Ocular Ultrasonography

Ultrasonography: Principle, Methods & Detection of various Ocular Disease

1. ULTRASONOGRAPHY: Principle , Method & Detection of Various Ocular Disease Sarmila Acharya B. Optometry 18 th Batch

2. Presentation layout Introduction History Physics Principles & instrumentation Terminologies Indications & contraindications Methods - A-Scan - B-Scan Interpretation

3. Introduction Sound has been used clinically as an alternative to light in the diagnostic evaluation of variety of conditions Advantage of sound over light is it can pass through opaque tissue An important tool in terms of diagnosis and management Is a non-invasive investigation of choice to study eye in opaque media

4. D efinition Ultrasound Waves are acoustic waves that have frequencies greater than 20 KHz The human ear can respond to an audible frequency range, roughly 20 Hz - 20 kHz

5. History In 1956 First time: Mundt and Hughes, American Oph . A-scan (Time Amplitude ) to demonstrate various ocular disease Oksala et al in Finland Ultrasound Basic Principle (Pulse-Echo Technique) Studied reflective properties of globe In 1958 , Baum and Greenwood Developed the first two-dimensional(immersion) (B-scan) ultrasound instrument for ophthalmology In the early 1960s , Jansson and associates, in Sweden, U sed ultrasound to measure the distances between structures in the eye

6. In the 1960s , Ossoinig , an Austrian ophthalmologist F irst emphasized the importance of standardizing instrumentation and technique D eveloped standardized A-scan In 1972 , Coleman and associates made F irst commercially available immersion B -scan instrument Refined techniques for measuring axial length, AC depth, lens thickness Bronson in 1974 made contact B scan machine

7. Advantages of USG Easy to use No ionizing radiation Excellent tissue differentiation Cost effectiveness

8. Primary Uses In Ophthalmology Posterior segment evaluation in hazy media / orbit Structural integrity of eye but no functional integrity Detection and differentiation of intraocular and orbital lesions Tissue thickness measurements Location of intra ocular foreign body Ocular biometry for IOL power calculations

9. Physics Ultrasound is an acoustic wave that consists of an oscillation of particles that vibrate in the direction of the propagation Longitudinal waves Consist of alternate compression and rarefaction of molecules of the media Oscillation of particles is characterized by velocity, frequency & wavelength

10. VELOCITY Velocity=wavelength*frequency v= λ * μ Depends on the density of the media Takes 33 micro sec to come back from posterior pole to transducer About 1500 m/sec average velocity in phakic eye and 1532 m/sec in aphakic eye

11. Sound wave velocities through various media Medium Velocity (m/sec) Water 1,480 Aqueous/ Vitreous 1,532 Silicon Lens 1,486 Crystalline Lens 1,641 PMMA Lens 2,718 Silicon Oil 986 Tissue 1,550 Bone 3,500

12. Frequency Ophthalmic ultrasonography uses frequency ranging from 6 to 20 MHz High frequency provide better resolution 8 MHz in A scan 10 MHz in B scan Low frequency (1-2 MHz)used in body scanning gives better penetration

13. Wavelength W avelength is approx. 0.2mm G ood resolution of minute ocular & orbital structures f α1/ λ α resolution α 1/penetration FREQUENCY VS PENETRATION

14. Reflectivity When sound travels from one medium to another medium of different density, part of the sound is back into the probe This is known as an echo; the greater the density difference at that interface - the stronger the echo, or - the higher the reflectivity

15. In A-scan USG echoes are represented as spikes arising from a baseline The stronger the echo, the higher the spike In B-scan USG echoes of which are represented as a multitude of dots that together form an image on the screen The stronger the echo, the brighter the dot

16. Absorption Ultrasound is absorbed by every medium through which it passes The more dense the medium, the greater the amount of absorption T he density of the solid lid structure results in absorption of part of the sound wave when B-scan is performed through the closed eye thereby compromising the image of the posterior segment

17. B-scan should be performed on the open eye unless the patient is a small child or has an open wound W hen performing an USG through a dense cataract, - more of the sound is absorbed by the dense cataractous lens - less is able to pass through to the next medium - resulting in weaker echoes and images on both A-scan and B-scan The best images of the posterior segment are obtained when the probe is in contact with the sclera rather than the corneal surface, bypassing the crystalline lens or IOL implant

