JP2002011001A - X-ray computed tomography - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a helical scan X-ray computed tomography with improved continuity of serial cross section image. SOLUTION: An X-ray tube samples the data during it moves along helical track against a test specimen together with a detector equipped with plural rows of detectors corresponding to multi-slice. Out of the sampled-data, each datum related to a prescribed number of re-sampling position, set within a prescribed slice thickness with a target slice position as a center, is re-sampled, and out of those re-sampled data, the data within a range of angle necessary for reconstruction of an image at specific period of heartbeat, are extracted, and out of those extracted data, an image related to the position of target slice is reconstructed. At the above dada extraction, it is possible to select a period of heartbeat, which extracts data at each re-sampling positions.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray tube which collects data while moving along a spiral trajectory with respect to a subject together with a multi-slice compatible detector having a plurality of detector rows. The present invention relates to an X-ray computed tomography apparatus (hereinafter abbreviated as CT scanner) for reconstructing an image of a target slice.

[0002]

2. Description of the Related Art In examining a fast-moving part of a subject, for example, a heart, it is necessary to reconstruct an image (tomographic image) by aligning raw data of a specific period of a heartbeat.

A conventional ECG-gated reconstruction method (for example, a helical half method) is based on data collected during, for example, three revolutions of a detector passing through a target slice position, by 180 ° + α centering on a specific period of a heartbeat. This is a process of extracting data for (α is a fan angle) and reconstructing an image from the extracted data.

In helical scan, the position of the top is constantly changing, and data of the target slice position is obtained.
It is necessary to make them uniform by an interpolation method called a helical filter interpolation method.

In the helical filter interpolation method, a plurality of slice positions (referred to as resampling positions) before and after a target slice position are set at, for example, equal intervals (or unequal intervals in some cases). The data at the resampling position is obtained from the data actually collected by the detector by interpolation or extrapolation,
This is a process of weighting and averaging the data averages at the resampling positions for each scan angle (usually represented by the angle of the X-ray tube) and reconstructing an image from the weighted and averaged data. Therefore, the actual slice thickness is
This corresponds to a distribution range of a plurality of resampling positions set around the target slice position.

FIG. 1 is a diagram illustrating a helical filter interpolation method to which a conventional ECG-gated reconstruction method is applied.
In the example of FIG. 1, the number of detector rows is assumed to be a general four, and the center trajectory of each detector row is shown over time. The processing flow of the conventional reconstruction processing method is as follows.

(Helical Filter Interpolation Processing) First, a period (t1 to t2) during which the four detector rows pass through the target slice position and a resampling position in each of the resampling positions within the region Rn limited to a predetermined slice thickness. The data is determined by interpolation between four detector rows collected at the same time. The data of the portion Tn outside the detector rows 1 and 4, for which a value is not obtained by interpolation between the detector rows, is created using extrapolation from the preceding and following detector rows. The data at the target slice position is obtained by weighting and averaging the completed raw data corresponding to, for example, more than ten resampling positions at each scan angle, that is, in the slice direction.

(Extraction of Raw Data for Half View Numbers) From raw data obtained by helical filter interpolation processing (region Rn for three rotations in the case of helical pitch 1), a specific period of the heartbeat, for example, R wave Among the heartbeats included in the region Rn, the heartbeat visited at the earliest time is specified in the range of 180 ° + α. The raw data in the range of 180 ° + α around the specified period of the specified heartbeat is extracted (FIG. 1).
Area Sn) indicated by oblique lines.

(Half Processing and Image Reconstruction) In the half processing, the raw data of 180 ° + α is extended to 360 °
Generate raw data for minutes. The half treatment includes a Parker method, a method in which a counter beam is used in combination with the Parker method, and the like. Reconstruct the extended 360 ° raw data to obtain the final image.

