A method for determining a trigger signal for an imaging device is based on receiving a film of a surface of a first body part of a patient. In an embodiment, image values in a region in the images of the film are averaged. The noise of the image values in the region is reduced by way of the averaging. The film is transformed into a temporal signal series on the basis of the averaging. The transformation takes place in such a manner that the temporal series is a measure of the timing pattern of the blood circulation in the area. Furthermore, the temporal signal series is analyzed to ascertain whether the temporal signal series satisfies a preset criterion. Finally, a trigger signal is determined for an imaging device if the temporal signal series satisfies the preset criterion.
