Physics us2010

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Physics of ultrasoud for MFM fellow training

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Physics us2010

  1. 1. MFM cmu 2010 Physics & Principles Basic Ultrasound 20 October 2010
  2. 2. MFM cmu 2010 Physics & Principles 1. Ultrasound pulses A. are poorly transmitted by liquids B. are poorly transmitted by air gaps C. are partially reflected at interfaces between two liquid media D. are partially transmitted at interfaces between two solid media
  3. 3. MFM cmu 2010 Physics & Principles 2. The Fraunhofer zone is the A. Image plane B. Image focus C. Near field D. Far field
  4. 4. MFM cmu 2010 Physics & Principles 3. Diagnostic ultrasound intensity is often measured in A. mW/cm2 B. grays C. decibels D. Hertz
  5. 5. MFM cmu 2010 Physics & Principles 4. The propagation speed of sound through soft tissue is A. 1450 m/s B. 1650 m/s C. 1540 m/s D. 1230 m/s
  6. 6. MFM cmu 2010 Physics & Principles 5. Axial resolution can be improved by A. damping B. increased spatial pulse length C. focusing D. increased bandwidth
  7. 7. MFM cmu 2010 Physics & Principles 6. Lateral resolution can be improved by A. focusing B. increased beam width C. decreased bandwidth D. increased line density
  8. 8. MFM cmu 2010 Physics & Principles 7. The axial resolution of a transducer is primarily determined by A. sptial pulse length B. the transducer diameter C. the acoustic impedance of tissue D. focusing
  9. 9. MFM cmu 2010 Physics & Principles 8. Crystals for ultrasound transducers are composed of A. sodium iodide B. quartz C. barium titanate D. lead zirconate titanate
  10. 10. MFM cmu 2010 Physics & Principles 9. The TGC control compensates for A. focusing B. machine instability C. scan line density D. attenuation
  11. 11. MFM cmu 2010 Physics & Principles 10. Phased array transducers A. have elements which emit ultrasound independently B. may be used to alter the beam direction C. are used only on real-time scanners D. have a variable frequency
  12. 12. MFM cmu 2010 Physics & Principles  Audible: 20 to 20,000 Hz  Ultrasound: 1 to 30 MHz  Hertz: 1 cycle per second  Megahertz: 1,000,000 Hz
  13. 13. MFM cmu 2010 Physics & Principles Diagnostic Imaging 0 20 Hz 20 kHz 1 MHz 30 MHz Infrared Audible NDT Sound Sound Sound Spectra
  14. 14. MFM cmu 2010 Physics & Principles Time (1 sec.) Sound Wave Wavelength = Distance a wave travels is a single cycle As frequency increase wavelength become smaller Amplitude (dB) Frequency = number of times wave is repeated per second
  15. 15. MFM cmu 2010 Physics & Principles การเดินทางผ่านของเสียง  คลื่นเสียงไม่สามารถเดินทางในสูญญา กาศได้  ก็าซเป็นตัวนำาพาคลื่นเสียงที่ไม่ดี  คลื่นเสียงจะเดินทางได้ดีขึ้นในตัวกลาง ที่หนาแน่นขึ้น Gas Liquid Solid
  16. 16. MFM cmu 2010 Physics & Principles - Mechanical vibration or wave - With frequencies above the range of human ear which is greater than 20 kHz. For medical diagnosis, typically ranging from 1 to 30 MHz. The Nature of Ultrasound Compressive Wave
  17. 17. MFM cmu 2010 Physics & Principles Velocity - Dependent on the medium and temperature - Relatively constant 1540 m/s in human body. Velocity = Frequency * Wavelength ( λ )
  18. 18. MFM cmu 2010 Physics & Principles Approximate velocities of sound in human medium Medium Velocity (m/s) Blood 1570 Brain 1540 Fat 1450 Kidney 1560 Muscle 1590 Distilled Water 1540
  19. 19. MFM cmu 2010 Physics & Principles General Overview Sea
  20. 20. MFM cmu 2010 Physics & Principles General Overview
  21. 21. MFM cmu 2010 Physics & Principles Amplitude Dept / Time
  22. 22. MFM cmu 2010 Physics & Principles Electric impulse Sound pulse
  23. 23. MFM cmu 2010 Physics & Principles
  24. 24. MFM cmu 2010 Physics & Principles Matching Layer Transducer Crystal Tissue Impedance Matching Transducer Case -To transmit as much power as possible from transducer to the tissue.
  25. 25. MFM cmu 2010 Physics & Principles Acoustic Output  Acoustic Output increases or decreases the system power during transmit. Always adjust gain before adjusting acoustic output.  Acoustic Output optimizes the image quality thereby minimizing exposure time to the patient while maximizing the penetration and echo return.
  26. 26. MFM cmu 2010 Physics & Principles Ultrasound Beam
  27. 27. MFM cmu 2010 Physics & Principles
  28. 28. MFM cmu 2010 Physics & Principles
  29. 29. MFM cmu 2010 Physics & Principles
  30. 30. MFM cmu 2010 Physics & Principles
