Spectroscopy Imaging Systems

Varian, Inc.

Varian Associates, Inc.

Agilent Technologies, Inc.

Alan R Rath

Wai Ha Wong

Robert S Codrington

Steven A Suddarth

A switchable birdcage coil functioning as a transmitter coil and a separate RF surface coil functioning as the receiver coil are utilize in NMR and MRI apparatus. To prevent the switchable birdcage coil from absorbing energy by coupling to the receiver coil or by absorbing power from the RF field produced by the precessing nuclear spins, one or more of the reactive elements of the birdcage coil are switched from a normal reactive impedance state to a high impedance state. The high impedance state is formed by switchably combining the reactive element with a complementary reactive element thereby forming parallel resonant high impedance circuit that is tuned to resonate at the NMR frequency.

Switchable birdcage coil

A detunable coil assembly includes a main coil which resonates at a specified resonance frequency and a switchable detuning coil which, when switched on, becomes inductively coupled to the main coil and serves to detune it from its resonance frequency. The detuning coil and the main coil are electrically insulated from each other. The main coil may be of a multiply tuned kind and it may be detuned from more than one of its specified resonance frequencies at the same time by switching on the detuning coil.

Detunable coil assembly and method of detuning RF coil for MRI

A saddle coil for multiple tuned response is realized by a segmented sequence of first LC elements each tuned to exhibit a low impedance at .omega..sub.1 and a second set of LC elements, each tuned to exhibit a low impedance at .omega..sub.2, at least some of said first set of LC elements having one of said second LC elements in parallel therewith.

Multi-resonant NMR coils

A double-tuned dual port segmented coil for NMR studies of a volume distributed sample is obtained by coupling corresponding junctions of respective segments of two segmented loop portions with legs comprising L.sub.x C.sub.x L.sub.x series combination. Four segment coil portions so coupled support two isolated input ports across C.sub.x for adjacent such legs.

Double tuned NMR coils

A double-tuned circuit is realized from 1/2.lambda..sub.1 transmission lines for connecting a pair of inductors in series at a first frequency and in parallel for a second frequency where said first and second frequencies are in the ratio of a power of two.

Series/parallel double-tuned NMR coils

A multiply tuned bird cage results from the combination of low pass and high pass filter elements to yield a band reject network behaving as a low pass network at a low frequency and a high pass network at a high frequency. A band pass bird cage coil is obtained by adding a parallel LC combination to each leg of a bird cage coil to create additional poles in the impedance curve z(f).

Double tuned bird cage coil

The invention demonstrates remote tuning of an NMR probe over a length of transmission line while retaining very high efficiency relative to the equivalent locally turned coil. Fixed capacitances for partial tuning are employed at the load such that a desired range of efficiency is achievable for a selected range of capacitance values at both load and source for the intervening transmission line.

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Fremont, CA, United States of America

Alan R Rath