X-ray computed tomography apparatus

Abstract

An X-ray computed tomography apparatus in which detection signals based on X-rays transmitted through an object to be examined are repeatedly integrated at predetermined intervals. The integral signal is sampled a plurality of times in an initial period of the interval, and the sampled signals are averaged. The integral signal is also sampled a plurality of times in a final period of the interval, and the sampled signals are averaged. Projection data are created by subtracting the initial average value from the final average value. Circuit noise can be reduced according to the increase in number of times of sampling with a detioration in X-rays available for processing since the integration time is substantially shortened. Circuit noise becomes conspicuous when the dose of transmitted X-rays is relatively small, and becomes latent when the dose of X-rays is relatively large. The number of sampling times is controlled by oversampling on the basis of scan conditions which allow estimation of the dose of transmitted X-rays in such a manner. When the dose of transmitted X-rays is relatively small, the circuit noise reducing effect can be improved at a cost of a reduction in the amount of X-rays available for processing. When the dose of transmitted X-rays is relatively large, the amount of X-rays available for processing can be improved.