JP2002010998A - DATA COLLECTING METHOD AND X-ray CT DEVICE - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make high image quality photographing and high-speed photographing be compatible while satisfying the conditions of scanning time and a scanning range. SOLUTION: A small helical pitch scanning range capable of improving image quality though a data collecting speed is low and a large helical pitch scanning range capable of accelerating the data collecting speed though image quality becomes low are combined and a given scanning range is helically scanned in given scanning time. Thus, a range as wide as possible near the position of interest is photographed with high image quality while satisfying the conditions of the scanning time and the scanning range.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a data collection method and an X-ray CT apparatus, and more particularly, to a data collection method capable of achieving both high-quality imaging and high-speed imaging while satisfying conditions of scan time and scan range. The present invention relates to a method and an X-ray CT apparatus.

[0002]

2. Description of the Related Art Helical scan (heli scan) using an X-ray CT system
When performing a scan, a helical pitch is selected for the scan plan. For example, small helical pitch p1 = 3 or large helical pitch p2 = 6
Is selected by the operator. Here, the helical scan is a scanning method in which at least one of an X-ray tube and a detector is relatively rotated around an imaging target and data is collected while being relatively linearly moved in the direction of the rotation center axis. The helical pitch is a linear moving speed of the X-ray tube and the detector, which is expressed by how many times the linear moving distance per rotation of the X-ray tube and the detector corresponds to the detector thickness.

When the small helical pitch p1 is selected,
Although the X-ray CT image can have high image quality because the data density in the linear movement direction is high, the actual scan time is long to scan a predetermined scan range because the linear movement speed is low. For example, scan range W = 300 mm, detector thickness D
= 2.5 mm, one rotation time τ = 0.8 seconds, and if the small helical pitch p1 = 3 is selected, the actual scan time T1
T1 = 0.8 × 300 / (2.5 × 3) = 32 seconds

On the other hand, when the large helical pitch p2 is selected, the X-ray C
Although the T image has low image quality, the linear scanning speed is high, so that a predetermined scan range can be scanned in a short actual scan time. For example, scan range W = 300 mm, detector thickness D =
When 2.5 mm and one rotation time τ = 0.8 seconds, if the large helical pitch p2 = 6 is selected, the actual scan time T2
Satisfies T2 = 0.8 × 300 / (2.5 × 6) = 16 seconds.

In order to avoid body movement due to respiration, when performing helical scan of the chest with the subject stopping breathing, the actual scan time needs to be, for example, 20 seconds or less. Therefore, conventionally, in the case of the above-described scanning conditions, the operator has selected the large helical pitch p2 = 6.

On the other hand, conventionally, when performing a helical scan of the heart and the vicinity of the heart, the operator has selected a large helical pitch p2 = 6 capable of high-speed imaging in order to minimize the influence of the heart beat.

[0007]

In the case of performing a helical scan on the chest as described above, if the large helical pitch p2 = 6 is selected, the actual scan time T = 16 seconds, and the breath-holding time becomes 20 seconds or less. However, there is a problem that the image quality of the X-ray CT image is reduced in the entire scanning range. There is also a problem that 4 seconds cannot be used effectively when the breath holding time is 20 seconds.

On the other hand, when a helical scan is performed on the heart and the vicinity of the heart as described above, the large helical pitch p2 = 6 is maintained even in the vicinity of the heart without the influence of the pulsation of the heart. There is a problem that becomes.

It is an object of the present invention to provide a data collection method and an X-ray CT apparatus capable of achieving both high quality imaging and high speed imaging.

[0010]

SUMMARY OF THE INVENTION In a first aspect, the present invention provides a method for acquiring data of a given scan range at a given scan time, with a relatively low data acquisition rate and a relatively high image quality. A data combining a high-quality scan range for collecting data capable of generating an image of a high speed and a high-speed scan range for collecting data capable of generating a relatively low-quality image at a relatively high data collection speed Provide a collection method. In the data collection method according to the first aspect, a high-quality scan range in which the data collection speed is low but the image quality can be increased, and a high-speed scan range in which the image quality is low but the data collection speed can be increased are combined. Since scanning is performed, it is possible to achieve both high-quality imaging and high-speed imaging while satisfying the conditions of the scan time and the scan range.

