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Ophthalmic ultrasound

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Ophthalmic ultrasound

  1. 1. OPHTHALMIC ULTRASOUND Dr. Yousaf Jamal 26/05/2012
  2. 2. Contents • Introduction • Instrumentation • Indications • Ultrasound Principles & physics • B-scan, UBM, A-scan & techniques • MCQs 3/15/2013 2
  3. 3. Objectives • To create awareness about basics of US • To emphasize on the importance of ophthalmic US • To create & follow standard operating protocol while performing ophthalmic US 3/15/2013 3
  4. 4. Introduction • Sound… • Noise… • Ultrasound… • What is… − Supersonic − Hypersonic − Transonic 3/15/2013 4
  5. 5. • Just for test of general knowledge • Who was the first one to use ultrasound? ? 3/15/2013 5
  6. 6. Echolocation types 3/15/2013 6
  7. 7. TYPES A – SCAN B – SCAN
  8. 8. Instrumentation • Pulsed-echo system − Transducer − Amplifier − Display monitor 3/15/2013 8
  9. 9. Transducer function ELECTRIC CURRENT TRANDUCER US WAVES SURFACE 3/15/2013 9
  10. 10. Artist: Dr. Yousaf Jamal 3/15/2013 10
  11. 11. B-Scan 3/15/2013 11
  12. 12. B-scan • Brightness mode scan • OPD procedure 3/15/2013 12
  13. 13. Indications • To examine intraocular structures with no direct visualization of posterior segment Or • To confirm or differentiate between pathologies in clear media 3/15/2013 13
  14. 14. Ultrasound physics & principles • Parts of Sound wave − Amplitude − Wavelength (crest & trough) − Frequency 3/15/2013 14
  15. 15. Frequency & its relations With resolution Image quality With penetration How much deep 3/15/2013 15
  16. 16. Frequency versus Resolution 3/15/2013 16
  17. 17. 3/15/2013 17
  18. 18. Frequency versus Penetration 3/15/2013 18
  19. 19. 3/15/2013 19
  20. 20. Medical Ultrasound frequencies • Abdominal US − 1-5 MHz • Ophthalmic US (B-scan) − 8-10 MHz • Ultrasound Biomicroscopy (UBM) − 20-50 MHz 3/15/2013 20
  21. 21. Ophthalmic US • B-scan − 10 MHz − 40 mm − 940 microns • UBM − 50 MHz − 5-10 mm − 40 microns 3/15/2013 21
  22. 22. Principles of US • Velocity • Reflectivity • Angle of incidence • Absorption 3/15/2013 22
  23. 23. Velocity • Depends upon density of medium • Distance = speed x time − Thru air − Thru aqueous & vitreous • 330 m/s • 1532 m/s − Thru water − Thru cornea & lens • 1500 m/s • 1641 m/s − Thru metal − Thru silicon oil…1000 CS • 5000 m/s • 980 m/s − Thru blood − Thru silicon oil…5000 CS • 1570 m/s • 1040 m/s 3/15/2013 23
  24. 24. Reflectivity (Echo) • Follows law of Acoustic impedance • A.I. = sound velocity x density of medium Medium Acoustic impedance (x106) kgm-2 s-1 Fat 1.38 Human tissue 1.63 Blood 1.61 Muscle 1.70 Bone 5.6-7.8 Vitreous 1.52 Aqueous 1.50 Lens 1.84 24 3/15/2013
  25. 25. • Higher gain for weaker echoes • Low gain for stronger echoes 3/15/2013 25
  26. 26. Angle of incidence Transducer 3/15/2013 26
  27. 27. Absorption • Dependent on density of medium • Closed lids should be therefore avoided but in children or open wound • Shadowing occurs bcz of it 3/15/2013 27
  28. 28. Probe positioning • Trans-ocular approach − Transverse − Longitudinal − Axial • Para-ocular approach 3/15/2013 28
  29. 29. Trans-ocular Transverse position − Most commonly used position − Shows about 6 clock hours − Used for basic screening − Detects lateral extent of pathology − Probe is placed opposite to the examined meridian 3/15/2013 29
  30. 30. − Probe marker is tangential to limbus − Mark is at nasal side when scanning 6 and 12 o’clock − For the rest…marker is superior − Limbus-to-fornix approach is used to detect from posterior pole to periphery Nasal 3/15/2013 Bridge 30