The following problems have been pointed out in such a conventional ECG-gated reconstruction method. The first point is that the continuity of the image in the slice direction (the direction perpendicular to the slice plane) of the three-dimensional image or the multi-section conversion (MPR) image is poor. There is a stripe pattern in the width direction (lateral direction) in the plane. "

Here, the cause will be described. FIG.
Is an MPR image, and it can be seen that this image has unevenness in the slice direction.

(Effects of Heartbeat Jump) The images in the stripe at several mm intervals observed in FIG. 2 are reconstructed from raw data corresponding to "one heartbeat". The distance between horizontal stripes is determined by the heart rate and the moving speed of the bed. This horizontal stripe boundary is called a “heartbeat jump”. Heartbeat jumps are caused by the following causes:

(Movement of heart not synchronized with heartbeat) It is assumed that the heart does not always make the same movement (position and size) for each heartbeat. This is the single heartbeat jump seen in FIG.

(Time Change of Contrast Agent Concentration) In the right atrium of FIG. 2, many heartbeat jumps are observed. This is because, while the concentration of the contrast agent in the heart changes continuously, the ECG-gated reconstruction method discretely extracts only the portion corresponding to the heartbeat. In other words, between each horizontal stripe, the time at which the heartbeat exists is different, that is, one image is reconstructed from data collected in one heartbeat, and the next image is data collected in the next or later heartbeat. , And a time interval opens between both images,
During that time, artifacts due to body movements and changes in the contrast agent density occur, so that the gray values of the images are different.

[0015]

SUMMARY OF THE INVENTION An object of the present invention is to provide a helical scan X-ray computed tomography apparatus for improving the continuity of a continuous cross-sectional image.

[0016]

According to the X-ray computed tomography apparatus of the present invention, the X-ray tube moves along a spiral trajectory with respect to the subject together with a multi-slice compatible detector having a plurality of detector rows. Means for sampling the data to
From the sampled data, means for resampling data for each of a predetermined number of resampling positions set within a predetermined slice thickness around the target slice position, from the resampled data,
Extraction means for extracting data for an angle range required for one image reconstruction in a specific period of a heartbeat, and means for reconstructing an image relating to the target slice position from the extracted data, wherein the extraction means comprises: It is characterized by having a function of selecting a heartbeat period for extracting data for each resampling position.

The X-ray computed tomography apparatus according to the present invention is a means for sampling data while the X-ray tube moves along a spiral trajectory with respect to the subject together with a multi-slice compatible detector having a plurality of detector rows. Means for resampling data relating to each of a predetermined number of resampling positions set within a predetermined slice thickness around the target slice position from the sampled data; and Extracting means for extracting data corresponding to an angle range required for one image reconstruction; and means for reconstructing an image relating to the target slice position from the extracted data, wherein the extracting means comprises: The data for the angle range for some of the resampling positions among the sampling positions is Wherein the aligning with a different cardiac phase from the resampling position relating to the angular range of data.

The X-ray computed tomography apparatus according to the present invention is a means for sampling data while the X-ray tube moves along a helical trajectory with respect to the subject together with a multi-slice compatible detector having a plurality of detector rows. Means for resampling data relating to each of a predetermined number of resampling positions set within a predetermined slice thickness around the target slice position from the sampled data; and Extracting means for extracting data for an angle range required for one image reconstruction, and means for reconstructing an image relating to the target slice position from the extracted data, wherein the extracting means The data for the angle range required for the above is aligned from the data of a plurality of heartbeat periods.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) Hereinafter, an X-ray computed tomography apparatus (C) according to the present invention will be described with reference to the drawings.
T scanner) will be described with reference to a preferred embodiment. Figure 1
2 schematically shows the configuration of the CT scanner according to the present embodiment. The gantry 1 includes an X-ray tube 11 and a plurality of components necessary for collecting projection data. An X-ray tube 11 that generates X-rays in a cone beam shape by supplying power from the X-ray control unit 12 is attached to a rotating ring, not shown. A plurality of, for example, four, multi-slice detectors 13 are attached to the rotating ring so as to face the X-ray tube 11 with a substantially cylindrical imaging region therebetween. Have been. At the time of data collection, the subject is inserted into the imaging region while lying on the couchtop. At the time of the helical scan, a movement is performed under the control of the gantry bed controller 14 such that the rotating ring continuously rotates and the top plate moves continuously. With this operation control,
In the moving coordinate system that moves with the subject, the X-ray tube 11 moves in a spiral trajectory together with the detector 13. During this movement, at a constant frequency, the output of the detector 13 is DA
It is sampled, amplified and digitized by a data collection system 15 called S.

