本文選題：多波長穩(wěn)態(tài)漫射光檢測 + 光子計數(shù)技術(shù)��； 參考：《天津大學(xué)》2012年碩士論文

【摘要】：穩(wěn)態(tài)擴(kuò)散光學(xué)成像(Continuous Wave Diffuse Optical Imaging, CW DOI)利用近紅外光在組織體內(nèi)相對較深的穿透深度實現(xiàn)器官級的人體信息檢測,其優(yōu)點包括無創(chuàng)、無電離、時間分辨率高以及適合臨床連續(xù)監(jiān)測等。CW DOI通常需要測量組織體在不同光波長從多個源點激勵下表面其它各點的漫反射光流分布,由此帶來光源波長與源點位置編碼的問題。當(dāng)前大多數(shù)CW DOI系統(tǒng)采用時分復(fù)用光源編碼方式,該方式測量時間長難以滿足某些快速變化生理信號實時監(jiān)測的要求。為此,本文提出了光源頻分復(fù)用編碼與探測器輸出信號數(shù)字鎖相檢測解復(fù)用的實現(xiàn)方案,減少了測量時間,提高了測量結(jié)果的時間分辨率。 圍繞上述方案所搭建的穩(wěn)態(tài)雙通道漫射光檢測系統(tǒng)包括光源、波分復(fù)用器、光子計數(shù)探測器、FPGA數(shù)字鎖相檢測電路、通信與數(shù)模轉(zhuǎn)換電路以及上位機軟件部分。實驗發(fā)現(xiàn),該系統(tǒng)存在測量暗噪聲較大,測量結(jié)果信噪比不夠好,入射光強與源探距離均不變的情況下測量結(jié)果間或出現(xiàn)粗大誤差現(xiàn)象以及FPGA檢測系統(tǒng)與PC機上位機之間數(shù)據(jù)傳輸速率不滿足要求等問題。 針對以上問題,本文分別進(jìn)行了原因分析、改進(jìn)方案設(shè)計以及改進(jìn)效果的實驗驗證。針對暗噪聲高與信噪比不夠好的問題,研究了實驗條件對測量結(jié)果的影響,采用了纖芯更細(xì)的光纖;針對測量結(jié)果中間或出現(xiàn)的粗大誤差現(xiàn)象進(jìn)行了前端探測器輸出信號的阻抗匹配以及FPGA輸入異步信號進(jìn)行了同步化處理;針對數(shù)據(jù)傳輸速率不滿足要求的問題,采用向量模式的CORDIC算法在FPGA內(nèi)部實現(xiàn)了均方根運算模塊,以此減輕上位機工作負(fù)擔(dān)且減少了實際需傳輸?shù)臄?shù)據(jù)量,提高了有效數(shù)據(jù)傳輸速率。 最后針對以上改進(jìn)方案進(jìn)行了實驗驗證。結(jié)果表明,改進(jìn)后的系統(tǒng)在相同源探距離下的測量值變化規(guī)律與實際入射光強變化規(guī)律基本一致,二者最大相對誤差為7.32%;在更大源探距離范圍內(nèi)測量結(jié)果的信噪比達(dá)到了35dB以上;在16-30mm源探距離范圍內(nèi),雙通道測量值與解析解結(jié)果變化規(guī)律基本一致,相對誤差保持在17%以內(nèi)。改進(jìn)后的系統(tǒng)暗噪聲測量值明顯減小,在測量準(zhǔn)確度與穩(wěn)定性均有較大幅度提高。
[Abstract]:Steady-state diffusion optical imaging continuous Wave Diffuse Optical Imaging, CW DOI) uses near-infrared light to detect organ-level human information at a relatively deep penetration depth in the tissue. Its advantages include non-invasive and non-ionizing. High temporal resolution and suitable for clinical continuous monitoring. CW DOI usually needs to measure the diffuse reflected light flow distribution of tissue at different light wave lengths from multiple source points, which leads to the problem of source wavelength and source position coding. At present, most CW DOI systems adopt time division multiplexing (TDM) light source coding method, which is difficult to meet the requirements of real-time monitoring of some rapidly changing physiological signals. Therefore, this paper proposes a scheme of demultiplexing for the frequency division multiplexing coding of light source and digital phase-locked detection of detector output signal, which reduces the measurement time and improves the time resolution of the measurement results. The steady-state dual-channel diffuse light detection system built around the above scheme includes light source, wavelength demultiplexer, photon counting detector FPGA digital phase-locked detection circuit, communication and digital-to-analog conversion circuit and upper computer software. The experimental results show that the system has large dark noise, and the signal to noise ratio is not good enough. Under the condition that the incident light intensity and the source detection distance are both invariable, there may be a gross error between the measurement results and the data transmission rate between the FPGA detection system and the PC computer. In order to solve the above problems, this paper analyzes the reasons, designs the improved scheme and verifies the effect of the improvement. Aiming at the problem of high dark noise and insufficient signal-to-noise ratio (SNR), the influence of experimental conditions on the measurement results is studied. The fiber with finer core is used. The impedance matching of the output signal of the front-end detector and the synchronous processing of the FPGA input asynchronous signal are carried out in view of the gross error phenomenon in the middle or the middle of the measurement results, and the problem that the data transmission rate does not meet the requirements is discussed. The CORDIC algorithm of vector pattern is used to implement the root mean square (RMS) operation module in FPGA, so as to reduce the workload of upper computer, reduce the amount of data needed to be transmitted, and improve the effective data transmission rate. Finally, the improved scheme is verified by experiments. The results show that the measured values of the improved system under the same source range are basically consistent with those of the actual incident light intensity. The maximum relative error is 7.322.The signal-to-noise ratio (SNR) of the measured results is above 35dB in the larger range of source range, and in the range of 16-30mm source detection, the law of variation between the measured values of two channels and the analytical solution is basically the same, and the relative error is kept within 17%. The measured value of dark noise of the improved system is obviously reduced, and the accuracy and stability of the system are greatly improved.
【學(xué)位授予單位】：天津大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2012
【分類號】：R318.51

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本文編號：1921063