate position z2. Assuming that the X-ray aperture width is d, as shown in the following (Equation 2), the portion of the distance L1 in the z direction range can be imaged by moving the distance L.
... (Formula 2)

  During this distance L1, tomographic images can be reconstructed continuously at intervals of Δz. Note that, in the helical shuttle scan tomogram in the range of the distance L1 at this time, the slice thickness may be Δz without overlap or the slice thickness may be 2 · Δz with overlap. By repeatedly moving the X-ray data collection system in the order of z0 → z2 → z0 →... Z2, tomographic imaging can be repeated continuously in the time direction at each coordinate position in the z direction within this distance L1.

In the time direction, as shown in the timing chart of FIG. 5, an axial scan is performed at the coordinate position z0 in the z direction at a time of [t10, t11], and X-ray data collection is also performed.
In the time [t11, t12], the cradle 12 of the imaging table 10 is accelerated to the z-direction coordinate position z2, and when it reaches a certain speed, it is moved at a constant speed and decelerated to arrive at the z-direction coordinate position z2.
An axial scan at the z-direction coordinate position z2 is performed at time [t12, t13], and X-ray data collection is also performed. In the time [t13, t14], the cradle 12 of the imaging table 10 is accelerated to the z-direction coordinate position z0, and when it reaches a certain speed, it is moved at a constant speed, decelerated, and arrives at the z-direction coordinate position z0.
An axial scan at the z-direction coordinate position z0 is performed at time [t14, t15], and X-ray data collection is also performed. In the time [t15, t16], the cradle 12 of the imaging table 10 is accelerated to the z-direction coordinate position z2, and when it reaches a certain speed, it is moved at a constant speed, decelerated, and arrives at the z-direction coordinate position z2.

By repeating this, tomographic imaging of a continuous tomographic image during the distance L1 in the z-direction range [z0−d / 2, z2 + d / 2] shown in FIG. 5 is performed at an average time Δt1 = t12−t10. it can.
For example, if the X-ray aperture width d is 40 mm, the maximum helical pitch is 1.375 and the table speed is about 140 mm / second in one rotation of 0.4 second scan, the range in the z-direction range of 200 mm is about 2 seconds on average. Tomographic images can be taken repeatedly.

  In the helical shuttle scan, there is no particular limitation on the range in the z direction, and it is possible to take an image as long as the cradle 12 of the imaging table 10 can move. For this reason, in the past, continuous imaging in the time direction by the cine scan could only have an X-ray aperture width d determined by the z-direction width of the X-ray detector, but the helical shuttle scan does not limit the z-direction range, but in the time direction. Continuous shooting can be performed.

  This imaging method is particularly effective in perfusion imaging of the abdomen, for example, the liver. A z-direction range of about 200 mm is sufficient for the liver perfusion examination and the movement of the contrast medium. Moreover, if tomographic imaging can be performed at intervals of about 2 seconds in the time direction, it is sufficient for examination of the liver. Similarly, a wide range of examinations can be performed in the z direction even in organs that are long in the z direction, such as lung fields.

<Three-dimensional reprojection display MIP display>
Consider re-projection display and MIP display in the time axis direction for the time-series three-dimensional image of this three-dimensional region. The reprojection display is generally a display method for displaying a reprojection image Repro processed by a reprojection process in which image values are added to or averaged in a reprojection direction specified in a three-dimensional space of an xyz axis. .
FIG. 6A is a conceptual diagram of three-dimensional reprojection, and FIG. 6B is a diagram showing an interpolated tomographic image.

  As shown in FIG. 6A, the three-dimensional reprojection image Repro is a two-dimensional image obtained by integrating each pixel value of the three-dimensional image along the reprojection direction R on the reprojection surface RS. For example, a fluoroscopic image by an X-ray film becomes a three-dimensional reprojection image Repro in the case of projection from an X-ray focal point. This reprojection image Repro makes it easy to intuitively grasp the three-dimensional state. Further, when the reprojected image Repro is viewed while being rotated, a three-dimensional stereoscopic effect is obtained. When the interval between the tomographic images in the z direction is larger than the pixel size of the tomographic image, conventionally, as shown in FIG. 6B, an interpolated image (interpolated G) between the tomographic images Gz is created and then reprojected. Accumulated in the direction. However, in this case, there are drawbacks such as (1) the image memory capacity is increased, and (2) the number of pixels to be processed increases, so that it takes time to create the three-dimensional reprojection image Repro. For this reason, as an algorithm that is equivalent in mathematical formula to “accumulate after creating an interpolated image”, “add an image first without creating an interpolated image, and the image to be interpolated between two tomographic images The “algorithm created by filtering” algorithm is also known.

In this way, after the processed reprojection image Repro is displayed in the designated reprojection direction, for example, the direction of the direction vector (a cos θ, a sin θ, b), θ is changed from 0 degrees to 360 degrees. A stereoscopic effect can be obtained by rotating the reprojection display image by rotating the reprojection direction.
In addition, MIP (Maximum Intensity
Projection) display also searches each pixel value of the three-dimensional image along the projection direction to obtain the maximum luminance (maximum pixel value). This process is set as the value of each pixel of the MIP display image. The three-dimensional state can be intuitively grasped also by this MIP display image. Further, when the MIP display image is viewed while being rotated, a three-dimensional stereoscopic effect can be obtained.

