Depth pulse sequences for surface coils: spatial localization and T₁ measurements

Abstract

The depth pulse sequences theta;[2 theta(+/- x, +/- y)]2 and 2 theta;theta(+/- x);[2 theta(+/- x, +/- y)]2 have been implemented with a 20 mm diameter two-turn surface coil operating at 31P resonance (89.96 MHz). In these sequences theta refers to the pi/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 microseconds) 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, 2 theta-tau-theta(+/- x);[2 theta(+/- x, +/- y)]2, where tau 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.

The slotted crossover surface coil: A detector for in vivo NMR of skin

“…However, since small pulse width values are employed, negative contributions do not appear to pose a significant problem. Should one desire to eliminate negative contributions and multiple tip angles, or to improve depth resolution, the respective use of adiabatic pulse sequences (26) and Bendall depth pulses (27,28) should be considered.…”

Magnetic resonance spectroscopy in the recognition of metabolic disease

“…In studies of muscle, localization was dependant on the coil size and position, but new localizing techniques have been developed to study deeper organs, permitted by the large whole body magnets. The different techniques have both advantages and disadvantages, but a few are promising to achieve true spatial localization (Bottomley et al, 1985b;Bogusky et al, 1986;Ng and Glickson, 1984) and quantitation (Styles et al, 1985). It is now possible to image an area defined for spectroscopy and permit anatomical localization (Bottomley et al, 1984), but the volumes studied are still large.…”

Magnets, molecules and medicine

“…Together with the B1 inhomogeneity, this phase cycling during the accumulation sequence produces self-cancellation of the N M R signals derived from certain regions within the 'field of view' of the surface coil and can be used to eliminate unwanted signals. The extent to which depth pulses improve the spatial resolution of the surface coil can be seen from the results presented in figure 18 showing the 31P spectrum obtained from rat liver (Ng et al 1984). A comparison was made between 31P signals obtained from the liver using a conventional and a depth pulse sequence.…”