Noise Reduction and Audio Output System for fMRI

描述（由申请人提供）：我们建议开发一种先进的降噪和音频刺激呈现系统，用于采用功能性磁共振成像（fMRI）进行听力研究。功能磁共振成像被广泛用于在受试者主动执行任务或接受感官刺激时产生大脑活动的图像。获取响应于听觉刺激的fMRI脑图像的过程特别困难，因为fMRI设备产生的噪声非常强烈，具有高达130 dB SPL的水平，并且因此显著地干扰预期的声学刺激。此外，FMRI装置采用强磁场，其排除了音频设备中常用的许多材料的使用，使得不可能使用传统的耳机来进行声音呈现。此外，商业上可获得的系统虽然被设计为充分地呈现声学刺激，但仅提供环境噪声的适度衰减。 所提出的系统的目标是在提供研究质量的音频信号的同时提供环境声音的最大可能衰减。用于实现这些目标的方法包括三种衰减技术的组合：（1）耳罩，（2）插入耳塞，以及（3）耳罩内的主动降噪（ANR）。ANR是耳塞和耳罩的有效补充，因为它在低频时提供最高的衰减，而耳塞和耳罩在高频时衰减得更好。一个小的静电传感器耦合到耳塞中的声音通道将提供刺激。另一个更大的静电传感器将与一个小麦克风和电路一起使用，形成一个ANR系统。在第一阶段，将构建一个完整的原型系统，用于评估可行性，衰减，音频质量和与fMRI磁场的兼容性。将使用受试者阈值偏移测量器械衰减。该系统将在第二阶段进行改进和进一步发展成为可制造的原型。

DESCRIPTION (provided by applicant): We propose to develop an advanced noise reduction and audio stimulus presentation system for use during studies of hearing employing functional Magnetic Resonance Imaging (fMRI). fMRI is being used extensively to produce images of brain activity while a subject actively performs a task or receives sensory stimulation. The process of acquiring fMRI brain images in response to auditory stimulation is especially difficult because the noise generated by fMRI equipment is extremely intense, with levels up to 130 dB SPL, and so interferes significantly with the intended acoustic stimuli. In addition, FMRI apparatus employs an intense magnetic field that excludes the use of many materials commonly used in audio devices so that it is impossible to use conventional earphones for sound presentation. In addition, commercially available systems, while designed to present acoustic stimuli adequately, provide only modest attenuation of ambient noise. The goal of the proposed system is to provide maximum possible attenuation of ambient sound while providing audio signals of research quality. The methods to be used to achieve these goals include the combination of three attenuation techniques: (1) a circumaural muff, (2) insert earplugs, and (3) active noise reduction (ANR) within the muff. ANR is an effective complement to an earplug and a muff because it provides highest attenuation at low frequencies, while plugs and muffs attenuate better at higher frequencies. A small electrostatic transducer coupled to a sound channel in the earplug will deliver stimuli. Another, larger electrostatic transducer in the muff will be used in conjunction with a small microphone and circuitry to form an ANR system. In Phase I a complete prototype system will be constructed for assessment of feasibility, attenuation, audio quality, and compatibility with the fMRI magnetic field. Device attenuation will be measured using subject threshold shifts. The system will be refined and further developed into a manufacturable prototype in Phase II.