title: Modified birdcage coils for targeted imaging.
abstract: The design of a radiofrequency coil of U-shaped geometry, specifically intended to image individual knuckle joints of the hand, has been investigated. The coil geometry is that of a "split and opened" birdcage coil. The optimum leg positions for such a U-shaped coil have been theoretically predicted using a novel technique that considers both the signal-to-noise ratio and the homogeneity of the field-of-view. Two particular coils of this type have been constructed, each optimum for a different size of image space and assuming a different source of image noise (sample-dominated or coil-dominated). The experimentally determined radiofrequency fields produced by the coils correspond well to theory. Either coil can be used to obtain good-quality, high-resolution (130 microns x 130 microns in-plane) images in vivo of the first, second, or fifth metacarpophalangeal joints of the hand, sites of particular interest in the study of arthritis.
authors.affiliation: Department of Physics, University of Exeter, UK.
authors.forename: J
authors.initials: J
authors.lastname: Gasson
authors.forename: I R
authors.initials: IR
authors.lastname: Summers
authors.forename: M E
authors.initials: ME
authors.lastname: Fry
authors.forename: W
authors.initials: W
authors.lastname: Vennart
mesh_terms: D001168:Arthritis / Q000175:diagnosis*; D004867:Equipment Design; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000295:instrumentation* / Q000379:methods; D008662:Metacarpophalangeal Joint / Q000033:anatomy & histology*