FIG. 7 is a diagram illustrating reprojection display in the time axis direction and MIP display in the time axis direction.
As shown in FIG. 7, in the reprojection display in the time axis direction, each time t _n−2 , t _n− for the image region g (x, y, z, t) at the same position in the three-dimensional space. ₁ ...... t _{n + 2} ...... t _N image region g (x, y, z, t _n−2 ), g (x, y, z, t _n−1 )... G (x, y , Z, tN) are added or averaged. FIG. 7 shows an addition formula. By performing such processing, a four-dimensional reprojection image Repro (x, y, z) can be obtained. Since the re-projected image Repro (x, y, z) of the three-dimensional image is a three-dimensional image, it can be displayed by the current three-dimensional image display technology.

Further, as shown in FIG. 7, in the MIP display in the time axis direction, each time t _n−2 , t _n for the image region g (x, y, z, t) at the same position in the three-dimensional space. ₋₁ ... T _{n + 2} ... _TN image region g (x, y, z, t _n−2 ), g (x, y, z, t _n−1 ). Among y, z, tN), the maximum pixel value is defined as an image region g (x, y, z, t) at the three-dimensional position. By doing so, a four-dimensional MIP image MIP (x, y, z) is obtained. Note that Max [] in FIG. 7 takes the maximum value of each pixel in [].

<Flow of time axis reprojection display and time axis direction MIP display>
FIG. 8A shows a flowchart of reprojection display in the time axis direction by the projection processing unit 35, that is, four-dimensional reprojection display.
In step r1, the projection processing unit 35 initializes each coordinate value. Let (x, y, z) = (0, 0, 0), and t = tn.
In step r2, the projection processing unit 35 adds or averages the pixel values from time t1 to time tN according to the mathematical formula described in FIG.
In step r3, the end check of each coordinate of x, y, z is performed.
In step r4, the coordinates of x, y, and z are updated.

In addition, when displaying the four-dimensional image colored for every time series, the projection process part 35 can color by replacing step r2 and step Cr2.
Step Cr2 shown in FIG. 8B is for N = 5 for the time series pixels t1 to tN.
100% of g (x, y, z, t1) as R component
g (x, y, z, t2) is 50% for R component and 50% for G component
100% of g (x, y, z, t3) as G component
g (x, y, z, t4) is 50% for G component and 50% for B component
100% of g (x, y, z, t5) as B component
Are assigned to the RGB components of each pixel. By doing so, the projection processing unit 35 can display a four-dimensional image colored for each time series.

FIG. 9A shows a flowchart of MIP display in the time axis direction of the projection processing unit 35, that is, four-dimensional MIP display.
In step m1, the projection processing unit 35 initializes each coordinate value. (X, y, z) = (0, 0, 0), t = tn
In step m2, the projection processing unit 35 obtains the maximum value of each pixel using the mathematical formula described in FIG.
However, Max [] assumes the maximum value of each pixel in [].
In step m3, the end check of each coordinate of x, y, z is performed.
In step m4, the coordinates of x, y, and z are updated.

In addition, when displaying the four-dimensional four-dimensional MIP colored every time series, the projection process part 35 can color by replacing step m2 and step Cm2.
In the formula shown in FIG. 9B, if the time of the pixel having the maximum value is t1, the pixel is set to 100% as the R component.
At t2, the pixel is 50% for the R component and 50% for the G component.
If t3, the pixel is set to 100% for the G component
At t4, the pixel is 50% for the G component and 50% for the B component.
If t5, the pixel is 100% for B component
Are assigned to the RGB components of each pixel.

<Contrast imaging>
Next, four-dimensional reprojection display and four-dimensional MIP display when contrast agent imaging is performed will be described based on such a flowchart.
FIGS. 10A and 10C show an image region g (x, y, z, t _n ) at each time t _n . FIGS. 10B and 10D are diagrams in which the image regions g (x, y, z, t _n ) at each time t _n are overlaid. FIG. 11A shows an image region g (x, y, z, t _n ) at each time t _n with a reduced time interval. FIG. 11B is a diagram in which the image regions g (x, y, z, t _n ) at each time t _n are overlaid. FIG. 11C illustrates a change in CT value in the blood vessel Ve.

As shown in FIG. 10A, when image reconstruction or MIP display is performed on the flowing contrast agent at the timings t _n−1 , t _n , and t _{n + 1} , the contrast agent flow v and the contrast agent peak The condition of the following (Formula 3) is required between the width w and the image reconstruction time interval Δt1.
... (Formula 3)

  However, the peak width of the contrast agent is determined as follows. The contrast agent peak of the CT value at each position in the blood vessel Ve containing the contrast agent at a certain time is drawn as shown in FIG. At this time, as shown in FIG. 11C, when the threshold value of the CT value that can be detected as a contrast agent is Th1, the CT value range equal to or greater than Th1 is determined as the peak width w of the contrast agent.

