Electricity: measuring and testing – Particle precession resonance – Spectrometer components
Patent
1993-10-21
1996-01-09
O'Shea, Sandra L.
Electricity: measuring and testing
Particle precession resonance
Spectrometer components
324322, G01R 3328
Patent
active
054831580
ABSTRACT:
An RF front end unit (32) for a magnetic resonance imaging (MRI) system (20) has transmit and receive channels to which a plurality of coils (22) can remain attached during operation (including RF coils having differing types of matching circuits), and facilitates switching between a plurality of attached coils. Methods and apparatus are additionally provided for selectively tuning differing RF coils, including both high power coils (22B, 22C) and varactor-tuned coils (22D). The tuning of a high power coil involves using a remote impedance match tuning network (RTU) (26) for a coarse tuning operation and, if necessary, a fine tuning operation. In performing the coarse tuning operation separately for In-Phase ("I") and Quadrature ("Q") channels, a tuning controller (60) determines the effective load impedance of each of the RF coil channels by quadrature demodulation of their reflected signals. The tuning controller (60) then evaluates a computerized model of the impedance match tuning network in order to determine and set coarse values for the adjustable impedances of the RTU. In tuning varactor coils, the tuning controller chooses a starting point for the varactor coil tune and then executes a two-dimensional bisection search operation to locate a candidate for the tuned point. The bisection search is followed by a starburst operation for examining the magnitude of reflected signals at points in a starburst or asterisk pattern about the candidate point.
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Arakawa Mitsuaki
Van Heteren John
Mah Raymond Y.
O'Shea Sandra L.
The Regents of the University of California
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