The portion of the MRI system that produces the RF current and delivers it to the transmitting coil (antenna). The RF signal produced by the transmitter is used to excite the protons in the imaging volume. Phase sensitive detectors (electronic device in which the output is dependent on the instantaneous difference in phase between two input signals) form part of the frequency synthesis pathway.

The sensitive point in an object (or a region) is the point from which information is being measured, as in sequential point imaging or in single voxel MR spectroscopy sequential point imaging used. To define a sensitive point, it must be selected in three dimensions. Different combinations of selective excitation, inversion, or saturation pulses can be used. Sometimes, combinations of two or more measurements are necessary to define the sensitive point (or volume).

See also Magnetic Resonance Spectroscopy.