18. ECHOLOCATION

19. Ultrasound Echo Ultrasound wave Refraction & reflection Echo (reflected portion of wave) Produced by acoustic interfaces Created at the junction of two media that have different acoustic impedances Determined by sound velocity & density Acoustic impedance = sound velocity × density

20. Factors influencing the returning echo ( Height in A-Scan & Brightness in B-Scan ) Angle of the sound beam Interface Size and shape of interfaces

21. A ngle at which a sound beam encounters an ocular structure S ound beam directed perpendicularly to a structure maximum amount of sound will be reflected back to the probe The farther away from the ideal angle the lower the amplitude a) Angle of Incidence

22. R elative difference between various tissues that the sound beam encounters S trong or weak echoes due to the significance of tissue interface For example: - The difference in interface between vitreous and fresh blood is very slight resulting in small echo - The difference between a detached retina and the vitreous is great producing a large echo b) Interface

23. Smooth surface like retina will give strong reflection Smooth and rounded surface scatters the beam Coarse surface like ciliary body or membrane with folds tend to scatter the beam without any single strong reflection Small interface produces scattering of reflection c) Texture and Size of Interface

24. Principle Pulse- Echo System Emission of multiple short pulses of ultrasound waves with brief interval to d etect , process and display the turning Echoes ELECTRIC CURRENT TRANSDUCER US WAVE SURFACE

25. Ophthalmic USG uses high-frequency sound waves transmitted from a probe into the eye As the sound waves strike intraocular structures , they are reflected back to the probe and converted into an electric signal The signal is subsequently reconstructed as an image on a monitor

26. Emitted Sound Beam Used in A scan echography Beam has parallel border Non-focused Beam Focused Beam Used in B scan Examination takes place in a focal zone The beam is slightly diffracted

27. 1. Probe Consists of piezoelectric transducer Device which converts electrical energy to sound energy [Pulse ] and vice versa [Echo] Basic Components : Piezoelectric plate Backing layer Acoustic matching layer Acoustic lens Instrumentation

28. Piezoelectric Element E ssential part generates ultrasonic waves Coated on both sides with electrodes to which a voltage is applied Oscillation of element with repeat expansion and contraction generates a sound wave Most common: Piezoelectric ceramic ( Lead zirconate , titanate )

29. Planer crystal - Produce relatively parallel sound beam (A- Scan) Acoustic lens - Produce focused sound beam (B-scan) - Improves lateral resolution Shape of the Crystal

30. Backing L ayer (Damping material: metal powder with plastic or epoxy) L ocated behind the piezoelectric element D ampens excessive vibrations from probe Improves axial resolution Acoustic M atching L ayer L ocated in front of piezoelectric element R educes the reflections from acoustic impedance between probe and object I mproves transmission

31. (longitudinal resolution or azimuthal resolution ) R esolution in the direction parallel to the ultrasound beam The resolution at any point along the beam is the same; therefore axial resolution is not affected by depth of imaging I ncreasing the frequency of the pulse improves axial resolution Axial Resolution

32.   Ability of the system to distinguish two points in the direction perpendicular to the direction of the ultrasound beam A ffected by the width of the beam and the depth of imaging Wider beams typically diverge further in the far field and any ultrasound beam diverges at greater depth, decreasing lateral resolution L ateral resolution is best at shallow depths and worse with deeper imaging Lateral Resolution  

33. Receives returning echoes Produces electrical signal that undergoes complex processing Amplification, Compensation, Compression, Demodulation and Rejection 2. Receiver ( computer unit)

34. Gain Relative unit of Ultrasound intensity Expressed in Decibel ( db ) Adjust of gain doesn't change the amount of energy emitted by transducer but change in intensity of the returning echoes for display Higher the gain – Greater the sensitivity of the instrument in displaying weaker echoes ( i.e Vitreous opacities) Lower the gain – Weaker the depth of sound penetration Terminologies

35. Acoustic impedance mismatch - Resistance of tissue to passage of sound waves - Difference of two tissues at the interface Homogeneous (Vitreous )- Sound passes through tissue with no returning signal Heterogeneous (Orbital Fat) - Different levels of acoustic impedance mismatch within tissue

