JPH0484941A - X-ray ct device - Google Patents

Abstract

PURPOSE:To execute the non-linearity correction corresponding to the heat accumulation quantity of an X-ray tube by correcting X-ray detection data of an X-ray detector by a non-linearity correction value in which the heat accumulation quantity of the X-ray tube and the channel number of the X-ray detector. CONSTITUTION:The device is provided with an X-ray detector 2 and a correcting means 3 in addition to a memory 1, and the memory 1 is divided by the heat accumulation quantity (j), and in accordance with one heat accumulation quantity (j), X-ray detector numbers 1-(n) are allocated, and a non-linearity correction value E corresponding to a channel. is stored in advance. In such a state, in the memory 1, by setting the channel number (i) and the heat accumulation quantity (j) as parameters and the corresponding non-linearity correction value E1j is read out, and on the other hand, from the X-ray detector 2, detection data D1j corresponding to the channel number is obtained. Subsequently, by correcting the detection data D1j by E1j at the time of actual measurement, by the correcting means 3, detection data which is not influenced by the heat accumulation quantity can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an XAIXCT apparatus that performs nonlinearity correction according to the amount of heat stored in an X-ray tube.

[Conventional technology]

In the conventional X@C,T device, correction of the inspection data of the X-ray detector includes non-linearity correction. What is nonlinearity correction?XI! We focused on the fact that the input characteristics for the X-ray intensity irradiated by the detector have different non-linear characteristics for each channel, and taking this non-linear characteristic into consideration,
This refers to correcting the detection data of the line detector.

This nonlinearity correction method has the following contents.

First, the nonlinearity correction value E(CH) is determined in advance and stored in the memory.

Here, CH indicates the channel number, E (CH) is the correction value corresponding to the channel number, and R (CH) is the correction value corresponding to the channel.
Actual measurement value of line detector.

I(CH) is theoretical detection data (theoretical value) of the X-ray detector corresponding to the channel.

Next, use E(CH) to perform X against the subject.
Correct the actual measurement value D(CH) of the line detector. The correction formula is as follows.

D, (CH) = D (CH) X (1+ E (C
H))...(2) Here, Dr(CH) is an actual measured value after correction.

The thus obtained (CH) is used as reconstruction data to obtain X-ray CT data.

[Problem to be solved by the invention]

In the above conventional example, the nonlinearity correction value corresponds to the channel, but does not take into account the amount of heat stored in the X-ray tube during scanning (when imaging the subject).
In the wire tube, the rotor shaft of the rotating anode and the like expand thermally depending on the amount of heat stored in the tube. This results in a shift in the focal position of the anode and a change in the x-ray geometry, resulting in a change in the input characteristics of each channel. However, conventional nonlinearity correction lacks accuracy because it does not take into account changes in the input characteristics of each channel due to the amount of heat storage.

An object of the present invention is to provide an X-ray CT apparatus that enables nonlinearity correction according to the amount of heat stored in an X-ray tube.

[Means to solve the problem]

The present invention provides a non-linearity correction value using the heat storage amount of the X-ray tube and the channel number of the X-ray detector as parameters, and calculates the non-linearity correction value corresponding to the channel from the actual heat storage amount of the X41 tube. The X-ray detection data of the X-ray detector at that time was corrected using the selected nonlinearity correction value.

C Effect] According to the present invention, the X-ray detection data of the X-ray detector is corrected using the nonlinearity correction value using the heat storage amount and the channel number as parameters. With this correction, the X-ray detection data becomes a value that is not affected by the amount of heat storage.

〔Example〕

FIG. 1 shows a structural side view of a memory 1 of the invention.

Memory l is divided by heat storage amount j, X-ray detector numbers 1 to n are assigned corresponding to one heat storage amount j, and nonlinearity correction values E corresponding to channels are stored as follows. There is.

Heat storage amount j → E 141 E za g ”・t E n
a Heat storage amount (j+1) → E 1 (a+41 + E z+
J+i+ t ”°+ E n+J+1) The same applies except for JtJ+1. Hereinafter, the nonlinearity correction value E is given by i as the channel number.

Generalize with EIJ. The division of j may be in units of several tens of degrees Celsius.

The nonlinearity correction value Era is as shown in the conventional example (1
) can be set using iJ as well as the formula. ILJ is a theoretical value, and R1□ is an actual value.

