A system comprising a plurality of electrodes adapted to measure bio impedance measurements using electrical currents passing in a target thorax area of a target therebetween during a learning phase, at least one radiofrequency (RF) sensor adapted to measure RF interaction measurements of RF radiation interacting with the target thorax area during the learning phase, and at least one processor adapted to: calculate calibration function according to the bio impedance measurements and the RF interaction measurements, and determine a target thorax area value by adjusting subsequent bio impedance measurements using subsequent electrical currents passing in the target thorax area during an operational learning phase using the calibration function.
