# ultrasound physics.txt

 reciprocal relationship btwn 2 numbers mutiplies together to equal one pascal unit of measurement for pressure sound is mechanical and longitudinal wave y- axis on a graph the vertical axis x-axis on a graph the horizontal axis in-phase if the rarefactions of 2 waves occur at the same time destructive interferance where the resultant wave is smaller then the one of its components kg/cm cubed proper unit to describe density waves with different frequencies type of wave will exhibit both constuctive and distructive interference energys what wave transfer from one location to another all types of sound mechanical energy transmitted by pressure waves in a medium vaccum sound waves can not travel through they cause vibrations in the medium properties common to all sound sources medium speed of sound depends on commpressions in sound wave, regions where the pressure is higher than normal longitudinal wave thype of sound wave that can propagate through soft tissue ( ultrasound waves) wavelength dertemined by mediumdistance a wave travels one period of oscillation of the source halves frequency doubles, wavelength Snell's Law predicts the direction of the transmitted beam speed of sound in tissue 1540m/s1.54 mm period p=1/freqtime it takes to complete a single cycle frequency f= 1/periodnumber of times the wave is repeated per secondnumber of cycles per unit of timedetermined by source amplitude peak pressure or height of wave when sound is traveling through same medium if frequency increases wavelength= decreasespropagation= stays the sameperiod= decreasesamplitude= stays the sam pulse duration pd=cycle# x periodpd=cycle#/freqis the time that the pulse is acually on duty factor (cycle) for continous wave ultrasound is 100% spatial pulse length space from start of pulse to the end of that pulse typical freq range in medial ultrasound imaging 1 to 32 MHz watts unit of power can sonographer adjust intensity of the US beam? YES speed of sound determined by medium can pulse duration be changed? NO when depth is adjusted, what parametes are affected PRP (PRF (pulse repetition frequency)Duty Factor if image depth increases PRF decreases PRF unit Hertz aspect of intensity refers to only the transmitted time pulsed sound intensity directly proportional to transducer frequency 7 parameters periodfrequencyamplitudepowerintensitywavelengthspeed acoustic variables pressure (pa)intensity (kg/cm3)distance (unit: cm,ft,mile) propagation speed determined by density and stiffness if density increases speed of sound decreases intensity doubled amplitude quadrupled power measured in wattsrate at which work is done ultrasound frequency >20KHz transducer determines the initial amplitude of the sound wave SPTP the highest intensity attenuation coefficient the amount of attenuation per depth traveled attenuation decreased power, amplitude and intensitydetermined by path length and freqmeasured in dB amplitude and intensity are directly related spatial pulse length are denoted by source and medium can intensity be adjusted by sonographer YES rayleigh scatterer a red blood cell acoustic insulator thickness is 1/4 wavelength axial longitudinalrangeradial active element PZT.5 or 1/2 wavelength backing material improves resolution by reducing ringing order of impedance from large to small PZTmaching layerskin low Q factor improved axial resolution and backing material imaging transducer characteristies of increased freq pulse wave transducer thinner PZT crystalfaster speed in crystal focal zone thinnest far zone fraunhfer transducer diameter affect beam divergance after focus, small diameter crystals diverge wider how does frequency alter beam divergance in far field decreased freq diverge more lateral resolution angulartransverselateral M-mode motion A-mode amplitude B-mode brightness actual speed in PZT crystal influences freq sonographer can change powerdensity TGC & over all gain brightening screen ALARA as low as reasonably achievable demodualization use retofication to convert neg voltage to pos voltageuses smoothing to smooth out the bumps reject low level echos don't get into machine picture element pixel 28 shades of gray= ? bits 2x2x2x2=16 not enough need 282x2x2x2x2=32 enough then we count the 2'sso 5 bits binary numbers 1's and 0's types of archieving and storage optical media (lazer, CD)magnetic media (floppy disk) preprocessing vs postprocessing pre= manipulate TGC, zoom in without loss of resolutionpost= zoom in but looses detail how do you find depth time- round trip transducer detector of soundwaves by recieving the sound waves from the body what sound parameter influences axial resolution? pulse duration 2 parameters that influences speed of sound in medium stifness and density how to depolorize a PZT transducer curray pointheat up to 365 infrasound <20 audiable sound >20 - 20k what's focal depth affected by? transducer diameterfreq of sound Authorachimb ID124810 Card Setultrasound physics.txt Descriptionultrasound physics review Updated2011-12-22T02:07:49Z Show Answers