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ultrasound physics 1
physics definitions
| Question | Answer |
|---|---|
| three types of sounds | 1) infrasounds 2) audible sounds 3) ultrasound |
| infrasound | sounds below level of human hearing RANGE: below 20Hz |
| audible sounds | sound that humans can hear RANGE: 20Hz to 20KHz |
| ultrasound | sounds above level of human hearing RANGE: above 20KHz |
| Relationships include: | unrelated related directly related or proportional inversely related or proportional |
| unrelated | 2 subjects that are not associated with each other |
| related / proportional | 2 subjects associated with each other |
| directly related /proportional | 2 subjects related in such a way that when one increases the other also increases |
| indirectly related/porportional | 2 subjects related in a way that when one increases the other decreases |
| reciprocals | 2 numbers with reciprocal relationship are multiplied together , results in ONE. -inverse relationship one increase other decrease |
| period and frequency formula | P=1/F ex) 3 & 1/3 or 100 & 1/100 |
| time units | s, ms |
| distance units | mm, km |
| frequency units | MHz , KHz |
| velocity units | m/s |
| area units | cm2 , km2 |
| volume units | cm3 or ft3 |
| T (tera) | 10^12 |
| G (giga) | 10^9 |
| M (mega) | 10^6 |
| K (kilo) | 10^3 |
| H (hecto) | 10^2 |
| da (deka) | 10^1 |
| d (deci) | 10^-1 |
| c (centi) | 10^-2 |
| m (milli) | 10^-3 |
| u (micro) | 10^-6 |
| n (nano) | 10^-9 |
| p (pico) | 10^-12 |
| metric conversion chart | Kilo, Hecto, Deca, BASIC,Deci, Centi, Milli |
| scientific notation with positive eponent | has value larger than 10 |
| scientific notation with negative exponent | has value less than 1 |
| if exponent is positive | move decimal to the right |
| if exponent is negative | move decimal to the left |
| what do all waves carry? | energy |
| 2 types of waves | electromagnetic , mechanical |
| mechanical waves | needs a medium - waves travel though molecules or particles in a medium and vibrate or collide passing energy |
| what is a medium? | some sort of matter to travel through ex) solid , liquid , gas ex) sounds can travel though air ,water or solids |
| what waves is used with ultrasound? | mechanical and longitudinal |
| electromagnetic waves | can travel in a medium AND vacuum. ex) light, heat , microwave, xray, radio |
| what is a vacuum? | an empty space or void of matter |
| what is sound? | pulses created by a transductor travel through biologic tissue or media. - sounds travel in a straight line |
| can sound travel though a vacuum? | no |
| compressed means | squeezed together |
| rarefied means | stretched apart |
| mechanical waves can be | longitudinal or transverse |
| mechanical waves move | back and forth |
| longitudinal waves move | in the direction of sound beam , parallel to direction of particle motion |
| transverse waves | particles move in perpendicular motions |
| particle oscillation in a wave | transfer energy t -he oscillation of particles undergo a series of compressions and rare-fractions |
| in-phase | pair of waves that when their peaks and troughs occur at the same time and same location |
| constructive interference | interference of a pair of in-phase waves result in a single wave of greater amplitude |
| out-phase | 2 waves are out of phase , their peaks occur at different times and so do their troughs |
| destructive interference | created when out of phase meet - one wave is smaller than the other - two out of phase waves are unequal |
| medical diagnostic sound | 2-15 MHz |
| acoustic variables | measures changes that occur in the medium as the wave travels through it |
| three kinds of acoustic variables | Pressure, distance and density |
| pressure definition | concentration of force in an area (Pascals) |
| density definition | mass and volume (kg/cm^3) |
| distance definition | measure of particle displacement from its original position |
| 7 acoustic parameters | Frequency, period, amplitude, power , intensity, wavelength , speed |
| frequency definition | amount of times an event occurs in a particular time frame (how many cycles per second ) determined by sound source ; not adjustable |
| frequency formula | F= 1/P |
| period definition | the time it takes for one cycle (s,ms) |
| period formula | P=1/F |
| Speed definition | the rate at which a sound wave travels through a medium (ms/micro sec ) determined by stiffness and density ; not adjustable |
| what is the speed in soft tissue | 1540 m/s or 1.54 mm/microsec |
| speed formula | c=F x WL |
| stiffness or( bulk Modules) | the ability of an object to resist compression |
| density (ELASTICITY) | relative weight of a material |
| As stiffness increases | speed increases |
| As Density increases | speed decreases |
| Pulse wave ultrasound | is used in most diagnostic medical ultrasound -group of cycles make up one pulse |