FIG. 2 shows a correction processing system diagram for actual detection data of an X-ray detector using the memory 1. In this embodiment, in addition to the memory 1, an X-ray detector 2. A correction means 3 is provided. The memory 1 is as shown in FIG. The X-ray detector 2 is an n-channel detector, and in reality, the correction means 3 may include a logarithmic converter or an AD converter in addition to the original X-ray detector.

Perform nonlinearity correction processing.

Now, in FIG. 2, the memory 1 reads out the corresponding nonlinearity correction values E and a using the channel number i and the amount of heat storage j as parameters. On the other hand, the xg tester 2 obtains detection data Di- corresponding to the channel number i.

The correction means 3 is similar to the formula (2) of the conventional example, D r g
I J = D5 JX (1 + EIJ) ・
...According to the formula (4), the corrected actual measurement values Dr, t□ are determined.

This data Dr and iJ are used as reconstruction data.

According to this embodiment, the correction value EIJ corresponding to the heat storage amount j is prepared in advance, and the detected data Di is used during actual measurement.
By correcting , using EIJ, it is possible to obtain detection data that is not affected by the amount of heat storage.

FIG. 1 shows all correction values EI determined by II j
In this example, J is stored, but an example for reducing the memory capacity is shown in FIG. In this embodiment, the minimum heat storage amount Hw
EtJ (win
), Eia(w+ax) are determined in advance, and the intermediate value thereof is determined by linear interpolation. For example, EtaO) is obtained for Hl.

In the above embodiments, the amount of stored heat j can be adjusted each time the temperature detector is installed near the X-ray tube.

FIG. 4 is a diagram showing the decreasing characteristic of the amount of heat storage during the OFF duration of the X-ray tube. This decreasing characteristic may be due to natural cooling or forced cooling. In any case, the characteristics shown in FIG. 4 can be uniquely determined for each X-ray tube.

If we consider this figure 4 together with the increase in heat storage amount during ON duration time, we can automatically calculate the heat storage amount at the time of ON start when the X-ray tube is started up and is being used repeatedly (scanning). can do. Such an example will be described below.

In many cases, an X-ray tube is turned on one after another at arbitrary time intervals to emit X-rays after being turned on.

This is shown in chronological order as follows.

0FF (0) → 0N (1) → ○FF (1) → 0N (2)
→0FF(2)→0N(3)→○FF(3)→ON (
4)→...Here, 0FF (0) indicates the OFF state of the X-ray tube which has not yet been started up. The heat storage amount Ha of the X-ray tube at this OFF point can be regarded as the heat storage amount at the environmental temperature. This is the initial value.

Next, enter 0N(1). The duration of this ON period is fixed, and the usage of the X-ray tube is also fixed.

Therefore, the amount of heat storage Hu during this ON period is calculated using the following equation.

Hu = c X t X M A X K V
...(5) C is a constant, t is ON period, MA
is the X-ray tube current and KV is the X-ray tube voltage.

Therefore, if the amount of heat storage at the end of the ○N period is Hal, then Hat=Ha+Hu ・-(6
) Next, in 0FF(1), with Ha 1 as the starting point,
Assuming that the to waiting time + OFF is continued, the amount of heat storage after that to time is calculated using Fig. 4, H
It becomes a2.

Next, since the amount of heat storage during the period of 0N(2) can also be found from equation (5), the amount of heat storage at the end of 0N(2) can also be found using the same concept as equation (6).

Power, 0N (1), 0N (2), 0N (3), -・
The amount of heat storage at each start time point of .

〔Effect of the invention〕

According to the present invention, image quality deterioration due to changes in the amount of heat of the X-ray tube can be prevented. Therefore, even when the X-ray tube is cold, after use (after several scans), 0N (2), 0N (3
), ...) can obtain equally good tomographic images even in a warm state.

[Brief explanation of drawings]

Fig. 1 is a side view of the data structure of the memory storing the nonlinearity correction value of the present invention, Fig. 2 is a system diagram of the nonlinearity correction processing of the present invention, and Fig. 3 is the interpolation side of the nonlinearity correction value of the present invention. 4 are diagrams showing the relationship between the time and the amount of heat storage during the OFF duration period. 1... Memory, 2... X-ray detector, 3... Correction means.

Claims (1)

[Claims] 1. Provide a nonlinearity correction value that uses the amount of heat storage in the X-ray tube and the channel number of the X-ray detector as parameters, and select the nonlinearity correction value corresponding to the channel from the amount of heat storage in the actual X-ray tube. Then, the X-ray CT apparatus corrected the X-ray detection data of the X-ray detector at that time using the selected nonlinearity correction value.