Short, shaped pulses in a large magnetic field gradient.
A number of materials MR developments require that measurements be made in a large magnetic field gradient, including unilateral (single-sided) magnet designs for portability and open access. In such cases, all radiofrequency (RF) pulses are slice selective. Typically, little effort is made to tailor the shape of the selected slice, because shaped RF excitations are viewed as too lengthy in duration to be useful in materials MRI, where signal lifetimes are mostly less than 1 ms. We compare measured magnetization responses to various standard shaped pulses under extreme conditions of application (approximately 30 micros duration, offset frequencies up to 0.3 MHz, and in the presence of a 13 T/m permanent magnetic field gradient). We discuss the feasibility of their implementation for materials MRI in a large gradient, including the difficulty of choosing optimized pulse area, and propose viable solutions.
Coarna
C
C
UNB MRI Centre, Department of Physics, University of New Brunswick, 8 Bailey Drive, PO Box 4400, Fredericton, NB, Canada E3B 5A3.
Newling
B
B
D003198:Computer Simulation; D004574:Electromagnetic Fields; D005583:Fourier Analysis; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008280:Magnetics; D011846:Radio Waves; D017550:Spectroscopy, Fourier Transform Infrared