ULTRASONOGRAPHY

(B-SCAN)

VASIUR RAHMANDr R. P. Centre, AIIMS

HISTORY

1793: Lazzaro Spallanzani (Italy) discovered that bats orient

themselves with the help of sound whistles while flying in

darkness. This was the basis of modern ultrasound application

Bats use ultrasounds to navigate in the darkness

INTRODUCTION

first used in the field of ophthalmology

by MUNDT and HUGHES.

Oksala et al report the sound velocities

in the various compartment of eye.

Contact Bscan was introduced by

Bronson and it being portable, become a

part of everyday use in ophthalmology.

physics

Ultrasound

○ Longitudinal wave

○ Alternating compressions and rarefactions of

molecules

>20khz (20,000 oscillations /sec) Ultrasound

Similar to sound waves

Reflected

Refracted

Low

frequency (1 to 5 MHz)

Longer

wavelength

Lower Resolution (abdominal and pelvic structure)

Abdominal ultrasound Ophthalmic ultrasound

High frequency (8 to 10 MHz)

Short wavelength (< 0.2mm)

Higher Resolution of minute ocular and orbital structure

By karl ossoing

Sound Wave Velocities

Medium Velocity (m/sec)

Water 1,480

Aqueous / vitreous 1,532

Soft tissue 1,550

Crystalline lens 1,641

Bone 3,500

based on physical principles of pulse-echo

technology

Echoes are generated at adjoining tissue

interfaces greater the difference, the

stronger the echo

having frequency greater than 20khz for

imaging the posterior segment-8 to 25 MHz

for imaging the anterior segment-50 MHz

Rule-greater the frequency lesser will be

penetration

Probe thick, with a mark

emit focussed sound beam at frequency 10mhz

mark on the Bscan probe indicates beam orientation-area towards which mark is directed appears at the top of the echogram on display screen

ULTRASOUND PRINCIPLES AND PHYSICS

Angle of incidence:

Perpendicularity to the

area of interest always

should be maintained to

achieve the strongest

echo.

A scan (amplitude) -

single dimensional

display of spikes through

the eye.

The spikes on A scan

represent amplitude /

reflectivity of an echo

A-Scan

Transverse scan

Longitudinal

Axial

B-scan Probe Orientations

Transverse scan

Movement of transducer is parallel to limbus

Produces a circumferential slice through several

meridians

Lateral extent of a lesion

Transverse Scan

Longitudinal scan Transducer - perpendicular to

the limbus

Probe marker - towards centre of cornea

Antero posterior extent of the lesion

Optic disc and posterior aspect of the globe –lower portion of screen

Best – demonstrating the insertion of membranes to optic disc

Axial scan

Probe centered on the cornea

Easiest to understand (displays lens & optic nerve)

Documenting lesions & membranes in relation to optic disc

Evaluates macular region

Hinder resolution of posterior portion of globe (Sound attenuation

and refraction )

AXIAL SCAN

CLOCK HOUR

PROBE POSITION

CLOCK AREA

SCREENED

3-limbus 9-posterior

3-equator 9-equator

3-firnix 9-anterior

6-limbus 12-posterior

6-equator 12-equator

6-fornix 12-anterior

Why we need B-scan..????

Evaluation of intraocular details

Evaluation of retrochoroidal lesions

especially tumors

Examination of retrobulbar soft tissue

masses

Identification, localization and

measurement of foreign bodies

Assessment of damage in trauma cases

PROCEDURE

mostly the Bscanning is done

transpalpebrum

Lesions must place at the centre of scanning

beam

Lowest possible decibel gain consistent with

the maintenance of adequate intensity

should be used

Measured in decibels

Higher gain –

Display weaker echos like

vitreous opacities

Lower gain

Stronger echoes (retina and

sclera)

Better resolution

Gain

Dot like lesions – vitreous floaters, vitreous hge, vitreous exudates.

Membranous lesions – vitreous membranes, PVD, RD

Mass lesions – choroidal or retinal tumors

Echotexture of Lesion

VITREOUS HAEMORRHAGE

To detect extent, density,

location and cause

Fresh haemorrhage shows

dots or lines

Old haemorrhage the dots

gets brighter

CHOROIDAL DETACHMENT KISSING CHOROIDS

POSTERIORLY DISLOCATED LENS

INTRAOCULAR FOREIGN BODY

SILICON OIL FILLED VITREOUS

Complete PVD

Choroidal melanoma

Endophthalmitis

Intra ocular foreign body

Non invasive

Performed in an office setting

Does not expose to radiation

High resolution echography provides

reliable and accurate assessment

Ideal for follow up of lesion

Advantages:

Disadvantages

High frequency sounds waves have limited penetration

THANK YOU