36. Anechoic : No Echo Attenuation : Sound is absorbed & scattered Shadowing : Sound is strongly reflected, nothing passes through it ( d rusen of o ptic nerve head, air) Reverberation : Collection of Reflected sounds bouncing back and forth between tissue boundaries (foreign b ody in eyeball )

37. Indications of Ocular B Scan

38. Enophthalmos Unilateral or Bilateral Exophthalmos Globe Displacement Lid Abnormalities - Ptosis , Retraction, Swelling, Ecchymosis Palpable or Visible Masses Chemosis Motility Disturbances; Diplopia Pain Indications of Orbital B Scan

39. Contraindications Obvious or suspected globe rupture Significant peri -orbital injuries Suspected clinically significant retrobulbar hematoma

40. Display M odes

41. 1. A-mode Display Time amplitude USG One dimensional acoustic display Tissue boundary - displayed graphically as function of distance along a selected axis Spacing of the spike - time taken for the sound beam to reach the given interface and its echo to reach the probe

42. Amplitude of echo on the display is proportional to the sound energy reflected at specific tissue boundary 8 MHz Probe emits unfocused beam The term “A-Scan” is often used to describe this mode, but it is not an appropriate term, since the transducer is fixed in one position during biometric procedure and is not scanning

43. Uses Axial length measurements Intraocular and intraorbital pathologies Detection Differentiation Localization

44. A-mode USG Biometry Axial length measurement To obtain the power of IOL Calculation of the total refracting power of the eye 44

45. Probe position Just touch the cornea Aligned with optical axis of eye - aimed towards the macula Corneal compression - A 0.4mm compression causes 1 D error in the calculated IOL power - Contact Vs immersion method

46. Tall echo – cornea, one peak – contact probe, double peak – immersion probe Tall echoes – ant. & post. lens capsules Tall sharply rising echo – retina Medium tall to tall echo – sclera Medium to low echoes – orbital fat A Scan Characteristics

47. 2. M-mode D isplay Motion mode or time motion mode Dilation and constriction of blood vessel Accommodation fluctuation Vascular pulsation in ocular tumor Motion of detached retina - PVD vs RD

48. 3. B-mode D isplay Intensity modulated USG B Stands for Brightness modulation Presents a cross sectional or 2D image True scanning Probe emits focused beam 10 MHz Each echo Represented as a dot on display screen Strength of the echo  brightness of the dot

49. Normal B-scan Initial line on left: probe tip Right side: fundus opposite to probe Upper part: portion of the globe where probe marker is directed Interpretation Based upon three concepts Real Time Gray Scale Three-Dimensional analysis

50. Real Time I mages can be visualized at approximately 32 frames/sec, allowing motion of the globe and vitreous to be easily detected B scan allows real time evaluation of any ocular pathology Real time ultrasonic information frequently aids in vitreoretinal surgery

51. Gray Scale D isplays the returning echoes as a 2D image Strong echoes are displayed brightly at high gain and remain visible even when the gain is reduced Weaker echoes are seen as lighter shades of gray that disappear when the gain is reduced Comparing echo strengths during examination is the basis for qualitative tissue analysis

52. Three-Dimensional Analysis Developing a mental 3D image or anatomical map from multiple 2D B-scan images is the most difficult concept to master This is essential, because it provides the vital architectural information that is the basis for B-scan diagnosis Especially important in the preoperative evaluation of complex retinal detachments and intraocular or orbital tumors

53. Examination Techniques For The Globe-B scan Probe Orientations

54. Axial Probe directly over cornea and directed axially Pt. fixating in primary gaze Posterior lens surface and optic nerve head are placed in the centre of the echogram Optic nerve head is used as an echographic centre section Easiest to perform

55. Mainly two varieties of axial scans H orizontal axial scan M arker at 3 0’clock RE and 9 0’clock LE Macular region is placed just below the optic disk Vertical axial scan M arker at 12 0’clock Macula is not seen in this scan Oblique axial scan Marker always superior S ections of all other clock hours can be performed

56. Points to be noted H igher decibel gain levels are needed to show structures at the posterior segment Because of scatter and strong sound attenuation created by the lens - In pseudophakia strong artifacts created by the lens implant hampers the adequate visualization Significance Easy orientation and demonstration of posterior pole lesions and attachments of membranes to optic nerve head

