Automatic Tuning and Matching of a Small Multifrequency Saddle Coil at 4.7 T

Abstract

A new circuit design for automatically tuning and matching a saddle coil for small animal imaging is presented. This design allows working at 1H, 19F, and 3He 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 19F and 1H NMR images acquired with a five-tube phantom. An application is also shown for the acquisition of 3He, 19F, and 1H lung images in a control rat. © 2004 Wiley-Liss, Inc.