Method and apparatus for filtering projection images

An image processing apparatus for reconstructing a tomographic image from a plurality of projection images obtained by irradiating a subject with radiation from a plurality of directions, the apparatus comprising:

• an obtaining unit configured to obtain, for each of the plurality of projection images, a weighting coefficient according to a difference between a pixel value of a filtering target pixel and a pixel value of a second pixel;
• a reconstructing unit configured to process each pixel of the plurality of projection images on the basis of a reconstruction filter coefficient weighted by the weight coefficient and to reconstruct the tomographic image based on the processed pixels;
• a calculating unit configured to calculate a difference value between a filtering target pixel of a projection image and a peripheral pixel of the target pixel;
• an output unit configured to output the weighting coefficient which is smaller as an absolute value of the calculated difference value is larger;
• a multiplying unit configured to multiply a filter coefficient by the weighting output by the output unit;
• and
• a processing unit, including a central processing unit, configured to filter a plurality of projection images on the basis of a result obtained by the multiplying unit.

An image processing method of reconstructing a tomographic image from a plurality of projection images, the method comprising:

• an obtaining step to obtain a plurality of radiation projection images from a digital radiation detector;
• a reconstructing step to execute a filtering process on the plurality of radiation projection images using a reconstruction filter and a reconstructing process to create a tomographic image on the basis of the obtained plurality of radiation projection images;
• and
• a processing step to reduce an influence on a value of a first pixel in a radiation projection image to be supplied to the reconstruction unit, the influence being exerted by a second pixel, in a case in which a difference between the value of the first pixel and the value of the second pixel is larger than a predetermined threshold value,
• wherein when an absolute value of the difference between the first pixel value and the second pixel value is smaller than the threshold value, the processing step outputs the difference value, and when the absolute value of the difference is larger than the threshold value, the processing step outputs a value smaller than the difference value;
• and
• wherein the reconstructing step executes the reconstructing process of the tomographic image on a basis of a value output by the processing step.

An image processing method of reconstructing a tomographic image from a plurality of projection images obtained by irradiating a subject with radiation from a plurality of directions, the method comprising:

• an obtaining step to obtain, for each of the plurality of projection images, a weighting coefficient according to a difference between a pixel value of a filtering target pixel and a pixel value of a second pixel;
• a reconstructing step to process each pixel of the plurality of projection images on the basis of a reconstruction filter coefficient weighted by the weight coefficient and to reconstruct the tomographic image based on the processed pixels;
• a calculating step to calculate a difference value between a filtering target pixel of a projection image and a peripheral pixel of the target pixel;
• an outputting step to output the weighting coefficient which is smaller as an absolute value of the calculated difference value is larger;
• a multiplying step to multiply a filter coefficient by the weighting output by the outputting step;
• and
• a processing step to filter a plurality of projection images on the basis of a result obtained by the multiplying step.

An image processing apparatus comprising:

• an obtaining unit configured to obtain a plurality of radiation projection images from a digital radiation detector;
• a reconstructing unit configured to execute a filtering process on the plurality of radiation projection images using a reconstruction filter and a reconstructing process to create a tomographic image on the basis of the obtained plurality of radiation projection images;
• and
• a processing unit, including a central processing unit, configured to reduce an influence on a value of a first pixel in a radiation projection image to be supplied to the reconstruction unit, the influence being exerted by a second pixel, in a case in which a difference between the value of the first pixel and the value of the second pixel is larger than a predetermined threshold value,
• wherein, on the basis of a magnitude relation between the threshold value and the difference between the first pixel value and the second pixel value, the processing unit is configured to switch between outputting the difference value and outputting a value smaller than the difference value to the reconstructing unit, and
• wherein the reconstructing unit is configured to execute the reconstructing process of the tomographic image on the basis of the value output by the processing unit.

An image processing apparatus comprising:

• an obtaining unit configured to obtain projection images of an object from a digital radiation detector;
• and
• a processing unit, including a central processing unit, configured to, for each of pixels of each of the obtained projection images, as a target pixel, perform a reconstruction filtering process in order to obtain a plurality of filtered data, based on the target pixel and a pixel different from the target pixel, the different pixel being in one of the projection images including the target pixel, and generate a tomographic image based on the obtained plurality of filtered data,
• wherein the processing unit processes the target pixel with a reconstruction filtering coefficient based on a value of the target pixel and a value of the different pixel, and with a correction coefficient based on a difference value between the value of the target pixel and the value of the different pixel, and
• wherein the processing unit determines an absolute value of the correction coefficient as a value smaller than an absolute value of the difference value in a case where the absolute value of the difference value is larger than a threshold value.

An image processing method of reconstructing a tomographic image from a plurality of projection images, the method comprising:

• an obtaining step to obtain projection images of an object from a digital radiation detector;
• and
• a processing step to, for each of pixels of each of the obtained projection images, as a target pixel, perform a reconstruction filtering process in order to obtain a plurality of filtered data, based on the target pixel and a pixel different from the target pixel, the different pixel being in one of the projection images including the target pixel, and generate a tomographic image based on the obtained plurality of filtered data,
• wherein the processing step processes the target pixel with a reconstruction filtering coefficient based on a value of the target pixel and a value of the different pixel, and with a correction coefficient based on a difference value between the value of the target pixel and the value of the different pixel, and
• wherein the processing step determines an absolute value of the correction coefficient as a value smaller than an absolute value of the difference value in a case where the absolute value of the difference value is larger than a threshold value.

An image processing apparatus comprising:

• at least one central processing unit;
• and
• a memory storing a program including instructions to be executed by the at least one processor to perform a method comprising:
• obtaining projection images of an object from a digital radiation detector;
• performing, for each of pixels of each of the obtained projection images, as a target pixel, a reconstruction filtering process in order to obtain a plurality of filtered data, based on the target pixel and a pixel different from the target pixel, the different pixel being in one of the projection images including the target pixel;
• and
• generating a tomographic image based on the obtained plurality of filtered data,
• wherein in the performing, (a) the target pixel is processed with a reconstruction filtering coefficient based on a value of the target pixel and a value of the different pixel, and with a correction coefficient based on a difference value between the value of the target pixel and the value of the different pixel and (b) an absolute value of the correction coefficient is a value smaller than an absolute value of the difference value in a case where the absolute value of the difference value is larger than a threshold value.