th  - 1987 - 51st ENC Conference

MF67
MAGNETIC RESONANCE IMAGING WITH PHASE-MODULATED STORED WAVEFORMS
Petra Schmalbrock, *,a Annjia T. Hsu, b
William W. Hunter, Jr. a and Alan G. Marshall, b,c
Dept. of Radiology, a (Dept. of Chemistry, b Dept. of BiochemistryC),
The Ohio State University, Magnetic Resonance Imaging Facility,
1630 Upham Drive, Columbus, OH 43210
Slice location in magnetic resonance imaging is typically achieved
by irradiation with narrow-bandwidth rf pulses in combination with
magnetic field gradients. However, theoretically optimal waveforms
require a large time-domain dynamic range and can perform poorly
experimentally--e.g., impreci se slice definition and T 2 errors in
spin-echo imaging experiments.
Our recently demonstrated Stored W_aveform Inverse F_ourier T_ransform
(SWIFT) technique I can generate any desired spectral profile while
minimizing the dynamic range of its time-domain representation. In this
poster, we report images in which slice selection was achieved with
SWIFT-generated waveforms on a GE 1.5 Tesla Signa ® whole-body imaging
system. Time-domain waveforms were generated by quadratic phase
modulation of a specified discrete excitation magnitude spectrum.
followed by inverse discrete Fourier transformation and apodization to
give a stored time-domain waveform that could then be clocked out via
real-time digital-to-analog conversion to the rf transmitter. SWIFT
waveforms for slice selection will be compared to the usual sin(x)/x
slice-selective pulse and to recent computer simulations by Kunz. 2
[This work was supported by N.S.F. CHE-8218998, General Electric
Company, and The Ohio State University.]
1. Hsu, A. T.; Hunter, W. W.. Jr.; Marshall, A. G.; Schmalbrock, P.; J.
Magn. Reson. (1987), in press.
2. Kunz, D.; Magn. Reson. Med._3, 377 (1986).