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Us imaging

  2. 2. SOUND  Sound-is a kind of mechanical (pressure) energy, that results from vibration of air molecules. Thus, in vacuum there is no sound, because no molecules that could undergo the vibration.  Velocity of sound in air is approximately 330 m/s.  In liquids the velocity of sound is 5-times higher, in solids there is a velocity even 20-times higher, but intensity (amplitude) is lower.  There are several requirements for sound to exist. Initially there must be a source of vibratory energy.  This energy must then be delivered to and cause a disturbance in a medium.  Any medium will do, actually, as long as it has mass and is compressible, or elastic, which most are.
  3. 3. WAVES  Wavelength () - length of one complete wave  Frequency () - # of waves that pass a point during a certain time period  hertz (Hz) = 1/s  Amplitude (A) - distance from the origin to the trough or crest
  4. 4. 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.  Typically at 2 – 20 Mhz.  The ultimate goal of any ultrasound system is to make like tissues look alike and unlike tissues look different.
  5. 5. ULTRASOUND (US) IMAGING  • US uses high frequency ultra-sound waves (i.e., not electromagnetic) to create static and real time anatomical images  • contrast results from reflections due to sound wave impedance contrast differences between tissues  • at diagnostic levels, no deleterious biological effects from US pulses  • technique similar to submarine ultrasound, a sound pulse is sent out, and the time delays of reflected "echoes" are used to create the image  • image texture results from smaller scatters (diffuse reflectors)  • boundaries result from specular reflections (large objects)
  6. 6. ULTRASOUND (US) IMAGING  by sending pulses out along different directions in a plane, slice images of anatomy are produced for viewing on monitor slice  US does not work well through lung or bone, used mainly for imag ing abdominal and reproductive organs imaging  one of the most well known US procedures is the examination of t he living fetus within the mother's womb  3D imaging scanners now available (real time, so called 4D)
  7. 7. THE ULTRASOUND MACHINE  A basic ultrasound machine has the following parts:  transducer probe - probe that sends and receives the sound waves  central processing unit (CPU) - computer that does all of the calculations and contains the electrical power supplies for itself and the transducer probe  transducer pulse controls - changes the amplitude, frequency and duration of the pulses emitted from the transducer probe  display - displays the image from the ultrasound data processed by the CPU  keyboard/cursor - inputs data and takes measurements from the display  disk storage device (hard, floppy, CD) - stores the acquired images  printer - prints the image from the displayed data
  8. 8. THE ULTRASOUND MACHINE  scanner features probes, data processing computer, and image viewing monitor  modern probes feature phased transmit/receiver arrays to electronically steer and focus the US beam
  9. 9. THE ULTRASOUND MACHINE  Ultrasound machine with various transducer probes  The transducer probe is the main part of the ultrasound machine.  The transducer probe makes the sound waves and receives the echoes.  It is, so to speak, the mouth and ears of the ultrasound machine.  The transducer probe generates and receives sound waves using a principle called the piezoelectric (pressure electricity) effect, which was discovered by Pierre and Jacques Curie in 1880.
  10. 10. PROBES/TRANSDUCERS  also called probes or transducers must be in contact with patient’s skin emits and detects sound  most common designs are linear and curved arrays
  11. 11. PROBES/TRANSDUCERS  In the probe, there are one or more quartz crystals called piezoelectric crystals.  When an electric current is applied to these crystals, they change shape rapidly.  The rapid shape changes, or vibrations, of the crystals produce sound waves that travel outward.  Conversely, when sound or pressure waves hit the crystals, they emit electrical currents.  Therefore, the same crystals can be used to send and receive sound waves.  The probe also has a sound absorbing substance to eliminate back reflections from the probe itself, and an acoustic lens to help focus the emitted sound waves.
  15. 15. THE ULTRASOUND MACHINE The CPU sends electrical currents to the transducer probe to emit sound waves, and also receives the electrical pulses from the probes that were created from the returning echoes.  The CPU does all of the calculations involved in processing the data.  Once the raw data are processed, the CPU forms the image on the monitor.  The CPU can also store the processed data and/or image on disk.  The transducer pulse controls allow the operator to set and change the frequency and duration of the ultrasound pulses, as well as the scan mode of the machine.  The commands from the operator are translated into changing electric currents that are applied to the piezoelectric crystals in the transducer probe.  The display is a computer monitor that shows the processed data from the CPU.  Displays can be black-and-white or color, depending upon the model of the ultrasound machine.
