JP4364382B2 - Double-row detector type X-ray CT system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a double-row detector type X-ray CT apparatus capable of obtaining a plurality of tomographic images of a subject in one scan.
[0002]
[Prior art]
An example of the use of an X-ray CT apparatus is a CT fluoroscopy technique. This is because when performing histological examination or treatment of a lesion, projection data is continuously obtained from a patient (subject) multiple times while the X-ray source is continuously rotated, and then reconstructed continuously. The image (the tomographic image of the subject) is displayed in real time, and this is used as, for example, a puncture guide.
[0003]
[Problems to be solved by the invention]
The above CT fluoroscopy technique becomes more effective by using a double-row detector type X-ray CT apparatus in which a plurality of rows of X-ray detectors are arranged in the slice direction. The reason is as follows. In the single-row detector type X-ray CT apparatus in which the X-ray detector is a single row, only one tomographic image can be obtained in one scan, and therefore one tomographic image can be displayed in real time. Therefore, a procedure such as puncture is performed while observing one tomographic image obtained at one slice position. For this reason, for example, when performing tumor puncture under CT fluoroscopy, for example, the tip of the puncture needle that needs to be observed may disappear from the image. This occurs because the inclination of the puncture needle into the subject (inclination in the bed direction) is large and the tip of the puncture needle deviates from the slice thickness range of the image. To avoid this, take measures such as making the puncture needle enter the slice thickness range, that is, making the puncture needle stand as perpendicular to the bed direction as possible and enter the subject. There are measures such as tilting the statue. However, there are many cases where such a measure alone cannot solve the problem that the tip of the puncture needle disappears from the image due to the position and size of the tumor.
[0004]
On the other hand, with a double-row detector type X-ray CT apparatus, since a plurality of tomographic images obtained simultaneously at a plurality of slice positions can be displayed in parallel and observed, the total slice thickness is consequently increased. Thus, the situation where the tip of the puncture needle disappears from the image can be effectively avoided. For example, if three tomographic images are obtained, the base end of the puncture needle is captured by the first tomographic image, even if the entire tomographic image cannot be captured by each tomographic image. The middle part of the puncture needle is captured by the tomographic image of the second image, and the tip of the puncture needle is captured by the third tomographic image. As a result, the entire puncture needle is easily captured in the image. It is possible to reduce a phenomenon that a necessary puncture needle part disappears from the image.
[0005]
As described above, the double-row detector type X-ray CT apparatus is effective when performing a puncture treatment or the like by CT fluoroscopy. However, on the other hand, the amount of X-ray irradiation increases as the number of rows of X-ray detectors increases, and as a result, there is a problem that the X-ray exposure amount of the patient and the operator increases.
[0006]
Accordingly, an object of the present invention is to reduce the X-ray exposure dose of the double-row detector type X-ray CT apparatus.
[0007]
[Means for Solving the Problems]
For the above purpose, in the present invention, in a double-row detector type X-ray CT apparatus in which X-ray detectors are provided in a plurality of rows in the slice direction, a region of interest is set for a subject as a region to obtain a tomographic image. A region-of-interest setting unit, and a limiting unit that restricts X-ray irradiation to a region other than the region of interest set by the region-of-interest setting unit.
[0008]
According to the present invention, in the double-row detector type X-ray CT apparatus, the limiting means includes a plurality of shields provided so as to correspond to the plurality of rows of X-ray detectors. It is characterized in that X-rays to the respective X-ray detectors are restricted from being irradiated outside the region of interest by the shield.
[0009]
According to the present invention, in the double-row detector type X-ray CT apparatus, the plurality of shields can individually limit the X-ray irradiation range.
[0010]
In the present invention, the region-of-interest scan projection data is included in the region-of-interest scan projection data acquired by scanning only the region of interest by limiting the X-ray irradiation range by the limiting unit in the double-row detector type X-ray CT apparatus. Image reconstructing means adapted to reconstruct an image after performing correction with the correction projection data captured in a state in which the restriction means does not limit the X-ray irradiation range prior to capturing the image. It is characterized by being.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described. The double-row detector type X-ray CT apparatus according to the present invention includes a region-of-interest setting means in addition to the X-ray detectors provided in a plurality of rows in the slice direction. The region of interest is set as a region for which a tomographic image is to be obtained preferentially for the subject. In other words, when puncturing a tumor under CT fluoroscopy, a tomographic image indicating the distance from the puncture needle to the tumor and the approach direction of the puncture needle is preferentially obtained. A region of interest is set in the obtained part. As setting means for setting such a region of interest, for example, the same means as those disclosed in JP-A-11-28201 and JP-A-11-28202 can be used.