As shown in FIG. 3, the output data from the data collection system 15 is supplied continuously from the output of the electrocardiograph 3 via the ECG interface board 16 and is derived from the output of the electrocardiograph 3. It is combined with the electrocardiographic data representing the heartbeat timing.

The data including the electrocardiogram data is taken into the computer system 2. The computer system 2 uses the CPU 21 as a center of control and calculation processing, using a control unit 22 that performs a scanning operation, a preprocessing unit 23 that performs preprocessing such as correction on data, and raw data that has been subjected to preprocessing. A reconstructing unit 24 for reconstructing image (tomographic image) data in accordance with a new heart rate filtering method, and a display unit 25 for displaying the image.

Next, the heartbeat filtering method important in the present invention will be described in the order of processing. FIG. 4 is an explanatory diagram of the heartbeat filtering method according to the present embodiment.

(Helical Interpolation Processing) First, resampling positions are set at, for example, dozens of positions at predetermined intervals (in some cases, not necessarily at constant intervals) within a range of a predetermined slice thickness around the target slice position. You. A plurality of resampling points are set on each of these resampling positions according to the sampling position at the time of data collection.
Raw data at each of these resampling points is determined by interpolation between four detector rows collected at the same time. In the present embodiment, unlike the conventional ECG-gated reconstruction method, raw data having a maximum length is generated at each resampling point within a range in which no extrapolated data is used. That is, the raw data at each of the resampling points in the parallelogram region V corresponding to three rotations in the figure where four detector rows pass through the predetermined slice thickness range centered on the target slice position is Calculated by interpolation. Weighted averaging cannot be performed on the raw data group created in this manner because the collected angles (view positions) are different from each other. Therefore, at this time, unlike the conventional ECG-gated reconstruction method, "filter processing (weighted averaging)" is not performed. By using only interpolation and not using extrapolation in this way, it is possible to reduce artifacts unique to extrapolation, but this is an essential point in the heartbeat filter method of the present invention. Instead of requirements, extrapolation may be employed as shown in FIG.

(Extraction of Raw Data for Half View Numbers) Next, data used for image reconstruction is extracted from raw data of resampling points in the parallelogram region V. This data extraction method is used. Is very important for the heart rate filtering method of the present invention.

In the region V, the earliest time at which the raw data of 180 ° + α (α is a fan angle) is complete, in the range of angles required for one image reconstruction centering on a specific period of the heartbeat (eg, R wave). Is selected independently for each resampling position, instead of selecting the heartbeat (A) to be visited in a slice unit as in the related art. If this angle range is an angle range required for one image reconstruction, for example, one end of the angle range is in a specific period of the heartbeat without centering on a specific period of the heartbeat (for example, R wave). May be.

That is, the reconstruction unit 23 has a function of selecting a heartbeat period for extracting data to be used for image reconstruction for each resampling position. Raw data is
The raw data of 180 ° + α for another continuous resampling position aligned within a certain heartbeat (A) is aligned within another heartbeat (B), that is, the data for the angle range required for one image reconstruction. Can be aligned from the data of a plurality of consecutive cardiac phases.

In FIG. 4, the boundary of the heartbeat is 180 °
The raw data for + α is set at the resampling position where the raw data for + α is not aligned in the heartbeat (A), and the raw data for 180 ° + α at the resampling position after the resampling position is set in the next heartbeat (B). It adopts a variable method in which the boundaries of the heartbeat fluctuate such that they are aligned with each other.

