MRI ACOUSTIC NOISE - SOUND PRESSURE AND FREQUENCY-ANALYSIS

The large gradient coils used in MRI generate, simultaneously with the pulsed radiofrequency (RF) wave, acoustic noise of high intensity tha t has raised concern regarding hearing safety. The sound pressure leve ls (SPLs) and power spectra of MRI acoustic noise were measured at the position of the human head in the isocenter of five MRI systems and w ith 10 different pulse sequences used in clinical MR scanning. Each pr otocol, including magnetization-prepared rapid gradient echo (MP-RAGE; 113 dB SPL linear), fast gradient echo turbo (114 dB SPL linear), and spin echo T1/2 mm (117 dB SPL linear), was found to have the high SPL s, rapid pulse rates, amplitude-modulated pulse envelopes, and multipe aked spectra, Slice thickness and SPL were inversely related, and T1-w eighted images generated more intense acoustic noise than the proton-d ense T2-weighted measures, The unfiltered linear peak values provided more accurate measurements of the SPL and spectral content of the MRI acoustic noise than the commonly used dB A-weighted scale, which filte rs out the predominant low frequency components, Fourier analysis reve aled predominantly low frequency energy peaks ranging from .05 to appr oximately 1 kHz, with a steep high frequency cutoff for each pulse seq uence, Ear protectors of known attenuation ratings are recommended for all patients during MRI testing.