JPH05111482A - Ct device - Google Patents

Abstract

PURPOSE:To provide the CT device which can suppress scan intervals in a short period of time even when gantry rotation reverses. CONSTITUTION:This CT device has the gantry which can rotate alternately in a CW direction and a CCW direction and a gantry driving mechanism which drives the gantry alternately rotationally in the CW direction and the CCW direction and executes irradiation with X-rays and detection while rotating the gantry. The above-mentioned device has a rotating speed detecting means 8 which detects the rotating speed of the gantry and an X-ray tube control means 9 which supplies the current proportional to the rotating speed of the gantry detected by the rotating speed detecting means to an X-ray tube.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CT apparatus, and more particularly to shortening the interscan delay of the CT apparatus.

[0002]

2. Description of the Related Art An X-ray CT apparatus (hereinafter referred to as a CT apparatus) irradiates a subject with X-rays, detects the X-rays that have passed through the subject, performs this over 360 °, and based on the detected X-rays It is a device that obtains a tomographic image of the subject by performing image reconstruction by using the image reconstruction and makes a diagnosis.

In the case of a CT device that does not use a slip ring, the gantry alternates between CW (clockwise direction) and CCW (counterclockwise direction) rotations. Therefore, it is necessary to repeat deceleration, stop, (reverse direction) acceleration, and deceleration, which requires a considerable amount of time.

Therefore, a scan interval (interscan delay) in the case of continuous scanning has a certain fixed time (usually 2).
~ 2.5 seconds). FIG. 8 shows the relationship between the conventional scan speed and the tube current of the X-ray tube. FIG. 8A is a characteristic diagram showing the angular velocity of the gantry, and FIG. 8B is a tube current of the X-ray tube corresponding to the angular velocity of the gantry.

[0005]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention As shown in this figure,
Since the tube current of the X-ray tube is made to flow after the scan speed becomes constant, a scan interval occurs during acceleration and deceleration. This scan interval is the cause of slowing down the measurement speed.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a CT apparatus capable of suppressing the scan interval to a short time even when the gantry is reversed.

[0007]

According to the present invention for solving the above-mentioned problems, a gantry that can be alternately rotated in the CW direction and the CCW direction, and a gantry drive mechanism that drives the gantry to alternately rotate in the CW direction and the CCW direction. In a CT device equipped with a gantry which rotates and irradiates and detects X-rays,
Rotation speed detection means for detecting the rotation speed of the gantry, and X-ray tube control means for supplying a current proportional to the rotation speed of the gantry detected by the rotation speed detection means to the X-ray tube. It is a thing.

[0008]

The X-ray irradiation and detection are performed in a state in which the gantry is rotationally driven so that the rotation direction is reversed every rotation. In this case, in the acceleration, deceleration state and constant speed rotation state of the gantry, a current corresponding to the speed of each state is supplied to the X-ray tube, so that an equal amount is obtained during acceleration, deceleration, and constant angular velocity rotation. X-rays are emitted. This shortens the scan interval.

[0009]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a configuration diagram showing the configuration of one embodiment of this embodiment. In this figure, G is an X-ray tube 1, a detector 2
It is a gantry that accommodates a table (not shown) on which the subject is placed and which is configured to be rotatable (the rotation direction can be reversed). Reference numeral 3 denotes a drive mechanism for rotationally driving the gantry G, which is connected to the motor M and the encoder E. Reference numeral 4 is a data acquisition device (DAS) for collecting data from the detector 2, and 5 is a CP that performs image reconstruction calculation and controls the entire device of this embodiment.
U, 6 are storage devices for storing the obtained intermediate data and image data, 7 is an image display device for displaying the image obtained by the image reconstruction calculation, and 8 is a gantry drive mechanism for controlling the position of the section to be photographed. A table / gantry control device for giving a drive instruction to 3 and an X-ray tube controller 9 for controlling a drive current value supplied to the X-ray tube.

The operation of the apparatus of this embodiment thus constructed is as follows. In the following description, the flowcharts of FIGS. 2 and 4 and the time chart of FIG. 3 will also be referred to. In the time chart of FIG. 3, the rotation speed ω is represented by the absolute value.

When the multi-scan is set, first, the gantry G is stopped and the position is reset (step (1)). Then, the gantry G is CWed by the drive mechanism 3.
Rotation is accelerated in the clockwise direction (step (2)). Here, the rotation speed is a predetermined value ω1 (ω1 <ω
At the time point 0) (during acceleration), the X-ray controller 9 drives the X-ray tube 1 to generate X-rays (step (3)). Then, acceleration is performed for t1 time, and the rotation speed is ω
When the value reaches 2, the gantry G is rotated at a constant speed (step (4)) and decelerated after a predetermined time (step (5)). Here, when the rotation speed reaches a predetermined value ω1, the driving of the X-ray tube 1 is stopped by the X-ray controller 8 and X
The line is turned off (step (6)). Then, data processing is performed (step (7)) and the gantry G is stopped (step (8)).