This and satisfies the condition (Equation 3), as shown in FIG. 10 (b), the the region _{r n-1} at time _{t n-1} of the contrast medium, a region _{r n} of the contrast medium at time _{t n,} the time t _{The n + 1} contrast agent regions r _{n + 1} overlap in space. Then, when performing the reprojection display and MIP display, _the time _t and the regions _{r n-1} of _n-1 of the contrast medium, a region _{r n} of the contrast medium at time _{t n, the} time _{t n + 1} in the region r of the contrast agent A three-dimensional region of the blood vessel Ve contrasted with _{n + 1} can be shown. That is, at each time t _n−1 , t _n , and t _{n + 1} , although the contrast agent has a small volume, a region of a continuous blood vessel Ve that is larger than the volume of the contrast agent is contrast-enhanced as an image. Image display can be performed. This clinically means a reduction in contrast agent. The burden on the subject is greatly reduced by reducing the contrast agent.

However, without satisfying the condition of (Equation 3), as shown in FIG. 10 (c), the contrast agent flow v, the contrast agent peak width w, and the image reconstruction time interval Δt1 are as shown in (Equation 4). It may become. Then, the time _{t n-1} region _{r n-1} of the contrast medium, a region _{r n} of the contrast medium at time _{t n,} FIG. 10 (d), the time _{t n +1} contrast agent region _{r n + 1} Cannot be overlapped, and a continuous three-dimensional region of the contrasted blood vessel Ve cannot be shown.
... (Formula 4)

  In order to avoid this, the image input unit 5 needs to shorten the image reconstruction time interval Δt1. In both the cine scan and the helical scan, X-ray projection data is continuously collected in the time direction, and therefore image reconstruction is only performed at a finer image reconstruction time interval Δt2. That is, calculation of image reconstruction increases, and the number of tomographic images to be reconstructed and three-dimensional images only increase. FIG. 11A shows a case where image reconstruction is performed at a finer image reconstruction time interval Δt2 than FIG. 10A or 10C. However, for example, the image reconstruction time interval Δt2 and the image reconstruction time interval Δt2 are set such that Δt2 is half of Δt1.

In the case of FIG. 11A, since a continuous tomographic image in the z direction, that is, a three-dimensional image, is reconstructed at a finer image reconstruction time interval Δt2, the contrast agent region r _{n at} time t _{n−2. -2,} the time _{t n-1} region _{r n-1} of the contrast medium, a region _{r n} of the contrast medium at time _{t n,} a region _{r n + 1} at time _{t n + 1} of the contrast agent, the time _{t n + 2} of the contrast agent Since the region rn _{+ 2} of the region overlaps sufficiently spatially, a three-dimensional region of a continuous blood vessel Ve that has been contrasted can be obtained.

Incidentally, when a small amount of contrast agent is a high CT value region has passed through the vascular Ve between _{t n-1, t n,} t n + 1 time, the _{t n-1, t n,} t n + 1 tertiary In the original image, only a part of the blood vessel Ve can be seen with a higher CT value (for example, CT value “200”) than the surroundings, and the whole state of the blood vessel Ve is not displayed as an image and is not known. However, when this time-series three-dimensional image is displayed by MIP display or reprojection display as shown in FIG. 10B or FIG. 11B, the CT value of the whole blood vessel Ve becomes higher than the surroundings, and the whole blood vessel Ve is displayed. The state is displayed as an image and becomes visible. For example, the CT value is “200/3” in the reprojection display, and the CT value is “200” in the MIP display. Further, when performing the four-dimensional MIP display and the reprojection display, the three-dimensional image at each time t _n , t _{n + 1} , and t _{n + 2} is colored to perform the three-dimensional tracking of the time change with the color. You can also see how the whole image looks.

<Processing of four-dimensional spatial filter FF>
The time-series three-dimensional images that have been described so far are displayed as four-dimensional data in a four-dimensional reprojection display and four-dimensional MIP display in the time direction as they are, but are subjected to filtering and four-dimensional reprojection display in the time direction. It may be displayed. For example, the projection processing unit 35 performs processing (smoothing filter, intermediate value filter, maximum value filter, minimum value filter, etc.) of a four-dimensional spatial filter FF that performs noise removal on the input image, or four-dimensional labeling processing. You may perform a four-dimensional reprojection display or a four-dimensional MIP display with respect to the four-dimensional segment area | region extracted by labeling later.

The four-dimensional image data becomes four-dimensional image data by arranging three-dimensional images in time series. A three-dimensional image having a three-dimensional structure in which pixel points are arranged in three directions of x, y, and z. In this embodiment, a three-dimensional image of an X-ray CT apparatus is used. A three-dimensional image is constructed from a tomographic image of a subject taken by a medical image diagnostic apparatus such as an X-ray CT apparatus or an MRI apparatus. Each pixel of these three-dimensional images is, for example, 8-bit or 16-bit gradation data, but may be 16-bit color data or binary data of “0” or “1”.
As described above, the projection processing unit 35 displays the four-dimensional continuous region included in the noise-reduced four-dimensional image as a continuous three-dimensional image on the monitor 6 by performing four-dimensional MIP display and four-dimensional reprojection display. .
FIG. 12 shows the processing flow.

