Active acoustic noise cancellation for MRI

描述（由申请人提供）：这项工作的长期目标是开发一种可行的声学噪声控制（ANC）系统，专门为MRI环境量身定制。本提案的具体目标是设计、构建和实现一个有效的主动降噪原型，该原型可以大幅降低MRI孔内的声压级。这需要深入了解MRI声场的真实特征。本研究的中心假设是MRI操作产生的强声能与梯度脉冲强相关；因此，它可以由一个主动的ANC系统来控制，而不会妨碍初级成像操作。我们相信，从我们的初步研究中揭示的MRI声谱的音调行为非常适合于主动噪声消除技术，这种技术通常对可预测的谐波信号工作得很好。其基本原理是，在MRI中抑制噪声的能力有望产生新的控制算法，可以用于原型评估。主动噪声控制在概念上很有吸引力，因为它避免了核心MRI系统的重大重建。此外，该控制系统的成功实施将消除，或至少减少，噪声作为非常高场强应用（bbb70特斯拉）的障碍之一，因此允许在未来更高的场用于医学成像和研究。本研究的具体目标是：1)识别和表征可控MRI噪声的性质——研究辐射声压特性，明确其与各种成像序列梯度脉冲的函数关系，识别可控制的显著特征。2)确定可行的传感和驱动概念——开发可行的传感和驱动方法，有效地抑制MRI扫描仪内的主要噪声特征。3)开发ANC系统-设计并实现患者耳口附近的主动ANC原型。

DESCRIPTION (provided by applicant): The long-term goal of this work is to develop a feasible acoustic noise control (ANC) system specifically tailored for MRI environment. The specific objective of this proposal is to design, construct and implement a working active noise reduction prototype that can substantially reduce the sound pressure levels inside the MRI bore. This requires an in-depth understanding of the true characteristics of MRI sound fields. The central hypothesis of this study is that the intense sound energy produced by the operation of MRI is strongly correlated with gradient pulses; and thus it can be controlled by an active ANC system that does not impede the primary imaging operation. It is our belief that the tonal behavior of the MRI sound spectrum revealed from our preliminary studies is well suitable for active noise cancellation techniques that normally work well for predictable harmonic signals. The rationale is that the ability of suppression acoustical noise in MRI is expected to seed new control algorithms that can be evaluated for prototyping. Active noise control is conceptually appealing because it avoids major reconstruction of the core MRI system. Furthermore, the successful implementation of this control system will remove, or at least diminish, acoustic noise as one of the barriers at very high field strength applications (> 7 Tesla), and hence allow for even higher fields to be employed for medical imaging and research in the future. In this proposed studies, the following specific aims will be pursued: 1) Identify and characterize the nature of controllable MRI noise - to investigate the radiated sound pressure characteristics, clarify their functional relationships with the gradient pulses of various imaging sequences, and identify significant features that can be controlled. 2) Determine feasible sensing and actuation concepts - to develop feasible sensing and actuation approaches that will be effective in suppressing the dominant acoustic noise signatures inside the MRI scanner bore. 3) Develop an ANC system - to design and implement a prototype for active ANC in the vicinity of the patient's ear and mouth.