Effects of RF amplifier distortion on selective excitation and their correction by prewarping.
In a magnetic resonance imaging system, an RF power amplifier is employed to boost an RF pulse to sufficient strength to excite the nuclear spins in a subject. The nonideal behavior of this amplifier distorts a selective-excitation pulse, and this distortion in turn degrades the slice profile. We have found two types of nonideal behavior particularly troublesome: nonlinearity and incidental phase modulation. One of their effects is the introduction of an unwanted "skirt" in the out-of-slice region of a slice profile. We present an effective method of correction in which a selective-excitation pulse is prewarped to compensate for the distortion.
Chan
F
F
Magnetic Resonance Systems Research Laboratory, Stanford University, California 94305.
Pauly
J
J
Macovski
A
A
D000465:Algorithms; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D011846:Radio Waves; D012815:Signal Processing, Computer-Assisted