Patent ID: 7825661

Claim:
An apparatus for evaluating an earth formation, the apparatus comprising: a downhole assembly configured to be conveyed in a borehole; a magnet arrangement on a tool on the downhole assembly configured to generate a static magnetic field in the earth formation; at least one radio-frequency (RF) coil on the downhole assembly configured to generate an RF field in the earth formation; and a processor configured to: activate the at least one RF coil with at least one pulse sequence which substantially saturates nuclear spins in a region of the earth formation, and generates at least one signal from the region of substantial saturation of spins and generates substantially no signal from outside the region; wherein there is an axial movement of the tool between a start time of the at least one pulse sequence and an end time of the at least one pulse sequence; and wherein the processor is further configured to alter a frequency spectrum of at least one pulse in the at least one pulse sequence using a shape of the region and a static magnetic field B 0 in the region for a resonance condition.