th  - 1987 - 51st ENC Conference

WF58
SPATIAL LOCALISATION OF ~lp ~LR SPECTROSCOPY USING PHASE
MODULATED ROTATING FRAI~E IMAGING.
Kartin J. Blackledse*, Peter Styles and Georse K. Radda
X.R.C. CLINICAL NAGNETIC RESONANCE FACILITY, JOHN RADCLIFFE HOSPITAL,
OXFORD ENGLAND U.K.
Rotating frame imaging (R.F.I.) using the B, field gradient of a
surface coil has been shown to be a viable method for localislng
phosphorus spectra in-vivo. Use of separate coils for transmitting and
receivin E signal ensures that the encoding field gradient is linear and
the shape of this field throughout the interrogated resion is flat and
planar. As normally implemented, R.F.I. is an inherently inefficient
technique; this is because the observation pulse is incremented, and
received signal is amplitude modulated with respect to incremental
pulse ansle. The magnetisatlon precesses about the x-axis of the
rotatin 5 frame_, so that of the two components (y and z), only the y
component is detected. To overcome this insensitivity, it i$ necessary
to detect the z component. This is achieved by 'flipping' the
masnetisation, immediately after the incremental pulse, into the x-y
plane usin 5 a 7/2 pulse applied alon E the y axis This signal is phase
modulated, the relative x and y component masnetisation in the rotatin$
frame varies with pulse angle. For this modulation to be useful, the
phase encoding pulse (p.e.p) is required to have a bandwidth in both
B, and Bo over which it is effective in accurately transposln8 the
phase of the mnsnetisation vector from the y-z to the x-y plane.
Usin 5 a double coil (with smaller receiver coil) we receive from the
region (.2-.8) radii of the transmitter coil away from the surface. In
this resion, the B, field strength varies from >.5 to