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초음파 SPI 기초물리 및 기초원리5

TYPEs OF INCIDENCE1. Normal Incidence (Perpendicular Incidence) 2. Oblique Incidence 3. Refraction 4. Acoustic Impedance (z) 5. Important Terms1. Normal Incidence (Perpendicular Incidence)1) Incident sound beam encounters a boundary between two media at a 0° incident angle- The sound beam is perpendicular to the boundary.2) Reflected sound returns in the same direction as the incident sound3) Transmitted sound continues on in the same direction as the incident sound4) There is no Refraction (bending of sound)2. Oblique Incidence [★]1) When the incident sound beam encounters the boundary between two media at an angle- The incident angle is something other than 0°2) The reflected angle is equal to incident angle3) Transmitted sound will also continue on an angle (Refraction)4) The angle of reflection will be oriented away from the transducer- resulting in decreased visualization of the structure3. Refraction1) A change in the direction of sound after encountering a boundary (bending of sound)2) Requirements for refraction- Oblique Incidence: Perpendicular/Normal Incidence = No refraction- Mismatch in Propagating speeds (c) of two media- M2>M1 than T>I: the transmission angle is greater than the incidence angle- M2< I: the transmission angle is less than the incident angle3) Matching PS and mismatched Impedance causes reflection but not refraction4. Acoustic Impedance (z)1) physical property of tissue- Resistance to travel that a sound beam encounters as it passes through a medium [rayls]Z [rayls] = d [kg/m³] x c [m/s] [★★★★]- affected by tissue stiffness, density and soundwave speed: not) frequency- density = most responsible factor2) An Impedance mismatch determines reflection- Tissue to Tissue: Reflection ≤2% (mostly transmitted = weakest reflected signal)- Tissue to Air: mostly reflected without coupling medium- Diagnostic application to adult brain is limited: great acoustic impedance mismatch between cranium and so tissue: causing most sound to be reflected at interface- With oblique incidence reflection can occur without refraction: when there are mismatched impedances, but matching propagating speeds5. Important Terms1) Intensity Reflection Coefficient (IRC)- The fraction of incident intensity that is reflected: IRC = Ir/Ii (reflected intensity/incident intensity)- IRC and impedance mismatch: proportional: ↑z mismatch → ↑IRC: ↓z mismatch → ↓IRC- If impedance of the two media are the same: no reflection2) Intensity Transmission Coefficient (ITC)- The fraction of incident intensity that is transmitted into the second medium: ITC = It/Ii (transmitted intensity/incident intensity): ITC = 1 – IRC- IRC and ITC should always equal one- IRC ↑ → ITC ↓, vice versa.6) Scattering- The diffusion or redirection of sound in several directions upon encountering a rough surface- Backscatter: Sound scattered back in the direction from which it originally came

의/약학| 2023.06.16| 3페이지| 1,500원| 조회(114)

