Details Title: Chapter 1 Hedricks Description: ultrasound physics Total Flash Cards: 120 Created: 02/18/2008 11:42:09		New Users: To study from this flashcard set, or to create your own your own study flash cards, REGISTER HERE. Existing Users: CLICK HERE. Additional Physics Flashcards
Cards in this set: Term Define:   Frequency Definition   1. the number of vibrations that a molecule makes per second.   2. the number of times the cycle is repeated each second Term Define:   Sound wave Definition Those pressure changes that the human ear can detect. Term   What is the frequency of an audible  sound wave? Definition     20-20,000 cycles/sec. (Hz) Term Define:   Propagation Definition the transmittal to distant regions remote from the sound source. Term Define:   Ultrasound wave Definition   Mechanical waves with higher frequencies than can be heard by the human ear Term   What is the frequency of an ultrasound wave? Definition     greater than 20,000 Hz Term Define:    Infrasound Definition Mechanical waves with frequencies lower than can be heard by a human ear Term   What are the frequencies of infrasound? Definition less than 20 Hz Term Define:   Compression Definition   a high-pressure region formed by a wave Term Define:   Rarefaction Definition   A low-pressure region formed by a wave Term   What are the two basic types of sound waves? Definition   longitudinal and transverse Term Define:   longitudinal waves Definition   particles move along the direction of the wave energy Term Define:   Transverse waves Definition   particles move perpendicular to the wave energy (ripples in a pond) Term   What type of wave is a US wave? Definition     Longitudinal Term Define:   Wavelength Definition The length of one comple wave cycle Term   What is the symbol for wavelength? Definition   Lambda Term What are the units for wavelength? Definition   um, mm, cm, m (distance measure) Term Define:   Amplitude Definition The change in magnitude of a wave. Term Define:   period of a wave Definition 1. The time necessary for one complete cycle   2. the time between two successive compression zones       Term What is the symbol for period? Definition tao Term What are the units for the period? Definition us, s (seconds or time) Term What is the symbol for frequency? Definition   f Term What are the units for frequency? Definition hertz or cycles/second Term How are the period and frequency of a wave related? Definition 1. frequency is the inverse of the period. 2. f= 1/tao 3. tao = 1/f Term What is a hertz? Definition Hz is the number of cycles per second Term Calc the period of a wave with a frequency of 3,000,000 Hz. Definition period = .25us Term Calc. the frequency of a wave with a period of        5 x 10 -7 s. Definition 2 MHz Term Define:   Acoustic velocity Definition The speed at which a wave propagates through a medium Term Define:   particle velocity Definition the speed at which particles vibrate back and forth across their average postion. Term Define:   Elasticity Definition the ability to return to it's original shape and volume Term Define:   density Definition the mass of a medium per unit volume Term If all other physical properties remain the same; if density increases what happens to the rate of sound propagation? Definition The sound propagation rate decreases. Term What is the relationship between the velocity of sound in a medium and density? (mathematical) Definition the velocity of sound in a medium is inversely proportional to the square root of the density of the medium. Term Define:   Compressibility Definition   the fractional decrease in volume when pressure is applied to the material. Term What is the symbol for compressibility? Definition K Term What is the relationship between compressibility and the velocity of sound in a medium? Definition the velocity of sound is is inversely proportional to the square root of the compressibility of the medium. Term Define:   bulk modulus Definition The negative ratio of stress and strain. Where stress is the force per unit area applied to a object and strain is the fractional change in volume of the object. Term What is the symbol for bulk modulus? Definition B Term What is the relationship between B, K & c? Definition As B increases and K decreases then c increases Term Define:   Diffuse Reflection Definition Multiple angles of reflection caused by a large, rough surface interface Term What is the relationship between compressibility and density? Definition They are interdependent. A change in density is often coupled with a larger and opposing  change in compressibility. Term What is the velocity of sound through:   soft tissue Definition     1540 m/s 1.54 um/s Term What is the velocity of sound through:   liver Definition   1550 m/s Term What is the velocity of sound through:   muscle Definition   1580 Term What is the velocity of sound through:   fat Definition   1459 m/s Term What is the velocity of sound through:   brain Definition 1560 m/s Term What is the velocity of sound through:   kidney Definition   1560 m/s Term What is the velocity of sound through:   spleen Definition   1570 m/s Term What is the velocity of sound through:   blood Definition   1575 m/s Term What is the velocity of sound through:   bone Definition   4080 m/s Term What is the velocity of sound through:   lung Definition   650 m/s Term What is the velocity of sound through:   air Definition   330 m/s Term What is the velocity of sound through:   water Definition   1480 m/s Term T or F   in the transmission of sound, soft tissue behaves similarly to liquid Definition True Term What is the relationship between density, velocity and compressibility? Definition As density increases so does velocity (because of low compressibility) Term The average speed in soft itssue is: Definition 1540 m/s   1.54 um/s Term Does velocity depend on temperature? Definition Yes, but it is not significant in clinical imaging. Term How are frequency, wavelength and velocity related mathematically? Definition velocity equals wavelength times frequency Term If the frequency increases the wavelength __________ Definition decreases Term What is the wavelength in tissue of a 2.5 MHz source? Definition .62 mm Term If the frequency is 1 MHz what is the wavelength (in ST)? Definition 1.54 mm Term Define   Scattering Definition Non-specular reflection that gives us internal texture of organs Term If the frequency is 2.5 MHz what is the wavelength (in ST)? Definition .62 mm Term If the frequency is 3.5 MHz what is the wavelength (in ST)? Definition .44mm Term If the frequency is 5 MHz what is