JPH0444543B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an X-ray tomography apparatus having an X-ray detector composed of a plurality of channels.

(Prior Art) An X-ray tomography device is a device that performs tomography of an affected area using X-rays. A schematic configuration of the X-ray tomography apparatus is shown in FIG. In the figure, reference numeral 1 denotes an X-ray tube that emits X-rays for performing X-ray tomography, and the emitted X-rays are shaped into a fan shape by a collimator 2 and irradiate a subject 3. Reference numeral 4 denotes an X-ray detector that converts the X-rays that have passed through the subject 3 and entered into an electrical signal proportional to the energy of the X-rays. There are several types of X-ray detectors, but the ionization chamber detector 4 shown in the figure is
It has an ionization chamber filled with a gas such as Xe, which has a high linear absorption rate, under high pressure.As shown in Figure 6, the channel 5 is formed in the space between two bias electrodes 6 in the ionization chamber. bias electrode 6
A positive high voltage is applied to the signal electrode 7, and the ion current due to the ionization of the Xe gas generated by the incident X-rays from the direction of the arrow in FIG. 5 is obtained from the signal electrode 7 to detect the X-ray intensity.

(Problem to be Solved by the Invention) In order for the output current obtained from the X-ray detector 4 to correctly reproduce the incident X-ray energy distribution regardless of changes in environmental temperature, each channel 5 must be Must keep the same shape. However, in reality, when the environmental temperature changes, taking the X-ray detector 4 shown in FIG. ), the adhesive fixing each electrode expands or contracts, changing the individual shape of the channel 5.
For this reason, conventional apparatuses sometimes produce ring artifacts in tomographic images. In order to avoid this, we must keep the environmental temperature of the X-ray tomography device as constant as possible, make X-ray detectors with higher precision to reduce the temperature coefficient, and conduct strict product inspections to minimize changes. to separate things. Alternatively, measures have been taken in the past, such as keeping only the X-ray detector at a constant temperature, but these measures not only cause an increase in costs, but also cannot be said to be a sufficient countermeasure.

The present invention has been made in view of the above points, and its purpose is to correct changes in the measured data of each channel caused by temperature changes at low cost, and to correct the
An object of the present invention is to realize an X-ray tomography apparatus capable of performing ray tomography.

(Means for Solving the Problems) The present invention solves the above problems in an X-ray tomography apparatus having an X-ray detector configured with a plurality of channels, in which the irradiated X-rays do not pass through the subject. In addition to using an X-ray detector with a representative channel arranged at a position where the irradiated X-rays are directly incident, a storage means for storing temperature characteristics of sensitivity of the representative channel and the measurement channel, or an X-ray detector that is directly incident with irradiated X-rays and outputs due to temperature changes. Storage means for storing temperature characteristics of the sensitivity of the representative channel with respect to the sensitivity of the reference channel and the sensitivity of the measurement channel with respect to the sensitivity of the reference channel, the fluctuation of which is sufficiently small compared to other channels; and the temperature stored in the storage means. The present invention is characterized in that it includes a calculation means for performing temperature correction on the actual measurement data in each measurement channel based on the characteristics and the actual measurement data on the representative channel.

(Function) The temperature characteristics of the sensitivity of the representative channel and the measurement channel, or the temperature characteristics of the sensitivity of the representative channel with respect to the sensitivity of the reference channel and the sensitivity of the measurement channel with respect to the sensitivity of the reference channel are stored in advance in the memory. , temperature correction of the actual measurement data in the measurement channel is performed using the temperature characteristics and the actual measurement data of the representative channel.

(Example) Examples of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing a schematic configuration of a main body and a data processing section according to an embodiment of the present invention. In the figure, the same parts as in FIG. 5 are given the same reference numerals. In the figure, 8 is a reference channel (hereinafter referred to as Rch) provided in the X-ray detector 4, which is provided as a reference for other channels at a position where the irradiated X-rays directly enter without passing through the object 3. This is to compensate for the intensity of the X-rays, which may constantly change during the scan. Since it is necessary to provide multiple Rch8,
In this embodiment, six are provided. 9 is the X-ray detector 4
The representative channel (hereinafter referred to as Mch) established within
This measurement channel (hereinafter referred to as Ach) 5 is provided at a position where the irradiated X-rays directly enter the object 3 without passing through it, in order to ascertain the temperature. The data of each channel is taken into the computer 11 via the data collection section 10, which includes a multiplexer, A/D converter, etc., and the computer 11 performs temperature correction processing and other preprocessing, which will be described later. There is. In this embodiment, calculations for image reconstruction are performed by a dedicated high-speed calculation device 12. Reference numeral 13 denotes an external memory that stores data (projection data) taken into the computer 11 as is, or stores data after preprocessing and reconstruction calculation processing. This memory 13 is, as described later, Mch
The temperature characteristics of the sensitivities of Ach 9 and Ach 5 are also stored. Note that storing the temperature characteristics of the sensitivities of Mch9 and Ach5 means storing data that allows knowing how the sensitivities of Mch9 and Ach5 change with respect to temperature changes.