  31. 31. Longitudinal positions − Detects axial (AP) extent of pathology − Useful for retinal tears detection − Shows only 1 clock hour scan 3/15/2013 31
  32. 32. − Probe mark is perpendicular to limbus − Pt looks towards the area of interest − Optic nerve shadow is always at bottom of scan − Limbus-to-fornix approach can be used 3/15/2013 32
  33. 33. Axial positions • Probe direct over the cornea • Pt looks in primary gaze • US waves pass thru center of lens and hit optic nerve rather than macula • Lens density affects the quality of image 3/15/2013 33
  34. 34. Positions of axial scan • Horizontal − Marker always nasal • Vertical − Marker always superior • Oblique − Marker always superior Nasal Bridge 3/15/2013 34
  35. 35. Basic screening technique • Done for screening purpose in opaque media • Highest gain settings are used so weaker signals shouldn’t be missed • Any pathology found…further scanning is required 3/15/2013 35
  36. 36. Technique • 05 scans in different positions will detect gross pathology • Transverse position with limbus-to-fornix approach in… − 12, 3, 6 and 9 o'clock • Horizontal axial scan…shows optic nerve & macula in one image • Print out of each position is taken with labels 3/15/2013 36
  37. 37. If pathology found… • Clock hour noted on transverse scan • Patient is asked to look in the direction of pathology • Probe should be perpendicular • Longitudinal scan, A-scan & change of gains…adds further info of pathology 3/15/2013 37
  38. 38. Localization of macula • 04 positions for macular detection − Horizontal axial − Vertical axial − Transverse…probe placed nasally − Longitudinal…probe placed nasally 3/15/2013 38
  39. 39. Anterior segment evaluation Immersion technique High resolution technique 3/15/2013 39
  40. 40. Immersion technique • Cornea, anterior chamber & lens create noise bcz of close contact with probe • Shell or water bath is used to create space 3/15/2013 40
  41. 41. High resolution technique • Ultrasound biomicroscopy • High resolution probes are used • Scleral shell technique is used • Image quality far superior to immersion technique 3/15/2013 41
  42. 42. 3/15/2013 42
  43. 43. Common examples Vitreoretinal disorders • Most common indication for B-scan − Vitreous hemorrhage − Retinal detachment − Intraocular tumors − Intraocular foreign bodies 3/15/2013 43
  44. 44. Vitreous hemorrhage • Fresh: − Dot-like…Echolucent or low reflectivity • Old: − Membrane-like…varying reflectivity & dense inferiorly 3/15/2013 44
  45. 45. Fresh VH Old VH 3/15/2013 45
  46. 46. 3/15/2013 46
  47. 47. Retinal detachment • Rhegmatogenous R/D: − Thin, continuous membrane anteriorly separated from globe wall − Echoes are of high amplitue-100% of scleral spike − Retinal cysts, subretinal hemorrhages may be seen 3/15/2013 47
  48. 48. 3/15/2013 48
  49. 49. • Tractional R/D: − Traction membranes are seen − R/D usually doesn’t extend to ora serrata − Lower mobility in contrast to Rheg. R/D 3/15/2013 49
  50. 50. 3/15/2013 50
  51. 51. 3/15/2013 51
  52. 52. • Exudative R/D: − Smooth elevation of retina − Shifting fluid 3/15/2013 52
  53. 53. Supine position Erect position 3/15/2013 53
  54. 54. Intraocular tumors • Retinoblastoma: − Single or multiple mass lesions arising from retina − Highly refractile calcium seeding in vitreous +/- orbital shadowing − R/D may be found 3/15/2013 54
  55. 55. 3/15/2013 55
  56. 56. • Choroidal melanoma: − Solid Dome shaped or mushroom shape − High surface reflectivity with low to medium internal reflectivity − A scan flickering spikes…internal blood flow − Choroidal excavation − Exudative R/D may be present 3/15/2013 56
