X-ray CT apparatus, x-ray CT apparatus afterglow correction method, and afterglow correction program

An X-ray CT apparatus comprising:

• an X-ray source for applying X-rays to an object;
• an X-ray detector arranged to face the X-ray source for determining the amount of transmitted X-rays of the object as projection data;
• actual-measurement acquisition means for acquiring the projection data of a step response as an actual measurement when continuous X-rays are irradiated to the X-ray detector with no object present and thereafter the irradiation is stopped;
• analyzing means for analyzing the step response of the acquired actual measurement into an impulse response, representing the calculation of the step response through the convolution integration of the analyzed impulse response, and calculating a plurality of time constants and their component ratios asymptotically and recursively that make the error between the actual measurement and the calculation lower than a set value;
• storage means for storing the calculated time constants and component ratios;
• correcting means for removing an afterglow component of the stored projection data from the projection data to produce corrected projection data during radiography of the object;
• reconstructing means for reconstructing an image using the produced corrected projection data;
• and display means for displaying the reconstructed image.

An X-ray CT apparatus comprising:

• an X-ray source for applying X-rays to an object;
• an X-ray detector arranged to face the X-ray source for determining the amount of transmitted X-rays of the object as projection data;
• basic-data acquisition means for acquiring response data of the projection data as basic data with no object in advance;
• analyzing means for analyzing an afterglow component of the acquired basic data into a plurality of time constants and their component ratios by using a genetic algorithm;
• storage means for storing the analyzed time constants and component ratios;
• correcting means for extracting an afterglow component of the projection data on the basis of the stored time constants and component ratios during radiography of the object and removing the extracted afterglow component of the projection data from the projection data to produce corrected projection data;
• reconstructing means for reconstructing an image using the produced corrected projection data;
• and display means for displaying the reconstructed image.

A method for correcting afterglow of an X-ray CT apparatus having an X-ray source for applying X-rays to an object and an X-ray detector arranged to face the X-ray source for determining the amount of transmitted X-rays of the object as projection data, comprising:

• a basic-data acquisition step of acquiring response data of the projection data as basic data with no object present in advance every time the image of the object is acquired;
• an analyzing step of analyzing an afterglow component of the acquired basic data into a plurality of time constants and component ratios of the afterglow component corresponding to the time constants;
• a storing step of storing the analyzed time constants and component ratios;
• a correcting step of extracting an afterglow component of the projection data on the basis of the stored time constants and component ratios during radiography of the object and removing the extracted afterglow component of the projection data from the projection data to produce corrected projection data;
• a reconstructing step of reconstructing an image using the produced corrected projection data and
• a displaying step of displaying the reconstructed image.

A method for correcting afterglow of an X-ray CT apparatus having an X-ray source for applying X-rays to an object and an X-ray detector arranged to face the X-ray source for determining the amount of transmitted X-rays of the object as projection data, comprising:

• an actual-measurement acquisition step of acquiring the projection data of a step response, as an actual measurement, when continuous X-rays are irradiated to the X-ray detector with no object present and thereafter the irradiation is stopped;
• an analyzing step of analyzing the step response of the acquired actual measurement into an impulse response, representing the calculation of the step response through the convolution integration of the analyzed impulse response, and calculating a plurality of time constants and their component ratios asymptotically and recursively that make the error between the actual measurement and the calculation lower than a set value:
• a storing step of storing the calculated time constants and component ratios;
• a correcting step of removing an afterglow component of the stored projection data from the projection data to produce corrected projection data during radiography of the object;
• a reconstructing step of reconstructing an image using the produced corrected projection data;
• and
• a displaying step of displaying the reconstructed image.

A method for correcting afterglow of an X-ray CT apparatus having an X-ray source for applying X-rays to an object and an X-ray detector arranged to face the X-ray source for determining the amount of transmitted X-rays of the object as projection data, comprising:

• a basic-data acquisition step of acquiring response data of the projection data as basic data with no object present in advance;
• an analyzing step of analyzing an afterglow component of the acquired basic data into a plurality of time constants and their component ratios by using a genetic algorithm;
• a storing step of storing the analyzed time constants and component ratios;
• a correcting step of extracting an afterglow component of the projection data on the basis of the stored time constants and component ratios during radiography of the object and removing the extracted afterglow component of the projection data from the projection data to produce corrected projection data;
• a reconstructing step of reconstructing an image using the produced corrected projection data;
• and
• a displaying step of displaying the reconstructed image.

A program for correcting afterglow of an X-ray CT apparatus having an X-ray source for applying X-rays to an object and an X-ray detector arranged to face the X-ray source for determining the amount of transmitted X-rays of the object as projection data, comprising:

• a basic-data acquisition step of acquiring response data of the projection data as basic data with no object present in advance every time the image of the object is acquired;
• an analyzing step of analyzing an afterglow component of the acquired basic data into a plurality of time constants and component ratios of the afterglow component corresponding to the time constants;
• a storing step of storing the analyzed time constants and component ratios;
• a correcting step of extracting an afterglow component of the projection data on the basis of the stored time constants and component ratios during radiography of the object and removing the extracted afterglow component of the projection data from the projection data to produce corrected projection data;
• a reconstructing step of reconstructing an image using the produced corrected projection data;
• and
• a displaying step of displaying the reconstructed image.

A program for correcting afterglow of an X-ray CT apparatus having an X-ray source for applying X-rays to an object and an X-ray detector arranged to face the X-ray source for determining the amount of transmitted X-rays of the object as projection data, comprising:

• an actual-measurement acquisition step of acquiring the projection data of a step response, as an actual measurement, when continuous X-rays are applied to the X-ray detector with no object present and thereafter the application is stopped;
• an analyzing step of analyzing the step response of the acquired actual measurement into an impulse response, representing the calculation of the step response through the convolution integration of the analyzed impulse response, and calculating a plurality of time constants and their component ratios asymptotically and recursively that make the error between the actual measurement and the calculation lower than a set value;
• a storing step of storing the calculated time constants and component ratios;
• a correcting step of removing an afterglow component of the stored projection data from the projection data to produce corrected projection data during radiography of the object;
• a reconstructing step of reconstructing an image using the produced corrected projection data;
• and
• a displaying step of displaying the reconstructed image.

A program for correcting afterglow of an X-ray CT apparatus having an X-ray source for applying X-rays to an object and an X-ray detector arranged to face the X-ray source for determining the amount of transmitted X-rays of the object as projection data, comprising:

• a basic-data acquisition step of acquiring response data of the projection data as basic data with no object present in advance;
• an analyzing step of analyzing an afterglow component of the acquired basic data into a plurality of time constants and their component ratios by using a genetic algorithm;
• a storing step of storing the analyzed time constants and component ratios;
• a correcting step of extracting an afterglow component of the projection data on the basis of the stored time constants and component ratios during radiography of the object and removing the extracted afterglow component of the projection data from the projection data to produce corrected projection data;
• a reconstructing step of reconstructing an image using the produced corrected projection data;
• and
• a displaying step of displaying the reconstructed image.