Depth pulse sequences for surface coils: spatial localization and T 1 measurements

The depth pulse sequences θ;[2θ(± x ,± y )] 2 and 2θ;θ(± x );[2θ(± x ,± y )] 2 have been implemented with a 20 mm diameter two‐turn surface coil operating at 31 P resonance (89.96 MHz). In these sequences θ refers to the π/2 rf pulse at the center of the sensitive region of the coil, ± x and ± y denote the four orthogonal phases of the rf pulses, and “;” represents an optional brief delay (e.g., 4 m̈sec) between pulses to facilitate switching between different phases. Localization of the sensitive region was demonstrated with phantom samples by in vivo monitoring of rat livers and detection of necrotic regions of subcutaneously implanted tumors. The inversion‐recovery pulse sequence, 2θ−τ−θ(± x );[2θ(± x ,± y )] 2 , where τ is a variable delay, was employed to measure the spin‐lattice relaxation time of a selected region. which could be varied by changing the pulse width and the size of the surface coil.