  57. 57. 3/15/2013 Dome shape 57
  58. 58. Collar stud shape Arrowhead in A scan shows bruch’s membrane 3/15/2013 58
  59. 59. Intraocular foreign body • Echodense signals with shadowing • Persistence of signals at low gains • Glass…reverberations • Air bubble…may simulate IOFB 3/15/2013 59
  60. 60. 3/15/2013 60
  61. 61. Dislocated lens • Signals depend on clarity of lens • Clear lens…Echolucent globular structure • Brunescent lens…highly reflective with shadowing 3/15/2013 61
  62. 62. 3/15/2013 62
  63. 63. 3/15/2013 63
  64. 64. A-Scan 3/15/2013 64
  65. 65. A - scan • Amplitude scan • 10 MHz probe • Measures axial length of eye and used for diagnostic purposes when combined with B-scan • Follows law of acoustic impedance 3/15/2013 65
  66. 66. • X-axis…time • Y-axis…amplitude • Method − Applanation technique − Immersion technique 3/15/2013 66
  67. 67. A-scan by Applanation • Cornea is anesthetized • Patients should look directly at the red fixation light • Probe placed directly on cornea • This causes a slight indentation (0.14 - 0.28 mm)
  68. 68. • Measurements vary slightly from each other due to inconsistent corneal compression • Also, will have a shallower AC depth than immersion • Takes (20) readings 3/15/2013 68
  69. 69. • At least (4) of these should be within 0.02 mm of each other, and should look like the previous slide • This way the measurements will be made to the center of the macula, giving the refractive axial length, rather than anatomical axial length
  70. 70. 3/15/2013 70
  71. 71. 3/15/2013 71
  72. 72. 3/15/2013 72
  73. 73. A- Scan facts • Average length of the eye: 23.5mm • Average A/C depth: 3.24mm (but can vary greatly) • Average lens thickness: 4.63mm ( but can vary with cataractous changes up to as thick as 7.0mm in density) • Average K’s : 43.00 – 44.00D
  74. 74. Summary • Ophthalmic US…high frequency • A & B scans mostly used • Different pathologies can be diagnosed easily when both scans are used simultaneously 3/15/2013 74
  75. 75. Take home message • Understanding of basic physics • Proper standardized technique should be applied in each case • ‘Eyes do not see what mind does not know’ • So background knowledge of pathologies and experience count the yield of US 3/15/2013 75
  76. 76. 3/15/2013 76
  77. 77. MCQs / Cases 3/15/2013 77
  78. 78. MCQs / Cases 1. A patient presents with bilateral granulomatous panuveitis with hazy fundus view due to cataract. No Hx of trauma. B scan picture is given below: 3/15/2013 78
  79. 79. A. What is the probe position? • Axial B. What do the arrow head and arrow show? • Retinal detachment • Choroidal thickening C. Probable diagnosis? • V-K-H 3/15/2013 79
  80. 80. 2. A young patient with blunt ocular trauma comes to your opd, complaining of floaters with normal visual acuity. You order B scan which is given below 3/15/2013 80
  81. 81. • Describe the picture • What is your probable diagnosis? • How you differentiate it from retinal detachment? 3/15/2013 81
  82. 82. 3. An old patient complains of decreased vision after trabeculectomy. There is large bleb but hypotonic eye. B scan shows 3/15/2013 82
  83. 83. • Describe the picture • Your probable diagnosis? 3/15/2013 83
  84. 84. 4. Describe the following A-scan Ans… Immersion technique A-scan 3/15/2013 84
  85. 85. 5. What you say about these A-scans? Ans… Artifacts By IOL (Reverberations) 3/15/2013 85
  86. 86. 6. Diagnosis? Ans…Hypotonic eye with choroidal thickening 3/15/2013 86
  87. 87. NEXT • Lecture • Dr. Bilal… corneal topography • Journal club • Dr. Maooz 3/15/2013 87

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