| two components of Pulse wave ultrasound | Transmit time or talk time and receive time or listening time |
| Pulse rate frequency (PRF) | number of pulses that the ultrasound system transmits into the body in 1 second determined by the sound source ; can be adjusted (HZ) NOT RELATED TO FREQUENCY |
| PRF equation | PRF = 1/DEPTH or PRF= 1/PRP -Inversely related to depth |
| Pulse repetition period (PRP) | the time from the start of one pulse to the start of the next pulse -determined by sound source ;can be adjusted PRP and Depth are DIRECTLY related |
| PRP formula | PRP= depth or PRP = depth x 13 microsec. |
| pulse duration definition | actual time from start of pulse to the end of that pulse determined by sound source ; not adjustable ; directly related to period ; inversely related to frequency |
| Pulse duration formula | PD=#cycles x Period or P= #cycles / frequency |
| spatial pulse length definition | the distance that a pulse occupies in a SPACE from start to end of a pulse determined by= sound source AND medium (mm); cannot be changed |
| Space pulse length formula | SPL= #cycles /F SPL= #cycles x WL SPL= #cycles x P |
| duty factor definition | fraction or percentage of time that the system transmits a pulse determined by= sound source ; can be changed |
| duty factor formula | DF=PD/PRP DF= PD x PRF DF= PD/ DEPTH |
| Attenuation definition | decrease in intensity , power, and amplitude - sound waves weaken as they go through medium -distance and attenuation = Directly related -farther sound travels = greater att. units = decibles |
| 3 processes of attenuation | reflection, absorption and scattering (RAS) |
| Attenuation coeff. formula | ATT= F/2 |
| Total Attenuation formula | ATT= F/2 x Distance |
| reflection definition | as sound strikes the boundary, a portion of waves energy may be redirected or reflected , back to the sound source . -reflection = weakens the portion of the sound wave that continues in forward direction. |
| two forms of reflection | specular and diffuse |
| specular reflection | reflection of sound occurs when a boundary is smooth and reflection occurs in ONLY ONE DIRECTION in organized manner |
| diffuse reflection | when wave reflects off an IRREGULAR surface it radiates MORE THAN ONE DIRECTION - creates back scatter |
| scattering definition | random direction of sound in many directions |
| rayleigh scattering | redirects sound wave equally in all directions |
| rayleigh scattering formula | RS= F^4 |
| absorption | occurs when ultrasonic energy is converted into another form of energy such as heat |
| impedance | the acoustic resistance to sound traveling in a medium -units=rayls (z) acoustic impedance = influences amt. of reflection determined by = medium |
| impedance formula | z= speed x density |
| three types of angles | right, acute and obtuse |
| oblique angle | anything angle other than 90 degrees |
| normal incidence | sound beam strikes the boundary at EXACTLY 90 degrees -Also called = perpendicular, orthagonal, rt.angle , 90 degrees |
| oblique incidence | occurs when the sound beam strikes the boundary at any other angle than 90 degrees |
| incidence intensity | sound waves intensity immediately before it strikes a boundary |
| reflect intensity | intensity of the portion of the incident beam AFTER striking the boundary (returns back) |
| Transmitted intensity | portion of incident beam that after striking boundary continues forward in the same direction |
| incident intensity formula | Ii = Ri + Ti |
| refractions definition | change in different direction of wave propagation when traveling from one medium to another |
| 2 conditions of refractions | oblique incident and different speed of 2 media (transmissions with a bend) |
| snells law | quantifies the physics of refraction (angle better, speed is better) - medium 1 is material the sound is traveling currently through -medium2 is material sound wave is entering |
| 13 microsecond rule | ALWAYA applies when sound travels through soft tissue -every 13 micro sec. , return time is 1cm deep in body -total distance of pulse is TWICE the reflector depth |
| PRP and imaging depth | PRP beginning of one pulse to the start of the next pulse. -therefore PRP is the go return time of a sound pulse between transducer and image |
| transducer | any device that concerts one form of energy into another |
| transducers perform 2 functions | during transmissions and during receptions |
| during transmissions | electrical energy from the system is converted into sounds (mechanical energy) |
| during receptions | reflected sound pulse is converted into electricity |
| piezoelectric material | a substance that coverts sound into electricity (and vice versa) - some found in nature but most common is lead zicronate titanate or PZT |
| piezoelectric effect | describes property of certain materials to create a voltage |
| piezoelectric crystal | -shaped like a coin -active element -start of transducer -responsible for electric sound conversions |
