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標題: | 超音波與光聲波在纖維性組織中的非均勻散射現象 Anisotropy of ultrasonic scattering and photoacoustic signal generation from fibrous tissues |
作者: | Yi-Ching Ho 何宜靜 |
指導教授: | 李百祺 |
關鍵字: | 超音波,光聲效應,非等向性,散射,纖維性組織, ultrasound,photoacoustic effect,anisotropy,scattering,fibrous tissue, |
出版年 : | 2012 |
學位: | 碩士 |
摘要: | 聲波傳遞方向與纖維性組織走向對於超音波散射有相當大的關聯性,纖維性組織像是肌腱、肌肉、神經皆有此特性,對於傳統的超音波B-mode影像會造成亮暗不均勻的現象造成醫師診斷的困難。本研究比較超音波與光聲現象對於纖維性組織的散射特性。我們使用肌腱做為實驗樣本,並使用許多文獻提出的參數積分散射值(AIB) 來計算超音波散射能量,實驗結果也證實非等向性組織排列與超音波傳遞方向夾角的改變的確對探頭收到的能量改變有相當大的關聯性。量測結果顯示能量改變隨著不同的纖維排列方向與探頭夾角改變有一定的規則性,在纖維方向與探頭方向垂直時,散射能量最大,而在平行時,散射能量則最小。我們定義由聲波與纖維走向垂直至平行的能量差異值稱作最大能量衰減,實驗結果顯示高頻聲波會造成較大的能量衰減,另外比較超音波和光聲波的實驗結果,我們發現光聲波傳遞方向較不受纖維性組織排列方向影響。因此我們提出一個假說來解釋超音波和光聲波對於纖維性組織會有不同能量衰減幅度的原因。以探頭產生的超音波面積遠大於組織散射子,對於散射子類似為平面波,對排列整齊的散射子造成等方向的散射,相同方向加成的結果造成散射波在不同方向有不同大小的振幅;相對的,光聲波由光纖產生熱膨脹接著產生聲波,產生聲波是以類似球面波的方向傳遞,造成傳遞方向對於每個散射子相關性低,相互抵銷的結果造成光聲波對於組織排列較不敏感,我們同時以實驗和模擬驗證這個假說。因此從此項發現我們推測光聲影像在纖維性組織上的診斷也許會比傳統超音波影像診斷更有優勢。 Anisotropy of ultrasound scattering in fibrous tissue depends on the specific direction of transducer with respect to the fiber orientation. The uneven brightness displayed on an ultrasound B-mode image depends on tissue fiber orientation, which causes difficulties in diagnosis. This study is aimed to investigate both the ultrasonic and photoacoustic wave scattering in anisotropic tissues. Tendon samples were used, and results showed that the apparent integrated scatter (AIS) from fibrous tissues was highly dependent on the angle of insonification. The energy scattered from tendon exhibited maximum scatter intensity when the direction of transducer was perpendicular to the fibers, and minimum scatter intensity for parallel incidence. The results show that higher detection frequency resulted in a larger maximum AIS decrement from perpendicular to parallel direction. Furthermore, significant angular dependence of ultrasound scattering was observed in the measurements as compared to photoacoustic scattering, which is less sensitive to the fiber orientation. A hypothesis is proposed to explain why photoacoustic waves are relatively less affected by the fibrous tissue. In ultrasonic scattering, incident direction for each scatterer was similar due to the relatively planar wavefront, hence the signal amplitudes scattered at the transducer direction are also similar. In photoacoustic scattering, the spherical-like wavefront causes different incident directions for different scatterers, therefore the variation of the signal amplitude collected by the transducer increases, resulting in a lower correlation with the microstructure. The smaller angular dependence in photoacoustic scattering implies that photoacoustic imaging may have the advantage to be applied to image anisotropic tissue. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/61800 |
全文授權: | 有償授權 |
顯示於系所單位: | 生醫電子與資訊學研究所 |
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