本計畫之主要目的是分析當以陣列式超音波換能器從事腦部病症治療時，超音波直接經由頭顱骨頭進入腦部後，其頭骨對音波強度造成的影響，如聚焦點的最大強度的改變與聚焦點位置的移動程度等。由於頭顱幾何外形使超音波波束之射入角度改變因而改變進入腦部的音波強度分布。從理論上推導音波在兩個不同聲音阻抗媒質(如超音波由水進入頭骨介質及由頭骨介質進入腦組織)的介面射入造成反射與折射現象，並探討相位所造成影響，最後求出整個進入腦部的音波強度分布。結果顯示當頻率為1.0 MHz 且骨組織衰減係數為26 dB/cm/ MHz 時，超音波在頭骨內行經距離為1.0 cm，音強度比值僅為0.2％。當有頭骨存在時，除了頭骨有較高的衰減係數外，加上音波行經兩個不同聲阻抗的介面導致造成進入腦組織內的波壓大小很明顯地比沒有頭骨的波壓值還要低很多。藉由調整各探頭的相位值結果顯示確實可改變進入腦組織前透射縱波垂直質點速度分佈情形。
The main purpose of this project is to investigate the influence of skull bone on the acoustic pressure field (for example, the focal intensity change and its location shift) using phased array ultrasound transducer through an intact skull for brain therapy. The relationship between the acoustic intensity pattern and the geometric parameters of skull bone and ultrasound transducers including its operating parameters will be theoretically investigated. Ultrasound wave reflection and refraction at the interface (a water-bone or a bone-brain tissue) must be taken into account to obtain the total acoustic pressure field within the brain and the phase shift due to the bone will also be investigated. Result illustrates that when the ultrasound wave with frequency of 1.0 MHz travels 1.0 cm distance inside the skull bone with the attenuation coefficient of 26 dB/cm/MHz, the acoustic intensity ratio reduces to 0.2%. Results also show that the resulting acoustic pressure for the case with a piece of skull bone in front of transducer is much less than that without skull bone. It is because the attenuation coefficient of skull bone is much higher than brain tissue and there are two mismatch acoustic impedance interfaces. Furthermore, by adjusting the phase differences between transducers one can really change the normal particle velocity of the refracted longitudinal wave on the right surface of bone.