MATCHED QUADRATURE COILS FOR MRI WITH MINIMIZED INTERCOIL COUPLING

First and second co-located axially and circumferentially extending RF coils (10) are displaced spatially with respect to one another by 90 degrees so as to produce a pair of RF signals from the enclosed generally cylindrical volume which are in phase quadrature. Each of the coils includes four spaced-apart and generally parallel leg sections (L, to L4; L'1 to L'4). The same coils (10) or one of them may also be utilized for transmitting NMR RF signals into the same volume. The coils have a common open-end through which objects to be imaged may be inserted and a common "closed" end for convenient location of RF coupling and feeding structures. Each of the coils (10) has an RF feedline structure (14, 16) which extends across a diameter of common closed end and the two feedline structures are disposed substantially perpendicular with respect to one another so as to minimize cross coupling. The feedlines are also spatially configured to faciliate mounting of associated tuning (Cp, Cf) and coupling (C1, C2, Ca, Cb) capacitors. A fixed coupling "paddle" provides cancellation coupling between the coils and a movably mounted coupling paddle is arranged to provide variable amounts of cancellation coupling between the orthogonal feedline structures. The phase guadrature RF signals emanating from the pair of coils are preferably amplified before being combined in a 90° RF hybrid circuit.