超声波

Ultrasound

A Deep Thermal & Non-thermal

Mechanical Modality

CAI BIN

▪对于一位前臂开刀半年后产生黏连性疤痕组织的病患，下列超声波治疗参数的组合，何着最为合适？

▪A. 間歇性：1MHZ ；0.5watt/cm2

▪B. 間歇性：1MHZ ；1-2 watt/cm2

▪C. 連續性：3MHZ ；0.5 watt/cm2

▪D. 連續性：3MHZ ；1-2 watt/cm2

纲要

▪基础部分▪临床部分

What is Ultrasound?

▪Located in the Acoustical Spectrum

▪May be used for diagnostic imaging, therapeutic tissue healing, or tissue destruction

▪Thermal & Non-thermal effects

▪We use it for therapeutic effects

▪Can deliver medicine to subcutaneous tissues (phonophoresis)

超声波

▪超声波是指频率在20KHz以上，不能引起正常人听觉反应(16~20KHz)的机械振动波

▪Therapeutic ultrasound waves range from 750,000 to 3,000,000 Hz (0.75 to 3 MHz)▪近年多采用1MHz、3MHz超声

物理特性▪超声波与声波的本质

相同，都是物体的机

械振动在弹性介质中

传播所形成的机械振

动波。

▪在传播时产生一种疏

密交替的弹性纵波，

具有一定的方向性；

Frequency

▪Frequency:number of times an event occurs in 1 second; expressed in Hertz or pulses per second

•Hertz:cycles per second

•Megahertz:1,000,000 cycles per second

▪In the U.S., mainly use ultrasound frequencies of 1,

2 and

3 MHz

▪1 = low frequency; 3 = high frequency

▪↓frequency = ↑depth of penetration

▪↑frequency = sound waves are absorbed in more superficial tissues (3 MHz)

Velocity

▪The speed of sound wave is directly related to the density (↑velocity = ↑density)

▪Denser & more rigid materials have a higher velocity of transmission

▪At 1 MHz, sound travels through soft tissue @ 1540 m/sec and 4000 m/sec through compact bone

物理特性

超声波的传播速度与介质的特性有关，而与声波的频率无关；

介質的密度越大，則音波的傳遞速度就愈

快。例如：空氣（344m/s）＜水

（1410m/s）＜肌肉、軟組織（1540m/s）

＜骨骼（4000m/s）

Influences on the Transmission of

Energy

▪Reflection–occurs when the wave can’t pass through the next density

▪Refraction–is the bending of waves as a result of a change in the speed of a wave as it enters a medium with a different density

▪Absorption–occurs by the tissue collecting the wave’s energy

Attenuation

▪Decrease in a wave’s intensity resulting from absorption, reflection, & refraction

▪US penetrates through tissue high in water content & is absorbed in dense tissues high in protein

▪the half value depth

•The average 1/2 value depth of 3MHz ultrasound is

taken at 2.5cm and that of 1MHz ultrasound as 4.0 cm

组织对超声波的吸收能力

▪組織中的含水量如果愈高，則能量的吸收就越少

▪人體組織中，蛋白質的含量愈高則能量的吸收就愈多

▪對超音波的吸收力：骨頭＞軟骨＞肌腱＞皮膚＞肌肉＞神經＞脂肪＞血液

Attenuation: Acoustic Impedance ▪Determines amount of US energy reflected at tissue interfaces

•If acoustic impedance of the 2 materials forming the

interface is the same, all sound will be transmitted

•The larger the difference, the more energy is reflected & the less energy that can enter the 2nd medium

▪US passing through air = almost all reflected (99%)▪US through fat = 1% reflected

▪Both reflected/refracted @ m. interface

▪Soft-tissue: bone interfaced = much reflected