Rapid projection MRI of short T(2) species with multiple small angle excitations and oscillatory-rotary field gradients.
The use of images weighted by transverse relaxation time T(2) in the identification of pathology in many organ systems is reported. Recent applications by R.C. Hawkes and S. Patz (1987) of steady-state free precision (SSFP) excitation to both static readout gradient (2DFT) and cosinusoidal readout gradient techniques have investigated species with T(2) values on the order of several milliseconds. This work is extended with a one-dimensional cosinusoidal gradient to a two-dimensional projection format through a gradient that simultaneously oscillates and rotates, proposed by S.J. Norton (1987). Each position of interest is encoded (and decoded) during free decay through the unique phase modulation (demodulation) determined by the continuously time-varying gradient. Ideal reconstruction consists of long term integration of the product of the observed signal and a phase demodulation kernel. The approach for a single (or set of independent) FID(s) following a nonselective 90 degrees pulse is modified to image short as well as long T(2) species with the periodic steady state obtained by SSFP excitation.
Rand
S D
SD
Dept. of Electr. Eng., Stanford Univ., CA.
Macovski
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