耳鳴之多通道腦電位分析及記錄系統之開發

Abstract

耳鳴常出現在較高的年齡層，在一般大眾中有高達10%的比例罹患耳鳴，並且有向上攀升的趨勢。在臨床診斷上，由於對耳鳴的機轉並不清楚且缺乏一套客觀的診斷方式，醫師在診斷上是有困難的。為了能夠瞭解耳鳴在大腦活動上的表現，並且用以作為客觀的診斷方式，我們藉由多通道的腦波記錄來研究耳鳴患者在事件相關電位（Event-Related Potentials）上的表現，並且與正常人的表現做比較。本研究蒐集了16個耳鳴患者及14個正常人的事件相關電位，且全部的受測者都不具有明顯的聽力損失。所使用的刺激事件分別為0.5、1、2以及4 kHz 的聲音，每種頻率中又包含五種不同聲音強度的刺激，包括50、56、62、68以及 74 dB SBL。在資料分析方面，以事件相關電位成份分析法(ERP components analysis)分析，使用N100與P200成份之間的振幅差以及N100的延遲時間計算出每一種刺激頻率下的強度相依關係（intensity dependence），並且在耳鳴與正常人的實驗群組中互相比較。除了事件相關電位成份分析法，本研究也使用等電位拓樸圖（isoelectric topography）與電流源密度拓樸圖（current source density topography）的分析法，分別可以提供電偶極（dipoles）與神經反應中心的資訊。目前的分析結果顯示耳鳴患者與正常人在事件相關電位中的N100與P200之振幅差以及N100的延遲時間上並無明顯差異（t-test，p > 0.05）。初步比較等電位拓撲圖與電流源密度拓撲圖，同樣得到在耳鳴患者與正常人沒有顯著差異的結果。 大多數的多通道腦波記錄系統都相當昂貴，由於目前多通道系統大都是將單一通道的電路複製做成多組，因此系統的體積、耗電量（power consumption）及成本都會隨著通道數目的增加而大幅提高。為了克服此問題，本論文的另一部分是開發以分時多工架構實現多通道記錄功能的方法。利用此方法，只需使用單一放大電路與濾波電路就能夠處理多通道的輸入訊號而達到多通道記錄的功能。在放大級與濾波級的多工架構設計與考量上都會加以討論。在分時多工架構下所造成的現象為濾波器的截止頻率會下降以及增益衰減。造成這些現象背後的原因都會詳加解釋並且對這些現象以數學式子描述。利用三種不同型態的濾波器來瞭解在分時多工架構下濾波器的響應，包括一階低通、一階高通、二階低通濾波器，並與前面的推論作比較與驗證。此外也推導出這種架構的濾波器轉換函數，並且建立一套完整的設計準則。

Tinnitus is prevalent among 10% of the general population and tends to increase in frequency among older ages. It has been difficult for the physicians to make a clinical evaluation of this annoying symptom since there lacks an objective approach to the diagnosis. To investigate the brain processes underlying tinnitus as well as to evaluate the symptoms objectively, multi-channel EEG recording is applied to investigate the appearance of ERPs (Event-Related Potentials) in tinnitus patients. ERPs were recorded from sixteen tinnitus patients and fifteen normal controls. All subjects have no significant hearing loss. A tone burst of 0.5, 1, 2, and 4 kHz are used as auditory stimuli. The stimuli of each frequency are presented at five different intensities: 50, 56, 62, 68, and 74 dB SBL. The intensity dependences of the N100/P200 amplitude and N100 latency are calculated for each frequency in each group. Aside from the component analysis, the isoelectric topography and current source density topography are developed to observe dipoles and active origins’ distribution of cortical activity respectively. The results show no significant differences in N100/P200 amplitude and N100 latency between the tinnitus and normal groups (two-tailed Student’s t-test, p > 0.05). There is also, no gross difference of isoelectric topography and current density topography between the two groups. Most multi-channel recording systems are very expensive. They are usually constructed by duplicating single-channel hardware into multiple copies. Their size, power consumption, and cost increase rapidly as the number of channels multiply. To resolve this problem, the other part of this thesis is dedicated to developing a time-division-multiplexing (TDM) system for multi-channel recording. By utilizing the TDM method, multiple input signals can be conditioned by using a single amplifier and filter stage. The design considerations of the multiplexing amplifier and filter stages are discussed herein. The phenomena in the filter caused by the TDM architecture are the drop of cutoff frequency and the attenuation of gain. The underlying mechanism of the phenomena is depicted and modeled with mathematics, whereby the responses of several types TDM filter were evaluated for understanding the behavior, including first-order low-pass, first-order high-pass, and second-order low-pass filters. The transfer function of such TDM-type filters are derived and verified, in addition to their design rule.