Report of measurement result of sound intensity of　MRI examination room

摘要

Recently, MRI (Magnetic Resonance Imaging) examination is an important examinationrnin the medical diagnosis. MRI is a technology to image the distribution of inside of bodyrnwith the nuclear magnetic resonance phenomenon. At this time, noise is generated by usingrnthe gradient magnetic field for decision of the imaging position. The noise level is aroundrn100dB though this noise level depends on the imaging method or the resolution parameter.rnThe noise makes subjects of MRI examination revolted, and it makes the ear-protectorrnnecessary. It is important to know the noise and to measure the noise for soundproofing.rnNow, it is not clear that the driving sound propagates in MRI examination room. We reportrnthe measured result on the sound intensity vector of the driving sound around the gantry ofrnMRI equipment. The probe of the tetra type with four non-magnetic electret condenserrnmicrophones was made for this measurement. Cross-spectral method was adopted forrncalculation of the sound-intensity vector. The analyzed signal was the pulse of the autotuningrnbrought by the first stage of imaging operation. It was shown the sound intensityrnvector of each frequency 250, 500 and 1000Hz in 1/1 octave. And, it was shown the MRIrndriving sound radiated from the gantry side surface.