Parameter estimation method and X-ray CT system
An X-ray CT device and a computing unit to use a projection-based method for image reconstruction are included. The computing unit sets a coordinate space having coordinate axes of the thicknesses of base materials and likelihood the thicknesses, and then based on X-ray attenuation responses, executes: a first search to search in a direction perpendicular to a ridge direction of likelihood contours for a first estimated thickness having the highest likelihood, starting with an estimated thickness input value set in the coordinate space; a second search to search for a second estimated thickness having the highest likelihood, starting with a shifted starting point at a position shifted from the estimated thickness input value; and a third search to search on a line connecting the first estimated thickness with the second estimated thickness for the highest likelihood estimator having the highest likelihood, to obtain an estimated thickness output value.
1. A parameter estimation method for an X-ray CT (Computer Tomography) system, the method comprising:
providing the X-ray CT system comprising an X-ray CT device with an x-ray tube and an x-ray detector and a computing unit with an input unit, a processor and a trans receiver;
irradiating an imaged subject using X-rays generated by the X-ray tube;
measuring X-rays attenuated by the imaged subject with the X-ray detector;
receiving the data from the X-ray detector;
applying a projection-based method to X-ray attenuation responses from the received data by using the computing unit, wherein the X-ray attenuation responses having X-ray energy distribution for an N, where N≥2, number of first parameters;
reconstructing an image with the computing unit by using estimated values on given values in the X-ray attenuation responses for an M, M≤N, number of second parameters, parameters, the second parameters being based materials;
setting a coordinate space to have coordinate axes that represent the M number of second parameters and a likelihood of the M number of second parameters;
executing a first step of setting a predetermined starting point in the coordinate space based on the X-ray attenuation responses, and doing a first search to search in a predetermined direction in the coordinate space from the predetermined starting point for a first value to have a highest likelihood;
executing a second step of doing a second search to search for a second value to have the highest likelihood, under the condition that at least one of a starting point and a direction for the second search is different from that for the first search; and
executing a third step of doing a third search to search on a line connecting the first value with the second value for a highest likelihood estimator to have the highest likelihood, and setting the highest likelihood estimator as an estimated value by the M number of second parameters,
wherein an angle formed by a ridge line with respect to one of the coordinate axes in a distribution of the likelihood with respect to one of the coordinate axes of the M number of second parameters in the coordinate space is input through an input unit, and
wherein the first and second searches in the first and second steps are executed in a direction perpendicular to the ridge line.
2. The parameter estimation method as claimed in claim 1 , wherein
the predetermined starting point for the second search is set to a location away from the starting point for the first search by a predetermined distance in a direction parallel to the ridge line.
3. An X-ray CT (Computer Tomography) system comprising:
an X-ray CT device comprising an x-ray tube and an x-ray detector, the X-ray tube irradiates X-rays and the X-rays irradiated by the X-ray tube and attenuated by an imaged subject are measured by the X-ray detector;
a computing unit comprising a processor, an input unit, and a transceiver coupled to the processor, the transceiver configured to receive data from the X-ray detector which includes X-ray attenuation responses through the imaged subject, having X-ray energy distribution for an N, where N≥2, number of first parameters, for obtaining an N number of projection data,
wherein the computing unit is configured to:
apply a projection-based method to the projection data, to reconstruct an image using estimated values on given values in the X-ray attenuation responses for an M, where M≤N, number of second parameters,
set a coordinate space to have coordinate axes that represent the M number of second parameters and a likelihood of the M number of second parameters,
and execute:
a first step of setting a predetermined starting point in the coordinate space based on the X-ray attenuation responses, and doing a first search to search in a predetermined direction in the coordinate space from the predetermined starting point for a first value to have a highest likelihood;
a second step of doing a second search to search for a second value to have the highest likelihood, under the condition that at least one of a starting point and a direction for the second search is different from that for the first search; and
a third step of doing a third search to search on a line connecting the first value with the second value for a highest likelihood estimator to have the highest likelihood, and setting the highest likelihood estimator as an estimated value by the M number of second parameters,
wherein an angle formed by a ridge line with respect to one of the coordinate axes in a distribution of the likelihood with respect to one of the coordinate axes of the M number of second parameters in the coordinate space is inputted through the input unit, and
wherein the first and second searches in the first and second steps are executed in a direction perpendicular to the ridge line.
4. The X-ray CT system as claimed in claim 3 , wherein
the predetermined starting point for the second search is set to a location away from the starting point for the first search by a predetermined distance in a direction parallel to the ridge line.