Passive Shield Structure to Reduce Acoustic Noise Around Magnetic Resonance Imaging Device and Prevent Deterioration of Images

A spatial arrangement of passive shield copper rings which prevents the deterioration of tomographic image was proposed to reduce acoustic noise around magnetic resonance imaging (MRI) devices. Tests for the copper rings, the conventional copper shield, and the non-shielded structures were conducted to compare the sound level in four kinds of pulse sequences and image quality in the fast spin echo (FSE) pulse sequence with a clinical 1.5 T MRI system. Numerical analyses revealed the influences of the electromagnetic force and unnecessary magnetic field caused by the eddy current. For the copper ring structures, the sound level outside the magnet decreased 5 dB(A) from that of the non-shielded structure. The percentages of image deterioration number in the FSE pulse sequence for the conventional and the copper ring structures were increased 15% and decreased 4%, respectively. Numerical results showed that the electromagnetic force of the MRI devices decreased 60% and the unnecessary magnetic field at the imaging space decreased 30%, supporting the test results. The position of the eddy current was the most important factor for each contribution. The proposed copper ring structure is able to reduce acoustic noise outside the magnet and prevent image deterioration.