| active element = | 1/2 WL thick |
| matching element = | 1/4 WL thick |
| backing material or damping element | -reduces ringing of PZT -redirect extent of PZT deformation -enhances axial res. |
| 3 consequences of backing material | - decrease in sensitivity - wide bandwidth -low QF |
| Quality factor formula | QF= main frequency / bandwidth |
| Band width formula | BW= 1/f |
| transducer frequency | a continuous wave ultrasound produces a continuous electrical signal that constantly excites the active element in transducer - frequency of sound of continuous wave = to frequency of electrical signal |
| 2 characteristics of a puled wave of the active element combine to determine frequency of sound = | speed of sound in PZT and thickness of PZT |
| speed of sound in PZT | when the speed of sound in PZT is faster, frequency of sound created by a pulsed wave transducer is higher - speed of sound and frequency of sound are DIRECTLY related |
| thickness of PZT | for pulsed wave transducer thinner active elements create higher frequency sound pulses -thicker active elements create pulses with lower frequency, longer wave lengths |
| shape definition | as sound travels , width of beam changes - starting point , beam width is the same as transducer diameter beam narrows until it reaches smallest diameter -after beam expands or diverges |
| divergence angle formula | DA= 1.8 / Diameter x F |
| 5 terms describing regions of sound beams | focus, near zone, focal , far zone, focal zone |
| focus | location of the beam is the narrowest -width of focus will be 1/2 of the beam diameter when it leaves transducer |
| near zone AKA : fresnel zone | the region from the transducer to the focus - beam gradually narrows within near zone - focus is located at the end of near zone |
| focal length (focal depth) | distance from the transducer to the focus |
| far zone (Fraunhofer zone) | region that starts at the focus and extends deeper - start of far zone, beam is 1/2 as wide as it is at the transducer |
| focal zone | region around the focus where beam is narrow - half focal zone is located in the near zone and other half in the far zone images are more accurate here |
| sound beam divergence | describes gradual spread of the ultrasound beam in the far field |
| 2 factors that determine beam divergence | transducer diameter and frequency of sound |
| transducer diameter | smaller diameter = beams spread out more in far field larger diameter = beams diverge less in far field |
| frequency of sound | lower freq. sound beams = spread out more in far zone higher freq. sound beams = spread out less in far zone |
| axial resolution definition | ability of a system to display 2 structures that are very close together when the structures are parallel to the sound beams main axis -in front of another |
| axial resolution is also called | LARRD = Longitudinal , Axial, Range, Radial , Depth |
| axial resolution formula | AR= SPL/2 ; AR=#CYCLES/F; AR=#CYCLES X WL / 2 |
| Lateral resolution | ability to identify 2 structures very close together when side by side or perpendicular to the sound beams main axis - best at focus -determined by= width of sound beam |
| lateral resolution is also called | LATA = Lateral, Angular, Transverse, Azimuthal |
| lateral resolution formula | LR = Beam diameter |
| what resolution is best | axial resolution |
| focusing | concentrates on the sound energy into a narrower beam and thus improves lateral resolutions |
| three methods of focusing | external, internal and phased array |
| external focusing | a lens is placed in front of the piezoelectric material ; focusing sound waves with this acoustic lens is similar to focusing light waves with a lens such as with eyeglasses - fixed focusing technique |
| internal focusiung | a curved piezoelectric crystal concentrates the sound energy into a narrower tighter beam - as curvature of PZT more pronounces = degree of focusing increases |
| phased array | systems electronic focuses the sound beam - can be adjusted - used only on multielement transducers - more versatile |
| effects of focusing | beam diameter in near field and focal zone narrow focal depth is shallower beam diam. in far zone increases focal zone is smaller |
| temporal resolution | is the time frame from the beginning of one frame to the next; it represents thr ability of the ultrasound syatem - cardiac cycle -shallower is better |
| temporal resolutions formula | TR=Frame rate |
| time frame and frame rate formula | TF X FR =1 ; TF=1/FR ; FR=1/TF |
| factors that increase frame rate and temporal resolution | imaging depth and number of pulses |
| factors that affect temporal resolution | - shallower imaging depth - # pulses per fram = more pulses = better TR |
| 3 display modes | amplitude , brightness and motion |
| amplitude mose (A mode) | appears as upward spikes |
| brightness mode (Bmode) | or 2D |
