USG B SCAN

ULTRASOUND OF EYE AND ORBIT DR PAWAN N JARWAL THIRD YEAR RESIDENT DOCTOR DEPARTMENT OF OPHTHALMOLOGY S.S.G. HOSPITAL VADODARA

CONTENTS1)HISTORY2)INTRODUCTION3) PRINCIPAL OF ULTRASOUND4)INSTRUMENTATION5)EXAMINATION TECHNIQUE6)INDICATION7)ADVANTAGES 8) A SCAN9)B SCAN10)MCQ

HISTORYUltrasound was first used in ocular diagnosis in 1956 by Hughes et al who employed the A- Scan Baum and greenwood developed the B scan in 1950The importance of the instrument and technique is emphasised by Karl ossoinig

INTRODUCTIONUltrasound is an acoustic wave that lies between light ray and x ray portion of electromagnetic radiation. By definition, ultra sound waves have a frequency greater than 20khz.Parts of Sound waveAmplitude(height)Wavelength (crest & trough)Frequency (no of compete cycle per sec.) Resolution PenetrationWavelength =1\frequency

Penetration = How much deep

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In standard ophthalmic ultrasound, frequencies are in range of 8-10 mhz. This high frequencies produces short wave lengths which allow precise resolution of smaller ocular structures.In contrast , the abdominal ultrasound typically use lower frequencies in the range of 1-5 MHz, which produce longer wavelengths that permits deeper penetration in tissues of abdomen . By this, resolution of structures is decreased, but resolution is less important issue in abdomen because the structures in the abdomen are much larger than eye.1)Abdominal US1-5 MHz2)Ophthalmic US (B-scan)8-10 MHz3)Ultrasound Bio microscopy (UBM)20-50 MHz

PRINCIPLE OF ULTRASOUND

1}VELOCITY The velocity of the ultrasound wave is primarily dependent on the medium through which it passes. for example water, is very compressible ; sound wave transmitted through water at a slower velocity than through more solid media, which are less compressible.As a result sound wave travel faster through a solid lens than it does through liquid vitreous.

2}ECHOEchoes are produced by acoustic interface created at the junction of two media that have different acoustic impedance.

The acoustic impedance of a medium is determined by its velocity and density(A.I=S.V*D).

The greater the difference in the acoustic impedance of the two media , the stronger the reflection of sound waves(i.e.echo)

because of this reason ,strong reflections occur at the interface between retina and vitreous ,which is essentially water When adjoining tissue interface have relatively small difference in acoustic impedance ,(e.g. vitreous gel and mild vitreous haemorrhage or clumped intravitreal white blood cells),weak reflections are seen.

3}Angle of incidenceThe acoustic wave directed by an ultrasound transducer is referred as sound beam. The angle at which the sound beam strikes an interface is an important factor in the strength of the returning echo.

4}ACOUSTIC INTERFACEThe size ,shape, and the smoothness of an interface also play important roles in the character of the returning echo.1) if incidence is perpendicular to a smooth straight surface i.e retina =mirror like reflection ,maxi echo2)if interface is convex(i.e. a collar button shaped choroid melanoma)=weaker echo3) if interface is not smooth but irregular i.e. ciliary body=scattered echo

5}ABSORPTIONUltra sound is gradually absorbed and converted to heat as it passes through a medium , although the amount of heat generated by diagnostic ultrasound is extremely low and has no harmful effects on tissue.

6}REFRACTIONRefraction occurs when a sound beam is directed obliquely to an interface that demarcates two media of different sound velocities. Refraction usually undesirable in ultrasound because it ,producing artefacts.

7}Pulse echo systemThe basis of pulse echo system is the piezoelectric element ,typically a quartz or ceramic crystal. The piezoelectric crystal ,located near the face of the probe , undergoes a mechanical vibration .This vibration cause a longitudinal ultrasonic wave to be propagated through the medium (i.e ocular and orbital tissue).A pause of several microseconds then occur ,which allow time to transducer to receive returning echoes.Returning echoes creates another mechanical vibration as it strike the crystal which in turn produce a electrical signal that is transmitted to receiver and display on screen .

Another important component of ultra sound probe or transducer is the damping material that is attached to back of crystal. This material consisting, metal powder mixed with plastic or epoxy, which serves to limit the vibrations of crystal that produce the pulse of ultrasonic energy , by this way there is shortening of pulse occur.

This factor ,in addition to the frequency relates directly to the axial resolution of the ultrasound system

Axial resolution is the minimum distance between two interface (echo surface)along the direction of sound beam that can be displayed. The shorter the pulse better the axial resolution

The shape of crystal is an important factor in determining the character of the sound wave.A planar crystal is results in relatively parallel sound beam whereas a concave crystal can focus the sound beam. Focusing increase both axial and lateral resolution of ultrasound instrument

8}Signal ProcessingThe electrical signal produced by returning echo is initially received by ultrasound instrument as a very weak radio frequency signal .This signal is then undergoes complex processing that can include amplification ,compression, demodulation ,and rejection.Three types of amplifications are commonly used. 1. Linear : Can show minor differences in echoes . 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)

9} GAINAll ultrasound system allow examiner to adjust the amplification of echo signals, displayed on instrument screen.It is important to realise that adjusting to gain does not change the amount of energy emitted from the transducer; it change only the intensity of returning echo that is displayed on the screen.The higher the gain level, the greater the ability of instrument to display the weaker echoes(i.e. vitreous opacities).conversely ,as the gain is lowered ,only the stronger echoes will continue to be displayed (i.e retina and sclera)

INSTRUMENTATIONAn ultrasound unit is composed of 4 basic element;pulser,receiver and display screen, all contained within the same unit and connected to the transducer located at the tip of the probe, which act as sending and receiving device.

