JPH0436697B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an X-ray CT scanning device, and particularly to automatic control of the amount of X-ray irradiation in the device.

(Prior Art) FIG. 1 is a diagram showing an example of a schematic configuration of a conventional X-ray CT scanning system section. In the figure, the intensity of X-rays emitted from an X-ray tube 1 is controlled by a controller (not shown), and the X-rays pass through a filter 2 and a subject 3 to a detector array 4. is incident on the A current signal corresponding to the intensity of incident X-rays is obtained from the detector array 4. The amount of transmitted X-rays (time integral value of the current signal) when irradiated for a certain period of time is recorded as projection data using a data acquisition system (hereinafter referred to as "Data Acquisition System").
(DAS), converted to a digital signal, and then stored in a computer. The computer calculates and reconstructs a tomographic image of the subject 3 from the projection data of each view, and the image thus obtained is displayed on the display device. The filter 2 has the role of providing an X-ray intensity distribution such that the output of each channel of the detector array 4 is approximately constant when scanning a standard object with X-rays. The required detection sensitivity is ensured within a range that does not cause overrange.

However, if the subject is flat (thin person) or is away from the center of the scan, this filter 2 will not function properly. That is, for example, in the channel indicated by P in FIG. 1, a detection signal of an appropriate value is obtained in FIG. This results in a large detection signal.
Read the projection data corresponding to the transmitted X-ray dose
DAS can cause overflow.

Therefore, although it is necessary to sufficiently increase the X-ray intensity for the subject 3 to ensure a sufficient S/N ratio, there is a drawback in that it is not possible to do so.

(Object of the Invention) The present invention has been made in view of the above points, and its purpose is to provide a system that does not cause overrange even at X-ray intensities that would cause overrange with conventional equipment. An object of the present invention is to provide an X-ray CT scanning device that can obtain a high amount of X-ray irradiation and a tomographic image with a good S/N ratio in a short scanning time.

(Structure of the Invention) The present invention achieves this object by arranging an X-ray tube and a detector array facing each other with the subject at the center, scanningly irradiating the subject with X-rays from the X-ray tube, and detecting the detector array. In an X-ray CT scan apparatus configured to obtain projection data necessary to reconstruct a tomographic image of the object, the output of the detector array is received and the emission time width of the X-rays is determined. means and
an X-ray controller for controlling the X-ray emission of the X-ray tube based on the output of the means, and the means for determining the emission time width detecting the maximum output value in each channel of the detector array; and a comparator that compares the output of the maximum value circuit with a reference value, and determines whether the time width from the start of X-ray radiation until the output of the maximum value circuit exceeds the reference value or a predetermined time width. This is characterized in that the shorter time width of either of these is determined as the X-ray emission time width.

(Embodiments) Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 2 is a schematic configuration diagram showing an embodiment of the present invention. In the figure, 1 is an X-ray tube and 4 is a detector array. 5 is a capacitor, and detector array 4
The output of each channel is individually converted into a received voltage. 7 is A/D which is the main part of DAS
The converter receives the output voltages of a large number of capacitors 5 via amplifiers 6, and converts them into digital signals. 8 is the calculator, 13 is the console,
14 is a display device. The console 13 is operated by an operator and supplies necessary control commands and information to the computer 8. The image of the subject 3 obtained by the computer 8 can be displayed on the display device 14.

On the other hand, 9 is a maximum value circuit that detects the maximum value of each output of the amplifier 6. 10 is a comparator that connects the output of the maximum value circuit 9 and the reference voltage source 11
Compare the voltage Vr of Reference numeral 12 denotes an X-ray controller which can generate a signal for controlling X-ray generation in the X-ray tube 1 based on the output of the comparator 10 and the X-ray control signal from the computer 8.

The operation of the X-ray CT scanning apparatus of the present invention in such a configuration will be explained below with reference to FIG. The operation of the scanning system, which is a feature of the present invention, will be explained here, and the processing of the obtained data, tomographic image reconstruction, and image display will be the same as in conventional devices, so The explanation will be omitted.