(Half processing) Raw data extracted from a plurality of consecutive heartbeats cannot be weighted and averaged as it is because the collected angles are different from each other. Therefore, 180 ° +
The raw data for the α-angle is expanded, and the raw data for 360 ° is expanded to generate the raw data for 360 °.

(Overlay of Raw Data) The raw data created by the half processing is weighted and averaged while adjusting the scan angle while the raw data having the same scan angle is adjusted.
This weighted averaging process corresponds to “filtering” in the conventional ECG-gated reconstruction method.

(Reconstruction process) 360 ° obtained in this way
The image data is reconstructed from the weighted averaging data.

The following four effects can be obtained by such a heartbeat filter method. This effect will be described in comparison with a conventional ECG-gated reconstruction method. (1) Reduction of Effect of Heartbeat Jump FIG. 5 shows an MPR image by the heartbeat filter method.
As can be seen by comparing FIG. 5 with FIG. 2, the heartbeat jump is reduced, and the images are smoothly connected in the slice direction. The reason is that the heartbeat filter method does not suddenly "switch" from one heartbeat to the next at slice positions before and after a heartbeat jump. That is, as shown in FIG. 6, the raw data on which the image at the n-th target slice position is based is the raw data on which the image at the (n + 1) -th target slice position adjacent thereto is located.
The heartbeat period partially overlaps, that is, in FIG. 6, the heartbeat of the data D2 at the rear resampling position in the raw data on which the image at the nth target slice position is based, and the (n + 1) th heartbeat adjacent thereto And the heartbeat of the data D3 at the preceding resampling position in the raw data based on the image at the target slice position of
As a result, even if some body movement occurs between the heartbeat (A) and the heartbeat (B), the effect is alleviated.

(2) There is no restriction on the image slice thickness (filter thickness) Similarly, since no extrapolated data is used, there is no “variation in image slice thickness before and after a heartbeat jump”. Therefore, it is possible to increase the image slice thickness (to increase the filter thickness) as compared with the conventional ECG-gated reconstruction method.

(3) Reduction of Slice Positions at Which No Image Can Be Created As described above, in the conventional ECG-gated reconstruction method, the image corresponding to the four black horizontal stripe slice positions in FIG. I can't create it. " That is, at this slice position, a phenomenon occurs in which raw data for the angle required for reconstruction cannot be aligned. As the helical pitch increases, the number of slice positions at which an image cannot be formed gradually increases.

On the other hand, in the heartbeat filter system according to the present embodiment, reconstructable heartbeats are included in some raw data of all slice positions for the number of resampling points (that is, slice positions inside the filter thickness). If not, an image can be created. The MPR image in FIG. 5 shows that the heartbeat filter method can continuously generate images without gaps compared to the conventional ECG-gated reconstruction method.

(4) The helical pitch can be increased. Accordingly, as a secondary effect, the heartbeat filter method may be able to increase the helical pitch as compared with the conventional ECG-gated reconstruction method.

(Modification) The heartbeat filter system of the present embodiment is also applicable to a high time resolution type electrocardiographic synchronous reconstruction system. This method requires 180 image reconstructions.
In the raw data of the angle of + °, for example, the first half is aligned from the heartbeat (A) and the second half is aligned from the next heartbeat (B). When the heart rate filter method is applied, for example, FIG.
As shown in (1), among the raw data in the first half, raw data on a part of the resampling positions can be aligned from the heartbeat (A), and raw data on the remaining resampling positions can be aligned from the next heartbeat (B). Will be possible. FIG. 8 shows an MPR image obtained by applying the heartbeat filter method to the high temporal resolution type electrocardiographic synchronous reconstruction method, and FIG. 9 shows an MPR image obtained without applying the heartbeat filter method. As can be seen from these images, it is understood that the heartbeat filter method is also effective for the high time resolution type ECG-gated reconstruction method.

The present invention is not limited to the above-described embodiment, and can be implemented in various forms without departing from the spirit of the invention at the stage of implementation.

