JP2001070297A - Method of giving information whether calibration is necessary or not and x-ray ct device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To give quick information that calibration is necessary. SOLUTION: Air is scanned as a part of the warm-up scan in the specified scanning condition, and the air data (Air warm-up i, j) per each channel number (i) and per each view number (j) is collected (ST1). The mean data in the view direction (Air warm-up i) is computed (ST2), and in the case where a difference between the previously stored mean data in the view direction in the same condition (Air ref i) is large (ST3-ST5), 'calibration promoting message' is displayed (ST6). Since necessity of calibration is discriminated per each warm-up scan performed in daily routine as a preparatory processing before the operation, quick information can be given that calibration is necessary.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for notifying the necessity of calibration and an X-ray CT (Compu
More specifically, the present invention relates to a calibration necessity notification method and an X-ray CT apparatus capable of promptly notifying that calibration is required.

[0002]

2. Description of the Related Art Calibration in an X-ray CT apparatus is an operation of detecting a variation in sensitivity for each channel of a detector array and obtaining calibration data for correcting the variation. By performing such a calibration, the ring artif
act) can be suppressed.

FIG. 5 is a flowchart showing a procedure for calibrating a sensitivity correction coefficient. In step J1, first scan conditions are set. The first scan condition is
For example, there is a scan condition in which an X-ray tube voltage having three stages of low, medium, and high is set to “low”, and a slice thickness set in a range of 1 to 10 mm is set to “1 mm”. Step J
At 2, the air is scanned and air data is collected. In step J3, a sensitivity correction coefficient is calculated from the air data.

At step J4, the water phantom is scanned to collect water phantom data. In step J5, the water phantom data is corrected using the sensitivity correction coefficient calculated in step J3. In step J6, another correction coefficient (for example, a correction coefficient for preprocessing such as a beam hardening correction coefficient) is calculated from the water phantom data corrected in step J5.

[0005] In step J7, it is determined whether or not scanning has been performed under specified all-scan conditions. The prescribed all scan conditions include, for example, a scan condition in which the X-ray tube voltage is “low, medium, high” and a slice thickness of “1 mm, 2 mm, 3 m”.
m, 5 mm, 7 mm, and 10 mm ″. In this case, 18 scans are performed for each of the air and water phantoms, so a total of 36 scans are required. If the scan is performed under the conditions, the calibration is completed, and if not, the process proceeds to step J8.
Then, the following scan conditions are set. Thereafter, the process returns to step J2.

[0006]

The calibration of the sensitivity correction coefficient is performed at a relatively low frequency, for example, about once a month. This is because calibration requires a relatively long processing time and cannot be performed frequently. For this reason, when the sensitivity fluctuation of the detector occurs earlier than usual, the processing is continued with an inappropriate sensitivity correction coefficient until the next calibration is performed, and an artifact is generated on the image during that period. There is a problem that causes inconvenience. Accordingly, an object of the present invention is to provide a calibration necessity notification method and an X-ray CT apparatus that can promptly notify that calibration is required.

[0007]

SUMMARY OF THE INVENTION In a first aspect, the present invention is directed to a method for scanning air under specific scanning conditions during a warm-up scan for warming up an X-ray tube, collecting air data, and acquiring the air data. And a pre-stored air data under the same conditions, and determines whether or not calibration is necessary based on the comparison result. I will provide a. In the method of notifying the necessity of calibration according to the first aspect, air data of a specific scan condition is collected during a warm-up scan performed as a daily routine work, and is compared with air data stored in advance under the same condition. Thus, since the necessity of the calibration is determined, when the calibration becomes necessary, it can be promptly notified.
In the above configuration, the specific scan condition may be one or plural.

In a second aspect, the present invention provides an X-ray tube warm-up means for warming up an X-ray tube, and air data for collecting air data by scanning air under specific scanning conditions during the warm-up. Collection means, calibration necessity determination means for comparing the air data with air data under the same condition stored in advance, and determining whether or not calibration is necessary based on the comparison result; An X-ray CT apparatus provided with a notifying unit for notifying. The second
In the X-ray CT apparatus according to the aspect described above, the method for notifying the necessity of calibration according to the first aspect can be suitably implemented, and the necessity of calibration can be accurately notified.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail with reference to the embodiments shown in the drawings. Note that the present invention is not limited by this. FIG. 1 is a block diagram showing an X-ray CT apparatus 100 according to one embodiment of the present invention. The X-ray CT apparatus 100 includes an operation console 1,
It has an imaging table 8 and a scanning gantry 9.
The operation console 1 includes an input device 2 that receives instructions and information from an operator, a central processing unit 3 that performs scan processing, interpolation processing, image reconstruction processing, and the like. A control interface 4 for outputting data to the scanning gantry 9, a data collection buffer 5 for collecting data acquired by the scanning gantry 9, a CRT 6 for displaying images and the like, and a storage device 7 for storing various data and programs. . The imaging table 8 moves in the body axis direction with the subject placed thereon. The scanning gantry 9
Is a rotator controller 15 for rotating the X-ray tube 11, the detector 13 and the like around the body axis of the subject, and the X-ray tube 11, collimator 12, and detector 13 of the fan beam system.
And an X-ray controller 10 for adjusting the timing and intensity of X-ray irradiation, and a data acquisition unit 14.

