Excitation of complex profiles by CARVE sequence: Accounting for spectral dispersion and relaxation

Completely Arbitrary Regional Volume Excitation (CARVE) is a technique that enables the excitation of complex shapes in two and three dimensions. It is based on the train of interleaved short RF pulses and gradient steps. For on-resonance magnetization, the CARVE parameters (amplitudes and phases of short RF pulses, and gradient magnitudes and directions) required to flip the magnetization from its initial orientation by 90° within the selected excitation profile are easily calculated. The main advantage of CARVE relative to other techniques for spatial selective excitation is its flexible sequence design which results in compact sequences with low gradient load. The basic CARVE theory is limited to a single, on-resonance, nonrelaxing magnetization. In this paper, we provide the full theory of CARVE including the off-resonance and relaxation effects and verify it experimentally in two and three dimensions. Based on the linearity of the sequence, we propose methods to eliminate undesirable effects and tailor CARVE for any particular application.