[0038]

According to the present invention, the continuity between adjacent images is improved and the images are smoothly connected.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a helical filter interpolation method to which a conventional ECG-gated reconstruction method is applied.

FIG. 2 is a halftone image showing an MPR image according to the method of FIG.

FIG. 3 is a schematic configuration diagram of an X-ray computed tomography apparatus according to an embodiment of the present invention.

FIG. 4 is an explanatory diagram of a heartbeat filtering method according to the embodiment.

FIG. 5 is a diagram showing an MP using a heart rate filter according to the present embodiment
A halftone image showing an R image.

FIG. 6 is an explanatory diagram showing the reason why images are smoothly connected by the heartbeat filter method of the embodiment.

FIG. 7 is a diagram showing an example in which the heartbeat filter method of the present embodiment is applied to a high temporal resolution type electrocardiographic synchronous reconstruction method.

8 is a halftone image showing an MPR image obtained by applying a heartbeat filter method to the high time resolution type electrocardiographic synchronous reconstruction method of FIG. 7;

9 is a halftone image showing an MPR image obtained without applying the heartbeat filter method to the high temporal resolution type electrocardiographic synchronous reconstruction method of FIG. 7;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... gantry 2, computer system, 3 ... electrocardiograph, 11 ... X-ray tube, 12 ... X-ray control part, 13 ... detector, 14 ... gantry bed control part, 15 ... Data acquisition system, 21 ... CPU, 22: control unit, 23: pre-processing unit, 24: reconstructing unit, 25: display unit.

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Manabu Hiraoka 1385-1 Higashiyama, Shimoishi-kami, Otawara-shi, Tochigi Prefecture F-term in the Toshiba Nasu Plant (reference) 4C093 AA22 BA03 BA10 CA50 DA02 EA02 EB18 FA34 FA47 FE13 FF38 5B057 AA08 BA03 BA19 BA28 CA02 CA08 CA12 CA16 CB02 CB08 CB12 CB16 CC03 CE06 CE06 CE10 DA08 DB02 DB09

Claims (3)

[Claims] 1. A means for sampling data while an X-ray tube moves along a helical trajectory with respect to a subject together with a multi-slice compatible detector having a plurality of detector rows, and a target from the sampled data. Means for resampling data relating to each of a predetermined number of resampling positions set within a predetermined slice thickness with the slice position as a center; from the resampled data, an angle range required for one image reconstruction in a specific period of a heartbeat Extracting means for extracting data of the target slice position from the extracted data, wherein the extracting means selects a heartbeat period for extracting data for each of the resampling positions. An X-ray computed tomography apparatus characterized by having a function to perform the operation. 2. A means for sampling data while the X-ray tube moves along a helical trajectory with respect to a subject together with a multi-slice compatible detector having a plurality of detector rows, and a target from the sampled data. Means for resampling data relating to each of a predetermined number of resampling positions set within a predetermined slice thickness with the slice position as a center; from the resampled data, an angle range required for one image reconstruction in a specific period of a heartbeat Extraction means for extracting data of the target slice position from the extracted data, the extraction means comprising: a part of the predetermined number of resampling positions; The data for the angular range for the sampling position is converted to the angle for the remaining resampling position. Range partial X-ray computed tomography apparatus characterized by aligning a different heartbeat period with data. 3. A means for sampling data while the X-ray tube moves along a helical trajectory with respect to a subject together with a multi-slice compatible detector having a plurality of detector rows, and a target from the sampled data. Means for resampling data relating to each of a predetermined number of resampling positions set within a predetermined slice thickness with the slice position as a center; from the resampled data, an angle range required for one image reconstruction in a specific period of a heartbeat Extracting means for extracting the data of the above, comprising: means for reconstructing an image related to the target slice position from the extracted data, wherein the extracting means converts data for an angle range required for the one image reconstruction, An X-ray computed tomography apparatus characterized in that data is obtained from data of a plurality of cardiac phases.