The present invention relates generally to an apparatus and method for obtaining an azimuthally resolved nuclear magnetic resonance measurement of an earth formation traversed by a borehole. The measurement can be made while drilling or using a wireline tool. At least one gradient coil is positioned circumferentially around the tool. A magnetic field is produced by the coil in a region of the formation facing the coil. The magnetic field is substantially parallel to the static magnetic field produced by a pair of permanent magnets which form a part of the tool. The additional field causes an additional phase shift for spins located in the region so that the spins subjected to the additional field do not form a spin-echo.