Analysis of acoustic noise in MRI and its applications

Abstract

Magnetic Resonance Imaging has been extensively applied to many areas of the diagnostic imaging and brain unctional imaging. But, one of the important obstacle in the use of MRI techniques has been the acoustic noise generated in MRI scanners, both in patient scanning as well as in many areas of the neuroscience research such as fMRI (functional MRI). Besides physical discomfort, acoustic noise acts on some negative effects to the study of fMRI by the decrease of activation or unwanted response in auditory sensory portions of the brain. Although a number of ideas have been suggested to reduce or eliminate acoustic noise, the progresses by them have been slow due to the basic role of gradient pulsing in MRI. The gradient pulsing means the switching of the current flows through the gradient coils in the main magnetic field of MRI scanners during imaging and it causes to the heavy and fast vibrations of the gradient coil. To solve this acoustic noise problem in MRI, the systematic analyses of acoustic noise behaviors and their characteristics in several MRI systems were studied firstly. In comparison, data from both a commercial MRI scanner (GE Signa 1.5 T) as well as a research-type MRI scanner (KAIS 2.0 T) are used. By the results of the analyses of the acoustic noise pattern in MRI, the DC gradient concept was introduced to the imaging technique. Because it did not use the gradient switching, it generates no Lorentz force in all directional coils. From the application of DC gradient, new imaging pulse sequences such as Silent Spin-Echo sequence using a rotating DC gradient and Silent FM DANTE sequences, are explored. And, to show other possibility to acoustic noise reduction using the circular type z-directional gradient characteristic, the acoustic noise reduction effect in fMRI dependent on imaging views of GE EPI was studied. From the result of fMRI studies using a typical commercial whole-body MRI scanner (GE Signa 1.5T), the acoustic noise level was able...