目前臨床上常用雙能X光吸收儀（DEXA）量取所謂骨密度作為骨質疏鬆症之診斷參考，然而近年來亦有研究指出：超音波的波速和波衰減亦能顯示骨頭品質之特性，例如微細結構、彈性係數、密度等，另外由於超音波不具有輻射的疑慮且具價格低廉之特性，使得超音波骨密度儀成為骨質疏鬆症的另一評估工具。上述超音波波速及波衰減的量測均需骨頭厚度的資訊，然而人體骨頭的真正厚度在傳統量測技術上是無法直接獲得，因此如何發展一種較新的技術來獲取上述之參數，將是發展超音波骨密度儀的一項重要課題。

　　本論文首先提出兩種新型之超音波技術，一種為利用兩個超音波換能器，放置於人體脛骨同ㄧ側，一個作為發射與接收超音波訊號，另外一個只設定為接收超音波訊號之雙探頭技術。如此一來不用事先知道人體脛骨真正厚度，只需知道兩個探頭所量到訊號的飛行時間及兩個探頭間之距離，即可求得人體脛骨之聲波波速。結果顯示，利用本技術進行18位門診病人之聲波波速與DEXA所量取之骨密度間之相關性高達0.93。另外，第二種技術為把兩個超音波換能器放置於人體腳跟骨之兩側，然後分別依序進行穿透與反射模式之雙侧探頭技術。這種技術一樣的只需知道各個訊號穿透及反射腳跟骨之時間，而不必知道腳跟骨之實際厚度即可求得人體腳跟骨之聲波波速。利用這種技術進行骨頭假體之測試除了顯示了非常高的準確度（＞99 %）及低的共變異數（＜0.5%）外，同時對14位健康個體之腳跟骨的量測結果，亦在本論文中報告。

　　骨頭組織另外一個重要之課題為波速散度，由於波速在骨頭中為頻率函數，因此波速散度大小（VDM）可能傳達評估骨質疏鬆症中所需骨頭機械特性之訊息。傳統上波速散度大小之量測需要由多個不同頻率之超音波脈波獲取，本論文提出所謂時域之分頻處理（SSP）技術把一個寬頻的超音波脈波訊號分解成一序列之窄頻脈波訊號，接著分別處理入射及穿透的寬頻脈波的分頻測量就可以得到VDM。利用此SSP技術所測得之VDM與預設參數之模擬超音波訊號，除有具有很高之ㄧ致性外；另外利用三個不同中心頻率的換能器對兩個不同之超音波商用腳跟骨假體測量所得到的VDM，也顯示了很好之結果。同時利用此技術量測9個活體腳跟骨VDM 之結果亦在本論文中報告。

　　綜合言之，本論文所提出三種新型超音波技術，都是非常簡單而且直接之方法，最後結果也顯示這些技術應用於臨床骨質疏鬆症的評估應該具有很大之潛力。

　The Dual Energy X-ray Absorptiometry (DEXA) is commonly used to measure the bone mineral density (BMD) for osteoporosis assessment. Recently, some researchers reported that the acoustic speed and attenuation of ultrasound waves on bone tissue may convey more information of bone quality, such as, microstructure, elasticity, density etc., to predict the bone fracture. Therefore, the ultrasound densitometry has become an alternative way for osteoporosis assessment with no X-ray exposure concerns and low cost. However, the acoustic speed and attenuation measurements are highly dependent on the information of bone thickness which is not available on traditional approaches. Therefore, how to develop a novel technique to obtain above ultrasonic parameters has become an important issue on ultrasound densitometry development.

　Two novel ultrasound techniques are proposed in this dissertation. The dual-transducer technique utilizes two transducers placed on the same side of tibia; one for transmitter and receiver, the other one for receiver only. The acoustic speed of tibia shaft can be estimated from the information of time-of-flight on both transducers and the separation distance between the transducer pair without the knowledge of tibia thickness. The measurements from 18 outpatients show a high correlation (r = 0.93) with the measurements of BMD from DEXA. In addition, the two-sided interrogation technique was used two transducers placed both sides of calcaneus. Those transducers are operated at echo mode and transmission mode, respectively. Then, the acoustic speed of bone tissue on calcaneus can be obtained without the information of bone tissue thickness. High accuracy (> 99%) and low standard deviation (<0.5 %) are shown on the bone phantoms measurements. The measurements of 14 healthy subjects are also reported.

　Another important issue is the dispersion of bone tissue. The acoustic speed is a function of frequency. The velocity dispersion magnitude (VDM) may convey more information of bone mechanical properties to osteoporosis evaluation. The traditional approaches need several measurements with different frequency ultrasound pulses. In this dissertation, the time domain split spectrum processing (SSP) technique is used to decompose the broadband ultrasound pulse into a serial narrowband pulses with different frequencies. Then, the VDM can be obtained from the processing of the incident ultrasound pulse and the transmitted pulse with one broadband pulse interrogation. The VDM evaluated by SSP technique are consistent with the simulation on model-based signals. In addition, The VDM measurements of two commercial calcaneus phantoms are agreeable to the results measured by three transducers with different central frequency. The estimation of velocity dispersion on 9 human heels were also reported.

　In summary, the proposed three novel ultrasound techniques are fairly simple and straightforward methods. The results reveal that the proposed techniques have potential on clinical applications for osteoporosis assessments.

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