title: Single point measurements of magnetic field gradient waveform.
abstract: Pulsed magnetic field gradients are fundamental to spatial encoding and diffusion weighting in magnetic resonance. The ideal pulsed magnetic field gradient should have negligible rise and fall times, however, there are physical limits to how fast the magnetic field gradient may change with time. Finite gradient switching times, and transient, secondary, induced magnetic field gradients (eddy currents) alter the ideal gradient waveform and may introduce a variety of undesirable image artifacts. We have developed a new method to measure the complete magnetic field gradient waveform. The measurement employs a heavily doped test sample with short MR relaxation times (T(1), T(2), and T(2)(*)<100 micros) and a series of closely spaced broadband radiofrequency excitations, combined with single point data acquisition. This technique, a measure of evolving signal phase, directly determines the magnetic field gradient waveform experienced by the test sample. The measurement is sensitive to low level transient magnetic fields produced by eddy currents and other short and long time constant non-ideal gradient waveform behaviors. Data analysis is particularly facile permitting a very ready experimental check of gradient performance.
authors.affiliation: MRI Centre, Department of Physics, P.O. Box 4400, University of New Brunswick, Fredericton, E3B 5A3 New Brunswick, Canada.
authors.forename: David J
authors.initials: DJ
authors.lastname: Goodyear
authors.forename: Maurice
authors.initials: M
authors.lastname: Shea
authors.forename: Steven D
authors.initials: SD
authors.lastname: Beyea
authors.forename: Nadim J
authors.initials: NJ
authors.lastname: Shah
authors.forename: Bruce J
authors.initials: BJ
authors.lastname: Balcom
mesh_terms: D000362:Agar / Q000737:chemistry*; D016477:Artifacts; D004574:Electromagnetic Fields; D007089:Image Enhancement / Q000295:instrumentation* / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000295:instrumentation* / Q000379:methods* / Q000592:standards; D008280:Magnetics / Q000295:instrumentation*; D011786:Quality Control; D011874:Radiometry / Q000379:methods* / Q000592:standards
chemical_list: D000362:Agar