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Ophthalmic ultrasound

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  • 1. OPHTHALMIC ULTRASOUND Dr. Yousaf Jamal 26/05/2012
  • 2. Contents • Introduction • Instrumentation • Indications • Ultrasound Principles & physics • B-scan, UBM, A-scan & techniques • MCQs3/15/2013 2
  • 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 US3/15/2013 3
  • 4. Introduction • Sound… • Noise… • Ultrasound… • What is… − Supersonic − Hypersonic − Transonic3/15/2013 4
  • 5. • Just for test of general knowledge • Who was the first one to use ultrasound? ?3/15/2013 5
  • 6. Echolocation types3/15/2013 6
  • 7. TYPES A – SCAN B – SCAN
  • 8. Instrumentation • Pulsed-echo system − Transducer − Amplifier − Display monitor3/15/2013 8
  • 9. Transducer function ELECTRIC CURRENT TRANDUCER US WAVES SURFACE3/15/2013 9
  • 10. Artist: Dr. Yousaf Jamal3/15/2013 10
  • 11. B-Scan3/15/2013 11
  • 12. B-scan • Brightness mode scan • OPD procedure3/15/2013 12
  • 13. Indications • To examine intraocular structures with no direct visualization of posterior segment Or • To confirm or differentiate between pathologies in clear media3/15/2013 13
  • 14. Ultrasound physics & principles • Parts of Sound wave − Amplitude − Wavelength (crest & trough) − Frequency3/15/2013 14
  • 15. Frequency & its relations With resolution Image quality With penetration How much deep3/15/2013 15
  • 16. Frequency versus Resolution3/15/2013 16
  • 17. 3/15/2013 17
  • 18. Frequency versus Penetration3/15/2013 18
  • 19. 3/15/2013 19
  • 20. Medical Ultrasound frequencies • Abdominal US − 1-5 MHz • Ophthalmic US (B-scan) − 8-10 MHz • Ultrasound Biomicroscopy (UBM) − 20-50 MHz3/15/2013 20
  • 21. Ophthalmic US • B-scan − 10 MHz − 40 mm − 940 microns • UBM − 50 MHz − 5-10 mm − 40 microns3/15/2013 21
  • 22. Principles of US • Velocity • Reflectivity • Angle of incidence • Absorption3/15/2013 22
  • 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. 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 1.84 243/15/2013
  • 25. • Higher gain for weaker echoes • Low gain for stronger echoes3/15/2013 25
  • 26. Angle of incidence Transducer3/15/2013 26
  • 27. Absorption • Dependent on density of medium • Closed lids should be therefore avoided but in children or open wound • Shadowing occurs bcz of it3/15/2013 27
  • 28. Probe positioning • Trans-ocular approach − Transverse − Longitudinal − Axial • Para-ocular approach3/15/2013 28
  • 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 meridian3/15/2013 29
  • 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 Nasal3/15/2013 Bridge 30
  • 31. Longitudinal positions − Detects axial (AP) extent of pathology − Useful for retinal tears detection − Shows only 1 clock hour scan3/15/2013 31
  • 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 used3/15/2013 32
  • 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 image3/15/2013 33
  • 34. Positions of axial scan • Horizontal − Marker always nasal • Vertical − Marker always superior • Oblique − Marker always superior Nasal Bridge3/15/2013 34
  • 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 required3/15/2013 35
  • 36. Technique • 05 scans in different positions will detect gross pathology • Transverse position with limbus-to-fornix approach in… − 12, 3, 6 and 9 oclock • Horizontal axial scan…shows optic nerve & macula in one image • Print out of each position is taken with labels3/15/2013 36
  • 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 pathology3/15/2013 37
  • 38. Localization of macula • 04 positions for macular detection − Horizontal axial − Vertical axial − Transverse…probe placed nasally − Longitudinal…probe placed nasally3/15/2013 38
  • 39. Anterior segment evaluation Immersion technique High resolution technique3/15/2013 39