In a second aspect, the present invention defines a high-quality scan range that includes a set position of interest and is as wide as possible, and removes the high-quality scan range from the scan range to obtain a high-speed scan. A data collection method having the above configuration, which is characterized by a range, is provided. In the data collection method according to the second aspect, the high-quality scan range is determined so as to include the position of interest and be as wide as possible. You can shoot quality images.

In a third aspect, the present invention defines a high-speed scan range that includes a set region of interest and is as narrow as possible, and removes the high-speed scan range from the scan range to obtain a high-quality scan. A data collection method having the above configuration, which is characterized by a range, is provided. In the data collection method according to the third aspect, the high-speed scan range is determined so as to include the region of interest and be as narrow as possible, and the rest is defined as the high-quality scan range. It is possible to perform high-speed imaging of a region of interest having a large motion and high-quality imaging of another scan range as wide as possible.

According to a fourth aspect of the present invention, in the data collection method having the above structure, the scan is a helical scan, and the helical pitch is relatively small in the high-quality scan range, and the helical pitch is in the high-speed scan range. Is relatively large. In the data collection method according to the fourth aspect, the data collection method having the above configuration can be suitably applied to a helical scan.

In a fifth aspect, the present invention provides an X-ray tube, a detector, and data at a relatively small helical pitch when collecting data for a given scan range at a given scan time. A helical scan plan creating means for creating a helical scan plan combining a small helical pitch scan range and a large helical pitch scan range for collecting data at a relatively large helical pitch;
A helical scan means for performing a helical scan based on the helical scan plan to collect data while relatively rotating at least one of a ray tube and the detector around an object to be photographed and relatively linearly moving in a direction of a rotation center axis thereof. An X-ray CT apparatus comprising: In the X-ray CT apparatus according to the fifth aspect, the data collection method according to the fourth aspect can be suitably implemented.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail with reference to the embodiments shown in the drawings. Note that the present invention is not limited by this.

First Embodiment FIG. 1 is a block diagram of an X-ray CT apparatus 100 according to a first embodiment of the present invention. This X-ray CT apparatus 100
Has an operation console 1, an imaging table 10, and a scanning gantry 20.

The operation console 1 includes an input device 2 for receiving an operator's instruction input and information input, a central processing device 3 for executing helical scan processing and image reconstruction processing according to the present invention, control signals and the like. A control interface 4 for exchanging data with the imaging table 10 and the scanning gantry 20, a data collection buffer 5 for collecting data acquired by the scanning gantry 20, a CRT 6 for displaying X-ray CT images and the like, and programs, data and X A storage device 7 for storing a line CT image.

The scanning gantry 20 includes an X-ray tube 21 and
X-ray controller 22, collimator 23, multi-detector 24, 4-row DAS (Data Acquisition System)
25, and a rotation controller 26 for rotating the X-ray tube 21 and the like around the body axis of the subject.

FIG. 2 is a perspective view of a main part of the multi-detector 24. The multi-detector 24 has a structure in which many X-ray detection elements are arranged in a matrix (1000 in the channel direction, 16 in the slice thickness direction). The X-ray detection element rows of det_1 to det_16 arranged in the slice thickness direction are each called a unit detector. The thickness of each of the unit detectors det_1 to det_16 in the slice thickness direction is referred to as a unit detector thickness Δd.

The four-row DAS 25 includes first to fourth DASs.
Four DASs are DASs that operate in parallel. When each of n columns of the unit detectors det_1 to det_16 that are continuous in the detector thickness direction correspond to the first DAS to the fourth DAS, the multi-detector 24 calculates X of the detector thickness D = n · Δd.
The line detector functions as a four-row four-row detector. For example, if n = 2 and Δd = 1.25 mm, the detector thickness D =
2.5 mm.

