Automatic tuning and matching of a small multifrequency saddle coil at 4.7 T

A new circuit design for automatically tuning and matching a saddle coil for small animal imaging is presented. This design allows working at 1 H, 19 F, and 3 He resonance frequencies in a 4.7 T spectrometer. It is based on a balanced circuit with commercial variable capacity diodes controlled by a computer using digital potentiometers. The change between two different frequencies can be accurately performed in a few seconds. System Q is compared, between 140–210 MHz, to the same coil tuned and matched with high Q variable capacitors. Differences lower than 5% were found with a loaded coil. The proposed design has initially been evaluated in 19 F and 1 H NMR images acquired with a five‐tube phantom. An application is also shown for the acquisition of 3 He, 19 F, and 1 H lung images in a control rat. Magn Reson Med 51:869–873, 2004. © 2004 Wiley‐Liss, Inc.