title: Signal-to-noise improvement in mid-field MRI surface coils: a degree in plumbing?
abstract: From a series of standard SE imaging sequences, performed on a Bruker 0.28 T imaging system, with the assistance of a healthy volunteer, the image signal-to-noise (S/N) ratio obtained from a 23-cm square surface coil has been shown to increase by up to 38% as the tube gauge is increased from 4 to 18 mm. The reason did not lie solely in the much improved Q factor of the unloaded coils. Despite a more than twofold increase in the unloaded Q factor, the loaded coil Q values only increased by 8%. It would appear, however, that the resistive, dielectric and inductive noise components are all reduced, and hence contribute to the observed improved S/N. The reduction in pure ohmic losses accounts for a quarter of the improved S/N, while the reduced inductive and dielectric losses provide the remaining three quarters. No independent quantification of the two latter noise sources was attempted, although a reduced dielectric contribution is confirmed qualitatively by a reduction in the negative frequency shift of the resonance frequency as a function of increasing coil gauge when the coil is loaded.
authors.affiliation: Laboratoire de Biophysique, Faculté de Médecine, Université de Nancy I, France.
authors.forename: P M
authors.initials: PM
authors.lastname: Walker
authors.forename: B
authors.initials: B
authors.lastname: Robin-Lherbier
authors.forename: J M
authors.initials: JM
authors.lastname: Escanyé
authors.forename: J
authors.initials: J
authors.lastname: Robert
mesh_terms: D006801:Humans; D007089:Image Enhancement / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000295:instrumentation* / Q000379:methods