A rectifier circuit includes a first MOS transistor, a first capacitor configured to connect between a gate and a source of the first MOS transistor, and a switching circuit configured to supply a bias voltage to the first capacitor in response to a control signal. The readout circuitry is formed on andor over the first substrate and the electrical junction region is formed in the first substrate and electrically connected to the readout circuitry. The larger radius of curvature portion of the optical element is brought into contact with the liquid encapsulant. The blood vessel is then cross-sectioned and used to identify its tissue type and to create a corresponding image. The septum embedded indicia is viewable visually and also by x-ray or computer tomography imaging. According to the invention, a sensor temperature is directly or indirectly determined by the sensor unit, and is compared to an exhaust temperature that is determined by a further sensor unit andor to model variables andor to defined threshold values, whereby a dismounting andor an inappropriate mounting of the sensor unit is indicated.