FIG. 3 is a flowchart showing a helical scan process by the X-ray CT apparatus 100 of FIG. The helical pitch that can be selected by this X-ray CT apparatus 100 is
Either the small helical pitch p1 or the large helical pitch p2.

In step S1, the operator inputs a scan time T as one of the scan parameters. For example, when performing a helical scan on the chest of the subject, 20 seconds during which the subject can stop breathing are input to avoid body movement due to breathing. In step S2, the operator inputs a scan range W as one of the scan parameters. For example, when performing a helical scan on the chest of the subject, W = 300 mm is input. In step S3, a position of interest Zo is input. For example, when a position 100 mm from the scan start position is set as the position of interest Zo, Zo =
Enter 100mm.

In step S4, when the small helical pitch scan range length is α, the large helical pitch scan range length is β, the detector thickness is D, and one rotation time is τ, α + β ≧ W ＋ α / (D × The conditions of α and β are calculated by p1) + β / (D × p2)｝ × τ ≦ T. By the way, α / (D
× p1) corresponds to the number of rotations in the small helical pitch scan range, and β / (D × p2) corresponds to the number of rotations in the large helical pitch scan range.

For example, scan time T = 20 seconds, scan range W = 300 mm, one rotation time τ = 0.8 seconds, small helical pitch p1 = 3, large helical pitch p2 = 6, and detector thickness D = 2.5 mm Sometimes α ≦ 75, β ≧ 225
Becomes

In step S5, a small helical pitch scan range is set within the scan range W such that the position of interest Zo is as close as possible to the center of the small helical pitch scan range. The small helical pitch scan range length is set to the maximum value of α so as to be as wide as possible. Next, the rest is set to a large helical pitch scan range.

For example, as shown in FIG. 4, first, a small helical pitch scan range [6] of 75 mm (the maximum value of the above α) is set so as to include the position of interest Zo = 100 at the center as much as possible.
2.5, 137.5]. Next, the remaining [0,6
2.5) and (137.5, 300) are defined as a large helical pitch scan range.When the position of interest Zo is near the end of the scan range W, the position of interest Zo is small as shown in FIG. It may not be the center of the helical pitch scan range.

Returning to FIG. 3, in step S6, a helical scan based on the small helical pitch scan range and the large helical pitch scan range set in step S5 is executed. Thus, the helical scan process ends.

According to the X-ray CT apparatus 100 of the first embodiment, while satisfying the conditions of the scan time T and the scan range W, the position of interest Zo and the vicinity thereof are raised by the helical scan with the small helical pitch p1. Image quality can be captured, and before and after the image can be captured by helical scanning at a large helical pitch p2.

Although only one position of interest Zo is set in the first embodiment, a plurality of positions may be set. In this case, it is necessary that the sum of the small helical pitch scan range lengths α1, α2,... Allocated corresponding to each position of interest Zo is equal to or less than the small helical pitch scan range length α.

Second Embodiment FIG. 6 is a flowchart showing a helical scan process of an X-ray CT apparatus according to a second embodiment of the present invention. In addition,
The helical pitch that can be selected by this X-ray CT apparatus is either the small helical pitch p1 or the large helical pitch p2.

In step S1, the operator inputs a scan time T as one of the scan parameters. For example, when performing a helical scan on the chest of a subject,
In order to avoid body movement due to respiration, 20 seconds during which the subject can stop breathing are input. In step S2, the operator inputs a scan range W as one of the scan parameters. For example, when performing a helical scan on the chest of the subject, W = 300 mm is input. In step S23, the operator inputs the region of interest Ro as one of the scan parameters. For example, 8 from the scan start position
To set the region of interest Ro from the position of 0 mm to the position of 160 mm, enter Ro = [80, 160].

In step S4, the small helical pitch is set to p
1, the large helical pitch is p2, the small helical pitch scan range is α, the large helical pitch scan range is β, the detector thickness is D, and one rotation time is τ, α + β ≧ W ｛α / (D × p1) + β / (D × p2)｝ × τ ≦ T The conditions of α and β are calculated.