[0012]
Further, the double-row detector type X-ray CT apparatus according to the present invention performs scanning in a state where X-ray irradiation other than the region of interest set by the region-of-interest setting means is suppressed as much as possible, that is, X-ray irradiation is performed in the region of interest. A mechanism for performing a region-of-interest scan limited to FIG. 1 schematically shows the mechanism. The mechanism for scanning the region of interest is a limiting unit provided with a shield (channel collimator) 1 that absorbs and attenuates X-rays outside the region of interest in order to limit the irradiation of X-rays outside the region of interest. 2 is provided. During the rotation of the X-ray source 3 for scanning, the X-ray is focused in the channel direction while operating the shield 1 in accordance with the set region of interest E, and the X-ray is irradiated outside the region of interest E. To suppress. For such a region-of-interest scan, in the case of CT fluoroscopy, the X-ray source 3 is continuously rotated to obtain projection data continuously from the subject a plurality of times. As such a control system for continuous scanning, for example, a system similar to that disclosed in JP-A-11-28201 and JP-A-11-28202 can be used.
[0013]
FIG. 2 schematically shows the relationship between the limiting means 2, the X-ray source 3, and the three rows of X-ray detectors 4 (4a, 4b, 4c) as an example of three rows. As shown in the figure, the X-ray detectors 4a, 4b, and 4c are provided in three rows in the slice direction, and the number of columns of the X-ray detectors 4a, 4b, and 4c is also corresponding to this in the limiting means 2. The same three shields 1a, 1b and 1c are provided. The X-rays to the three rows of X-ray detectors 4a, 4b, 4c are shown in FIG. 1 by three shields 1a, 1b, 1c provided to correspond to the three rows of X-ray detectors 4a, 4b, 4c. Irradiation to areas other than the region of interest E is individually limited. As described above, in the double-row detector type X-ray CT apparatus provided with the multiple rows of X-ray detectors 4a, 4b, and 4c, a plurality of images (tomographic images) are simultaneously obtained for each scan. An example is shown in FIG. In the example of FIG. 3, three images are displayed simultaneously corresponding to three rows of X-ray detectors.
[0014]
As described above, the shields 1a, 1b, and 1c of the restricting unit 2 are individually controlled and operated according to the set region of interest E while the X-ray source 3 is rotating. An example of a structure enabling such individual control is shown in FIG. In this example, the three shields 1a, 1b, and 1c are each formed as a set of two shield plates 5 made of a material having a high X-ray absorption coefficient such as lead. A linear motor 7 with an encoder 6 is connected to each shielding plate 5 via an arm 8, and the linear motor 7 causes the linear movement to cause each shielding plate 5 to take an arbitrary position. A shielding range for X-rays can be set for each of the three shielding bodies 1a, 1b, and 1c. FIG. 5 shows an example of setting such a shielding range. In addition, there may be an example of driving other than the linear motor and an example of operating the collimator using the rotational motion of the CT apparatus.
[0015]
Here, when the shielding ability against X-rays by the shielding body is high and the degree of attenuation of X-rays in the shielding range is larger than a certain level, a strong streak-like artifact is generated on the reconstructed image. In order to avoid this problem, it is preferable to perform some correction during the image reconstruction process. Therefore, the image reconstruction means has a function for such correction. Examples of preferable correction include embedding correction. For example, as disclosed in Japanese Patent Application Laid-Open No. 11-28201, embedding correction is performed by performing a normal scan prior to a region-of-interest scan, that is, a scan that does not limit the X-ray irradiation range. This is a method of preventing deterioration in image quality by performing correction for embedding the obtained correction projection data as projection data outside the region of interest that is lost when the region of interest is scanned.
