4. Physics of Ultrasound
• Ultrasound passes through the tissue , part of the
wave is reflected back towards the probe
• Echoes formed at -- acoustic interfaces that are
created at the junction of media with different
sound velocities.
• The greater the difference in sound velocities of
the media at the interface, the stronger is the
echo.
8. GAIN
Highest gain widest sound beam
Highest penetration Max Spike Height
(Visualisation of Weak Signals)-PVD,Vitreous Opacities
LOWEST GAIN WEAKEST PENETRATION
DECREASED SPIKE HEIGHT (RETINA , SCLERA )
9. Indications
• To detect ,measure and differentiate tumours
and follow up.
• Biometry for accurate Axial length
measurement for IOL calculation.
• Morphological characteristics – AC depth,
Corneal thickness,Lens thickness and relative
position.
10. ADVANTAGES
• Easy to use
• No Ionizing radiation
• Excellent Tissue Differentiation
• Cost Effectiveness
11. Interpretation
a: Initial spike (probe tip and cornea)
b: Anterior lens capsule
c: Posterior lens capsule
d: Retina
e: Sclera
f: Orbital fat
14. Topographic Echography
Category Point-like Membrane-like Space-occupying
Echogram Single spike Single spike or
chain of spikes
Chain of Spikes
Differential
diagnosis
Foreign body Retinal
detachment
Melanoma
Vitreous opacities Choroidal
detachment
Retinoblastoma
Vitreous
membranes
Hemangioma
Tumor surfaces Vitreous
Haemorrhage
Assessment of shape, location and elevation of lesions
28. Adjustments to UltraSound Velocity
settings
OCULAR
MEDIA
ULTRA SOUND
VELOCITY
THICKNESS CORRECTION
FACTOR
CORNEA 1641 M/SEC +0.55 +0.04 mm
AQUEOUS 1532 M/SEC
LENS 1628 + 4.72 +0.28 mm
VITREOUS 1532 M/SEC
TRUE AXIAL LENGTH = AAL 1532 + 0.04 mm + 0.28 mm
= AAL 1532 + 0.32 mm
29. COMPARISON BETWEEN CONTACT
TECHNIQUE AND IMMERSION
TECHNIQUE OF BIOMETRY
Contact technique Immersion technique
Patient is in a more comfortable
position, sitting
Patient is in a supine or reclining
position
Variability from one test to next is
present due inconsistent corneal
compression
No variability since probe does not
come in contact with cornea
Axial length measured is shorter by
an average of 0.24 mm
Axial length measured is closer to
the true value
30. Limitations and Pitfalls
• Multiple Artifacts
• Attenuation Artifacts
• Low reflective Spike
• Small tumours with False Negatives
• Intraocular foreign body
• Contact technique problem
• Misalignment