spi, 초음파 물리, 초음파 기초

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초음파 SPI 기초물리 및 기초원리4

SOUND WAVES1.Acoustic waves 2.Mechanical waves 3.Terms describing sound waves/The properties of sound 4.Termas describing pulsed waves 5.Level of sound1. Acoustic Waves1) Traveling variation (oscillation) in acoustic variables- Molecules oscillate back and forth to propagate sound waves- Do not move from one end of the medium to another- Acoustic variables: Temperature: Pressure - Concentration of force in an area: Density - Concentration of mass in a volume: Distance - Measure of particle moon2) Mechanical longitudinal wave3) Vacuum: a space void of matter- Sound cannot travel in a vacuum- Electromagnetic radiation, light/x-ray can travel through a vacuum2. Mechanical Waves1) require a medium for propagation (gas, liquid, or solid)- cause motion of the particles they are moving through- molecules do not travel from one end to the other (it is not a flow of particles).: Molecules vibrate back and forth- can be either Transverse or longitudinal.2) Longitudinal Waves- particles of mediumsure region of a wave.4) Frequency (f)- The number of cycles that occur in one second [MHz, kHz or Hz]: F = 1/p (frequency = 1/period): F= c/λ (frequency = propagating speed/wavelength)- Hertz (Hz): One cycle per second: MHz = 1,000,000 cycles/second : kHz = 1,000 cycles/sec- Diagnostic ultrasound frequency Range: 1-16MHz- frequency is important in diagnostic ultrasound: affects penetration and image quality.5) Period (T)- Time it takes for one cycle to complete itself [seconds(s) or microseconds (μs)]- Time between two successive compression zones or rarefaction zones: T = 1/f (Period = 1/frequency): frequency and period are reciprocals6) Wavelength (λ)- The distance one cycle takes up [meters(m), centimeter (cm), or millimeter (mm)]- The distance between two successive density zones.: λ = c/f (wavelength = Propagating speed/frequency)- wavelength and frequency: inversely proportional7) Propagation- Changes in pressure conveyed from one location to another8) Propagating Speed (Acoustiating speed in so tissue: 1.54mm/us or 1540 m/s- speed used to calibrate range-measuring circuits on diagnostic sonography instruments: 1540 m/s - Tissue Type & Correlating Speeds: Propagating speed through gas is low: Propagating speed through liquid is higher: Propagating speed through a solid is the highest.- Air: 300 m/s - Lung: 500 m/s - Fat: 1,450 m/s - Water: 1,480 m/s - So Tissue.: 1,540 m/s - Liver: 1,560 m/s - Blood: 1,560 m/s - Muscle: 1,600 m/s - Tendon: 1,700 m/s - Bone: 3,500 m/s ~ 4080 m/s - Metals: 2,000 – 7,000 m/s9) Properties of the medium that effect Propagating Speed- Elasticity: the ability of an object to return to its original shape and volume after a force: Force applied to an object cause a change in its shape or volume (distortion)- The strength of the force determines the amount of distortion.- Density (d): The mass of a medium per unit volume.: The relative weight of an object.: d = m/v- larger mass requires more force to cause motion- larger mass requires determined by both the medium and the source11) Interference [★★]- algebraic summation of waves leading to patterns of minima and maxima- interference patterns of reflected waves cause acoustic speckle: to reduce speckle- use frame averaging (persistence)- use compound imaging- two waves overlap at the same location, at the same time: combine into a single new wave- constructive interference: sound waves are in phase and resulting amplitude is increased- destructive interference: amplitude of new wave is decreased: complete destructive interference creates black pixels4. Terms describing Pulsed Waves [★★★]1) Pulse “A Burst of Cycles”- collection/group of two or more cycles followed by a resting me.- We use pulsed waves for diagnostic ultrasound- pulsed wave US is necessary for real-me imaging: depth of interface from which the echo originated can be determined2) Pulse Duration (PD)- Time from the beginning to the end of a single pulse of ultrasound- Time it takes for one pulse to occurpulser): operator adjustable: Determined by the maximum imaging of the system- limited by the speed of sound in tissue: there must be enough me between pulses for US to travel to and back from the reflector: or else, range ambiguity occurs: if sound travels faster in tissue, maximum PRF can be increased- Relationships: PRF & depth of view – inversely proportional- imaging depth ↓ → short listening time, PRP ↓, PRF ↑- Imaging depth ↑ → longer listening time, PRP ↑, PRF ↓: PRF & PRP – inversely proportional: PRF and frame rate - proportional- PRF ↑ → frame rate ↑- If PRF is too high for the imaging depth: range ambiguity: a pulse should be received before the next pulse is transmitted: if pulse is transmitted before echoes from first pulse are received→ echoes would be misplaced axially on the image- operator adjustable.- pulsed-wave doppler: PRF ↑ → acoustic exposure ↑5) Spatial Pulse Length (SPL)- the length of space over which one pulse occurs [mm]: SPL = n x λ (Spatial pulse length =ng

