b scan

B – SCAN ULTRASONOGRAPHY

Dr. Parameshwar Rao Dr. Haridev Dr. Ashok Dr. Siva Kumar.W (PG)

INTRODUCTION

B-scan ultrasonography is an important adjuvant for the clinical assessment of various ocular and orbital diseases.

This presentation is designed to describe the principles, techniques, and indications for echographic examination, as well as to provide a general understanding of echographic characteristics of various ocular pathologies.

B- SCAN is a two dimensional imaging system which utilises high freq sound waves ranging from 8-10 MHz.

B stands for bright echoes.

B - SCAN

It was first introduced by Baum and Greenwood in 1958

First commercially available B scan is developed by Coleman et al in seventies

The importance of the instrument and technique is emphasised by Karl Ossoinig

Physics: It is an acoustic wave that consists of particles

within the medium Frequencies used in diagnostic ophthalmic

ultrasound are in the range of 8-10 MHz These high frequencies produce shorter wave

lengths which allow good resolution of minute ocular and orbital structures

Multiple short pulses are produced with a brief interval that allows the returning echos to be detected, processed and displayed.

The basis of the echo system is piezoelectric element which is a quartz or ceramic crystal located near the face of the probe

sound waves from transmitter

Echoes are received by receiver

Amplification

Oscilloscope screen

Target tissue

Low frequency: orbital tissue

Medium frequency : ( 7 – 10 mhz ) Retinal , vitreous , optic nerve

High frequency : ( 30 – 50 mhz) : ant chamber upto 5 mm

Types of frequency

IMPEDENCE : The difference between the strength of the returning echoes from tissues with abrupt changes in acoustic properties.

GAIN : Increase in gain is associated with increase in tissue penetration and sensitivity but decrease in resolution.

HIGH FREQUENCIES - LOW PENETRATION BUT GOOD RESOLUTION.

(abdominal US-1-2MHz )

INCREASE IN GAIN - INCREASE IN TISSUE PENETRATION AND SENSITIVITY – DECREASE IN RESOLUTION.

INCREASE IN GAIN - INCREASE IN TISSUE PENETRATION AND SENSITIVITY – DECREASE IN RESOLUTION.

DISPLAY MODES: A SCAN/ B SCAN / BOTH

TIME GAIN COMPENSATION: to enhance echoes from deeper structures.

AMPLIFICATION

Three types are commonly used. 1. Linear : Can show minor differences in

echos . Limited range .(A SCAN) 2. Logarithmic : Wider range. Minor

differences cannot be seen.(B SCAN) 3. S Curve : Combines the benefits of both

the above.(in the standardized A SCAN for tissue differentiation)

The probe has ‘ Dampening material’ which limits the vibrations of the crystal thus shortening the pulse

Shape of the crystal is useful in determining the character of the sound beam

The electrical signal produced by returning echos is of very weak radio frequency signal

This signal undergoes complex processing before displayed on the screen

Adjust the amplification of the signal displayed on the screen, this is referred as ‘gain’ or ‘sensitivity’ of the instrument

The higher the gain level the greater the sensitivity of the instrument

It produces Two dimensional section It uses both horizontal and vertical

dimensions of screen to indicate configuration and location

A section of tissues is examined by an oscillating transducer

Instrumentation:

An echo is represented by a dot on the screen

The probe is filled inside with a fluid , a crystal oscillates sending sound waves out in a fan like array called Sector scan

Image documentation modes :

They are of 2 types stationary/static moving/dynamic

The images may be saved in different methods

1. Polaroid photographs2. 35 mm photo3. Ink prints4. Thermal prints5. Videotapes

Anterior segment:1. Opaque ocular media (i.e. corneal opacities) Pupillary membrane Dislocation / Subluxation lens Cataract / after cataract Posterior capsular tear Pupillary size / reaction2. Clear ocular media Diagnosis of iris and ciliary body tumors

Indications:

Posterior segment:1. Opaque ocular media Vitreous haemorrhage Vitreous exudation Retinal detachment (type / extent) Posterior vitreous detachment (extent) Intraocular foreign body (size/ site/ type)2. Clear ocular media Tumour (size/ site/ post treatment follow up) Retinal detachment (solid / exudative) Optic disc anomalies 3. ocular trauma

The patient is either reclining on a chair or lying on a couch. The probe can be placed directly over the conjunctiva or the lids.

Examination technique:

Probe positions

Transverse : most commonLateral extent, 6 clock hours

Longitudinal : radial ,1 clock hrs, AP diameter in Retinal tumors and tears

Axial : lesion in relation to lens and optic nerve .

Transverse scan

EYE anaesthetised. 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 and inferior).

6 clock hrs examined at a time.

The clock hour 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.

If examining nasal area -12 – 6 clock hrs temporal - 6- 12 clock hrs superior - 9 -3 clock hrs inferior - 3- 9 clock hrs

NASAL AREA TEMPORAL AREA

SUPERIOR AREA INFERIOR AREA

Longitudinal scan EYE Anaesthetised. 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

or towards the area of interest regardless of the clock hour to be examined.

Optic nerve shadow always at the bottom on the right side.

1 clock hour.

Axial scan

EYE anaesthetised. EYE – in primary gaze PROBE – centered on the cornea .

LENS: Oval highly reflective structure with intralesional echoes with none to highly reflective echoes.

VITREOUS is echolucent.

RETINA, CHOROID AND SCLERA: Are seen as a single reflective high structure.

OPTIC NERVE : Wedge shaped acoustic void in the retrobulbar region.

EXTRA 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.

Always examine the other eye before coming to a conclusion regarding the lesion .

