The invention relates to a projection data acquisition apparatus (14) for acquiring projection data for being used for reconstructing a computed tomography image. In acquisition intervals projection data are acquired only at certain acquisition rotational positions of a radiation source (2) relative to an object, wherein an acquisition rotational position of a current acquisition interval divides a largest non-acquisition angular region covering rotational positions, at which projection data have not already been acquired, into two smaller non-acquisition angular regions. Because of this acquisition of the projection data, after each acquisition interval the acquisition rotational positions, at which projection data have been acquired already, are relatively homogeneously distributed. This allows for an improved image quality of a computed tomography image which is reconstructed based on the acquired projection data.