When the X-ray control signal that controls the X-ray controller 12 from the computer 8 becomes active at time _t1 as shown in FIG. (b) indicates the operating state of the X-ray output, and a high level indicates that X-ray radiation is being performed). In the detector array 4, a power signal corresponding to the incident X-ray intensity is obtained, and each capacitor 5 is charged by this current. The voltage across each capacitor increases over time. These voltages obtained via amplifier 6 are applied to maximum value circuit 9
At this time, the maximum value circuit 9 detects the maximum value among these voltages, and its output changes as shown in FIG. 3C. This maximum value detection voltage is compared with a reference voltage (threshold voltage) Vr in a comparator 10. Here, Vr is set to the value of the DAS maximum input voltage at which no overflow occurs in the DAS. The output of maximum value circuit 9 is Vr
When the time exceeds 1 (time t ₂ ), the output of the comparator 10 is reversed as shown in FIG.

In such an operation, if the output of the maximum value circuit 9 does not exceed Vr during the elapse of time T from time _t1 (when no overflow occurs in the DAS), X-ray emission continues for time T. After time T has elapsed, the X-ray control signal from the computer 8 falls as shown in FIG.
The ray tube 1 is controlled to stop X-ray emission.

With the above operations, in each view,
The time width of the X-ray emission is limited to (t ₂ −t ₁ ) or T, whichever is shorter. This automatically prevents the X-ray pulse width from extending unnecessarily and reducing the resolution of scan data in the rotational direction.

In addition, not only each view data obtained by the detector array 4, but also the time width of X-ray emission in each view,
The data is read into the computer 8, and within the computer 8, the view data is multiplied by a magnification according to the time width of the X-ray emission.
The obtained data is used as tomographic image reconstruction data.

(Effects of the Invention) As explained above, according to the present invention, when overrange is about to occur for each view, X-ray emission is stopped before it occurs, and X-ray emission is started in the next view. Therefore, it is possible to always determine the optimal X-ray irradiation amount for each view, so it is possible to avoid overrange in certain conditions of the subject with conventional equipment, and it is necessary to reduce the overall X-ray intensity. Even if there is a problem, it is possible to scan at a desired X-ray intensity without worrying about overrange, and therefore, an image with a good S/N ratio can be obtained in a short scanning time. In particular, when scanning is performed with the X-ray intensity set to the maximum, a tomographic image with the best S/N ratio depending on the condition and position of the subject can be obtained in the shortest scanning time.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing a conventional X-ray CT scanning system part, Fig. 2 is a schematic configuration diagram showing an embodiment of an X-ray CT scanning device according to the present invention, and Fig. 3 is an operation time of the embodiment. It is a chart diagram. 1... X-ray tube, 3... Subject, 4... Detector array, 5... Capacitor, 6... Amplifier, 7...
Analog multiplexer and A/D conversion circuit, 8
... Calculator, 9 ... Maximum value circuit, 10 ... Comparator, 11 ... Reference voltage source, 12 ... X-ray controller.

Claims (1)

[Claims] 1 An X-ray tube and a detector array are arranged facing each other with the subject at the center, and the X-ray tube scans the subject with X-rays, and the detector array provides the necessary information to reconstruct a tomographic image of the subject. An X-ray CT scan apparatus configured to obtain projection data includes means for receiving the output of the detector array and determining the emission time width of the X-rays; The means for determining the emission time width includes an X-ray controller for controlling X-ray radiation, and the means for determining the radiation time width includes a maximum value circuit for detecting the maximum output value in each channel of the detector array; a comparator for comparing with a reference value, and calculates the shorter of the time width from the start of X-ray emission until the output of the maximum value circuit exceeds the reference value or a predetermined time width, whichever is shorter. An X-ray CT scan device characterized in that the radiation time width is determined as a radiation time width.