SPI Study Guide

SPI STUDY GUIDE 109 106 103 102 101 10-1 10-2 10-3 10-6 10-9 giga mega kilo hecto deca deci centi milli micro nano G M k h da d c m u n billion million thousand hundred ten tenth hundredth thousandth millionth billionth Acoustic variables (PPTD)  pressure  particle motion (distance)  temperature  density Sound is a mechanical, longitudinal wave Parameters describing sound:  period (can’t change)  frequency (can’t change)  amplitude (change)  power (change)  intensity (change) Propagation speed Wavelength Determined by sound source: 1. period 2. frequency 3. amplitude 4. power 5. intensity Determined by sound source and medium: 1. wavelength Determined only by the medium: 1. propagation speed Period- length of time it takes to complete 1 cycle or time from start of 1 cycle to next Frequency- number of cycles per second  Hertz: 1 cycle/second  Typically, 1 to 10 MHz  affects penetration and axial resolution Amplitude- the difference between the average value and maximum value of an acoustic Variable (not between max and min. that would be peak to peak amplitude) Power- the rate that work is performed or energy is transferred Intensity- the concentration of energy in a sound beam  Typically, 0.001 (1mW/cm2) to 100 W/cm2 Wavelength- distance or length that 1 cycle occupies  Typically, 0.1 to 0.8mm  influences longitudinal resolution  can’t change Propagation speed-speed that sounds travels through a medium  determined by density and stiffness  Density and stiffness=opposite  Speed and stiffness=same  compressibility and elasticity= opposite of stiffness Speed of Sound (mm/µs)  Air 0.33  Fat 1.45  Water 1.48  Soft Tissue 1.54  Blood 1.57  Muscle 1.58  Bone 4.0  PZT 4.08  Steel 5.0-6.0 GO OVER AMPLITUDE AND INTENSITY Pulse duration- the time from start a pulse to the end of the pulse  determined by source  can’t be changed  .5 to 3 microseconds  short the pulse=better the image  doesn’t change with depth Pulse repetition period- time from the start of one pulse to the start of the next  determined by source  can be change because can change “listening time” Pulse repetition frequency- number of pulses that occur in 1 second  determined by source  can be changed because can change “listening time”  as depth increases, PRF decreases  1 to 10kHz Duty Factor- % of time that the system is transmitÝng a pulse  determined by the source  can be changed-when change depth  0.001 to 0.01  If PRF increases, DF increases  depth increases, DF decreases  PRP increases, DF decreases  PD increases, DF increases Spatial Pulse Length- distance from start of pulse to end of pulse  determined by source and medium  can’t be changed  0.1 to 1mm  DETERMINES LONGITUDINAL RESOLUTION Intensity- the concentration of energy in a sound beam  determined only by sound source  can be changed 1. 2. 3. 4. 5. 6. SPTP SATP SPTA SATA SPPA SAPA Bio-effects SPTP= SPTA and SATP=SATA for continuous wave Decibels- ratio for intensity I/Io 3 6 9 10 1/2 1/4 1/8 1/10 Attenuation- decrease in intensity and amplitude as sound travels  Greater the frequency/pathlength= greater attenuation 1. absorption 2. reflection-depends on acoustic impedance RE ZE a. specular=smooth boundaries- WAVELENGTH IS SMALL IN RELATION TO BOUNDARY ROUGHNESS 3. scattering-BOUNDARY BETWEEN MEDIA HAS IRREGULARITIES (size similar/smaller than pulses wavelength a. Rayleigh-REFLECTOR IS SMALLER THAN PULSES WAVELENGTH  higher frequency undergoes this Attenuation coefÏcient- the amount of attenuation per cm  does not change with path length Half value layer- depth at which intensity is reduced 1/2  decreases when attenuation coefÏcient increases, frequency increases  depends on medium and frequency  does not change with path length Impedance- resistance to sound travel through a medium  characteristic of medium IRC + ITC= 100% Reflected +transmitted intensity= incident intensity IRC=RI/II x 100 ITC=TI/II With oblique incidence- reflection angle=incident angle NOT SURE if reflection will occur with oblique incidence????????????? Refraction- change in direction of wave propagation-SNELL  C mismatch and oblique Sin transmission angle Sin incidence angle = Prop speed 2 Prop speed 1 Distance= 0.77mm/microsecond x time 13 microseconds for every cm in ST PAY ATTENTION TO WHETHER IT IS DEPTH OR DISTANCE Piezoelectric effect- materials create voltage when they’re mechanically deformed PZT is also called ceramic curie temperature- if material heated over this, loses its piezoelectricity- depolarizes Damping material advantages: Increases quality by improving LARRD Shortens SPL and PD Decreases numerical value of LARRD Disadvantages: Decreases transducer sensitivity Increases Bandwidth Decreases Q factor Bandwidth- the difference between the lowest and highest frequency emitted shorter the pulse the broader the BW Quality factor- degree of damping  lower Q factor: o greater damping o pulse length is short o Bandwidth is wide o image is good For an unfocused transducer at the end of near zone: beam diamtere is ½ the transducer diameter and at 2 NZLs beam diameter is equal to transducer diameter