Process for the synthesis of compounds of formula :wherein R1 and R2, which may be the same or different, each represent a linear or branched alkoxy group or form, together with the carbon atom carrying them, a 1,3-dioxane, 1,3-dioxolane or 1,3-dioxepane ring. Venting is performed by boring a control port, separate from the output port, into the driver. Subsequently, in a second time segment the x-ray beam is limited to a partial beam that irradiates only a sub-area of the reception area containing the breast, or a part of the breast, and the irradiation is continued only with this partial beam. The system also includes a calibration control unit configured to provide a digital calibration control signal to the RF receiver based on the phase difference as provided by the phase detector.