[0016]
Below, the case where the above double row detector type | mold X-ray CT apparatus by this invention is used for CT fluoroscopy is demonstrated. As described above, CT fluoroscopy continuously obtains projection data from a subject a plurality of times while continuously rotating the X-ray source 3, and displays it in real time while continuously reconstructing an image. This technique is used as a guide for puncture or biopsy. In the case of such CT fluoroscopy, the operator also performs a procedure while viewing a real-time image, and thus receives an X-ray exposure together with the patient (subject). The exposure dose received by the operator and the patient increases as X-ray irradiation continues for a long time for CT fluoroscopy, and also increases due to the presence of a plurality of X-ray detectors. The region-of-interest scan as described above provides a safer condition by reducing such X-ray exposure. In other words, the limiting means 2 is provided to suppress the irradiation of X-rays outside the region of interest, thereby reducing the X-ray irradiation amount as much as possible and reducing the exposure dose received by the operator and the patient.
[0017]
Thus, by reducing the exposure dose of the operator and the patient, CT fluoroscopy using the double-row detector type X-ray CT apparatus can be utilized under safer conditions. FIG. 6 and FIG. 7 show the relationship between the slice state and the image when puncturing is performed by CT fluoroscopy with the double-row detector type X-ray CT apparatus. 6 (a) and 7 (a) show sagittal images of puncturing the subject (phantom) F, and FIG. 6 (b) and FIG. 7 (b). Are axial images, that is, tomographic images obtained by reconstruction. However, only one axial image that should actually be displayed as three images as shown in FIG. 3 is shown. For convenience of explanation, FIGS. 6 and 7 show an example in which a region of interest for region-of-interest scanning is not set.
[0018]
When the X-ray detector has three rows as in the example of FIG. 3, three-layer slices Sa, Sb, and Sc are obtained as shown in FIG. 6 (a) and FIG. 7 (a). As shown in the example of FIG. 6, the puncture needle P inserted with a certain inclination from the central slice Sb first appears only in the image Ib in the slice Sb including the tip side, and then the puncture proceeds. Accordingly, as shown in FIG. 7, the distal end side of the puncture needle P enters the portion of the left slice Sa, and this portion appears in the image Ia in the slice Sa. That is, it is possible to capture the puncture needle P from any of the images, and therefore, even if the inclination of the puncture needle P is considerably large, the tip portion of the puncture needle P that is a portion to be observed particularly disappears from the image. Can be avoided.
[0019]
Next, the setting of the region of interest will be described. FIG. 8 shows three tomographic images obtained from the three-layer slices Sa, Sb, and Sc in the state shown in FIG. Each of the three images Ia, Ib, and Ic is reconstructed from projection data obtained by detecting X-rays transmitted through the three-layer slices Sa, Sb, and Sc by the three detectors 4a, 4b, and 4c. . The distal end portion of the puncture needle P appears in the image Ia obtained from the slice Sa, and the other portion of the puncture needle P appears in the image Ib obtained from the slice Sb. However, the puncture needle P does not appear in the image Ic obtained from the slice Sc because the puncture needle P does not enter the slice Sc.
[0020]
In a CT fluoroscopic procedure performed while displaying such an image in real time, unlike a general CT examination, an image around the puncture needle P, that is, the distance from the tip of the puncture needle P to the tumor and the puncture needle P It is necessary and sufficient if an image showing the entry direction is prioritized and such an image can be obtained. Therefore, as shown in FIG. 9, the region of interest E is set by enclosing a portion where an image is to be obtained preferentially as an example with a circle as shown in the figure. Then, the region-of-interest scan that limits the X-ray irradiation range to the region of interest E is performed by the region-of-interest scanning mechanism as described above.
[0021]
The utility of CT fluoroscopy using the double-row detector X-ray CT apparatus as described above is easier to understand than CT fluoroscopy using the single-row detector X-ray CT apparatus. FIGS. 10 and 11 show examples corresponding to FIGS. 6 and 7 in the case of CT fluoroscopy using a single-row detector type X-ray CT apparatus. FIG. 10 corresponds to FIG. 6, and in this state, the tip of the puncture needle P is in the range of a single slice S, which appears in the image I. However, in the state of FIG. 11 corresponding to FIG. 7 as the puncture progresses, the tip of the puncture needle P is out of the range of the slice S, and as a result, the tip of the puncture needle P disappears from the image I. In the double-row detector type X-ray CT apparatus of the present invention, this is solved.