Next, a method of temperature correction will be explained with reference to FIGS. 2 and 3 in conjunction with the operation of the above embodiment. Figure 2 is
It is a graph showing an example of temperature characteristics of Mch9,
FIG. 3 is a graph showing an example of the temperature characteristics of an arbitrary channel (here, the m-th channel) in Ach5. In these figures, each symbol is defined as follows. That is, at a temperature t°C
The output of Mch9 is Mt, the output at t° C. when the subject 3 is not present in the m-th channel of Ach5 is Amt, and the average value of the six Rch8 outputs at t° C. is Rt. The reason why the average value is used for the output of Rch 8 is because in the channel shown in Figure 5, even if one electrode is deformed due to temperature change and the volume changes, the total volume with the adjacent channels does not change. This is because, by determining , the output of Rch 8 becomes approximately constant even with temperature changes, and the temperature coefficient is considered to be almost 0. In this example, as each actual measurement data of Mch9 and Ach5, irradiation
To prevent the influence of fluctuations in line strength, Mch9,
Instead of using each output of Ach5 as is, the data obtained by dividing these output data by the average value of the output of Rch8 is used. In this case, the temperature coefficient of the average value of the output of Rch 8 is considered to be almost 0 as described above, so it is not necessary to take data every time the scan of each channel is performed.
Although data for one temperature may be used, in this example, to ensure greater accuracy, measurements are taken each time each channel is measured.

Mch9 and Ach prior to tomography of subject 3
We need to read the temperature characteristics of No. 5, which can be done as follows. In the absence of the object 3, the output for the X-ray input of each channel is obtained when the temperature of the X-ray detector 4 is t ₁ °C and t ₂ °C, and after storing this in the memory 13, Read out the output and find its average value Rt ₁ at each temperature,
Rt ₂ is determined and the outputs of Mch9 and Ach5 at each temperature are divided to obtain data as shown in FIG. 4, which is stored again in the memory 13 as actual measurement data for each channel of Mch9 and Ach5. Mch
9. The temperature characteristics of each channel of Ach5 are not constant, but since the main cause is expansion and contraction due to heat, if we focus on one channel, it is proportional to the temperature change, and its reproducibility is also good. Therefore, the temperature characteristics can be considered to be linear with respect to temperature, for example,
From the measurement results shown in Figure 4, the actual measurement data of Mch9 draws the temperature characteristic curve shown in Figure 2, and one channel of Ach5 draws a temperature characteristic curve as shown in Figure 3.However, this temperature characteristic curve is for illustration purposes only. The memory 13 only stores actual measurement data for each channel at two points, t ₁ °C and t ₂ °C. However, by reading each data at these two points, the temperature characteristics of the sensitivity of Mch9 and Ach5 are read.

Next, the actual scanning operation of the X-ray tomography apparatus will be explained. During this scan, Ach5,
Data is collected by Rch8 and Mch9, and one scan at a certain point in time will be explained. The computer 11 first uses Rch8, Mch9,
The output of Ach5 is taken in via the data collection unit 10, and the temperature t of the X-ray detector 4 at that time is determined.
Specifically, Mt/Rt changes linearly with temperature t, and the following equation (t ₂ − t ₁ ): (t − t ₁ )=(Mt ₂ /Rt ₂ −Mt ₁ /Rt ₁
): (Mt/Rt−Mt ₁ /Rt ₁ ) is established. When this equation is rearranged with respect to temperature t, equation (1) is obtained.

t={( _t2 − _t1 )(Mt/Rt− _Mt1 / _Rt1 )/( _Mt2
/Rt ₂ −Mt ₁ /Rt ₁ )}+t ₁ (1) Then, the computer 11 calculates the temperature t from equation (1). Next, using this temperature t and the measured data of temperatures t ₁ and t ₂ of Ach 5 stored in the memory 13,
The actual measurement data when the subject 3 is not present in all channels of Ach5 is predicted. Now, if we take the m-th channel of Ach5 as an example, this prediction is
Amt/Rt changes linearly with temperature t, and the following formula (t ₂ - t ₁ ): (t - t ₁ ) = (Amt ₂ / Rt ₂ - Amt ₁ /
Rt ₁ ): Uses the fact that (Amt/Rt−Amt ₁ /Rt ₁ ) holds. If we rearrange this equation regarding Amt/Rt, we get the following equation (2) Amt/Rt=[{(t-t ₁ )(Amt ₂ /Rt ₂ −Amt ₁ /Rt
₁ )}/(t ₂ −t ₁ )]+Amt ₁ /Rt ₁ (2), so the predicted value can be easily obtained by performing this calculation. Actual measurement data at reference temperature For example, actual measurement data at temperature t ₁ Amt ₁ /
If Rt ₁ is used, the measured data PAmt/Rt obtained when subject 3 exists (however, PAmt is
can always be converted into data at the reference temperature _t1 . That is, if the actual measurement data to be obtained converted into temperature t ₁ is PAmt ₁ /R ₁ , then the temperature-corrected actual measurement data PAmt ₁ /Rt can be obtained by the following equation.

