A system for measuring Bone Mineral Density comprising: a computational unit which includes a parametric EIT p model of a plurality of constituents of at least a portion of a subject, the model comprising at least one bone constituent; said model representing the geometry of a section of a body with a plurality of constituents which differ in conductance; a plurality of injection electrodes for injecting electric current into the portion of the subject, such that at least part of the current flows through the at least one bone constituent; a plurality of pickup electrodes for measuring a plurality of values of electric potential at a plurality of locations on a surface of the portion of the subject; wherein the computational unit is configured to: receive input of what value of the injected electric current is injected into the portion of the subject; receive input of said plurality of measured values of electric potential at said plurality of locations on the surface of the subject; use the value of the injected electric current and the measured values of the electric potential as input to the model to calculate a value of conductance of the bone constituent corresponding to the value of the injected electric current and the measured values of the electric potential; wherein, to calculate the value of the conductance of the bone constituent, the computational unit is further configured to use a LUT, the LUT relating electrical potentials to BMD values produced by a computer simulation of electric potentials applied to a 3D model of a human body. a computational unit which includes a parametric EIT p model of a plurality of constituents of at least a portion of a subject, the model comprising at least one bone constituent; said model representing the geometry of a section of a body with a plurality of constituents which differ in conductance; a plurality of injection electrodes for injecting electric current into the portion of the subject, such that at least part of the current flows through the at least one bone constituent; a plurality of pickup electrodes for measuring a plurality of values of electric potential at a plurality of locations on a surface of the portion of the subject; wherein the computational unit is configured to: receive input of what value of the injected electric current is injected into the portion of the subject; receive input of said plurality of measured values of electric potential at said plurality of locations on the surface of the subject; use the value of the injected electric current and the measured values of the electric potential as input to the model to calculate a value of conductance of the bone constituent corresponding to the value of the injected electric current and the measured values of the electric potential; receive input of what value of the injected electric current is injected into the portion of the subject; receive input of said plurality of measured values of electric potential at said plurality of locations on the surface of the subject; use the value of the injected electric current and the measured values of the electric potential as input to the model to calculate a value of conductance of the bone constituent corresponding to the value of the injected electric current and the measured values of the electric potential;