  16. 16. DIFFERENT TYPES OF ULTRASOUND  3D ultrasound imaging and Doppler ultrasound  ultrasound machines capable of three-dimensional imaging have been developed. In these machines, several two- dimensional images are acquired by moving the probes across the body surface or rotating inserted probes.  The two-dimensional scans are then combined by specialized computer software to form 3D images.
  17. 17. DIFFERENT TYPES OF ULTRASOUND  3D imaging allows you to get a better look at the organ being examined and is best used for:  Early detection of cancerous and benign tumors  examining the prostate gland for early detection of tumors  looking for masses in the colon and rectum  detecting breast lesions for possible biopsies  Visualizing a fetus to assess its development, especially for observing abnormal development of the face and limbs  Visualizing blood flow in various organs or a fetus
  18. 18. DIFFERENT TYPES OF ULTRASOUND  Doppler ultrasound has been used mostly to measure the rate of blood flow through the heart and major arteries.  Doppler ultrasound used to measure blood flow through the heart.  The direction of blood flow is shown in different colors on the screen.
  19. 19. DOPPLER ULTRASOUND MEASURES BLOOD FLOW  Using a special form of US called Doppler (just like police speed RADAR) the speed and direction of flowing blood can be measured and illustrated in color images speed  Doppler US allows Radiologists to image vasculature and detect blocked blood vessels in the neck, and elsewhere
  20. 20. DOPPLER IN ULTRASOUND  Used to evaluate and quantify blood flow  – Transducer is the sound source and receiver  – Flow is in motion relative to the transducer  Doppler produces an audible signal as well as a graphical representation of flow • The ultrasound probe emits an ultrasound wave • A stationary blood cell reflects the incoming wave with the same wavelength: there is no Doppler shift
  21. 21. DOPPLER IN ULTRASOUND  The ultrasound probe emits an ultrasound wave  A blood cell moving away from the probe reflects the incoming wave with a longer wavelength  In reality, there is actually two Doppler shifts. The first one occurs between the probe and the moving blood cell (not shown here) and the second one occurs as the red blood cell reflects the ultrasound.
  22. 22. DOPPLER IN ULTRASOUND  Now, the blood cell moves towards the probe. It reflects the incoming wave with a shorter wavelength
  25. 25. IMAGING PLANES  Transverse or Axial  Longitudinal or Saggital  Coronal
  26. 26. FREQUENCY
  28. 28. INTERACTIONS OF ULTRASOUND WITH TISSUE  • Reflection  • Transmission  • Attenuation  • Scattering
  29. 29. REFLECTION  – Occurs at a boundary between 2 adjacent tissues or media  – The amount of reflection depends on differences in acoustic impedance (z) between media  – The ultrasound image is formed from reflected echoes
  30. 30. REFLECTION Interface Reflected intensity (%) Fat / muscle 1.1 Bone / muscle 41.0 Soft tissue / lung 52.5 Soft tissue / air 99.9 Soft tissue / water 0.2
  31. 31. REFLECTION  Gel is used to remove air interfaces between the transducer and the skin.  It is difficult to image the lung and behind bones, and impossible to image across bowel gas.  There are not many interfaces in the body that are large and smooth on the scale of ultrasound wavelength (1mm or less). Examples include the diaphragm/liver, bladder wall and some large blood vessels. Interface Reflected Intensity (%) Fat/kidney 0.6 Fat/muscle 1.1 Bone/muscle 41.0 Soft tissue/air 99.9 Soft tissue/lung 52.5 Soft tissue/PZT 79.8 PZT/air 99.99
  32. 32. SCATTERING  Redirection of sound in several directions  Caused by interaction with small reflector or rough surface  Only portion of sound wave returns to transducer
  33. 33. TRANSMISSION  Not all the sound wave is reflected, some continues deeper into the body  These waves will reflect from deeper tissue structures
  34. 34. ATTENUATION  The deeper the wave travels in the body, the weaker it becomes  The amplitude of the wave decreases with increasing depth
  36. 36. IMAGE QUALITY DEPENDS ON  Acoustic Impedance  • Resolving capability of the system  – axial/lateral resolution  – spatial resolution  – contrast resolution  – temporal resolution  • Beam formation  – send and receive  • Processing Power  – ability to capture, preserve and display the information
