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Emergency us physics and instrumentation

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Emergency us physics and instrumentation

  1. 1. Emergency Ultrasound Physics & Instrumentation : Basic & Technical Facts For The Beginner Nik Ahmad Shaiffudin Nik Him Emergency Physician Hospital Sultanah Nur Zahirah drnikahmad@gmail.com
  2. 2. Presentation Outline 1. Introduction to basic ultrasound physics 2. Ultrasound Modes 3. Artifacts 4. Probes 5. Terminology 6. Your machine functions 7. Summary
  3. 3. WHAT DO WE UNDERSTAND ABOUT ULTRASOUND PHYSICS? Introduction…… 1. Basic Ultrasound physics
  4. 4. Bats navigate using ultrasound
  5. 5. Bats make high-pitched chirps which are too high for humans to hear. This is called ultrasound Like normal sound, ultrasound echoes off objects The bat hears the echoes and works out what caused them • Dolphins also navigate with ultrasound • Submarines use a similar method called sonar We can also use ultrasound to look inside the body…
  6. 6. Sound…? Sound is a mechanical, longitudinal wave that travels in a straight line Sound requires a medium through which to travel
  7. 7. Cycle  1 Cycle = 1 repetitive periodic oscillation Cycle
  8. 8. frequency 1 cycle in 1 second = 1Hz 1 second = 1 Hertz
  9. 9. What is Ultrasound? Ultrasound is a mechanical, longitudinal wave with a frequency exceeding the upper limit of human hearing, which is 20,000 Hz or 20 kHz.  Medical Ultrasound 2MHz to 16MHz
  10. 10. to the audible frequency range ~ 20Hz - 20kHzThe human ear can only respond to the audible frequency range ~ 20Hz - 20kHz
  11. 11. ULTRASOUND – How is it produced? Produced by passing an electrical current through a piezoelectrical (material that expands and contracts with current) crystal….. “Pulse Echo” principle Naturally occurring - quartz Synthetic - Lead zirconate titanate (PZT)
  12. 12. In ultrasound, the following events happen: 1. The ultrasound machine transmits high-frequency (1 to 12 megahertz) sound pulses into the body using a probe. 2. The sound waves travel into the body and hit a boundary between tissues (e.g. between fluid and soft tissue, soft tissue and bone). 3. Some of the sound waves reflect back to the probe, while some travel on further until they reach another boundary and then reflect back to the probe . 4. The reflected waves are detected by the probe and relayed to the machine.
  13. 13. 5. The machine calculates the distance from the probe to the tissue or organ (boundaries) using the speed of sound in tissue (1540 m/s) and the time of the each echo's return (usually on the order of millionths of a second). 6. The machine displays the distances and intensities of the echoes on the screen, forming a two dimensional image.
  14. 14. Velocity in tissue Medium Velocity of US (m/sec) Air 330 Fat 1450 Water 1480 Soft tissue 1540 Kidney 1560 Blood 1570 Muscle 1580 Bone 4080
  15. 15. Ultrasound Production  Transducer produces ultrasound pulses  These elements convert electrical energy into a mechanical ultrasound wave  Reflected echoes return to the scanhead which converts the ultrasound wave into an electrical signal
  16. 16. Piezoelectric Crystals  The thickness of the crystal determines the frequency of the scanhead Low Frequency 3 MHz High Frequency 10 MHz
  17. 17. What determines how far ultrasound waves can travel?  The FREQUENCY of the transducer  The HIGHER the frequency, the LESS it can penetrate  The LOWER the frequency, the DEEPER it can penetrate  Attenuation is directly related to frequency
  18. 18. Frequency vs. Resolution  The frequency also affects the QUALITY of the ultrasound image  The HIGHER the frequency, the BETTER the resolution  The LOWER the frequency, the LESS the resolution  A 12 MHz transducer has very good resolution, but cannot penetrate very deep into the body  A 3 MHz transducer can penetrate deep into the body, but the resolution is not as good as the 12 MHz Low Frequency 3 MHz High Frequency 12 MHz
  19. 19. 2. Ultrasound Modes  A-mode: A-mode (amplitude mode) is the simplest type of ultrasound. A single transducer scans a line through the body with the echoes plotted on screen as a function of depth. 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 or 2D mode: In B-mode (brightness mode) ultrasound, a linear array of transducers simultaneously scans a plane through the body that can be viewed as a two-dimensional image on screen. More commonly known as 2D mode now.  C-mode: A C-mode image is formed in a plane normal to a B-mode image. A gate that selects data from a specific depth from an A-mode line is used; then the transducer is moved in the 2D plane to sample the entire region at this fixed depth. When the transducer traverses the area in a spiral, an area of 100 cm2 can be scanned in around 10 seconds.[10]  M-mode: In M-mode (motion mode) ultrasound, pulses are emitted in quick succession – each time, either an A- mode or B-mode image is taken. Over time, this is analogous to recording a video in ultrasound. As the organ boundaries that produce reflections move relative to the probe, this can be used to determine the velocity of specific organ structures.  Doppler mode: This mode makes use of the Doppler effect in measuring and visualizing blood flow  Color Doppler: Velocity information is presented as a color-coded overlay on top of a B-mode image  Continuous Doppler: Doppler information is sampled along a line through the body, and all velocities detected at each time point is presented (on a time line)  Pulsed wave (PW) Doppler: Doppler information is sampled from only a small sample volume (defined in 2D image), and presented on a timeline  Duplex: a common name for the simultaneous presentation of 2D and (usually) PW Doppler information. (Using modern ultrasound machines color Doppler is almost always also used, hence the alternative name Triplex.)  Pulse inversion mode: In this mode two successive pulses with opposite sign are emitted and then subtracted from each other. This implies that any linearly responding constituent will disappear while gases with non-linear compressibility stands out.  Harmonic mode: In this mode a deep penetrating fundamental frequency is emitted into the body and a harmonic overtone is detected. In this way depth penetration can be gained with improved lateral resolution