PAmt ₁ / Rt ₁ = (PAmt / Rt) × {(Amt ₁ / Rt ₁ ) /
(Amt/Rt)}...(3) The computer 11 performs the calculation according to equation (3) over all channels of Ach 5, and after performing any necessary preprocessing, the data is sent to a high-speed calculation device. 12 to perform image reconstruction calculations, and the obtained image data is temporarily stored in the memory 13, from which necessary data is extracted and the instructed image is displayed.

As mentioned above, in this example, the temperatures t ₁ and t ₂ are set in advance.
Obtain the actual measurement data that does not pass through the object 3 of all channels at the two points, and then calculate the temperature by calculating the formula (1) from the actual measurement data of Mch 9 during the scan of the object 3. Using Equation (2), we obtain the predicted value of the actual measured data in each constituent channel of Ach 5 at that temperature when the object 3 is not present, and based on that value, we calculate the predicted value of the actual measurement data obtained from Ach 5 by scanning with object 3 placed. The data is converted to actual measurement data at the reference temperature using equation (3), and temperature correction is performed. In this process, in practice, the actual measurement data of Mch9 is taken during the first scan of the object 3, and the required temperature correction of Ach5 is performed, but after that, the scan takes time and the temperature may change. In some cases, for example, Ach9 every few minutes
Update the actual measurement data and perform temperature correction.

Note that the present invention is not limited to the above embodiments. For example, in the above embodiment, an ionization chamber type detector is used as the X-ray detector, but it is also possible to use a semiconductor detector with a collimator partitioned by a tungsten plate for each channel in front Good too. Further, the amount of adhesive for fixing the electrode plate may be adjusted so that the representative channel is sensitive to temperature, and an electrode plate such as a bimetal that deforms greatly in response to temperature changes may be used. further t ₁
℃, t ₂ ℃ using the measured data, equations (1) and (2)
The formula was calculated, and the data shown in the characteristic curves shown in Figures 2 and 3 were stored in the memory 1 over each temperature.
The correction may be performed by storing the data in 3 and sequentially reading the data. Further, it is not necessary to perform the calculations of equations (1) to (3) sequentially, and the correction may be performed using a combination of these equations. Furthermore, the sensitivity of Mch9/sensitivity of Rch8 and the sensitivity of Ach5/sensitivity of Rch8 were stored in the memory 13 and used as data indicating temperature characteristics.
When the X-ray energy is stable, Rch 8 may not be used, and the sensitivities themselves (actual measurement data) of Mch 9 and Ach 5 may be stored in the memory 13 as data indicating temperature characteristics.

(Effects of the Invention) As explained above, according to the present invention, actual measurement data can be obtained at low cost without requiring any special equipment and by using the storage means and calculation means that X-ray tomography apparatuses normally have. It is possible to realize an X-ray tomography apparatus that can perform temperature correction.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a schematic configuration of the main body and processing section of an embodiment of the present invention, FIG. 2 is a diagram showing an example of the temperature characteristic curve of a representative channel, and FIG. 3 is a diagram showing one example of the temperature characteristic curve of a representative channel. A diagram showing an example of the temperature characteristic curve of the channel, Figure 4 shows the temperature stored in memory.
An explanatory diagram of the measured data of each channel at t ₁ and t ₂ , FIG. 5 is a schematic configuration diagram of a conventional X-ray tomography apparatus, and FIG. 6 is an electrode arrangement diagram of an ionization chamber detector. 1... X-ray tube, 2... Collimator, 3... Subject, 4... X-ray detector, 5... Measurement channel (Ach), 6... Bias electrode, 7... Signal electrode,
8... Reference channel (Rch), 9... Representative channel (Mch), 10... Data collection section, 11...
Computer, 12... High-speed arithmetic device, 13...
memory.

Claims (1)

[Claims] 1. An X-ray tomography apparatus having an X-ray detector composed of a plurality of channels, in which a representative channel is arranged at a position where the irradiated X-rays directly enter the subject without passing through it. Using a detector, a storage means for storing temperature characteristics of the representative channel and measurement channel sensitivity, and actual measurement in each measurement channel based on the temperature characteristics stored in the storage means and actual measurement data in the representative channel. An X-ray tomography apparatus characterized by comprising: arithmetic means for temperature-correcting data. 2. In an X-ray tomography system that has an X-ray detector composed of multiple channels, a representative channel is placed at a position where the irradiated X-rays directly enter without passing through the subject, and fluctuations in the irradiated X-ray intensity are For detection, an X-ray detector is installed at a position where the irradiated X-rays directly enter the subject without passing through it, and the output fluctuation due to temperature changes is sufficiently small compared to other channels. , storage means for storing the temperature characteristics of the sensitivity of the representative channel with respect to the sensitivity of the reference channel and the sensitivity of the measurement channel with respect to the sensitivity of the reference channel, and the temperature characteristics stored in the storage means and the actual measurement data in the representative channel. 1. An X-ray tomography apparatus characterized by comprising: a calculation means for correcting the temperature of actual measurement data in each measurement channel based on the temperature.