  37. 37. ACOUSTIC IMPEDANCE • Acoustic impedance is crucial in defining how ultrasound is reflected at interfaces between different media • For perfect plane wave conditions, the specific acoustic impedance of the medium is: • Acoustic impedance can be given in units of Mrayls (short for Rayleigh) speed of sound in the medium density of the medium 𝑍 = 𝜌𝑐
  38. 38. ACOUSTIC IMPEDANCE  The product of the tissue’s density and the sound velocity within the tissue  • Amplitude of returning echo is proportional to the difference in acoustic impedance between the two tissues  • Velocities:  – Soft tissues = 1400-1600m/sec  – Bone = 4080  – Air = 330  Thus, when an ultrasound beam encounters two regions of very different acoustic impedances, the beam is reflected or absorbed  – Cannot penetrate  – Example: soft tissue – bone interface
  39. 39. ACOUSTIC IMPEDANCE  Two regions of very different acoustic impedances, the beam is reflected or absorbed
  40. 40. ACOUSTIC IMPEDANCE  Acoustic properties vary tremendously between different biological tissues Material ρ Density (kg m-3) c Speed (m s-1) Z Impedance (Mrayl) Perspex 1180 2680 3.16 Air 1.2 330 0.004 Bone 1912 4080 7.8 Water 1000 1480 1.48 Lung 400 650 0.26 Fat 952 1459 1.38 Soft Tissue 1060 1540 1.63
  41. 41. TYPES OF RESOLUTION  Axial Resolution  – specifies how close together two objects can be along the axis of the beam, yet still be detected as two separate objects  – frequency (wavelength) affects axial resolution
  42. 42. TYPES OF RESOLUTION  Lateral Resolution  – the ability to resolve two adjacent objects that are perpendicular to the beam axis as separate objects  – beamwidth affects lateral resolution
  43. 43. TYPES OF RESOLUTION  Spatial Resolution  – also called Detail Resolution  – the combination of AXIAL and LATERAL resolution  Contrast Resolution  – the ability to resolve two adjacent objects of similar intensity/reflective properties as separate objects
  44. 44. TYPES OF RESOLUTION  Temporal Resolution  – the ability to accurately locate the position of moving structures at particular instants in time  – also known as frame rate  VERY IMPORTANT IN CARDIOLOGY  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  • The frequency of a transducer is labeled in  Megahertz (MHz)
  45. 45. 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
  46. 46. HOW IS AN IMAGE FORMED ON THE MONITOR?  The amplitude of each reflected wave is represented by a dot  The position of the dot represents the depth from which the echo is received  The brightness of the dot represents the strength of the returning echo  These dots are combined to form a complete image
  47. 47. POSITION OF REFLECTED ECHOES  How does the system know the depth of the reflection?  How does the system know the depth of the reflection?  TIMING  – The system calculates how long it takes for the echo to return to the transducer  – The velocity in tissue is assumed constant at 1540m/sec
  48. 48. REFLECTED ECHOES  Strong Reflections = White dots  – Pericardium, calcified structures,diaphragm  • Weaker Reflections = Grey dots  – Myocardium, valve tissue, vessel walls,liver  • No Reflections = Black dots  – Intra-cardiac cavities,gall bladder
  49. 49. THE DOPPLER EFFECT  Apparent change in received frequency due to a relative motion between a sound source and sound receiver
  50. 50. US MODES  A mode: amplitude   B mode: brightness   Real time (frames/sec)   M mode: motion
  51. 51. A-SCAN  The A-scan presentation displays the amount of received ultrasonic energy as a function of time.  The relative amount of received energy is plotted along the vertical axis and the elapsed time (which may be related to the sound energy travel time within the material) is displayed along the horizontal axis  Applications: ophthalmology (eye length, tumors), localization of brain midline, liver cirrhosis, myocardium infarction  • Frequencies: 2-5 MHz for abdominal, cardiac, brain; 5-15 MHz for ophthalmology, pediatrics, peripheral blood vessels  • Used in ophthalmology to determine the relative distances between different regions of the eye and can be used to detect corneal detachment  – High freq is used to produce very high axial resolution  – Attenuation due to high freq is not a problem as the desired imaging depth is small
  52. 52. B-SCAN  The B-scan presentation is a profile (cross-sectional) view of the test specimen.  In the B-scan, the time-of-flight (travel time) of the sound energy is displayed along the vertical axis and the linear position of the transducer is displayed along the horizontal axis
