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A signal‐to‐noise calibration procedure for NMR imaging systems
Author(s) -
Edelstein W. A.,
Bottomley Paul A.,
Pfeifer Leah M.
Publication year - 1984
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.595484
Subject(s) - calibration , resistor , signal (programming language) , noise (video) , imaging phantom , electromagnetic coil , nuclear magnetic resonance , signal to noise ratio (imaging) , johnson–nyquist noise , radiofrequency coil , physics , inductance , acoustics , capacitor , materials science , optics , computational physics , computer science , detector , voltage , quantum mechanics , artificial intelligence , image (mathematics) , programming language
A nuclear magnetic resonance (NMR) imaging system signal‐to‐noise calibration technique based on an NMR projection of distilled water in a cylindrical bottle is proposed. This measurement can characterize any arrangement of rf coils in any magnetic field as signal to noise per ml times root Hz. Inductive losses in a typical patient must be included in the calibration, and such losses can be simulated in a particular system by an externally attached resistor(s) appropriate to that system. Alternatively, an rf inductive damping phantom consisting of a conducting loop of wire containing an appropriate resistor is suggested that can be inserted into any NMR imaging coil to simulate subject Q damping. The same resistor can be used, independent of the details of the coil construction. Furthermore, if the loop inductance is tuned out at each frequency with a series capacitor, then the same loop resistance will serve for all frequencies as a good approximation to human subject damping. This “projection method” signal‐to‐noise ratio is related to the conventional signal‐to‐noise ratio measured from a Lorentzian‐shaped spectral line as ψ P =ψ L [2/ T 2 ] 1/2 , where ψ stands for signal‐to‐noise ratio, subscripts P and L stand, respectively, for the projection and “Lorentzian” methods, and T 2 is the transverse relaxation time of the spectral line used in the Lorentzian method.