의/약학| 2023.06.16| 8페이지| 1,500원| 조회(140)

spi, 초음파 물리, 초음파 기초

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초음파 SPI 기초물리 및 기본원리3

SOUND BEAM1.shppe of sound beam 2.parts of sound beam 3.Beam diameter 4. Determining the Focal depth1. Shape of sound beam1) Sound beam is not uniform as it travels (beam width changes as it travels)- The beam width is the same as the transducer diameter at the starting point (beam width=disk diameter)- The beam narrows as it travels to the focus: smallest diameter at NZL (beam width= 1/2 disk diameter)- Aer the beam reaches the focus it diverges (expands) (beam width = disk diameter at 2 NZL, then rapidly diverges)2. Parts of the Beam [★]1) Near Zone (= Fresnel Zone, Near Field)- Region from the transducer to the focus- Beam gradually narrows (converges) within the near zone- At the end of the near zone, the beam narrows to only ½ width of the active element- Determined by the size and operating frequency of the elementNZL (mm)= Diameter (mm) X Frequency (MHz): If aperture increases, near-zone length increases: If frequency increase, near-zone length increases2) Focal Length/focal Depth- The distance (length) from the transducer to the focus.- The length of the Near Zone (Near Zone Length)3) Focus/Focal Point- Narrowest part of the beam : Beam width = ½ Disk diameter- Located at the end of the near zone- The starting point of the far zone- The middle of the focal zone- point of maximum intensity in a sound beam4) Focal Zone- Region around the focus : Region on either side of the focal point where the beam is relatively narrow- The area that creates more accurate images5) Far Zone (= Fraunhofer Zone, Far Field)- starts at focus and extends deeper (Region of the beam beyond the NZL)- Can’t focus in far zone- At 2 near zone lengths from the transducer: Beam width = Disk diameter: depth past 2 near zone lengths are wider than disk diameter3. Beam Diameter1) Depends on crystal aperture, frequency, and distance from transducer- Beam diameter = transducer diameter- Beam diameter = ½ transducer diameter at the focus- Beam diameter = transducer diameter at 2 near zone lengths- Beam diameter > transducer diameter deeper than 2 near zone lengths2) large beam diameter → focus at greater depths4. Determining the Focal Depth1) focal depth [mm] = D2 f/6 or D2 /4λ2) Transducer/Disk Diameter: directly related to focal depth- Large diameter = deeper focus- small diameter = shallow focus3) Frequency: directly related to focal depth- Higher frequency = deeper focus- lower frequency = more shallow focus3) Divergence- the divergence of the beam in the far field is also determined by disk diameter & frequency- Disk diameter (inversely proportional to divergence): smaller diameters = greater divergence in far field: large diameters = less divergence in the far field- Large disk diameter improves Lateral Resolution- Frequency (inversely proportional to divergence): lower frequency = greater divergence in far field: higher frequency = less divergence in the far field-High frequency improves Lateral Resolution

의/약학| 2023.06.16| 3페이지| 1,500원| 조회(98)

