IMPLEMENTATION OF A MODIFIED BIRDCAGE RESONATOR FOR F-19 H-1 MRI AT LOW FIELDS (0.14 T)/

Fluorine-19 nuclear magnetic resonance of perfluorinated blood substit ute materials provides a method for determination of oxygen tension (P O2) in vivo. Use of a double resonant F-19/H-1 radio frequency coil al lows convenient correlation between the high resolution anatomic prese ntation of proton images and the fluorine distribution. However, quant itative F-19 measurements require an RF coil with good H-1 field homog eneity over the image volume and a high quality factor (Q) to minimize errors caused by the low signal-to-noise levels available in in vivo imaging and image nonuniformities introduced by the large chemical shi ft of fluorocarbons. The birdcage coil design provides a high Q struct ure with optimum H-1 field uniformity and fill factor. However, at low resonance frequencies, the inherently low inductance of the birdcage geometry requires the use of a large number of chip capacitors giving rise to unwieldy coil fabrication and increased cost. This communicati on describes a modification to the birdcage design that reduces the ch ip capacitor requirement by at least a factor of 4 for a given dimensi on, yet retains the essential characteristics of the birdcage design. The modified structure was tuned for double resonance at 5.7/6.0 MHz f or F-19/H-1 magnetic resonance imaging at 0.14 T. For a coil with a le ngth to diameter ratio of 1.67, an H-1 uniformity of +/-2% for the F-1 9 resonance was obtained over a cylindrical region with radius approxi mately 0.6r (r = radius of coil) and length approximately 1.8r within the coil.