In step S1, the projection processing unit 35 inputs a time-series three-dimensional image.
In step S2, the projection processing unit 35 performs processing of the noise removal four-dimensional spatial filter FF.
In step S <b> 3, the projection processing unit 35 performs processing of the contrast-enhanced four-dimensional spatial filter FF in the CT value range of interest after noise removal.
In step S4, the projection processing unit 35 binarizes with a threshold value that can depict the target region.
In step S5, a four-dimensional continuous region is extracted by a four-dimensional labeling process.
In step S6, i = 1.
In step S7, the projection processing unit 35 performs projection in the time axis direction on the four-dimensional continuous region i, degenerates the three-dimensional region, performs four-dimensional MIP display, and four-dimensional reprojection display. Extract.
In step S8, it is determined whether all four-dimensional continuous areas i have been processed. If Yes, the process goes to step S9, and if No, the process goes to step S10.
In step S9, each continuous three-dimensional area is three-dimensionally displayed.
In step S10, i = i + 1 is set, and the process returns to step M7.

In such a flowchart, the process of the four-dimensional spatial filter FF used in step S2 and step S3 will be described below.
FIGS. 13A and 14A show processing examples of the contrast-enhancing four-dimensional spatial filter FF.
FIG. 13A shows an example of a four-dimensional spatial filter FF having a size of 3 × 3 × 3 × 3. For the pixel of interest ATT in FIG. 13A, the local region in the vicinity of the four-dimensional spatial filter FF of the time axis + three-dimensional space axis in the four-dimensional image processing is 3 × 3 × 3 × 3. Nearby 80 pixels.
FIG. 14A shows an example of a four-dimensional spatial filter FF having a size of 5 × 5 × 5 × 5. For the pixel of interest ATT in FIG. 14A, the local region in the vicinity of the four-dimensional spatial filter FF of the time axis + three-dimensional space axis in the four-dimensional image processing is 5 × 5 × 5 × 5. There are 624 pixels in the vicinity.

A four-dimensional spatial filter coefficient w near 80 of 3 × 3 × 3 × 3 pixels is w (i, j, k, l), where [1,3] &#8714; i, j, k, l. The four-dimensional image is g (i, j, k, l), where [1, N] &#8714; i, j, k, l. If the four-dimensional image after superimposing the four-dimensional spatial filter FF in the case of 3 × 3 × 3 pixels is g1 (i, j, k, l), the following (Formula 5) is obtained.
... (Formula 5)

The four-dimensional spatial filter coefficient w in the vicinity of 624 of 5 × 5 × 5 × 5 pixels is [1,5] &#8714; i, j, k, l. The four-dimensional image g1 (i, j, k, l) after the superimposition of the four-dimensional spatial filter FF in the case of 5 × 5 × 5 × 5 pixels is expressed by the following (Equation 6).
... (Formula 6)

In order to perform the processing of the four-dimensional spatial filter FF that performs contrast enhancement in the CT value range of interest in step S3, it is necessary to make the coefficients of the four-dimensional spatial filter FF depend on the CT value.
For this reason, FIGS. 13B and 14B show examples in which the four-dimensional spatial filter coefficient w in the processing of the contrast-enhanced four-dimensional spatial filter FF is changed depending on the CT value. In this example, as shown in FIGS. 13B and 14B, a four-dimensional spatial filter coefficient for contrast enhancement depending on the CT value is used. In this case, the filter F1 acts as a contrast-enhanced four-dimensional spatial filter FF, and the filter F2 acts as a four-dimensional spatial filter FF that maintains the original image. This four-dimensional spatial filter FF operates as follows. Note that a 3 × 3 × 3 × 3 size four-dimensional spatial filter FF has a W3 code, and a 5 × 5 × 5 × 5 size four-dimensional spatial filter FF has a W5 code.

(1) When the threshold value is 1 or less and the CT value ≦ Th1, the filter F1 is used.
(2) Between the threshold values 1 and 2 and Th1 <CT value ≦ Th2, a weighted addition image of the image on which the filter F1 is superimposed and the image on which the filter F2 is superimposed is used.
(3) The filter F2 is used when Th2 <CT value ≦ Th3 between the threshold values 2 and 3.
(4) Between thresholds 3 and 4 and Th3 <CT value ≦ Th4, a weighted addition image of the image on which filter F1 is superimposed and the image on which filter 2 is superimposed is used.
(5) When the threshold value is 4 or more and Th4 <CT value, the filter F1 is used.
In other words, the contrast-enhanced four-dimensional spatial filter FF acts below the CT value threshold Th2 and above the CT value threshold Th3. Accordingly, it is possible to apply a four-dimensional spatial filter FF that is dependent on the CT value, in other words, selectively contrast-enhanced for each tissue having a different X-ray absorption coefficient. That is, a four-dimensional spatial filter FF in which the time axis characteristic and the spatial axis characteristic are adjusted for each tissue is realized.