the wavelength (in ST)? Definition .21 mm Term If the frequency is 7.5 MHz what is the wavelength (in ST)? Definition .15 mm Term If the frequency is 10 MHz what is the wavelength (in ST)? Definition .15 mm Term If the frequency is 15 MHz what is the wavelength (in ST)? Definition .1 mm Term If the frequency is 20 MHz what is the wavelength (in ST)? Definition .08 mm Term Define:   resolution Definition the ability to distinguish objects that are located close together as separate entities Term Are us images are based on reflected or transmitted energy? Definition reflected Term What is the job of the transducer? Definition To transmit the US wave and detect the reflected energy Term Attenuation is affected by all of the following EXCEPT   reflection, refraction, scattering, diffraction, divergence, interference, absorption Definition interference   (reflection is often treated separately) Term Define:   attenuation Definition reduction in the intensity of the beam Term Define:   normal incidence Definition   a sound beam directed at 90 degrees (right angle) Term Define:   specular reflector Definition smooth interface and larger the the width of the ultrasound beam Term If you are not at a normal incidence, how are the angle of reflection and angle incidence related? Definition They are equal Term How can you maximize the reflected echo? Definition Orient the transducer so that the generated sound beam strikes the interface at a right angle Term Define:   acoustic impedance Definition 1. similar to momentum but not looking at individual molecules, but at their concerted action   2. a measure of the resistance to sound passing through the medium Term What is the symbol for acoustic impedance? Definition Z Term What is the mathematical formula for acoustic impedence? Definition acoustic impedence equals velocity times density Term Which has a greater magnitude? Scattered or Specular reflections? Definition Specular Term What are the units for acoustic impedence? Definition rayls kg/m2/s Term What is Z of ST which has a density of 1060 kg/m3? Definition z= 1.63 Mrayls Term If a material is high density there will be  high or low acoustic impedences? Definition high Term What property allows visualization of ST structures at a biological interface? Definition acoustic impedence Term What is the mathematical formula for the reflection coefficient? Definition the reflection coefficient is equal to the acoustic impedence of material 2 (distal) minus the acoustic impedence of material 1 (proximal) divided by theacoustic impedence of material 2 (distal) plus the acoustic impedence of material 1 (proximal) squared. Term Why do fluid region produce weak signals? Definition They do not have scattering centers and therefore produce weak signals. Term How do you find the percentage reflection (%R)? Definition Multiply the reflection coefficient by 100. Term What is the formula for the transmission coefficient? Definition 1.   1- the reflection coefficient 2. 4 times the acoustic impedence of material 2 (distal) multiplied by the acoustic impedence of material 1 (proximal) divided by the acoustic impedence of material 2 (distal)plus the acoustic impedence of material 1 (proximal) squared   Term How can you calculate the percentage transmission? Definition 1.  100 - the reflection coefficient 2. the transmission coefficient times 100 Term Does frequency effect the transmission and reflection coefficients? Definition No, they are independent of each other. Term As the angle of incidence increase the reflection coefficient: decreases or increases? Definition increases Term If the acoustic impedence in large then:   %R will be large and % T will be large %R will be small and % T will be large %R will be large and % T will be small %R will be small and % T will be small Definition %R will be large and % T will be small Term Calculate the %R for a bone tissue interface using Table 1-4. Definition %R = 43% Term Calc. %T for a ST-bone interface using table 1-4. Definition 57% Term Calc. %R for an air-tissue interface using table 1-4. Calc %T. Definition %R = 99.9% %T = .1% Term Define:   parenchyma Definition functional part of the organ Term Define   Hyperechoic Definition Increased US signals as compared to the surrounding tissue Term Define   Hypoechoic Definition Decreased us signals as compared to the surrounding tissue. Term Define   Rayleigh Scattering Definition   Scattering by small particles whose dimensions are much smaller than the wavelength. Term True or False   nonspecular reflection have a strong frequency dependence. Definition True Term True or False   Specular reflectors have a strong frequency dependence Definition False Term Define   Refraction Definition The bending of sound waves that happens when the wave strikes an interface and the incident angle is not 90 degrees. Term What is Snell's Law? Definition 1. the law that describes how sound waves are refracted. 2. Relates the angle of transmission to the relative velocities of sound in the 2 media Term What type of refraction occurs when the velocity in the incident medium is greater than the velocity in the transmitted medium? Definition the sound wave is bent towards the normal Term What happens when the velocity in the incident medium is less than the sound wave in the transmitted medium? Definition The sound wave is bent away from normal. Term True or False   Refraction can cause artifacts in images Definition True Term Define   Diffraction Definition the divergence of the sound beam as it moves away from the source. Term Define   interference Definition the superposition of sound waves Term Define   Constructive interference Definition Results in an increase in amplitude Term If 2 waves are in phase, what type of interference will you have? Definition Constructive Term Define   Destructive interference Definition Results in a decrease in amplitude Term If 2 waves are out of phase, it results in what type of interference Definition Destructive interference Term Define   Absorption Definition 1. The (only) process by which sound energy is dissipated in a medium   2. the process by which us energy is transformed into other energy forms (heat) Term What 3 things influence absorption? Definition f, viscosity, and relaxation time of the medium Term What is the relationship between absorption and frequency? Definition They are directly related, if frequency doubles, so does absorption Term What are the Units of acoustic pressure? Definition mm Hg, pascal, atmospheres Term What are the units of particle density Definition kg/m3 Term Definition