  • 40. Immersion technique • Cornea, anterior chamber & lens create noise bcz of close contact with probe • Shell or water bath is used to create space3/15/2013 40
  • 41. High resolution technique • Ultrasound biomicroscopy • High resolution probes are used • Scleral shell technique is used • Image quality far superior to immersion technique3/15/2013 41
  • 42. 3/15/2013 42
  • 43. Common examples Vitreoretinal disorders • Most common indication for B-scan − Vitreous hemorrhage − Retinal detachment − Intraocular tumors − Intraocular foreign bodies3/15/2013 43
  • 44. Vitreous hemorrhage • Fresh: − Dot-like…Echolucent or low reflectivity • Old: − Membrane-like…varying reflectivity & dense inferiorly3/15/2013 44
  • 45. Fresh VH Old VH3/15/2013 45
  • 46. 3/15/2013 46
  • 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 seen3/15/2013 47
  • 48. 3/15/2013 48
  • 49. • Tractional R/D: − Traction membranes are seen − R/D usually doesn’t extend to ora serrata − Lower mobility in contrast to Rheg. R/D3/15/2013 49
  • 50. 3/15/2013 50
  • 51. 3/15/2013 51
  • 52. • Exudative R/D: − Smooth elevation of retina − Shifting fluid3/15/2013 52
  • 53. Supine position Erect position3/15/2013 53
  • 54. Intraocular tumors • Retinoblastoma: − Single or multiple mass lesions arising from retina − Highly refractile calcium seeding in vitreous +/- orbital shadowing − R/D may be found3/15/2013 54
  • 55. 3/15/2013 55
  • 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 present3/15/2013 56
  • 57. 3/15/2013 Dome shape 57
  • 58. Collar stud shape Arrowhead in A scan shows bruch’s membrane3/15/2013 58
  • 59. Intraocular foreign body • Echodense signals with shadowing • Persistence of signals at low gains • Glass…reverberations • Air bubble…may simulate IOFB3/15/2013 59
  • 60. 3/15/2013 60
  • 61. Dislocated lens • Signals depend on clarity of lens • Clear lens…Echolucent globular structure • Brunescent lens…highly reflective with shadowing3/15/2013 61
  • 62. 3/15/2013 62
  • 63. 3/15/2013 63
  • 64. A-Scan3/15/2013 64
  • 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 impedance3/15/2013 65
  • 66. • X-axis…time • Y-axis…amplitude • Method − Applanation technique − Immersion technique3/15/2013 66
  • 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. • Measurements vary slightly from each other due to inconsistent corneal compression • Also, will have a shallower AC depth than immersion • Takes (20) readings3/15/2013 68
  • 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. 3/15/2013 70
  • 71. 3/15/2013 71
  • 72. 3/15/2013 72
  • 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. Summary • Ophthalmic US…high frequency • A & B scans mostly used • Different pathologies can be diagnosed easily when both scans are used simultaneously3/15/2013 74
  • 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 US3/15/2013 75
  • 76. 3/15/2013 76
  • 77. MCQs / Cases3/15/2013 77
  • 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. 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-H3/15/2013 79
  • 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 below3/15/2013 80
  • 81. • Describe the picture • What is your probable diagnosis? • How you differentiate it from retinal detachment?3/15/2013 81
  • 82. 3. An old patient complains of decreased vision after trabeculectomy. There is large bleb but hypotonic eye. B scan shows3/15/2013 82
  • 83. • Describe the picture • Your probable diagnosis?3/15/2013 83
  • 84. 4. Describe the following A-scan Ans… Immersion technique A-scan3/15/2013 84
  • 85. 5. What you say about these A-scans? Ans… Artifacts By IOL (Reverberations)3/15/2013 85
  • 86. 6. Diagnosis?Ans…Hypotonic eye with choroidal thickening 3/15/2013 86
  • 87. NEXT • Lecture • Dr. Bilal… corneal topography • Journal club • Dr. Maooz3/15/2013 87