  For example, in the case of contrast enhancement, a 3 × 3 × 3 × 3 pixel four-dimensional spatial filter F1W3 has a = 2.04, b = −0.1, and C = −0.01. In the case of contrast enhancement, the 5 × 5 × 5 × 5 pixel four-dimensional spatial filter F1W5 has a = 2.21, b = −0.1, and C = −0.01. The sum of the coefficients a, b, and c is 1, respectively. By multiplying such coefficients, a four-dimensional spatial filter FF with adjusted time axis characteristics and space axis characteristics is realized.

  Furthermore, it can be used not only as contrast enhancement but also as a noise improvement filter depending on the CT value in the four-dimensional spatial filter FF used in step S2. In this case, the four-dimensional spatial filter coefficient W5 of 5 × 5 × 5 × 5 pixels is a = 0.28, b = 0.05, and C = 0.01. The sum of these coefficients is 1. By multiplying such coefficients, a four-dimensional spatial filter FF with adjusted time axis characteristics and space axis characteristics is realized.

The noise improvement four-dimensional spatial filter FF acts on the CT value threshold Th1 or more and the CT value threshold Th4 or less.
In step S5, after performing the four-dimensional labeling process, the projection processing unit 35 performs projection in the time axis direction for each of the four-dimensional continuous areas one by one, degenerates the three-dimensional areas, and makes the three-dimensional continuous areas. Four-dimensional MIP display or four-dimensional reprojection display is performed. The projection processing unit 35 can convert each piecewise four-dimensional continuous region into one continuous three-dimensional continuous region so that an image can be displayed. That is, it is possible to perform projection processing in the time axis direction on a region of a certain CT value range and convert it to a three-dimensional image, and display a temporal change in the region of the CT value range which is a three-dimensional image display.

  In the description of the present embodiment, the contrast enhancement process and the noise improvement process are exemplified as the process of the four-dimensional spatial filter FF. However, the edge enhancement process, the smoothing process, the deconvolution process, the maximum value filter process, the intermediate value filter, and the like. Processing, minimum value filtering processing, abnormal point detection processing, and the like can also be performed. Further, the dimension can be expanded as the processing of the four-dimensional spatial filter FF.

<3D display of left coronary artery with few contrast agents>
For example, FIG. 15 shows an example of the shape of the left coronary artery of the heart. For example, consider a three-dimensional display of the entire left coronary artery with a small amount of contrast medium. As shown in FIG. 15, the time for image reconstruction in the time axis direction is sufficiently dense, that is, the time interval Δt is sufficiently shortened. Then, the three-dimensional regions g _n−2 , g _n−1 , g _n , g _{n + 1} , and g _{n + 2} become a four-dimensional continuous region as a four-dimensional region, are projected in the time axis direction, and are degenerated in three dimensions. In this way, a fragment of the blood vessel Ve contrasted with the contrast agent that was a fragmentary three-dimensional region at each time can be made into a continuous three-dimensional region as the entire left coronary artery. By displaying the continuous three-dimensional region in three-dimensional MIP display and three-dimensional reprojection display, four-dimensional MIP display and four-dimensional reprojection display can be realized. Further, by measuring an image of this three-dimensional continuous region, a three-dimensional image feature amount such as a volume and a surface area can be obtained.

By using such contrast agent synchronous imaging according to the flowchart of FIG. 16, it is possible to image a long range of the blood vessel Ve with less contrast medium.
In step C1, the operator places the subject on the cradle 12 and performs positioning.
In step C2, the operator performs scout image collection.
In step C3, the operator sets shooting conditions.
In step C4, the operator performs baseline tomography.
In step C5, a baseline tomographic image display is performed.
In step C6, the operator performs contrast agent synchronous imaging condition setting. Set the region of interest on the baseline tomogram.

In step C7, the image input unit 5 starts a monitor scan.
In Step C8, it is determined whether the average CT value of the region of interest exceeds a set threshold value. If Yes, the process goes to Step C9. If NO, repeat step C8.
In step C9, the image input unit 5 prepares for the main scan. The cradle 12 of the imaging table 10 is moved to the main scan position.
In step C10, the image input unit 5 starts a main scan.
In step C11, the main scan tomographic image display is performed.
In this process, the contrast agent for the main scan is reduced as compared with the conventional case, and the X-ray CT apparatus 100 can perform imaging of a long range of the blood vessel Ve with a small amount of contrast agent.

<Adaptive reprojection display, adaptive MIP display>
In this embodiment, the adaptive reprojection display and the adaptive MIP display can be further improved. The adaptive type is a concept that changes processing according to conditions.
FIG. 17 shows an example of the first adaptive filter AdFg1 (x, y, z1, t1) extending in the time axis direction. In FIG. 17, the first adaptive filter AdFg1 (x, y, z1, t1) is located in the vicinity of the target pixel ATTg (x, y, z1, t1) in the time axis direction in the range from t1−Δt to t1 + Δt. Is set.

