超声波

UltrasoundA Deep Thermal & Non-thermalMechanical ModalityCAI 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 and3 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 ofEnergy▪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 energyAttenuation▪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 istaken 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 theinterface 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物理特性超声波在两种不同介质中传播，在声阻不同的两界面就会发生反射和折射现象，两种介质的声阻差愈大，则反射能量愈多。

Soft-tissue: bone interfaced = much reflectedIntensity Output & Power▪Power:measured in watts (W);•amount of energy being produced by the transducer▪Intensity:strength of sound waves @ a given location within the tissues being treatedIntensity Output & Power▪Spatial Average Intensity (SAI):amount of US energy passing through the US head’sERA(Effective Radiating Area );•expressed in watts per square centimeter (W/cm2)(power/ERA)•Changing head size affects power density (larger headresults in lower density)•Limited to 3.0 W/cm2 of maximum output▪Spatial Peak Intensity (SPI):max. output (power) produced within an ultrasound beamIntensity Output & Power▪Spatial Average Temporal Peak Intensity (SATP): average intensity during the “on”time of the pulse •Output meter displays the SATP intensity▪Spatial Average Temporal Average Intensity (SATA) or Temporal (time) Average Intensity:•Power of US energy delivered to tissues over a given period of time •Only meaningful for Pulsed US•SAI x Duty CyclesBeam Nonuniformity Ratio (BNR) Ratio between the spatial peak intensity (SPI) to the average output as reported on the unit’s meter•The lower the BNR, the more uniform the beam is•A BNR greater than 8:1 is unsafe•Because of the existence of high-intensity areas in the beam (hot spots), it is necessary to keepthe US head movingBNR spatial peak intensity SPI物理特性超声波的声场不均匀，因此，在治疗时声头位在治疗部位缓慢移动。

Duty Cycle vs.Pulse Ratio▪Percentage of time that US is actually being emitted from the head▪Ratio between the US’s pulse length & pulse interval when US is being delivered in the pulsed mode•Pulse length= amount of time from the initial nonzerocharge to the return to a zero charge•Pulse interval–amount of time between ultrasonicpulses•Duty cycle= pulse length/(pulse length + pulseinterval) x 100•100% duty cycle indicates a constant US output•Low output produces nonthermal effects (20%)Pulse Ratio▪Duty Cycle=on: (on+off)▪Pulse Ratio=on:offMode Pulse Ratio Duty CycleContinuous100%Pulsed1:150%1:233%1:325%1:420%1:910%纲要▪基础部分▪临床部分超声波与热疗超声波属于深层热疗，它具有别的热疗所没有的按摩效果，更是所有热疗中透热深度最深的，也是最需要治疗技术的。