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