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초음파 SPI 원리 및 기초 물리

GENERAL TERMS1.Amplitude,Power, Intensity 2.Attenuation 3.Range Equation/13 m/s Rule/time of flight 4. Bandwidth and Quality Factor1. Amplitude, Power, and Intensity: indicators of the strength of sound1) Amplitude [★★]- difference between average value and maximum value of acoustic variable= maximum cyclical change in quantity2) Power (P)- The rate of energy transfer or the rate at which work is performed [mW,W]- Determined by - sound source - rate of decrease depends on wave and medium- Operator adjustable - Relationships: Power is directly related to amplitude3) Intensity (I) [★★]- Intensity = Power/beam area (I=P/a)- Relationships- Intensity is proportional to power- Intensity is proportional to amplitude2- Intensity is inversely proportional to beam area- strength of the beam over specific area [mW/cm2 ]- the concentration of energy in a sound beam- Important parameter of bioeffects- Determined by - sound source - rate of decrease depends on wave and medium- Operator adjustableSPT temporal peak)SATP (spatial average, temporal peak)SPTA (spatial peak, temporal average)SATA (spatial average, temporal average)SPPA (spatial peak, pulse average)SAPA (spatial average, pulse average)- spatial: US beam does not have same intensity at different locations within a beam>- temporal: pulsed US beam does not have same intensity at different time- SPTP: greatest intensity- SPTA: Tissue heating- highest SPTA: PW doppler- lowest SPTA: gray-scale imaging (ophthalmic)- SATA: smallest intensity- SPPA, SAPA: not applicable for continuous-wave US* Decibel (dB)- relative measurement of intensity or amplitude based on logarithmic scale: dB>0 = Larger than reference intensity: dB = Smaller than reference intensity- Not an absolute value- B (dB) = 10 x log[I/I0]: output power increased by 10 → signal intensity increased by a factor of 10- Intensity x 2 → 3 dB, Intensity x 4 → 6 dB- Intensity x ½ → -3 dB, Intensity x ¼ → -6 dB2. Attenuation [★★]1) weakening of amplitude and intensity as rough the medium- image in the far field is less bright compared to the near field.2) Attenuation Coefficient (a)- rate at which the amplitude and Intensity decrease as sound moves through a medium; [dB/cm]- Attenuation coefficient = ½ x frequency3) Attenuation = attenuation coefficient x path length = ½ frequency x path length4) Relationships: frequency, Attenuation coefficient, and Attenuation are directly related- frequency ↑ → Attenuation coefficient ↑, Attenuation ↑[★★★★★]- pathlength↑ → Attenuation ↑5) Contributions to Attenuation [★★★★★]- Absorption: dominant form of attenuation in so tissue: conversion of sound energy into heat.: Not) redirection of sound energy- Reflection: travels in the opposite direction of the main beam. Back to the source.- Refraction: bending of the sound beam as it travels.- Scattering: Occurs when surface is rough. Redirection to all different directions.6) Attenuation & Media- Attenuation properties very with the medium through which it is traveling- owest in water, Highest in air: Low in blood, urine, biologic tissue, and fat: Intermediate in so tissue: High in muscle & bone, calcification: Highest in lung3. Range Equation/13 Microsecond Rule/Time of Flight1) Range Equation (Echo ranging) [★★]- Estimates the depth of a reflector- Based on the Go-Return Time (Time-of-Flight, echo arrival time): Calculated using the average propagating speed of so tissue, 1.54 mm/us or 1540 m/s- D (mm) = V x T / 2(D= depth; V= acoustic velocity; T= me)2) 13 Microsecond Rule- For every 13μs, a reflector is 1 cm deeper within the anatomy and on the display: Ex) If a reflector is 2cm deep, the pulses time of flight is 26μs4. Bandwidth and Quality Factor1) Bandwidth [★]- range (difference between the highest and the lowest frequencies) of frequencies in a pulse: the frequency emitted is not uniform- Long duration events are narrow bandwidth and short duration events are wide bandwidth.: axial resolution is improved with wide bandwidth (shorter pulse durrs: axial resolution worse with narrow bandwidth (longer pulse duration) transducers- wide bandwidth pulses (2-5Hz): echo signals will be shied down in frequency (due to increased attenuation of higher frequencies)- Fractional bandwidth: bandwidth divided by the operating frequency: The strongest frequency within the bandwidth is the operational frequency.2) Operating Frequency (=Resonance frequency)- Operating frequency (Resonant frequency) is the frequency of choice.- Fo = Ct / (2 x thickness) (Thinner element = higher frequency) (Thicker element = lower frequency)3) Quality Factor (QF)- Imaging: Short distinct pulses and length are needed: Improved Axial Resolution- Wide bandwidth, lower Q factor : most energy is lost after first few vibrations: Use backing material to reduce ringing- Q Factor = fo/bandwidth: Wide bandwidth (multifrequency selection) – low Q factor – short duration- used for diagnostic pulsed-wave ultrasound (Low QF is good quality): Narrow bandwidth – high Q factor

의/약학| 2023.06.13| 5페이지| 2,500원| 조회(182)

