A medical CT imaging system, the imaging system comprising: - a radiation source for emitting photons, and - a detection device for detecting photons emitted by the radiation source, the detection device comprising: - a signal generation unit for generating a detection signal indicative of the energy of a detected photon while photons strike the detection device, wherein the signal generation unit is adapted to generate a baseline signal while photons are prevented from striking the detection device, the baseline signal being affected by photons that previously struck the detection device, - a baseline shift determination unit for determining a baseline shift of the detection signal, wherein the baseline shift determination unit is adapted to determine the baseline shift depending on the baseline signal, - an energy determination unit for determining the energy of a detected photon depending on the detection signal and the determined baseline shift, characterized in that the imaging system further comprises: - a sychronization unit for synchronizing the detection device with the irradiation by the radiation source such that the baseline shift determination unit determines the baseline shift during a baseline shift determination time interval during which the radiation source is prevented from irradiating the detection device, wherein the radiation source comprises a switching device for switching the emission of photons on and off, wherein the synchronization unit is adapted to provide a synchronization signal (SYNC) to the switching device such that during the baseline shift determination time interval the switching device is signaled to switch the emission of photons off. - a radiation source for emitting photons, and - a detection device for detecting photons emitted by the radiation source, the detection device comprising: - a signal generation unit for generating a detection signal indicative of the energy of a detected photon while photons strike the detection device, wherein the signal generation unit is adapted to generate a baseline signal while photons are prevented from striking the detection device, the baseline signal being affected by photons that previously struck the detection device, - a baseline shift determination unit for determining a baseline shift of the detection signal, wherein the baseline shift determination unit is adapted to determine the baseline shift depending on the baseline signal, - an energy determination unit for determining the energy of a detected photon depending on the detection signal and the determined baseline shift, characterized in that the imaging system further comprises: - a sychronization unit for synchronizing the detection device with the irradiation by the radiation source such that the baseline shift determination unit determines the baseline shift during a baseline shift determination time interval during which the radiation source is prevented from irradiating the detection device, - a signal generation unit for generating a detection signal indicative of the energy of a detected photon while photons strike the detection device, wherein the signal generation unit is adapted to generate a baseline signal while photons are prevented from striking the detection device, the baseline signal being affected by photons that previously struck the detection device, - a baseline shift determination unit for determining a baseline shift of the detection signal, wherein the baseline shift determination unit is adapted to determine the baseline shift depending on the baseline signal, - an energy determination unit for determining the energy of a detected photon depending on the detection signal and the determined baseline shift, - a sychronization unit for synchronizing the detection device with the irradiation by the radiation source such that the baseline shift determination unit determines the baseline shift during a baseline shift determination time interval during which the radiation source is prevented from irradiating the detection device,