| motions mode ( M mode) | horizontal wavy lines and primarily used for cardiac |
| 2 types of major functions for pules echo instramentation | 1) preparation and Transmission = electrical signals to the transducer which creates sound beam 2) reception of electrical signals from the transducer , with subsequent processing into images and audio |
| ultrasound system 6 major components | transducer, pulser & beam former, reciever, display, storage , master synchronizer |
| transducer | is out probe that transmits electrical energy |
| what does the the transducer do during transmission? | the transducer transforms electrical energy into mechanical or acoustic energy |
| what does the transducer do during reception? | the transducer converts the returning acoustic energy into electrical energy |
| pulser | created electrical signals that excite the transducers PZT crystals and create sound beams |
| beam former | is an electrical device that receives the pulsers single electrical spike and distributes it to numerous active elements of an array transducer |
| receiver | transforms electrical signals from transducer to the display |
| 5 operations of the receiver | 1)amplification 2)compensation 3) compression 4) demodulation 5) reject |
| amplification or receiver gain | 1st function of the receiver -entire image made brighter or darker when the sonographer adjusts the amplitude |
| compensation (TGC) | sound waves weaken as they travel -w/o this , the image would come out darker as depth increases -creates am image uniformly bright -adjustable |
| compression (dynamic range) | -performed twice - first ) is used to decrease range of signals to one the system can handle -2nd) keeps images gray scale content within the range of detection by the human eye |
| how many shades of gray can we distinguish | 20 -adjustable |
| demodulation | changes electrical signals within receiver into a form more suitable for display on monitor |
| demodulation 2 parts = | 1) rectification= converts all neg. voltages into positive voltages 2) smoothing = places a smooth line around the "bumps" and even them out - not adjustable |
| reject (threshold or suppression) | eliminates low level noise - adjustable |
| contrast | determines the range of brilliances within the displayed image - are high contrast |
| scan converters | store info and later display it -changes format of data -creates gray scale |
| analog | "real world" can have an unlimited and continuous values or choices |
| digital | is computer, will have discrete values and limited choices |
| pixel | the smallest element of a digital picture - when picture is divided into a grid, each box is a pixel -entire pixel is a single shade of gray |
| pixel density | the number of picture elements per inch |
| special resolution | (detail) improves with high pixel density and creates an image with greater detail |
| bit | is the smallest amount of computer memory -1 bit= 2 shades |
| byte | 1 byte = 8 bits |
| word | 2 bytes = 16 bits |
| increase bits per pixel = | more gray shades on image |
| many gray shades | better contrast resolution |
| how many shades of gray are there with 5 bits? | 32 (2x2x2x2x2) |
| preprocessing | any processing of the reflected signals before storage -manipulation of an image data before storage -adjustable -once stores cannot be undone |
| postprocessing | any processing after storage in digital scan converter -manipulation of image data after storage -adjustable - can be revised |
| magnification | sonographer can improve visualization of anatomic detail be enlarged a portion of an image to fill screen |
| region of interest (ROI) | selected part of an image 2) forms = -read magnification -write magnification |
| read magnification | occurs after image data is stored in scan converter |
| read magnification 3 steps | 1) the ultra sound system scans anatomy 2)image converted A to D and stored 3) sonographer identifies ROI and system reads and displays only the OG data |
| write magnification | applied during data aquisition before storage in scan converter |
| write magnification 4 steps | 1) ultrasound system scans anatomy AND creates images 2) image converted from A-D and stored 3) sonographer identifies region of interest 4) ultrasound system then rescans only the region of interest and writes new data into scan converter |
| edge enhancement | an imaging process method that makes pictures look sharper |
| fill in interpolation | 2D images are created |
| PACS | Picture Achieving and Communication System -describes the digital ultrasound laboratory in which images and medical info are stored in large network |
| DICOM | Digital Imaging Computers and Medicine - a set of rules or protocols that allow imaging systems to share info on a network |
| dynamic range | method of describing the extent at which a signal can vary and still maintain accuracy ex) a bathroom scale weighs objects b/w 30 and 300lbs |
