Patent ID: 7639776

Claim:
An X-ray CT apparatus comprising: an X-ray tube; an X-ray detector positioned with respect to the X-ray tube; an X-ray data acquisition device configured to acquire X-ray projection data by performing a scan including irradiating X-rays to a subject from the X-ray tube and transmitting the X-rays through the subject to the X-ray detector, the X-ray tube and the X-ray detector being rotated around the subject with respect to an axis extending along a Z-direction that is a body axis direction of the subject; an image reconstructing device configured to reconstruct the X-ray projection data acquired by the X-ray data acquisition device to obtain a tomographic image; and an imaging or scanning condition setting device configured to set a plurality of parameters as a condition for obtaining the tomographic image, the plurality of parameters including an X-ray tube current value, the imaging or scanning condition setting device comprising: a first setting device configured to: obtain a plurality of desired values of the X-ray tube current value corresponding to a plurality of X-ray irradiation positions, the plurality of desired values facilitate maintaining image noise of the tomographic image substantially constant in the Z-direction; and set the plurality of desired values of the X-ray tube current value within a predetermined range; and a second setting device configured to: set a desired value of the X-ray tube current value to be smaller than a first value of the X-ray tube current value obtained by the first setting device, the first value corresponding to an X-ray irradiation position at which the X-ray tube current value is not within the predetermined range; and set at least one parameter of the plurality of parameters to a desired value corresponding to the X-ray irradiation position at which the X-ray tube current value is not within the predetermined range to facilitate maintaining the image noise of the tomographic image substantially constant in the Z-direction, the at least one parameter different than the X-ray tube current value.