JP3253990B2 - Multi-dimensional image measurement device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a remote sensing image measured by scanning a multi-element detector such as a one-dimensional line sensor or a two-dimensional area sensor, a multi-gradation image reader image, or a measured image. X-ray CT
The present invention relates to a multidimensional image measuring device for images and the like, and more particularly to a multidimensional image measuring device having a data processing function for correcting a sensitivity difference between elements of a multi-element detector.

[0002]

2. Description of the Related Art Multi-element detectors such as a one-dimensional licensor and a two-dimensional area sensor have sensitivity variations due to processing accuracy of each element and non-uniformity of materials. The variation in sensitivity of the element appears as stripes in the scanning direction in the measurement data. Normally, calibration correction is performed using preparatory data for calibration. However, it is often the case that correction cannot be performed with calibration data due to the environment in which the apparatus is used or changes over time.

Here, X to which the multi-element detector is applied is used.
The line CT apparatus will be described in detail as an example. As shown in FIG. 3, the X-ray CT apparatus is arranged in a range where the multi-element detector 102 faces the X-ray source 101 and covers the imaging region 104.
The X-ray transmission data of the inspection object 107 is collected by the measurement device 103 while rotating around the inspection object 107. The measured data is input to the image reconstruction device 105, and the reconstructed tomographic image is displayed on the display device 106. At this time, as shown in FIG. 4, the sensitivity difference component 40 in the multi-element detector 102 is included in each X-ray transmission data. When an image is formed without any correction to the X-ray transmission data, stripes appear in the scanning direction in the positioning X-ray transmission data image (scanogram), and concentric patterns are formed in the reconstructed tomographic image. Artifacts appear. Artifacts may cause a decrease in diagnostic ability and should be removed.

[0004] In order to remove this artifact, conventional X-ray transmission data is collected to create sensitivity correction data at the time of image creation, and the object 107 to be inspected due to the sensitivity difference of the multi-element detector 102 is created based on the sensitivity correction data. X-ray transmission data error is corrected. However, in the conventional method,
Since the X-ray dose and the radiation quality of the X-ray CT device change with time, the sensitivity difference cannot be corrected in many cases.

[0005] For example, the resistance (temperature) of the filament of the X-ray tube as the X-ray source 101 changes with the passage of time, or the X-ray dose and quality change as the target is activated. In addition, the temperature characteristics and the electrical characteristics of the multi-element detector 102 change with time.

As described above, a change in the X-ray dose and the quality characteristic of the X-ray CT apparatus causes a difference in the X-ray dose and the quality characteristic between the respective elements of the multi-element detector 102. There is a subtle difference between the time and the time of X-ray transmission data collection of the subject. Therefore, the sensitivity difference cannot be accurately corrected, and the artifact cannot be sufficiently removed.

On the other hand, in the invention already proposed by the present applicant and having the content of Japanese Patent Application No. 58-158662, the artifact difference is filtered in the element direction to reduce the sensitivity difference component. It finds a way to extract and correct. That is, as shown in FIG. 6, the averaged data is averaged in the scanning direction by the average value calculator 60. The averaging may be over all the measured data, or may be a divided average. In any case, the average value data is reduced in noise as compared with the original measurement value, which is convenient for extracting the sensitivity difference. If the average value data M (u) in the scanning direction is used, the sensitivity difference component R
(U) is extracted by using the moving average shown in the following equation (1) or by using the convolution operation shown in the equation (2).

[0008] These processes are performed by a filter processor 61 shown in FIG.

[0009]

(Equation 1)

[0010]

(Equation 2)

FIG. 5A is a graph showing an average value in the scanning direction with respect to the element direction, and FIG.
Is a graph showing the extracted sensitivity difference with respect to the element direction.

Thereafter, an image reconstruction processing device 6 shown in FIG.
2 to be reconstructed.

[0013]

However, in a multidimensional image measuring apparatus having such a configuration, both detectors positioned on both sides of a detector whose sensitivity difference is corrected perform correction of the sensitivity difference. If the detector is unnecessary, no particular problem occurs, but if not, accurate sensitivity difference correction cannot be performed.

That is, since the correction of the detector for correcting the sensitivity difference is performed based on the outputs of the detectors positioned on both sides of the detector, each of these detectors corrects the sensitivity difference. This is because it is a prerequisite that the detector must not be indispensable.