  31. 31. MFM cmu 2010 Physics & Principles
  32. 32. MFM cmu 2010 Physics & Principles Attenuation Attenuation of ultrasound wave occurs when it is propagating through the medium. Loss of propagating energy will be in the form of heat absorbed by the tissue, approximately 1 dB/cm/MHz, or caused by wavefront dispersion or wave scattering.
  33. 33. MFM cmu 2010 Physics & Principles
  34. 34. MFM cmu 2010 Physics & Principles Skin Level Near Gain Delay Far Gain Knee Slope Rate 1cm /1Sec 2cm /2Sec 3cm /3Sec 4cm /4Sec DGC or TGC or STC
  35. 35. MFM cmu 2010 Physics & Principles DGC or TGC or STC
  36. 36. MFM cmu 2010 Physics & Principles Spatial Resolution
  37. 37. MFM cmu 2010 Physics & Principles Spatial Resolution
  38. 38. MFM cmu 2010 Physics & Principles Lateral Resolution
  39. 39. MFM cmu 2010 Physics & Principles Lateral resolution is a function of the number of scan lines, transducer elements and probe type and size. Lateral Resolution
  40. 40. MFM cmu 2010 Physics & Principles Beam Profile & Focus Focal Zone Transducer Electronic Focusing
  41. 41. MFM cmu 2010 Physics & Principles Axial Resolution
  42. 42. MFM cmu 2010 Physics & Principles Spatial Resolution Frequency Low High Resolution Better Penetration Better
  43. 43. MFM cmu 2010 Physics & Principles Transducer Frequency
  44. 44. MFM cmu 2010 Physics & Principles Contrast Resolution • Contrast resolution is the ability to distinguish subtle differences in similar tissues. • Grayscale maps depicting 256 shades of gray are used to display contrast.
  45. 45. MFM cmu 2010 Physics & Principles Dynamic Range and Contrast 256 dBNarrow Wide Which photo gives a better representation of the baby? Which photo gives enough sensitivity to detect a tear on the baby’s face?
  46. 46. MFM cmu 2010 Physics & Principles Dynamic Range  Dynamic Range controls how echo intensities are converted to shades of gray, thereby creating a range of gray scale that can be adjusted.  Dynamic Range is useful for optimizing tissue texture to differentiate between echo levels that are close together.
  47. 47. MFM cmu 2010 Physics & Principles
  48. 48. MFM cmu 2010 Physics & Principles Temporal Resolution Fast frame rates = Temporal Resolution = Anatomic Accuracy
  49. 49. MFM cmu 2010 Physics & Principles Frame Rates Depend on: PRF, Depth, Line density, Sector width Frame Rates = PRF / Line number per frame 25 Frame Per second Real Time
  50. 50. MFM cmu 2010 Physics & Principles Depth or Field of View organ 15 cm FOV 5 10 15 organ 10 cm FOV 5 10 Display all of the relevant area appropriately. Zoom can help
  51. 51. MFM cmu 2010 Physics & Principles 1. Ultrasound pulses A. are poorly transmitted by liquids B. are poorly transmitted by air gaps C. are partially reflected at interfaces between two liquid media D. are partially transmitted at interfaces between two solid media
  52. 52. MFM cmu 2010 Physics & Principles 2. The Fraunhofer zone is the A. Image plane B. Image focus C. Near field D. Far field
  53. 53. MFM cmu 2010 Physics & Principles 3. Diagnostic ultrasound intensity is often measured in A. mW/cm2 B. grays C. decibels D. Hertz
  54. 54. MFM cmu 2010 Physics & Principles 4. The propagation speed of sound through soft tissue is A. 1450 m/s B. 1650 m/s C. 1540 m/s D. 1230 m/s
  55. 55. MFM cmu 2010 Physics & Principles 5. Axial resolution can be improved by A. damping B. increased spatial pulse length C. focusing D. increased bandwidth
  56. 56. MFM cmu 2010 Physics & Principles 6. Lateral resolution can be improved by A. focusing B. increased beam width C. decreased bandwidth D. increased line density
  57. 57. MFM cmu 2010 Physics & Principles 7. The axial resolution of a transducer is primarily determined by A. sptial pulse length B. the transducer diameter C. the acoustic impedance of tissue D. focusing
  58. 58. MFM cmu 2010 Physics & Principles 8. Crystals for ultrasound transducers are composed of A. sodium iodide B. quartz C. barium titanate D. lead zirconate titanate
  59. 59. MFM cmu 2010 Physics & Principles 9. The TGC control compensates for A. focusing B. machine instability C. scan line density D. attenuation
  60. 60. MFM cmu 2010 Physics & Principles 10. Phased array transducers A. have elements which emit ultrasound independently B. may be used to alter the beam direction C. are used only on real-time scanners D. have a variable frequency

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