FIG. 2 is a flowchart showing a reference air data collecting process by the X-ray CT apparatus 100. This reference air data collection processing is executed following normal calibration (see FIG. 5). In step S1, air is scanned under specific scanning conditions, and the air data is collected as reference air data Air ref. (I, j) (reference air data scan). Specific scanning conditions are:
For example, the X-ray tube voltage is set to “medium” and the slice thickness is set to “3 m”.
m ". Note that (i, j) represents the number of the reference air data, of which i represents the channel number and j represents the view number. In step S2, Each channel i (i = 1, 2, 2, 3) of the detector 13
.., Max_ch), the average of the air data in all view directions is calculated as the reference air view direction average data Air ref.
Calculated as (i). max_ch is the maximum value of the channel number and is equal to the total number of channels. In step S3, the reference air view direction average data Air ref. (I) is stored in the storage device 7.

FIG. 3 is a flowchart showing a calibration necessity notification process by the X-ray CT apparatus 100.
This calibration necessity notification process is performed as part of a warm-up scan performed as a routine work before the start of operation. For example, in a warm-up scan,
The X-ray tube 11 and the detector 13 are rotated several times, during which the output of the X-ray tube 11 is increased. At the last rotation, the necessity of calibration is notified. Step ST
In step 1, air is scanned under the same specific scan conditions as in step S2 in FIG.
ir warmup. (i, j) (comparison air data scan). The reason for performing this scan in the final phase of the warm-up scan is that preheating of the X-ray tube 11 is almost completed, and X-rays can be stably emitted.

In step ST2, the average of air data in all view directions corresponding to each channel i of the detector 13 is compared. Average air view direction average data Air warmup. (I)
Is calculated as

In step ST3, the reference air view direction average data Air ref. (I) stored in the storage device 7 is read out, and δAir (i) = | Air warmup (i) −Air ref.
(i) | is used to calculate the difference data δAir (i). Also, To calculate integrated difference data △ Air.

In step ST4, it is determined whether or not the difference data δAir (i) corresponding to any one of the channels i of the detector 13 is larger than a predetermined value. If any of the difference data δAir (i) is larger than a predetermined value, it is determined that calibration is required, and the process proceeds to step ST6. Otherwise, the process proceeds to step ST5.

In step ST5, the accumulated difference data △ A
It is determined whether or not ir exceeds a threshold Th. If the accumulated difference data △ Air exceeds the threshold value Th, it is determined that calibration is required, and the process proceeds to step ST6. If not, the calibration necessity notification process ends. The threshold value Th is empirically determined as integrated difference data △ Air at which ring artifacts begin to occur. In step ST6, a "calibration prompting message" is displayed on the screen of the CRT 6 to notify the operator that calibration is required. After that, the calibration necessity notification processing ends.

FIG. 4 is a graph schematically showing the relationship between the number of days elapsed after the calibration and the accumulated difference data △ Air. The accumulated difference data △ Air is “0” immediately after the calibration, but increases as the number of elapsed days increases. When the accumulated difference data △ Air exceeds the threshold value Th during the elapsed days p to (p + 1), the “calibration promotion message” is displayed at the time of the elapsed days (p + 1). With this as a trigger, calibration is executed, and the accumulated difference data △ Air becomes “0”.
(On the other hand, in the past, there has been an inconvenience such as continuing to increase as shown by the dotted line and deteriorating the image quality).

The above embodiment may be modified as follows. (1) In the calibration necessity notification processing of FIG. 3, a message is not displayed when calibration is unnecessary, but a “calibration unnecessary message” may be displayed. (2) Statistically process the accumulated difference data △ Air for each number of days elapsed after the calibration to display the trend, and use the trend to predict the time when it is necessary to perform the next calibration. The approach of the time may be displayed. Thus, the operator can determine whether or not to perform the calibration early in consideration of the photographing schedule and the like, and can improve the driving efficiency.

[0018]

According to the method of notifying the necessity of calibration and the X-ray CT apparatus of the present invention, the necessity of calibration is determined each time a warm-up scan is routinely performed as a preparation process before operation. Thus, it is possible to promptly notify that calibration is required.
Therefore, calibration can be performed at a necessary time, and a high-quality CT image can always be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an X-ray CT apparatus according to one embodiment of the present invention.

FIG. 2 is a flowchart showing a reference air data collection process by the X-ray CT apparatus of FIG. 1;

FIG. 3 is a flowchart showing a calibration necessity notification process by the X-ray CT apparatus of FIG. 1;

FIG. 4 is a graph schematically showing the relationship between the number of days elapsed after calibration and the accumulated difference data.

FIG. 5 is a flowchart showing a procedure of calibration of a sensitivity correction coefficient.

[Explanation of symbols]

 Reference Signs List 100 X-ray CT apparatus 1 Operation console 2 Input device 3 Central processing unit 4 Control interface 5 Data acquisition buffer 6 CRT 7 Storage device 8 Imaging table 9 Scanning gantry 10 X-ray controller 11 X-ray tube 12 Collimator 13 Detector 14 Data collection unit 15 Rotating unit controller

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4C093 AA22 BA03 CA36 EA02 FB11 GA06

Claims (2)

[Claims] 1. During a warm-up scan for warming up an X-ray tube, air is scanned under specific scan conditions to collect air data, and the air data and previously stored air data under the same conditions are collected. A method of notifying the necessity of calibration, comprising: comparing and judging the necessity of calibration based on the comparison result, and notifying if calibration is necessary. 2. An X-ray tube warm-up means for warming up an X-ray tube, an air data collecting means for scanning air under specific scanning conditions during the warm-up to collect air data, It is provided with a calibration necessity determining means for comparing the air data under the same conditions stored in advance and determining the necessity of calibration based on the comparison result, and a notifying means for notifying if calibration is necessary. X-ray C characterized by the following:
T device.