b scan
TRANSCRIPT
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