For example, scan time T = 20 seconds, scan range W = 300 mm, one rotation time τ = 0.8 seconds, small helical pitch p1 = 3, large helical pitch p2 = 6, and detector thickness D = 2.5 mm. Sometimes α ≦ 75, β ≧ 225
Becomes

In step S25, a large helical pitch scan range is set within the scan range W such that the set region of interest Ro is as close as possible to the center of the large helical pitch scan range. The large helical pitch scan range length is set to the minimum value of β so as to be as narrow as possible. Next, the large helical pitch scan range is removed from the scan range, and the remainder is defined as a small helical pitch scan range.

For example, as shown in FIG. 7, first, a region of interest Ro [80, 160] should be included in the center as much as possible.
A large helical pitch scan range [7.5, 232.5] of 25 mm (the minimum value of β) is determined. Next, the remaining [0, 7.5] and (232.5, 300) are set as the small helical pitch scan range.

In step S26, the above-mentioned step S25
The helical scan is executed based on the small helical pitch scan range and the large helical pitch scan range set in. Thus, the helical scan process ends.

According to the scan plan creation processing according to the second embodiment described above, a portion having a large body motion (heart H in the example of FIG. 7) can be photographed at high speed by a helical scan with a large helical pitch p2, and before and after that. The helical scan at the small helical pitch p1 enables high-quality imaging.

Other Embodiments A conventional processing mode in which an operator selects a helical pitch, and an operator sets a scan time to optimize a high-quality scan range and a high-speed scan range as in the first embodiment. Processing mode to be
It is preferable that the operator can select a processing mode in which the operator sets the scan time and optimizes the high-quality scan range and the high-speed scan range as in the second embodiment.

[0039]

The data acquisition method and X-ray CT of the present invention
According to the apparatus, it is possible to achieve both high-quality shooting and high-speed shooting while satisfying the conditions of the scan time and the scan range.

[Brief description of the drawings]

FIG. 1 is a block diagram of an X-ray CT apparatus according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram showing a multi-detector.

FIG. 3 is a flowchart showing a helical scan process by the X-ray CT apparatus of FIG. 1;

FIG. 4 is an explanatory diagram schematically showing a helical scan when a position of interest is set in a part of a lung.

FIG. 5 is an explanatory diagram schematically showing a helical scan when a position of interest is set near an end of a scan range.

FIG. 6 is a flowchart illustrating a helical scan process according to a second embodiment of the present invention.

FIG. 7 is an explanatory diagram schematically showing a helical scan when a region of interest including a heart is set.

[Explanation of symbols]

 Reference Signs List 3 Central processing unit 5 Data acquisition buffer 7 Storage device 21 X-ray tube 24 Multi-detector 25 4-row DAS 100 X-ray CT device

Claims (5)

[Claims] 1. A high-quality scan range for collecting data capable of generating a relatively high-quality image at a relatively low data collection speed when collecting data of a given scan range at a given scan time. And a high-speed scan range for collecting data capable of generating a relatively low-quality image at a relatively high data collection speed. 2. A high-quality scan range is defined so as to include a set position of interest and to be as wide as possible, and the high-quality scan range is removed from the scan range to form a high-speed scan range. The data collection method according to claim 1. 3. A high-speed scan range is defined so as to include the set region of interest and to be as narrow as possible, and the high-speed scan range is removed from the scan range to form a high-quality scan range. The data collection method according to claim 1. 4. The data collection method according to claim 1, wherein the scan is a helical scan, the helical pitch is relatively small in the high-quality scan range, and the helical pitch is in the high-speed scan range. A data collection method characterized by a relatively large helical pitch. 5. An X-ray tube, a detector, and a small helical pitch scan area for acquiring data at a relatively small helical pitch when acquiring data for a given scan area at a given scan time. A helical scan plan creating means for creating a helical scan plan in combination with a large helical pitch scan range for collecting data at a large helical pitch, and at least one of the X-ray tube and the detector being relatively rotated around the imaging target An X-ray CT apparatus comprising: helical scan means for performing helical scan for acquiring data while relatively linearly moving in the direction of the rotation center axis based on the helical scan plan.