In the above case, the gantry rotation speed ω calculated by the TGP 8 according to the detection result of the encoder E is set so that the X-ray irradiation amount is the same as during constant speed rotation during acceleration and deceleration. With reference to this, the tube current I1 of the X-ray tube which is proportional to the rotation speed is set.

The tube currents I1 and I2 are set as I1 = (ω1 / ω0) I0 I2 = (ω2 / ω0) I0.

Then, the constant speed ω2 is set so that the scan time ts is the same as the conventional one including the acceleration and deceleration times.
To be faster than the conventional ω 0. in this case,
If the scan time is ts and the time during acceleration (deceleration) is t1 (constant angular acceleration during acceleration and deceleration), then 2t1 + (2π−ω2t1) / ω2 = ts From this, ω2 = 2π / (ts-t1 ) Is required.

Incidentally, the data processing of step (7) is as shown in FIG.
As shown in, data is transferred from the DAS 4 to the CPU 5, and corrections such as body movement correction and view direction sensitivity correction are performed,
Perform image reconstruction calculation. Here, the body movement correction is performed for the purpose of suppressing the influence of unstable elements of data due to acceleration / deceleration on the image as much as possible at the rising and falling edges. This body movement correction is performed by weighting coefficient k as shown in FIG.
Is applied to the data to reduce the weight at the beginning and the end of the data, and increase the weight of the opposite view.

Then, for CCW (counterclockwise direction), similarly, acceleration, X-ray irradiation, constant speed rotation, deceleration, X-ray off, data processing, and gantry stop are performed. Further, if scanning is to be performed, the process is repeated from step (1), and if not, all processing is terminated.

In the case of the above embodiment, it can be seen that the scan interval ti is shortened as shown by the solid line in FIG. In this example, the scan time t in the conventional example indicated by the broken line in FIG.
Whereas s is 4 seconds and the scan interval is 2 seconds, the scan interval ti is shortened to 1 second in this embodiment.

Further, as shown in FIG. 6 and FIG. 7, the tube current I starts to flow at the same time as the acceleration from the stopped state, and the tube current continues to flow until it is decelerated and stopped, so that the scan interval ti is completely completed. It is possible to eliminate it. However, it is desirable to leave a certain scan interval in consideration of the influence on the image. In the above description of the embodiment, the case where the acceleration and the deceleration are performed at the same acceleration is shown, but there is no problem even if the time required for the acceleration and the time required for the deceleration are different.

[0019]

As described above in detail, in the present invention, the X-ray irradiation is performed by supplying the X-ray tube current corresponding to the rotation speed during the acceleration and deceleration of the gantry, so that the scan interval can be reduced. It is possible to realize a shortened CT device.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a flowchart showing an operating state of an embodiment of the present invention.

FIG. 3 is an explanatory diagram showing the relationship between the gantry rotation speed and the tube current of the X-ray tube in the operating state of the embodiment of the present invention.

FIG. 4 is a flowchart showing details of a part of the operating states of the embodiment of the present invention.

FIG. 5 is an explanatory diagram showing a weighted state of body movement correction.

FIG. 6 is an explanatory diagram showing the relationship between the gantry rotation speed and the tube current of the X-ray tube in the operating state of another embodiment of the present invention.

FIG. 7 is an explanatory diagram showing the relationship between the gantry rotation speed and the tube current of the X-ray tube in the operating state of yet another embodiment of the present invention.

FIG. 8 is an explanatory diagram showing the relationship between the gantry rotation speed and the tube current of the X-ray tube in the operating state of the conventional apparatus.

[Explanation of symbols]

 1 X-ray tube 2 Detector 3 Drive mechanism 4 Data acquisition device 5 CPU 6 Storage device 7 Display device 8 Table / Gantry control device 9 X-ray controller G Gantry

Claims (1)

[Claims] 1. A gantry that can rotate in the CW direction and the CCW direction alternately, and a gantry drive mechanism that drives the gantry to rotate alternately in the CW direction and the CCW direction, and perform X-ray irradiation and detection while rotating the gantry. In the CT device to be performed, a rotation speed detecting means (8) for detecting the rotation speed of the gantry
And a X-ray tube control means (9) for supplying a current proportional to the rotation speed of the gantry detected by the rotation speed detection means to the X-ray tube.