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USES OF ULTRASOUND WAVES
USES OF ULTRASOUND WAVES
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Sonography

  1. 1. 1
  2. 2. 2 Ultrasound is cyclic sound pressure with a frequency greater than the upper limit of human hearing. Although this limit varies from person to person, it is approximately 25 kilohertz (25,000 hertz) in healthy, young adults and thus, 25kHz serves as a useful lower limit in describing ultrasound. SONAR (SOund NAvigation and Ranging)—or sonar—is a technique that uses sound propagation under water to navigate, communicate or to detect other vessels. There are two kinds of sonar—active and passive. Acoustic location in air was used before the introduction of radar. Sonar may also be used in air for robot navigation SODAR (an upward looking in-air sonar) is used for atmospheric investigations. The term sonar is also used for the equipment used to generate and receive the sound. The frequencies used in sonar systems vary from infrasonic to ultrasonic.
  3. 3. 3 Ability to hear ultrasound
  4. 4. 4 Ultrasound Physics Diagnostic Ultrasound X-rays wave type longitudinal mechanical waves electromagnetic waves transmission requirements elastic medium No medium generation stressing the medium accelerating electric charges velocity depends on the medium through which it propagates It is relatively constant: 299,792.456.2 m/s
  5. 5. 5 Velocity of sound in some Biological Materials Material Velocity of Sound (m/s) Impedance (Rayl x 10 -6) Air 330 0.0004 Fat 1450 1.38 Water 1480 1.48 Average Human Soft Tissue 1540 1.63 Brain 1540 NA Liver 1550 1.65 Kidney 1560 1.62 Blood 1570 1.61 Muscle 1580 1.7 Lens of eye 1620 NA Skull Bone 4080 7.8
  6. 6. 6 Piezoelectricity Piezoelectricity is the ability of some materials(notably crystals and certain ceramics) to generate an electric potential[1] in response to applied mechanical stress. This may take the form of a separation of electric charge across the crystal lattice. The piezoelectric effect is reversible in that materials exhibiting the direct piezoelectric effect The effect finds useful applications such as the production and detection of sound, generation of high voltages, and electronic frequency generation.
  7. 7. 7 Medical Sonographic Instrument
  8. 8. 8 From sound to image Producing a sound wave1- Receiving the echoes 2- Forming the image3- Sound in the body4-
  9. 9. 9 Producing a sound wave1- A sound wave is typically produced by a piezoelectric transducer encased in a probe. Strong, short electrical pulses from the ultrasound machine make the transducer ring at the desired frequency. The frequencies can be anywhere between 2 and 15 MHz. The sound is focused either by the shape of the transducer, a lens in front of the transducer, or a complex set of control pulses from the ultrasound scanner machine. This focusing produces an arc-shaped sound wave from the face of the transducer. The wave travels into the body and comes into focus at a desired depth. Linear Array Transducer
  10. 10. 10 •Thereturnofthesoundwavetothetransducerresultsinthesame processthatittooktosendthesoundwave. 1-Thereturnsoundwavevibratesthetransducer. 2-Thetransducerturnsthevibrationsintoelectricalpulses. 3-Thattraveltotheultrasonicscannerwheretheyareprocessed:- (a)convergedtodigits (b)deleveredtoacomputerprogram (©)transformedintoadigitalimage. Receiving the echoes 2- Forming the image3- The sonographic scanner must determine three things from each received echo: 1- How long it took the echo to be received from ? (time). 2- From what focal length for the phased array is deduced ? (distances) . 3- How strong the echo was ? (energy ).
  11. 11. 11 •Ultrasonography(sonography)usesaprobecontainingoneormoreacoustic transducerstosendpulsesofsoundintoamaterial(body). *Asoundwaveencountersamaterialwithadifferentdensity(acousticalimpedance). *Apartofthesoundwaveisreflectedbacktotheprobeandisdetectedasan echo. *Thetimeittakesfortheechototravelbacktotheprobeismeasuredandusedto calculatethedepthofthetissueinterfacecausingtheecho(depthX=V*t). *Thegreaterthedifferencebetweenacousticimpedances,thelargertheechois. *Thefrequenciesusedformedicalimagingaregenerallyintherangeof1to18MHz. *Theattenuationofthesoundwaveisincreasedathigherfrequencies,soinorder tohavebetterpenetrationofdeepertissues,alowerfrequency(3-5MHz)isused. Sound in the body4-
  12. 12. Modes of sonography • • A-mode: A-mode is the simplest type of ultrasound. 1- A single transducer scans a line through the body. 2- Echoes plotted on screen as a function of depth. 3- Therapeutic ultrasound aimed at a specific tumor or calculus is also A-mode, to allow for pinpoint accurate focus of the destructive wave energy. • B-mode: In B-mode ultrasound:- 1- A linear array of transducers are used. 2- Simultaneously, that array scans a plane through the body. 3- That plane can be viewed as a two-dimensional image. • M-mode: M stands for motion. 1- A rapid sequence of B-mode scans specific area. 2- images follow each other in sequence on screen, which enables doctors to see and measure range of motion, as the organ boundaries that produce reflections move relative to the probe. • Doppler mode: This mode makes use of the Doppler effect. • 12
  13. 13. Doppler sonography • The total Doppler effect may result from: 1- motion of the source (probe ) 2- motion of the observer probe 3-motion of the medium ( i.e blood). • Each of these effects is analyzed separately using spicial computer program. 13
  14. 14. 14 Spectral Doppler of Common Carotid Artery Color Doppler of Common Carotid Artery
  15. 15. Strengths of sonography • It images muscle and soft tissue very well and is particularly useful for delineating the interfaces between solid and fluid-filled spaces. • It renders "live" images, where the operator can dynamically select the most useful section for diagnosing and documenting changes, often enabling rapid diagnoses. • It shows the structure of organs. • It has no known long-term side effects and rarely causes any discomfort to the patient. • Equipment is widely available and comparatively flexible. • Small, easily carried scanners are available; examinations can be performed at the bedside. • Relatively inexpensive compared to other modes of investigation 15
  16. 16. Weaknessesofultrasonicimaging • Sonographic devices have trouble penetrating bone. For example, sonography of the adult brain is very limited. • Sonography performs very poorly when there is a gas between the transducer and the organ of interest, due to the extreme differences in acoustic impedance. • The depth penetration of ultrasound is limited, even in the absence of bone or air, making it difficult to image structures deep in the body. • The method is operator-dependent. A high level of skill and experience is needed to acquire good-quality images and make accurate diagnoses. • There is no scout image as there is with CT and MRI. Once an image has been acquired there is no exact way to tell which part of the body was imaged. 16
  17. 17. Thank You 17 Prof. Galal Zidan Farag M. G. Zidan

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