  53. 53. M MODE: MOTION  M-mode (“motion” mode) or T-M mode (“time-motion” mode): displays time evolution vs. depth  Sequential US pulse lines are displayed adjacent to each other, allowing visualization of interface motion  M-mode is valuable for studying rapid movement, such as mitral valve leaflets
  54. 54. REAL TIME  Real-time B-mode scanners display a moving gray scale image of cross sectional anatomy
  55. 55. MAJOR USES OF ULTRASOUND  Here is a short list of some uses for ultrasound:  Obstetrics and Gynecology  Cardiology  Urology
  56. 56. OBSTETRICS AND GYNECOLOGY  measuring the size of the fetus to determine the due date  determining the position of the fetus to see if it is in the normal head down position or breech  checking the position of the placenta to see if it is improperly developing over the opening to the uterus (cervix)  seeing the number of fetuses in the uterus  checking the sex of the baby (if the genital area can be clearly seen)
  57. 57. OBSTETRICS AND GYNECOLOGY  checking the fetus's growth rate by making many measurements over time  detecting ectopic pregnancy, the life-threatening situation in which the baby is implanted in the mother's Fallopian tubes instead of in the uterus  determining whether there is an appropriate amount of amniotic fluid cushioning the baby  monitoring the baby during specialized procedures - ultrasound has been helpful in seeing and avoiding the baby during amniocentesis (sampling of the amniotic fluid with a needle for genetic testing). Years ago, doctors use to perform this procedure blindly; however, with accompanying use of ultrasound, the risks of this procedure have dropped dramatically.  seeing tumors of the ovary and breast
  58. 58. CARDIOLOGY  seeing the inside of the heart to identify abnormal structures or functions  measuring blood flow through the heart and major blood vessels
  59. 59. UROLOGY  measuring blood flow through the kidney  seeing kidney stones  detecting prostate cancer early  In addition to these areas, there is a growing use for ultrasound as a rapid imaging tool for diagnosis in emergency rooms.
  60. 60. SOME EXAMPLES  breast clinic ultrasound scanner  •common to have ultrasound at a mammography clinic  •fine detail  –require high resolution  •low contrast structures  –subtle details are important  •not too deep  –about 10 cm maximum
  61. 61. FOETUS FEET This is a 2D ultrasound scan through the foot of a foetus. You can see some of the bones of the foot. We can process the image in a computer to find the outline of the foot. This is called surface rendering. Here, the foot has been surface rendered
  63. 63. IMAGING THE HEART heart valves atrium ventricle
  64. 64. CAROTID ARTERY  Doppler imaging looks at artery  Get image and trace of blood flow  This is a healthy artery. The flow is smooth and all in the same direction, like water in a large, slow river
  65. 65. CAROTID ARTERY  This is also a carotid artery.  The flow is not all in the same direction. It is turbulent, like rapids in a river.  This is usually due to a build-up of fatty deposits in the artery
  66. 66. 4D DOPPLER ULTRASOUND  This is a complicated image of the heart of a foetus. It shows the blood moving between the ventricles and the arteries. Ventricles Atria
  67. 67. SAFETY  Question: 2D ultrasound has been used to image the foetus for about 50 years. It is thought to be completely safe and does not cause significant heating • 4D ultrasound is new, requires more energy and therefore generates more heating. We think it is safe. • Ultrasound is energy and is absorbed by tissue, causing heating • Should we use it to diagnose foetal illness? • Should we use it to make videos of healthy babies for parents?
  68. 68. WHAT ARE THE LIMITATIONS OF GENERAL ULTRASOUND IMAGING?  Ultrasound waves are disrupted by air or gas; therefore ultrasound is not an ideal imaging technique for air-filled bowel or organs obscured by the bowel.  • Large patients are more difficult to image by ultrasound because greater amounts of tissue attenuates (weakens) the sound waves as they pass deeper into the body.  • Ultrasound has difficulty penetrating bone and, therefore, can only see the outer surface of bony structures and not  what lies within (except in infants).  For visualizing internal structure of bones or certain joints, other imaging modalities such as MRI are typically used.
  69. 69. THANK YOU