| compression of dynamic range | compression reduces dynamic range of signal without errors - largest signals stay the largest -smallest signals stay smaller -range of signals is reduced |
| fundamental frequency | frequency of sound created by the transducer and transmitted into the body - if transducer emits sound pulse with a frequency of 2 MHz , fundamental frequency is 2MHz |
| harmonic frequency | creation of an image from sound reflections at TWICE the frequency of transmitted sound - arise from NONLINEAR behavior ex) fundamental frequency = 4MHz SO harmonic frequency = 8MHz |
| linear behavior | proportional or symmetrical , respond in even manner |
| nonlinear behavior | irregular . a system is nonlinear when behaves unevenly |
| fundamental image | image created by processing reflections that have the same frequency as transmitted sound |
| harmonic image | image created by processing reflections that are TWICE the fundamental frequency -most useful in improving poor quality images |
| 2 forms of harmonics | 1) tissue harmonics 2) contrat harmonics |
| tissue harmonics | as a sound wave travels in the body, a miniscule amount of energy is converted from the fundamental frequency to harmonic frequency |
| contrast agents | 1) safe 2) metabolic inert 3)long lasting 4) strong reflector of ultrasound 5) small enough to pass through capillaries |
| micro-bubbles | when exposed to a sound beam of adequate strength , contrast harmonics are created bc of the nonlinear change in size of bubbles |
| bubbles | grow and shrink in relation to compensation and rare-fractions -size of RBCs - low pressure = bubbles expand uneven behavior = called resonance |
| mechanical index | the amount of contrast harmonics produced may be estimated by number called the mechanical index (MI) |
| numerical value of MI increases with | lower frequency sound and stronger sound waves |
| Mechanical index formula | MI= Pressure / F |
| Hemodynamics | study of blood flow through the circulatory system |
| velocity | the speed of fluid moving from 1 location to another |
| flow or volume flow rate | indicates the volume of blood moving at a certain time - liters per min - Volume / Time |
| 3 basic forms of blood flow | 1) pulsatile flow 2) phasic floe 3) steady floe |
| pulsatile flow | occurs when blood moves through the vessels in a variable velocity - blood will accelerate and decelerate as a result of cardiac contractions -common in arterial system |
| phasic fllow | also occurs when blood moves with a variable velocity -blood accelerates as a result of RESPIRATIONS -min venous system |
| steady flow | when blood moves through the vessels at a CONSTANT speed or velocity - NO acceleration or deceleration as a result of cardiac contractions or respirations |
| laminar flow | occurs when the floe streamlines are parallel - found in normal physiologic states -characterized by layers of blood -SILENT FLOW |
| 2 types of laminar flow | 1) plug flow 2) parabolic flow |
| plug flow | occurs when all the layers of blood are moving at the same velocity |
| parabolic flow | layers of blood are still parallel but in the middle of the vessel , the blood is traveling fast -forms bullet shape |
| turbulent flow | a chaotic flow pattern, floe moving in many directions at many speeds -associated with cardiovascular pathology |
| eddy current or vortex | a small hurricane like swirling pattern |
| turbulent flow converts | energy into other forms such as sound, and vibrations also called a murmur or bruit |
| a thrill | is tissue vibration associated with turbulence. - you can feel it |
| reynolds number | number predicts of flow is laminar or turbulant |
| laminar flow range | less than 1500 |
| turbulent flow range | greater than 2000 |
| energy gradient | is blood from regions of high energy to low energy |
| forms of energy associated with blood | kinetic , pressure and gravitational energy |
| kinetic energy | associated with movement -determined by objects mass and speed |
| pressure energy | this energy is a form of stored or potential energy - to perform work |
| gravitational energy | form of speed or potential energy |
| energy loss in circulation | blood flows fast through circulation , energy is lost in 3 ways |
| three ways of energy lost in blood flow | viscous loss, frictional loss and inertial loss |
| viscous energy loss | more energy is lost with movement and high velocity fluids (thicker fluids) - viscosity= describes thickness -measured in POISE |
| frictional energy loss | occurs when energy is converted to heat |
| stenosis | a narrowing in the lumen of a vessel -high velocity as vessel narrows -blood has to speed up to get through narrow channel |
| flow formula | Flow= Pressure Gradient / Resistance |
| pressure gradient formula | pressure gradient= flow x resistance |
| venous hemodynamics | veins are thin walled and collapsable |
Created by:
alexporcelli