An apparatus (130) and a method for adjusting, in perfusion imaging system, a periodic contrast agent injection rate signal (IS) for an injector (135) as function of an image sampling rate determined by the rotational speed of an X-ray source (107)-detector (109) assembly of an X-ray imager (100). Frequency, periodicity and pulse width of the contrast agent injection rate signal (IS) is adjusted to mitigate temporal signal aliasing in a sample of a time attenuation contrast (TAC) signal.