Therefore, the present invention has been made in view of such circumstances, and an object of the present invention is to provide a plurality of detectors adjacent to each other for correcting a sensitivity difference. Even so, it is an object of the present invention to provide a multi-dimensional image measurement device capable of accurately correcting the sensitivity difference between the detectors.

[0016]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a projection data measuring means for measuring projection data having measurement symmetry by detecting means having a multi-element detector; A first average value calculating means for calculating an average value over the scanning direction, and filtering the average value calculated by the first average value calculating means in the element direction of the detecting means, thereby performing the filtering between the detecting elements. First sensitivity difference component extracting means for extracting the sensitivity difference component of the second average value for calculating an average value in the element direction of the detection means with respect to the average value calculated by the first average value calculating means Calculation means, and second sensitivity difference component extraction for extracting a sensitivity difference component between the detection elements by filtering the average value calculated by the second average value calculation means in the element direction of the detection means. Means,
Addition means for adding the output of the first sensitivity difference component extraction means and the output of the second sensitivity difference component extraction means; and subtraction means for subtracting the output of the addition means from the output of the projection data measurement means. The tomographic image is reconstructed using the corrected projection data obtained by the subtraction means.

[0017]

The multi-dimensional image measuring apparatus thus constructed is capable of extracting the sensitivity difference component between the detecting elements of the detecting means in the scanning direction of the projection data and continuously distributing the sensitivity difference component in the detecting element direction of the detecting means. A means for extracting a sensitivity difference component to be provided is provided,
The projection data is corrected by using the sensitivity difference data extracted by these means. For example, the average of two average values of two detector groups positioned on both sides of two adjacent detector groups, respectively, is corrected. A correction means for correcting the difference in sensitivity between the two adjacent detectors from the value is further provided. And this newly provided correction means, especially when it is necessary to correct the sensitivity difference in the same way as the certain detector group in at least one of the detector groups positioned on both sides of the certain detector group, It works effectively. That is, two detector groups are assumed sequentially from one end side of the adjacent detector group, and the exactly same method as in the past is performed based on the output average value of each of these detector groups. .

In this way, even if detectors having a prominent sensitivity difference are arranged adjacent to each other, the sensitivity difference of each of the detectors can be accurately corrected. Note that the case where three detectors that need to perform sensitivity difference correction are arranged adjacent to each other is extremely low in terms of establishment, but is theoretically considered. In this case, the three detectors positioned on both sides of the three detector groups adjacent to each other are used.
Correction means for correcting the sensitivity difference between the three adjacent detectors based on the average value between the average values of the detector groups may be provided.

[0019]

FIG. 1 is a block diagram showing an embodiment of a multidimensional image measuring apparatus according to the present invention, and in particular, is a block diagram showing an image reconstructing apparatus of an X-ray CT apparatus. In the figure, reference numeral 401 denotes an average calculator for calculating an average of projection data in the scanning direction. Reference numeral 402 denotes a filter processor.
This is to extract the first sensitivity difference component by performing filter processing on the output of the average value calculator 401 in the element direction. 403 is a buffer memory 1 and a filter processor 4
The first sensitivity difference component extracted in step 02 is stored. Reference numeral 404 denotes an average calculator for calculating the average of the output of the average calculator 401 in the element direction. 4
Numeral 05 denotes a filter processor for filtering the output of the average value calculator 404 in the element direction to extract a second sensitivity difference component. Reference numeral 406 denotes a buffer memory 2 for storing the second sensitivity difference component extracted by the filter processor 405. The adder 407 is for adding the first and second sensitivity difference components. Reference numeral 408 is for subtracting the final sensitivity difference component obtained by the adder 407 from the original projection data. Further, reference numeral 409 denotes an image reconstruction processing apparatus for reconstructing a tomographic image from the projection data subjected to the sensitivity difference correction.

Next, the operation of the image reconstruction apparatus according to the present embodiment will be described.

The measured projection data P (i, j) is input to the image reconstruction device 105. Here, i is a detector element number, and j is a number indicating a measurement position in the scanning direction. The average calculator 401 calculates an average M (i) of the projection data P (i, j) in the scanning direction. M (i) may be the average of all the measured values, the divided average, or the moving average. For example, assuming that the number of measurements in the scanning direction is n, using all the measured values, the following equation (3) is used.

[0022]

(Equation 3) become that way. Here, the data thus obtained is as shown in FIG.

In the filter processing 402, a first sensitivity difference component R1 (i) is extracted from M (i) by moving average processing in the element direction shown in the equation (1). For example, when a three-point moving average is used, the following equation (4) is obtained.