FIG. 18 shows an example of the second adaptive filter AdFg2 (x, y, z1, t1) extending in the time axis direction and the space axis direction. In FIG. 18, t1− (K−1) / 2 to t1 + (K−1) in the time axis direction around the target pixel ATTg (x, y, z1, t1) and in the spatial axis direction in the x and y directions. ) / 2, x− (K−1) / 2 to x + (K−1) / 2, and y− (K−1) / 2 to y + (K−1) / 2. An adaptive filter AdFg2 (x, y, z1, t1) is set.
FIG. 19 is an example showing a histogram distribution of CT values of pixels in the vicinity region of the target pixel ATTg.

FIG. 20 is a flowchart illustrating an example of adaptive reprojection processing and adaptive MIP processing. When the process is changed according to the histogram distribution of the CT values of the pixels in the vicinity of the target pixel ATTg (x, y, z1, t1), the following process is performed.
In step A1, the projection processing unit 35 sets x = 1 and y = 1.
In step A2, the projection processing unit 35 reads pixels in the vicinity of the target pixel ATTg (x, y, z1, t1) of the tomographic image.
In step A3, it is determined whether it belongs to group 1. If YES, go to step A4, and if NO, go to step A5.
In step A4, the pixels in group 1 are averaged or weighted addition processing is performed.
In step A5, it is determined whether it belongs to group 2. If YES, go to step A6, and if NO, go to step A7.

In step A6, the pixel in group 2 is averaged or weighted addition processing is not performed. In step A7, it is determined whether x = K. If YES, the process goes to step A8. If NO, the process goes to step A2. go.
In step A8, it is determined whether y = K. If YES, the process goes to step A9. If NO, the process goes to step A2.
In step A9, the projection processing unit 35 performs a four-dimensional reprojection process or a four-dimensional MIP process. For example, when the group 1 is the background and the group 2 is the part, if the target pixel ATTg (x, y, z1, t1) belongs to the group 1, the average or weighted addition processing is performed, and the processing is not performed in the group 2. . Thereby, the noise in the background of the group 1 is improved, and the contrast and the spatial resolution of the structure of the group 2 are not lost.

  If group 1 is organization 1 and group 2 is organization 2 and both have no structure with no contrast, group 1 performs an average or weighted addition with the pixels in group 1 and group 2 performs group 2 The average or weighted addition is performed with the pixels within. In any group, it is possible to perform processing adapted to the case where noise can be improved.

  Whether to belong to group 1 or whether to belong to group 2 is determined by obtaining the standard deviation σ1 of group 1 and the standard deviation σ2 of group 2 to determine which group is statistically close. It may be determined, or it may be determined whether it is within three times the standard deviation σ1, σ2. By performing the four-dimensional reprojection process, the four-dimensional MIP process, and the like after applying the adaptive filter, the image quality such as noise and contrast of the four-dimensional reprojection process and the four-dimensional MIP process can be improved.

  In the present embodiment, an embodiment in which adaptive N-dimensional reprojection display or adaptive N-dimensional MIP display is performed on a time-series multidimensional image of four dimensions or more is shown. Multi-dimensional time-series images of three or more dimensions include multi-band images in remote sensing and superimposed images of multiple modalities of medical diagnostic equipment.

  For example, FIG. 21 shows a case where a time-series three-dimensional image of a subject by an X-ray CT apparatus and a time-series three-dimensional image of a subject by an MRCT apparatus are superimposed. At this time, the coordinate system of the time-series three-dimensional image of the X-ray CT apparatus is x, y, z, each pixel value is c (x, y, z, t), and the coordinate system of the time-series three-dimensional image of the MRCT apparatus. Is xm, ym, zm, and each pixel value is r (xm, ym, zm, t). In a time-series image obtained by superimposing a time-series 3D image in an X-ray CT apparatus and a time-series 3D image in an MRCT apparatus, a certain pixel is represented by (c (x, y, z, t), r (x, y, z, t)) is a five-dimensional multidimensional image.

  In this way, the order of the multidimensional image is increased by superimposing the three-dimensional images of a plurality of modalities. In this multidimensional image, it is possible to project in the time axis direction using a time-series multidimensional image. As a result, the above-described reprojection display, MIP display, adaptive reprojection display, and adaptive MIP display can be performed, and similar effects can be obtained.

The values of the time-series X-ray CT and MRCT three-dimensional images at the target pixel g (x, y, z, t) are (c (x, y, z, t), r (x, y, z, t)). Then, [t− (K _t −1) / 2, t + (K _t −1) / 2], x, y, z axes in the time axis direction around the target pixel g (x, y, z, t). [X− (K _x −1) / 2, x + (K _x −1) / 2], [y− (K _y −1) / 2, y + (K _y −1) / 2], [z The pixel range of − (K _z −1) / 2, z + (K _z −1) / 2] is set as the neighborhood region of the adaptive filter.

  FIG. 19 shows a case where the histogram distribution of the CT values of the pixels in these neighboring regions is obtained. The flowchart of the adaptive reprojection process or the adaptive MIP process when the histogram distribution of the CT value or the MRCT pixel value of the pixel in the vicinity region of the target pixel is divided into group c1, group c2, or group r1, group r2 is shown in FIG. As shown in FIG.

