Abstract: A simultaneous acquisition process of a transmission image and an emission image with a gamma camera equipped with a detector (3), the detector (3) being opposite the patient (5) who has received an injection of a first radioactive isotope emitting gamma-ray photons (&ggr;2) in a first energy range (P1), the process including the movement of a radioactive source (4) behind the patient (5), the source (4) consisting of a second isotope emitting gamma-ray photons (&ggr;1) in a second energy range (P2), and the production, during the detection of an impact of a gamma-ray photon on the detector (3) of the coordinates of the impact of the photon on the detector and information relevant to the energy of the photon during the impact, the process having the particularity that it differentiates between the photon impacts according to their energy levels and the position of the impact in relation to the position of the source (4).