a scan ultrasonography
TRANSCRIPT
A Scan Ultrasonography
Presenter : Dr Samuel PonrajModerator : Dr PRR
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.
Instrumentation
• Pulser • Reciever• Display System
A Scan Mode
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 )
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.
ADVANTAGES
• Easy to use• No Ionizing radiation• Excellent Tissue Differentiation• Cost Effectiveness
Interpretation
a: Initial spike (probe tip and cornea)b: Anterior lens capsulec: Posterior lens capsuled: Retinae: Scleraf: Orbital fat
Topographic Echography
Category Point-like Membrane-like Space-occupyingEchogram Single spike Single spike or
chain of spikesChain 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
Quantitative Echography
1. Internal Structure Reflectivity (Size & Arrangement of interfaces)- Regular low – Melanoma- Regular High – Haemangioma- Irregular – Metastatic Carcinoma
2. SOUND ATTENUATION Scattering,absorption or reflectivity of Sound energy
Steeper the Kappa angle
Greater the Sound attenuation(Bone, Foreign Body)
KINETIC ECHOGRAPHYKinetic Echography
(Low gain)
Spontaneous movements(Stationary eye ) – vascular lesion
After movements{ Following Cessation of Eye Movements }
- PVD,RD
Common Ocular Pathologies
VITREOUS FLOATER
VITREOUS HAEMORRHAGE
ENDOPHTHALMITIS
POSTERIOR VITREOUS DETACHMENT
RETINAL DETACHMENT
Intra Ocular Lens
CHOROIDAL MELANOMA
CHOROIDAL HEMANGIOMA
METASTATIC CARCINOMA
RETINOBLASTOMA
CHOROIDAL DETACHMENT
DISLOCATED LENS INTO VITREOUS
APHAKIC EYE
CONTACT TECHNIQUE
IMMERSION TECHNIQUE
Immersion B-scan/vector A-scan technique
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
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
Limitations and Pitfalls
• Multiple Artifacts• Attenuation Artifacts• Low reflective Spike• Small tumours with False Negatives• Intraocular foreign body• Contact technique problem• Misalignment
MISALIGNMENT
SILICON OIL GLOBE