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초음파 SPI 원리 초음파 물리2

COMPONENTS of ULTRASOUD1.pulser 2.Beam former 3.Transducer 4 .Receiver 5.Memory 6.Display* In order: Pulser → Beam former → Transducer → Receiver → Memory (scan converter) → Display* Analog signal- does not have discrete steps –values may vary continuously between minimum and maximum point(continuous variation of the signal is possible)* Digital signal- have discrete values that have fixed steps between values- bits determine levels in digital system1. Pulser (= Voltage Generator, Transmitter) [★]1) originates action2) Sends an Electric voltage pulse (EVP) to transducer through the beam former- EVP (electric) = analog part- Starting piezoelectric effect3) Output power control- adjust to increase or decrease the intensity of transmitted pulse- output power: most closely affects patient exposure4) PRF (Pulse repetition frequency) of Pulser = PRF of Transducer2. Beam Former [★★]1) Sends EVP to Transducer.- EVP (electric) = analog part2) Responsible for- Aperture control- Beam steering- Fs when an electric voltage is applied to certain crystal materials: Varying electrical signal is produced when the crystal structure is mechanically deformed- When electric signal is applied to a piezoelectric element: element expands and contracts to produce mechanical vibrations (sound waves)- EVP and MVP: neither analog nor digital: Mechanical Voltage pulse (MVP) = sound wave- Sends long MVP into body. Receives returning MVP- Converts returning MVP to EVP, sends EVP to receiver4) Matching layer: between piezoelectric element and tissue- places on face of element- reduce acoustic impedance mismatch between the element and tissue: improve sound transmission, reduces reflection- multiple matching layers: increase transducer bandwidth (short duration) → improve axial resolution- optimal thickness = ¼ wavelength- not) used for focusing5) Backing material- Advantage: dampen US pulse and reduce spatial pulse length → improves axial resolution: control ringing of piezoelectric element- Disaportion of transducer that protects the insertion of the cable into the transducer housing- area prone to wear and tear with repeated use and bending of the cable- strain relief area should be regularly inspected for cracks and exposed wiring- use of a transducer should be discontinued if a crack appears in any area9) Damage to the lens or transducer crystals- result: degradation of image quality: underestimation of maximum flow velocity4. Receiver/Signal Processor1) Receives EVP signals from Transducer- EVP (electric) = analog part2) Alters the signal to make suitable for processing in memory- Improves image- Any pre-processing function = Receiver- Refines signal through 5 functions of Pre-processing (ACDCR)* Gain- brightness of entire image changes.- system control that determines the amount of amplification that occurs in the receiver3) Between Receiver and Memory: Analog to Digital Converter (ADC)5. Memory/Image Processor/Scan Converter (if digital) [★★]1) Storage for the signals re bit can represent 2 levels of information: 8bits (Matrix boards) = 1 Byte- Matrix boards can be stacked: Allows multiple signals stored per single location → Beer Image: Usually 6-8 matrix boards- spatial resolution of scan converter is determined by # of pixels in the matrix- Between Memory (scan converter) and Display: Digital to Analog Converter (DAC)6. Display/Cathode Ray Tube (CRT)1) Viewing Tube- Phosphor covered tube- the image is made for viewing –not what we see. inside machine2) Sends EVP to the monitor- EVP (electrical) = analog3) Three colors used on color monitor to produce range of available colors- RGB (red, green, blue)7. Five Functions of the Receiver (ACCDR) [★★★]1) Amplification (= receiver gain) [dB]- Returning echoes vary in strength- Each returning signal is amplified uniformly- purpose of preamplification of incoming signal: to increase echo voltages before noise is induced through the cable- Operator adjustable2) Compensation [=Time Gain Compensation (TGC); Deperator adjustable3) Compression (=Log Compression; Dynamic Range) [dB]- Dynamic Range/Shades of Gray: ratio of the largest to the smallest signal that a system can handle: Determines the extent a signal can vary and maintain accuracy: Narrow dynamic range = fewer shades of gray (High contrast): Wide dynamic range = many shades of gray (Low contrast)- display cannot accommodate the wide dynamic range of the incoming signals- Decreases dynamic range of the processed signal (Equalizes difference between signals): Increases smaller signals, reduces larger signals: Keeps gray scale images within 20 distinguishable shades of gray- Does not alter the incoming signals; i.e. larger signals are still large and smaller signals remain small.- Partially operator adjustable (gray scale adjustments)4) Demodulation (=Detection)- Changes the form of echo voltages into an appropriate form for the display monitor.1. Rectification: Turns negative portion of radiofrequency (RF) signal to positive2. Smoothable

의/약학| 2023.06.13| 7페이지| 2,500원| 조회(185)

물리, 기초, 초음파, SPI 초음파

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