[0022]
FIG. 12 shows a control system of the collimator 2. The control system includes a control unit 100, a region of interest setting unit 101, a view angle detection unit 102, and a drive unit 103. The region-of-interest setting unit 101 is a part of an operation unit including, for example, a keyboard and a mouse, and is set by the region of interest E. The control unit 100 creates control data (shielding bodies 1a, 1b, 1c) such that the region of interest is shielded under CT fluoroscopy at a predetermined view angle, and stores it in a memory. Then, under CT fluoroscopy, the actual view angle is detected by the detection means 102, and the control data of the corresponding shields 1 a, 1 b, 1 c is read at each time when the predetermined view angle is reached and shielded via the drive unit 103. The position of the bodies 1a, 1b, 1c is controlled.
[0023]
FIG. 13 is a flowchart of the flow, in which the flow 110 indicates the operation of the setting unit 101, and the flows 110 to 114 indicate the operations performed by the apparatuses 100, 103, and 104 (note that the flow 114 may be a CT fluoroscopic operation system process). . In the flow 115, the reconstructed images under CT fluoroscopy reconstructed by the reconstructing means are displayed one after another.
[0024]
The predetermined view angle may be all view angles (view unit angles) in CT scan, or may be a multiple view unit angle such as 5 °.
[0025]
Although an example under CT fluoroscopy has been described, the present invention is not limited thereto, and can be applied to normal scanning and helical scanning.
[0026]
【The invention's effect】
As described above, according to the present invention, the double-row detector type X-ray CT apparatus can reduce the amount of X-ray exposure. For example, the double-row detector type X-ray CT apparatus is useful for using it. Safety such as puncture under highly transparent CT fluoroscopy can be further enhanced.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram relating to a region of interest scanning mechanism.
FIG. 2 is a schematic diagram showing the relationship between the limiting means, the X-ray source, and the X-ray detector in the double-row detector type X-ray CT apparatus according to one embodiment.
FIG. 3 is a diagram showing a display example of an image obtained by a double-row detector type X-ray CT apparatus.
FIG. 4 is a schematic diagram of an example of a shield in the limiting unit.
FIG. 5 is a schematic diagram of a state where the shield of FIG. 4 is in operation.
FIG. 6 is an explanatory diagram showing a relationship between a slice state and an image when puncturing is performed by CT fluoroscopy using a double-row detector type X-ray CT apparatus.
7 is an explanatory diagram of a state in which puncturing has progressed from the state of FIG.
FIG. 8 is an explanatory diagram corresponding to FIG. 7 showing a plurality of images.
FIG. 9 is an explanatory diagram for setting a region of interest.
FIG. 10 is an explanatory diagram showing a relationship between a slice state and an image when puncturing is performed by CT fluoroscopy using a single-row detector type X-ray CT apparatus.
11 is an explanatory diagram of a state in which puncturing has progressed from the state of FIG.
FIG. 12 is a diagram showing a control system of a collimator.
FIG. 13 is a flowchart illustrating the operation.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Shield 2 Limiting means 3 X-ray source 4 X-ray detector E Region of interest F Subject

Claims (3)

  In a double-row detector type X-ray CT apparatus in which X-ray detectors are provided in a plurality of rows in the slice direction, a region of interest is set for each column of the double-row detector as a region for obtaining a tomographic image. A double-row detector type X-ray CT apparatus comprising: a region-of-interest setting means; and a limiting means for restricting irradiation of X-rays other than the region of interest for each row of the double-row detector.   The restricting means includes a plurality of shields provided so as to correspond to the respective rows of the plurality of rows of X-ray detectors, and the X-rays to the X-ray detectors by the shields are provided. The double-row detector type X-ray CT apparatus according to claim 1, wherein the irradiation is limited to a region other than the region of interest.   Limiting the X-ray irradiation range by the limiting unit prior to capturing the region-of-interest scan projection data into the region-of-interest scan projection data acquired by scanning only the region of interest by limiting the X-ray irradiation range by the limiting unit 3. A double-row detector according to claim 1, further comprising image reconstruction means adapted to reconstruct an image after correction is performed using the correction projection data fetched in a state where no correction is made. Type X-ray CT system.

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