Rotating frame zeugmatography.

The proton sensitivity obtainable at 5 MHz from a baby is sufficiently large to suggest the possibility of obtaining images with millimetre solution in seconds. Such goals present difficulties; for example, the high quality factor of the receiving coil necessary for good sensitivity limits the receiver bandwidth and leads to long pulse recovery times, and large, rapidly switched field gradients require power engineering. Solutions to these problems are being pursued at the National Institutes of Health (N.I.H.), where a high speed imaging system is under construction. For example, bandwidth and recovery time problems may be resolved with the aid of a low noise preamplifier with imaginary gain and Miller feedback, large gradients may be generated with a magnet comprising two rotatable hemispherical windings and switching of gradients may be eliminated by performing zeugmatography in the rotating frame. It is upon this latter aspect of the design that the present article concentrates.