In step A11, x = 1, y = 1, and z = 1.
In step A12, the neighborhood region of each pixel (c (x, y, z, t), r (x, y, z, t)) of the time-series X-ray CT and MRCT three-dimensional image is read.
In Step A13, it is determined whether or not the pixel c (x, y, z, t) belongs to the group c1, and if YES, go to Step A14, if NO, go to Step A15.
In step A14, an average or weighted addition process is performed on the pixels in the group c1.
In step A15, it is determined whether the pixel c (x, y, z, t) belongs to the group c2. If YES, the process goes to step A16, and if NO, the process goes to step A17.
In step A16, an average or weighted addition process is performed on the pixels in the group c2. Alternatively, no processing is performed.

In step A17, it is determined whether the pixel r (x, y, z, t) belongs to the group r1, and if YES, go to step A18, and if NO, go to step A19.
In step A18, an average or weighted addition process is performed on the pixels in the group r1.
In Step A19, it is determined whether or not the pixel r (x, y, z, t) belongs to the group r2. If YES, the process goes to Step A20, and if NO, the process goes to Step A21.
In step A20, an average or weighted addition process is performed on the pixels in the group r2. Alternatively, no processing is performed.

In step A21, it is determined whether x = _{K x,} if YES go to Step A22, if NO the process returns to step A12.
In step A22, it is determined whether y = _{K y,} if YES go to Step A23, if NO the process returns to step A12.
In step A23, it is determined whether z = _{K z,} if YES go to Step A24, if NO the process returns to step A12.

In step A24, a four-dimensional reprojection process or a four-dimensional MIP process is performed.
For example, when the group c1 or the group r1 is the background and the group c2 or the group r2 is a structure, if the group c1 or the group r1 belongs to the group c1 or the group r1, an average or weighted addition process is performed in the groups c1 and r1, and the group c2 or If it belongs to the group r2, no processing is performed in the groups c2 and r2. Thereby, the noise in the background of the group c1 or the group r1 is improved, and the contrast or spatial resolution of the structure of the group c2 or the group r2 is not lost. Or it does not deteriorate so much.

  In addition, if the group c1 or the group r1 is the organization 1, the group c2 or the group r2 is the organization 2, and both are organizations without a structure having a small contrast, the group c1 or the group r1 includes the group c1 or the group r1. An average or weighted addition process is performed on the pixels, and an average or weighted addition process is performed on the pixels in the group c2 or the group r2, and noise can be improved in any group.

  The determination of whether or not it belongs to group c1, group r1, group c2, and group r2 is performed by obtaining standard deviations σc1, σr1, σc2, and σr2 of group c1, group r1, group c2, and group r2, respectively. It can also be determined whether it is statistically close to group c1, close to group c2, close to group r1, or close to group r2 compared to the standard deviation.

  Although the case where N = 4 has been described in the above embodiment, the same effect can be obtained even when N is an integer value greater than 4.

  In the embodiment described above, a storage medium (or recording medium) in which a program code of software that realizes the above-described function is recorded is supplied to the system or apparatus, and the computer (or CPU or MPU) of the system or apparatus is supplied. ) Can also be realized by reading and executing the program code stored in the storage medium. In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the storage medium storing the program code constitutes the present invention.

  As a storage medium for storing such program code, for example, a floppy disk (registered trademark), a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a magnetic tape, a nonvolatile memory card, a ROM, a DVD-RAM, a DVD- ROM and CD-RW can be used. Furthermore, it may be downloaded via a medium called a network (for example, the Internet).

It is obvious that the above program can be applied to firmware.
In the present embodiment, four-dimensional display is performed by the X-ray CT apparatus 100. However, other modalities of MRI, PET, MRI-CT apparatus, ultrasonic diagnostic apparatus, industrial X-ray CT apparatus, and industrial ultra-high speed are used. The same effect can be obtained even if image synthesis is performed by an acoustic flaw detector or an electron microscope device, and processing is performed in a dimension exceeding four dimensions.

