Acoustic noise‐optimized verse pulses

Variable‐rate selective excitation RF pulses modulate the slice selection gradients during RF transmission, especially to reduce the total RF power. Amplitude‐modulated slice selection gradients can lead to increased gradient noise, in particular in high‐field MRI where variable‐rate selective excitation techniques are often used. In this work, an algorithm is presented that calculates a variable‐rate selective excitation pulse modulation from given RF pulses with constant slice selection gradient. The algorithm avoids the known acoustic resonance frequencies of the gradient system to minimize sound pressure levels. It was tested with four different slice‐selective RF pulse shapes (Sinc, Gaussian, and two Shinnar‐LeRoux). Sound measurements revealed a reduction of the mean sound pressure level by up to 13dB, and simultaneously, the specific absorption rate was reduced by 55%. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.