Kim Annink

239 7.0T MRI in neonates Figure 1: Different positions of the infant model in the RF coil. On the left the adult head and torso is shown which was used as a reference. Preparation - Acoustic Noise protection In the 3.0T MRI, acoustic noise protection is guaranteed by Alpine Muffy Baby (Alpine Hearing Protection, Soesterberg, the Netherlands), Natus MiniMuffs (Natus Medical Incorporated, San Carlos, CA, USA) and a hood for acoustic noise protection (19), respectively leading to 6.4-31.6 dB, 7dB and 4-13.6dB reduction. A prototype of the hood (190cm long) for noise protection that fits in the 7.0T MR scanner was developed using a layer of 5cm foam (EASYfoam TC2, Easy Noise Control). A test setup with a dummy MR bore (old 7.0T MR bore) was made in a sound isolated booth to test the attenuation of acoustic noise with the different hoods and no hood. We conducted all sound level measurements using a Brüel & Kjær Sound Level Meter (type 2250, Brüel & Kjær, Nærum, Denmark). A microphone (Brüel & Kjær, type 4189) was placed in the isocenter of the dummy bore to record the sound volumes in dB(A). Four speakers (Yamaha MSP5A, Hamamatsu, Shizuoka, Japan) were positioned around this test setup: one on each end of the dummy bore and one on both sides (Figure 2). The speakers were separately calibrated on an acoustic noise level of 55dB(A). The acoustic noise was measured with the 3.0T hood, the 7.0T hood and without hood with the acoustic noise coming from the speakers at both ends, both sides and from all four speakers. 11