The utilization of two frequency-shifted sinc pulses for performing volume-selected in vivo NMR spectroscopy
✍ Scribed by David D. Doddrell; Graham J. Galloway; William M. Brooks; J. Mark Bulsing; James C. Field; Michael G. Irving; Hiram Baddeley
- Publisher
- John Wiley and Sons
- Year
- 1986
- Tongue
- English
- Weight
- 310 KB
- Volume
- 3
- Category
- Article
- ISSN
- 0740-3194
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✦ Synopsis
A new approach to volume-selected in vivo NMR spectroscopy uses two frequencyshifted sinc pulses, in conjunction with pulsed field gradients, to destroy the coherence of the unwanted signals. A hard u/2 pulse can then be used to read the z magnetization in the region of interest. This method is independent of T2, provides complete volume selection in a single acquisition, and can be readily implemented on most high-field commercial imaging/spectroscopy systems. o 1986 Academic press, Inc.
In a recent publication (1) we described a sine-sinc pulse, which is a pulse whose rf shape profile is given by
where CY and p are as defined in Fig. 1 and& is the maximum value of (sin r a t sin apt)/at. When combined with field gradients this pulse can be used to perform volumeselected NMR spectroscopy in a single acquisition. The action of such a { ssc} pulse is to excite regions of gradient-induced frequency space shifted to either side of the carrier frequency but not excite at the carrier frequency. The ratio of the excitation band to the central unexcited region is given by ~, B / ( c Y -p), CY > p. Although the use of the {ssc} pulse appears to be the most elegant and efficient way of performing this experiment, pulse programming of this pulse does put severe demands upon the instrument hardware and software. We note that, in principle, any suitable combination of rfpulses such as a 133i pulse train (2) and variant (3) thereof or, as we demonstrate in this paper, two frequency-shifted sinc pulses can be utilized in a similar manner. The basic idea is to use the slice-selection gradient both to select a specific spatial region and to act as a mechanism for irreversible dephasing of spins contained within the excitation band. Thus, for performing volume-selected high-resolution NMR using the procedure outlined above, the preconditioning gradient/pulse episodes must eliminate phase coherence for all spins within the homogeneous region of the static magnetic