57. Transverse EYE – looking in the direction of observer’s interest PROBE –parallel to limbus and placed on the opposite conjunctival surface Probe Marker superior (if examining nasal or temporal) or nasal(if examining superior or inferior ) 6 clock hrs examined at a time Limbus -to-fornix approach is used to detect from posterior pole to periphery Quadrant examination Gives lateral extent of the lesion

58. The clock hr which the marker faces is always at the top of the scan The area of interest in a properly done transverse scan is always at the centre of the right side of scan Nasal Bridge

59. Longitudinal EYE - looking in the direction of observer’s interest PROBE – perpendicular to the limbus and placed on the opposite conjunctival surface PROBE MARKER - directed towards the limbus Optic nerve shadow always at the bottom on the right side 1 clock hr per time examination Determines the antero -posterior (axial) extent of the lesion Significance - Best for peripheral tears and documentation of macula Nasal Bridge

60. Examination Procedure Positioning the patient Topical anesthesia Techniques Contact Technique Probe is placed directly on the globe Immersion Technique Methylcellulose - a coupling medium (B-Scan)

61. Sources of Error in contact technique Corneal compression (Shorter Axial length) 1mm error in Axial length – 2.5 to 3.0 Ds error in IOL Power Misalignment of sound beam Source of error in i mmersion technique Small air bubbles in the fluid gives falsely long AL measurement

62. Localization Of Macula

63. Horizontal Probe placed on the corneal vertex Marker nasally (as with a horizontal axial scan) The probe should be aimed straight ahead to center the macula The macula will be centered to the right of the echogram, with the posterior lens surface centered to the left

64. Vertical Probe placed on the corneal vertex Marker is in the 12-o'clock position The nerve will not appear in these scans because this is a vertical (instead of horizontal) slice of the macula

65. Transverse Patient fixes slightly temporally Probe on nasal sclera with marker at 12’o clock Optic nerve as the centre of imaged clock macula is at 9’o clock in right eye and 3’o clock in left Bypasses the lens

66. Longitudinal Probe held on sclera, bypassing crystalline lens Optic nerve is seen at the bottom with macula just above

67. Orbital Screening Orbit highly reflective owing to heterogeneity of orbital fat which produce large acoustic interface B scan- bright zone A scan- highly packed tall spike fading from left to right T hree major portions O rbital soft tissue assessment E xtraocular muscle evaluation R etrobulbar optic nerve examination

68. Two Approaches T ransocula r (through the globe) - For lesions located within the posterior & mid aspects of the orbital cavity P araocular (next to the globe) - For lesions located within the lids or anterior orbit

69. Three methods: Axial, transverse & longitudinal Transverse Longitudinal

70. A-SCAN B-SCAN AMPLITUDE MODULATION SCAN . BRIGHTNESS MODULATION SCAN. FREQUENCY OF ULTRASOUND IS 8 MHERTZ. FREQUENCY OF ULTRASOUND IS 10 MHERTZ. ONE DIMENTIONAL IMAGE OF SPIKES OF VARYING AMPLITUDES ALONG A BASELINE. TWO DIMENTIONAL IMAGING OF SERIES OF DOTS AND LINES THAT FORM THE ECOGRAM. EMITS UNFOCOUSED BEAM. EMITS FOCUSED BEAM. PROVIDES QUANTITATIVE INFORMATIONS. PROVIDES TOPOGRAPHIC INFORMATIONS. IS A BASIS OF OCULAR BIOMETRY. ALLOWS REAL TIME EVALUATION OF ANY OCULAR PATHOLOGY.

71. Anterior Segment Evaluation

72. Immersion Technique E xamining the anterior segment with a standard 10 MHz contact probe can be accomplished only with the use of a scleral shell This shifts the anterior segment to the right and into the area of focus of the sound beam, improving resolution of anterior segment pathology The shell is filled with methylcellulose or some other viscous solution to a meniscus, avoiding air bubbles within the shell

73. The probe is placed on top of the shell This produces an echolucent area on the left side of the echogram corresponding to the shell and methylcellulose  Diagnostic A-scan also can be performed through the shell, directly over the lesion, for tissue differentiation.