[0024]

(Equation 4) The extracted first sensitivity difference component is stored in the buffer memory 1. Here, the data stored in the buffer memory 1 is as shown in FIG.

Further, M (i) is input to the averaging unit 404, and as shown in the following equation (5), averaged data in the element direction is calculated. For example, (1) of 1/2 sample data obtained by averaging every two elements is obtained.

(Equation 5)

The filter processor 405 extracts the second sensitivity difference component by moving average processing in the element direction, similarly to the filter processor 402. For example, when a three-point moving average is used, the following equation (6) is used.

[0027]

(Equation 6) Is stored in the buffer memory 2. here,
The data stored in the buffer memory 2 is shown in FIG.
It is as shown in Further, the data R1 and R2 stored in the buffer memories 1 and 2 are added by the adder 407 as shown in the following equation (7).

(Equation 7)

The second sensitivity difference R2 is obtained by calculating the deviation from the moving average of every two elements, so that the extracted sensitivity difference component is the one crossing the two elements. Also, the first sensitivity difference component R1
Is the independent sensitivity difference (not crotch) for one element,
R obtained by adding them has improved accuracy of sensitivity difference extraction as compared with the related art. By subtracting this from the original projection data by the subtractor 408, the correction of the sensitivity difference is completed. The corrected projection data is input to the reconstruction processing device, and a tomographic image is calculated. The reconstructed tomographic image is a good image without artifacts. When the detectors are arranged two-dimensionally, the moving average in the element direction may be implemented in one dimension or two dimensions.

In a multi-level image reader, a sensitivity difference which is not a problem in a binary image reader may also be a problem. In that case, the present invention can be applied as it is, and the rotation direction of the X-ray source in the case of the X-ray CT apparatus only corresponds to, for example, the scanning direction of the CCD line sensor.

According to the above-described embodiment, the average value of the two detector groups positioned on both sides of the two adjacent detector groups is calculated from the average value of the adjacent two detector groups.
Correction means for correcting the sensitivity difference between the individual detectors is further provided. However, furthermore,
Correcting means for correcting the sensitivity difference between the two adjacent detectors from the average of the respective average values of the two detector groups positioned on both sides of the two adjacent detector groups, Needless to say, it may be further provided. In this case, even when three detectors having a prominent sensitivity difference are arranged in parallel, the sensitivity difference can be accurately corrected for each.

[0031]

As is apparent from the above description,
ADVANTAGE OF THE INVENTION According to the multidimensional image measurement apparatus by this invention, even if the detector which corrects a sensitivity difference is arrange | positioned adjacently, the correction of the sensitivity difference of each detector can be performed accurately. Become like

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a multidimensional image measurement device according to the present invention.

FIGS. 2 (a) to 2 (c) are graphs showing data formed in respective parts in the configuration diagram of FIG.

FIG. 3 is a schematic configuration diagram showing an embodiment of an X-ray imaging apparatus to which the multidimensional image measurement device according to the present invention is applied.

FIG. 4 is an explanatory diagram showing sensitivity difference components with respect to an element direction and a scanning direction.

FIGS. 5A and 5B are graphs respectively showing an average value in a scanning direction with respect to an element direction and an extracted sensitivity difference.

FIG. 6 is a block diagram showing an example of a conventional multidimensional image measurement device.

[Explanation of symbols]

 40 sensitivity difference component 401 average value calculator 402 filter processor 403 buffer memory 404 average value calculator 405 filter processor 406 buffer memory 407 adder 408 subtractor

Claims (1)

(57) [Claims] 1. Projection data measuring means for measuring projection data having measurement symmetry by detecting means having a multi-element detector;
First calculating an average value of the projection data over the scanning direction;
Average value calculation means and the first average value calculation means
Filter in the element direction of the detection means
Processing to extract a sensitivity difference component between the detection elements.
One sensitivity difference component extracting means, and the first average value calculating means
With respect to the average value calculated in
Second average value calculating means for calculating the average value, and the second average value calculating means.
The average value calculated by the average value calculating means
Filtering is performed in the element direction and the sensitivity between the detection elements
A second sensitivity difference component extracting means for extracting a difference component;
The output of one sensitivity difference component extracting means and the second sensitivity difference component
Adding means for adding the output of the extracting means;
Subtracting the output of the adding means from the output of the data measuring means.
A multidimensional image measurement apparatus including a calculating means and a reconstructing means for reconstructing a tomographic image using the corrected projection data obtained by the subtracting means .