Opacities produce dots or short lines Membranous lesions produce an

echogenic line

Anterior segment evaluaton

Immersion technique

High resolution technique

ULTRASONOGRAPHIC CHARACTERISTICS

VITREOUS HAEMORRHAGE

To detect extent, density, location and cause

Fresh haemorrhage shows dots or lines

Old haemorrhage the dots gets brighter

POSTERIOR VITREOUS DETACHMENT

Posterior vitreous detachment:The detached posterior vitreous is seen as membranous lesion with no/some attachments to the optic disc

POSTERIOR VITREOUS DETACHMENT

Mobility of PVD is more than RD.

The spike of RD is more than PVD.

PVD becomes more prominent in higher gain settings

RETINAL DETACHMENTThe detachment produces a bright continuous, folded appearance with insertion into the disc and ora serrata.

It is to determine the configuration of the detachment as shallow, flat or bullous

EXUDATIVE RETINAL DETACHMENT

RHEGMATOGENOUS RD

RHEGMATOGENOUS RETINAL DETACHMENT

CLOSED FUNNEL RD WITH RETINAL CYST

CLOSED FUNNEL RD WITH RETINAL CYST

APPEARS AS RD BUT IT IS A PVD.CLUES: NON UNIFORM THICNESS OF MEMBRANE VERY THIN ATTACHMENT TO THE DISC.

RETINAL TEAR

RETINAL TEAR WITH FREE SUPERIOR END .THE MEMBRANE IS CONVOLUTED ON ITSELF.POSTERIOR VITREOUS IS ATTACHED AT THE SUPERIOR END OF THE TEAR.

ASTEROID HYALOSIS

Asteroid hyalosis:

Calcium soaps produce bright point like echos

Differentiation, extrascleral extension, size, assessing tumour growth or regression.

Measurement of tumour dimensions such as elevation and base.

Help in distinguishing solid from cystic lesions.

TUMOURS

RETINOBLASTOMA

Size of the tumour

Shows irregular configuration

Calcification shows high internal reflectivity

Collar button or mushroom shape.Large tumours shows acoustic hallowing

MELANOMA

TUMOURS - OSTEOMA

CHOROIDAL DETACHMENT KISSING CHOROIDS

Smooth, thick, dome shaped membrane in the periphery with very little after movement

360 degree detachment shows a pathognomonic “scalloped appearance

CHOROIDAL DETACHMENT KISSING CHOROIDS

CHOROIDAL DETACHMENT

Intraocular foreign bodies:

Localisation and extent of intraocular damage Metallic foreign bodies produce very high

bright signal Shadow present posterior to the foreign body Wood, glass and organic material produce

specific echographic finding

INTRA OCULAR FOREIGN BODY

CUPPED DISC

MACULAR EDEMA

PERSISTENT HYALOIDAL VESSEL

POSTERIOR STAPHYLOMA

LACRIMAL GLAND TUMOUR

NANOPHTHALMOS

RETINOSCHSIS

Retinoschisis: Smooth, thin dome shaped membrane that

doesn’t insert on optic disc

Diabetic retinopathy: Nature and extent of the disease To monitor progress of the disease Aids in pre – vitrectomy evaluation

ENDOPHTHLMITIS

CYSTICERCOSIS WITH RETINAL TEAR

COLOBOMA OF THE CHOROID AND DISC

PERSISTENT FETAL VASCULATURE

RETINOPATHY OF PREMATUIRITY

POSTERIORLY DISLOCATED LENS

INTRA OCULAR AIR / GAS

SILICON OIL FILLED VITREOUS

Sclera:

Thickening in hyperopic and nanopthalmic eyes

Infolding in severe hypotony or a ruptured globe

SCLERITIS

Normal muscles show less echo dense than

surrounding orbital soft tissue

Documenting the gross size and contour of a muscle

’

Evaluation of extraocular muscles:

Nodular posterior scleritis with fluid in the Tenon capsule. Positive T-sign at the insertion of the optic nerve.

Evaluation of optic nerve

General topography, relationship to structures, optic disc anomalies and alteration in contour of the globe

The subarachnoid space surrounding optic nerve appears as echolucent cresentric or circle around the nerve called ‘Doughnut sign’

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

Useful in the following conditions: Abnormal size of eye Abnormal shape of eye Congenital abnormalities Vitreous alterations Retinal detachments (type/ location) Ocular and orbital tumours Trauma

ULTRASONOGRAPHY IN PAEDIATRIC PATIENTS:

Artefacts:

Insufficient fluid coupling ( i.e., lack of methyl cellulose) cause entrapment of air between the probe and eye leading to display of bright echos which represent multiple signals

PITFALLS

REVERBERATION ARTEFACTS

ANGLE OF INCIDENCE ARTEFACT

PITFALLS

Tumours: Mass may be missed is less than 0.75

mm False –ve results in case of small

lesion and fibrotic tissue False + ve in subretinal haemorrhage

and metastatic tumour with massive infiltration

Vitroretinal disease: In RD unable to detect actual tear In vitrectomsed eyes vitreous

haemorrhage is diffuse leading to echolucency

Silicon oil decrease in sound velocity

PITFALLS

PITFALLS

Intraocular foreign body:Small Intraocular foreign body of < 1mm may be missed.Orbit:

An orbital mass can be detected or differentiated if > 3 mm in size if anterior and > 5 mm in posterior orbits.

B- SCAN REPORTING

Describe the features and correlate with clinical findings.

Dont jump to diagnosis. Always examine both in sitting and

erect postures in case of RD. Examine other eye also. Try to take the best picture possible.

FOUR TRANSVERSE SCANS

ONE HORIZONTAL AXIAL SCAN TO EVALUATE THE POSTERIOR POLE ARE SUFFICIENT.

THANK YOU