74. Immersion B-scan image of an iris melanoma extending into the ciliary body Modified immersion B-scan. Immersion

75. Immersion/normal AC, anterior chamber; C,cornea ; F, fluid in scleral shell; I, iris; L, lens. Lens/cataract . AC, anterior chamber; arrow, lenticular opacities ; C, cornea; F, fluid; L, lens.

76. High Resolution Technique Ultrasound biomicroscopy Probes ranges from 20MHz to 50 MHz, with penetration depths of about 10 mm to 5 mm respectively The zone of focus is quite small Scleral shell technique is used Image quality far superior to immersion technique High-resolution B-scan images of an iris melanoma

77. OCT vs UBM

78. Normal USG Characteristics Lens : Oval highly reflective structure Vitreous : Echolucent Retina , Choroid , Sclera : Each is single highly reflective structure Optic Nerve : Wedge shaped acoustic void in r etrobulbar region E xtra ocular muscles : Echolucent to low reflective fusiform structures - The SR- LPS complex is the thickest, IR is the thinnest - IO is generally not seen except in pathological conditions Orbit : Highly reflective due to orbital fat

79. Normal B Scan

80. Topographic Echography P oint-like e.g . fresh V.H M embrane-like e.g . R.D M ass-like e.g . choroidal melanoma Opacities produce dots or short lines Membranous lesions produce an echogenic line

81. Interpretations And Clinical Examples

82. Fresh: Dot-like: Echolucent or low reflectivity Old: Membrane-like: Varying reflectivity & dense inferiorly Fresh VH Old VH

83. Multiple, densely packed, homogeneously distributed echodense dots of medium to high reflectivity with a clear preretinal space suggestive of Asteroid Hyalosis AH is highly ecogenic,they are still visible when the gain setting is reduced upto 60dB whereas VH which usually disappears by 60 dB

84. PVD at high gain (90dB) PVD (arrowheads) and retina (arrow) PVD at low gain (39 dB ) As the gain is reduced, the PVD (arrowheads) disappears in contrast to the retina (arrow), which remains visible even at low gain settings

85. Posterior Vitreous Detachment

86. KISSING CHOROIDALS Smooth, dome shaped, thick, less mobile with double high spike suggestive of Choroidal Detachment

87. PVD RD CD Topographic Smooth, with or without disc insertion Smooth or folded with disc insertion Smooth without disc insertion Quantitative < 100 % spike 100 % spike Double 100 % spike Kinetic Marked Moderate None

88. Differentiating Features of RD Rhegmatogenous RD Tractional RD Exudative RD Convex elevation , Undulating folds, PVR Concave elevation,Fibrous tractional band Convex elevation, Shifting fluid changes Configuration with postural change

89. Total retinal detachment

90. PHPV: Longitudinal B-scan demonstrates taunt, thickened vitreous band adherent to the slightly elevated optic disc

91. Globular/Oval echoic structure in p osterior vitreous signifying a Dislocated Lens

92. Retinoblastoma : Transverse B-scans demonstrate a large, dome- shaped lesion with marked internal calcification

93. Extremely thin IOFBs (< 100 mm ) can be differentiated, localized Metallic IOFB s are echo dense—even at low gain settings—and often produce shadowing of intraocular structures and the orbit

94. Transverse B-scan shows marked vitreous opacities and membrane formation consistent with endophthalmitis

95. Panophthalmitis

96. Papilloedema Transverse B-scan shows marked elevation of the optic disc Optic Disc Drusen Longitudinal B-scan shows highly calcified, round drusen at the optic nerve head with shadowing

97. T sign collection of fluid in subtenon space suggestive of Posterior Scleritis High reflective thickening of retinochoroid layer and sclera

98. Posterior Staphyloma in High Myopia Shallow excavation of posterior pole Smooth edges

99. Anophthalmos Microphthalmos with cyst

100. Phthisis

101. Conclusion Knowledge about the anatomy, pathology and ultrasound signs together with systemic and ocular approach can provide useful diagnostic information.

102. References Clinical Procedures in Optometry by J. D. Barlett , J. B. Eskridge & J. F. Amos Ophthalmic Ultrasound: A Diagnostic Atlas by C. W. DiBernardo & E. F. Greenberg Internet Previous presentations Thank You!!