X-ray CT device and processing device
This X-ray CT device uses iterative reconstruction to obtain a CT image with the desired noise reduction or X-ray reduction ratio. An iterative approximation reconstruction unit ( 136 ) is provided which, from measured projection data obtained by an X-ray detection unit of the X-ray CT device, iteratively reconstructs a CT image in a reconstruction range of a subject, and iteratively corrects the CT image such that calculated projection data, calculated through forward projection of a CT image, is the same as the difference between measured projection data detected by the X-raw detection unit and calculated projection data. The iterative approximation reconstruction unit is provided with a parameter determination unit ( 151 ), an iterative correction unit ( 152 ), and a table unit ( 153 ) which calculates in advance the relation between each parameter used in the iterative reconstruction, and noise reduction or X-ray reduction ratio in the CT image. The parameter determination unit ( 151 ) determines the parameters from a calculation table in the table unit ( 153 ) depending on the desired reduction ratio.
1. An X-ray CT device comprising:
an X-ray generation unit for generating X-ray;
an X-ray detection unit for detecting the X-ray after transmitting through a subject to acquire measured projection data;
an image-taking unit that includes a mechanism provided with the X-ray generation unit and the X-ray detection unit, and rotates around the subject; and
an image generation unit that includes an iterative approximation reconstruction unit for iteratively correcting a CT image generated by the image-taking unit from the measured projection data so as to substantially equalize a difference between calculated projection data acquired by a forward projection calculation from the CT image and the measured projection data, wherein
the image generation unit includes a table unit that stores a relationship between a noise or an X-ray reduction ratio of the CT image and a parameter used for iterative correction,
the iterative approximation reconstruction unit determines the parameter from the table unit in accordance with the noise or the X-ray reduction ratio of the CT image,
the iterative approximation reconstruction unit includes a weight calculation unit for calculating a weight used for iteratively correcting the CT image from the measured projection data, and determines the parameter from the table unit in accordance with the weight calculated by the weight calculation unit,
the weight calculation unit calculates a ratio between a reference weight W b as a value derived from summing the weight of at least one of a plurality of detection elements which constitute the X-ray detection unit under at least one image-taking condition, at least one reconstruction condition, and at least one reference position, and a weight W I as a value derived from summing the weight of at least one detection element under conditions other than the image-taking condition, the reconstruction condition, or at a position other than the reference position, and
the iterative approximation reconstruction unit determines the parameter under conditions other than the image-taking condition, the reconstruction condition, or at the position other than the reference position from a parameter of the reference weight W b and the calculated ratio between the weights W b and W I .
2. The X-ray CT device according to claim 1 , wherein:
the weight calculation unit calculates a weight set as a constant value for adding the same weight to output data of the plurality of detection elements; and
the iterative approximation reconstruction unit determines the parameter from the ratio between the reference weight W b calculated from the weight set as the constant value, and the weight W I as a value derived from summing weights each set as the constant value of at least one detection element under conditions other than the image-taking condition, the reconstruction condition, or at the position other than the reference position.
3. The X-ray CT device according to claim 1 , wherein:
the weight calculation unit calculates the weight set as a constant value for adding the same weight to the output data of the plurality of detection elements, and a weight of a statistic value which makes the weight added to the output data of the plurality of detection elements different in accordance with an output volume of the plurality of detection elements; and
the iterative approximation reconstruction unit determines the parameter from the ratio between the reference weight W b calculated from the weight set as the constant value and the weight W I of the statistic value.
4. The X-ray CT device according to claim 1 , wherein the weight calculation unit calculates the ratio between the weights W b and W I by using the representative weight W b with the shortest distance among the two or more reference weights for the parameter at the position other than the reference position.
5. The X-ray CT device according to claim 1 , wherein the iterative approximation reconstruction unit determines the parameter from the table unit in accordance with a value acquired from the CT image.
6. The X-ray CT device according to claim 5 , wherein the iterative approximation reconstruction unit determines the parameter in accordance with a noise value measured from the CT image so as to acquire a desired noise image from the table unit.
7. The X-ray CT device according to claim 1 , wherein the iterative approximation reconstruction unit determines the parameter from the table unit in accordance with an input image-taking condition or the reconstruction condition.
8. The X-ray CT device according to claim 1 , wherein the iterative approximation reconstruction unit determines the parameter from the table unit in accordance with subject information acquired from the CT image.
9. The X-ray CT device according to claim 8 , wherein the iterative approximation reconstruction unit determines the parameter from the table unit in accordance with weights of the two or more detection elements.
10. The X-ray CT device according to claim 9 , wherein the iterative approximation reconstruction unit subjects the weights of the two or more detection elements to fitting with an approximation function, and determines the parameter from the table unit in accordance with an acquired coefficient of the approximation function.