  20. 20. 2. Ultrasound Modes
  21. 21. M-mode: In M-mode (motion mode) ultrasound, pulses are emitted in quick succession – each time, either an A-mode or B-mode image is taken. Over time, this is analogous to recording a video in ultrasound.
  22. 22. Doppler mode: This mode makes use of the Doppler effect in measuring and visualizing blood flow
  23. 23.  Shadowing  Posterior enhancement  Edge shadowing  Comet tail  Mirror Imaging 3. Artifacts Attenuation artifact Miscellaneous artifact  Ring down  Side lobe
  24. 24. Echogenic : When ultrasound waves pass through solids (bones – stone) all waves are reflected and appears as white color with posterior shadow . Shadowing
  25. 25. It means the reflection of waves , and this depends on the material which is penetrated by US. • Echo free : When ultrasound waves pass through fluids ( ascites- simple cyst- blood vessels) no reflection occurs and these areas appears as black areas with posterior enhancement . Posterior Enhancement & Mirrored Side Posterior Enhancement, Side Lobe and Mirror Image
  26. 26. Mirror-image artifacts Feldman M K et al. Radiographics 2009;29:1179-1189 US beam bounces between structure and deeper strong reflector e.g. diaphragm. This means probe receives signals as if from same object on other side of reflector.
  27. 27. Edge artifact Edge Artifact
  28. 28. Reverberations artifacts Ultrasound echoes being repeatedly reflected between two highly reflective interfaces
  29. 29. Comet Tail
  30. 30. Ring-down Feldman M K et al. Radiographics 2009;29:1179-1189 Ring of bubbles with fluid trapped centrally. Fluid vibrations detected as strong signal and displayed as line behind true source.
  31. 31. 4. Probes  Linear  Large convex  Sector  Intracavity ( Microconvex)
  32. 32. Probe types Sector Linear array Curved array
  33. 33. 5. Common Terminology Image Interpretation  Anechoic / Echolucent - Complete absent of returning sound ( area is black)  Hypoechoic – Structures has very few echoes and appears darker than surrounding tissue  Hyperechoic/ Echogenic – Structure appears brighter than surrounding tissues
  34. 34.  No Reflections = Black dots  Fluid within a cyst, urine, blood Anechoic / Echolucent - Complete absent of returning sound ( area is black)
  35. 35. Hypoechoic – Structures has very few echoes and appears darker than surrounding tissue Weaker Reflections = Grey dots  Most solid organs,  thick fluid – „isoechoic‟
  36. 36. Hyperechoic/ Echogenic – Structure appears brighter than surrounding tissues  Strong Reflections = White dots Diaphragm, tendons, bone
  37. 37. • Acoustic impedance (AI) is dependent on the density of the material in which sound is propagated - the greater the impedance the denser the material. • Reflections comes from the interface of different AI‟s • greater of the AI = more signal reflected • works both ways (send and receive directions) Medium 1 Medium 2 Medium 3 Transducer Interactions of Ultrasound with Tissue
  38. 38. Sound is attenuated by tissue More tissue to penetrate = more attenuation of signal Compensate by adjusting gain based on depth near field / far field AKA: TGC
  39. 39. Gain controls receiver gain only does NOT change power output Increase gain = brighter Decrease gain = darker
  40. 40. Use of Gain GainMin Max Near field Far field Attenuation Time-gain compensation (TGC) ProcessedOriginal
  41. 41. Balanced Gain  Gain settings are important to obtaining adequate images. balanced bad near field bad far field
  42. 42. Goal of an Ultrasound System The ultimate goal of any ultrasound system is to make like tissues look the same and unlike tissues look different
  43. 43. Liver metastases
  44. 44. Epidermis Loose connective tissue and subcutaneous fat is hypoechoic Muscle interface Muscle fibres interface Bone Skin, subcutaneous tissue
  45. 45. Transverse scan – Internal Jugular Vein and Common Carotid Artery
  46. 46.  Image Acquisition / Probe position  Tranverse plane/ axial plane/ cross section separates superior from inferior  Sagittal plane – Oriented perpendicular to the ground separating left from right.  Coronal plane – Frontal plane, separates anterior from posterior  Oblique Plane – The probe is oriented neither parallel to nor at the right angles from coronal, sagittal or tranverse plane.
  47. 47. 6. Your machine function
  48. 48. Your machine function
  49. 49. Summary  Know your anatomy – Skin, muscle, tendons, nerves and vessels  Recognise normal appearances – compare sides!  Resolution determines image clarity  Frequency & wavelength are inversely proportional  Attenuation & frequency are inversely related  Display mode chosen determines how image is registered  Diagnostic Medical Ultrasound is safe!
  50. 50. Conclusions 1. Imaging tool – Must have the knowledge to understand how the image is formed 2. Dynamic technique 3. Acquisition and interpretation dependant upon the skills of the operator.

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