There is provided an apparatus comprising processing circuitry configured to: receive first medical image data obtained using a first type of imaging procedure, wherein the first medical image data is representative of an anatomical region of a subject; and apply a simulator to perform a simulation process on the first medical image data to obtain simulated second medical image data, the simulated second medical image data having properties so as to simulate image data that is obtained using a second type of imaging procedure. The simulator comprises an image synthesizer that is trained in combination with a discriminator in an adversarial fashion by repeatedly alternating an image synthesizer training process in which the image synthesizer is trained to produce simulated medical image data, and a discriminator training process in which the discriminator is trained to distinguish between real medical image data and simulated medical image data.