It is a block diagram which shows the X-ray CT apparatus concerning one Embodiment of this invention. It is a flowchart which shows the outline | summary of operation | movement about the X-ray CT apparatus of this embodiment. (A) is a figure which shows each time series tomogram of a cine scan, (b) is a figure which shows each time series tomogram of a helical scan. It is a figure which shows the operation | movement of an axial shuttle scan. It is a figure which shows operation | movement of a helical shuttle scan. (A) is a conceptual diagram of three-dimensional reprojection, and FIG. 6 (b) is a diagram showing an interpolated tomographic image. It is a figure which shows a time-axis direction reprojection display and a time-axis direction MIP display. It is a flowchart of a four-dimensional reprojection display. It is a flowchart of a four-dimensional MIP display. It is a figure which shows the example which images the blood vessel Ve with a small amount of contrast agents. (A) And (b) is a figure which shows the example which images the blood vessel Ve with a small amount of contrast agents with a short period, (c) is a figure which shows the width | variety of the peak of a contrast agent. It is a flowchart of the process which performs the three-dimensional display of each four-dimensional continuous area | region. It is explanatory drawing of the example (3x3x3x3 example) of the four-dimensional spatial filter FF. It is explanatory drawing of the example (example of 5x5x5x5) of four-dimensional spatial filter FF. It is a figure which shows the example of the shape of the blood vessel Ve, and a figure which shows the change of the contrast agent distribution in the blood vessel Ve in each time. It is a flowchart which shows the process of contrast agent synchronous imaging. It is a figure which shows the adaptive filter of a time-axis direction. It is a figure which shows the adaptive filter extended in the time-axis direction and the space-axis direction. It is a figure which shows grouping of the pixel in a neighborhood pixel. It is a flowchart which shows the example of an adaptive reprojection process and an adaptive MIP process. It is the figure which overlap | superposed the time-sequential 3D image of the subject and the time-sequential 3D image of the subject by the MRCT apparatus. It is a flowchart of an adaptive reprojection process or an adaptive MIP process when divided into groups.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Operation console 2 ... Input device 3 ... Central processing unit 5 ... Image input part (data collection buffer)
6 ... Monitor 7 ... Storage device 12 ... Cradle 15 ... Rotating unit 20 ... Scanning gantry 21 ... X-ray tube 23 ... Collimator 24 ... Multi-row X-ray detector 25 ... Data acquisition device (DAS)
26: Rotating unit controller 28 ... Beam forming X-ray filter 29 ... Control controller 30 ... Slip ring 31 ... Pre-processing unit 33 ... Beam hardening processing unit 34 ... Image reconstruction unit 35 ... Projection processing unit d ... On the rotation center axis Multi-row X-ray detector width

Claims (17)

An image input unit for inputting an image by using N-1D images arranged in time series as an N-dimensional image;
A projection processing unit that performs projection processing of the N-dimensional image in the time direction;
An N-dimensional image display apparatus, comprising: an image display unit that displays an N-dimensional image projected by the projection processing unit as an N-1D image.   2. The projection processing unit according to claim 1, wherein the projection processing unit performs a time-direction projection process on a time-series N−1-dimensional image with respect to a limited range of CT values on the N-dimensional image. Dimensional image display device.   The projection processing unit performs reprojection processing in the time direction or MIP processing (Maximum Intensity Projection) in the time direction, using the N-1D images arranged in time series as the N-dimensional image. The N-dimensional image display device according to claim 1 or 2.   The N-dimensional image display apparatus according to claim 3, wherein the projection processing unit performs reprojection processing or MIP processing in which a color is changed at each time.   The N-dimensional image display device according to claim 3, wherein the projection processing unit performs adaptive reprojection processing.   The N-dimensional image display device according to claim 3, wherein the projection processing unit performs adaptive MIP processing. While rotating the X-ray generator and the multi-row X-ray detector for detecting X-rays relative to each other around the rotation center between the X-ray generator and the multi-row X-ray detector, In an X-ray tomographic imaging apparatus for collecting tomographic images by collecting X-ray projection data transmitted through a subject,
An image input unit for inputting the tomographic image as a time-series aligned N-dimensional image;
A projection processing unit that performs projection processing of the N-dimensional image in the time direction;
An image display unit that displays an image of the N-dimensional image projected by the projection processing unit as an N-dimensional image;
An X-ray tomographic imaging apparatus comprising:   8. The X-ray tomographic imaging apparatus according to claim 7, wherein processing of N-dimensional spatial filters arranged in time series is performed on a target pixel at a certain time of the N-dimensional image.   The X-ray tomographic imaging apparatus according to claim 7 or 8, wherein the scan for collecting the X-ray projection data is a cine scan or a shuttle scan.   10. The projection processing unit performs a time-direction projection process on a time-series N−1-dimensional image with respect to a limited range of CT values on the N-dimensional image. The X-ray tomographic imaging apparatus according to any one of the above.   The projection processing unit performs reprojection processing in a time direction or MIP processing in a time direction by using the N-dimensional images arranged in time series as an N-dimensional image. The X-ray tomographic imaging apparatus according to one item.   The X-ray tomographic imaging apparatus according to claim 11, wherein the projection processing unit performs reprojection processing or MIP processing in which a color is changed at each time.   The said image input part determines the scanning interval which collects the said X-ray projection data in consideration of the temporal change of CT value of a predetermined area | region in the said N-dimensional image. X-ray tomographic imaging apparatus.   The X-ray tomographic imaging apparatus according to claim 11, wherein the projection processing unit is adaptive reprojection processing in a time axis direction.   The X-ray tomographic imaging apparatus according to claim 11, wherein the projection processing unit is adaptive MIP processing in a time axis direction.   The X-ray according to claim 6, further comprising an image reconstruction unit that performs image reconstruction by determining a time-series interval of each tomographic image in consideration of temporal changes in a region of a certain CT value range. Tomographic imaging device. In consideration of a temporal change in a region of a certain CT value range and an expanded size of the region, an image reconstruction unit that performs image reconstruction by determining a time series interval of each tomographic image is included. The X-ray tomographic imaging apparatus according to claim 6.