The pulsar produce electric pulses that excite the piezoelectric quartz of the transducer probe generating sound waves.The returning echoes are received by transducer and transformed into electric signal, which are processed in receiver and displayed on screen as echogramThe examiner can adjust the amplitude of the echo signal displayed by changing the gain or sensitivity of instrument. The display may be in one of the two modes

A modeA scan ( A stand for amplitude) is a one dimensional ,time -amplitude display . In the vertical dimension ,the height of the displayed spike indicate the amplitude or strength of the echo. These spikes represent reflectivity ,location, and size of anatomic structure.The horizontal baseline represent the distance and depends upon the time required for the sound beam to reach a given interface and for its echo to return to the probe.

B modeB scan ( B stands for brightness modulation)differ from A scan in that it produce a two-dimensional ,cross-sectional display of globe and orbit.The image is displayed in variable shades of grey colour ,and the shades depends on the echo strength. Strong echoes appear white, and weaker reflections are seen as grey.Example of strong echoes include retinal tissue , sclera and calcification.weaker echoes are noted from clotted vitreous cells.B scan images may be more easily interpreted than A scan because the microscopic and gross cross-section evaluation of ocular abnormalities is often similar to the B scan image.

Vector A scan displayA scan display is provided with some B scan units which allows a simultaneous display of both mode.

Examination technique1} TOPOGRAPHIC ECHOGRAPHY

It entails the assessment of shape ,location, and elevation or extension of lesionThe pathological finding are classified in to one of the three categories1)Point like2)Membraneous3)Sace occuyping

2}QUNANTITATIVE ECHOGRAPHY

1. reflectivity; of a lesion evaluated by observing the height of the spike on A scan and the signal brightness on B scan. 2. the internal structure refers to the degree of variation in the histologic architecture with in a mass lesion. ## Regular internal structure means homogeneous architecture and is noted by minimal or no variation in the height of spikes on the A scan and a uniform appearance of echoes on the B scan. ##in contrast, an irregular internal structure means heterogeneous architecture and characterized by variation in the echo appearance3. sound attenuation occur when acoustic wave is scattered ,reflected ,or absorbed by a tissue and is noted by a decrease in the strength of echoes . Decreased signal strength , void posterior to the lesion that is referred to as shadowing.

3}KINETIC ECHOGRAPHY

Aftermovement is determined by observing the motion of lesion echoes after cessation of eye movements. The rapid movement of a vitreous haemorrhage is distinguished from the slower, undulating movement of retina in an acute rhegmatogenous retinal detachment

EXAMINATION METHOD:

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.

Scan method Transverse : most common Lateral extent, 6 clock hours

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

Axial : lesion in relation to lens and optic nerve .

PROBE MARKER It acts the orientation point and corresponds to the upper portion of echogram.

Transverse scanEYE anaesthetized.EYE looking in the direction of observers interestPROBE parallel to limbus and placed on the opposite conjunctival surfacePROBE MARKER superior (if examining nasal or temporal) or nasal(if examining superior and inferior).6 clock hrs examined at a time.

Longitudinal scan

PROBE perpendicular to the limbus and placed on the opposite conjunctival surface.PROBE MARKER- directed towards the limbus or towards the area of interest .1 clock hour.

Axial scan

PROBE FOR Horizontal AXIAL SCANMarker always nasal FOR Vertical AXIAL SCANMarker always superior FOR Oblique AXIAL SCANMarker always superior

Nasal Bridge

Image Documentation Modes :

They are of 2 types stationary/static moving/dynamic

The images may be saved in different methods

Polaroid photographs35 mm photoInk printsThermal printsVideotapes

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

INDICATIONS OF USG

Posterior segment:

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

Biometry1.Axial length2.A C depth3.Lens thickness

Non invasivePerformed in an office settingDoes not expose to radiationHigh resolution echography provides reliable and accurate assessmentIdeal for follow up of lesion

Advantages:

Anterior segment evaluationImmersion Technique is accomplished by inserting a small scleral shell between the lids, filling the shell with methylcellulose solution, and placing the probe in the solution

Posterior segmentContact Method, in which the probe is placed directly on the globe , is used to evaluate the posterior segment. For contact technique each quadrants of the globe is scanned systematically.

A scanAmplitude scan10 MHz probeMeasures axial length of eye and used for diagnostic purposes when combined with B-scanFollows law of acoustic impedance

X-axistimeY-axisamplitudeMethodApplanation techniqueImmersion technique

A-scan by ApplanationCornea is anesthetizedPatients should look directly at the red fixation lightProbe placed directly on cornea This causes a slight indentation (0.14 - 0.28 mm)Measurements vary slightly from each other due to inconsistent corneal compressionAlso, will have a shallower AC depth than immersionTakes (9-10) readings

At least (4) of these should be within 0.02 mm of each other, This way the measurements will be made to the center of the macula, giving the refractive axial length, rather than anatomical axial lengthAverage length of the eye: 23.5mmAverage A/C depth: 3.24mm (but can vary greatly)Average Ks : 43.00 44.00D

Characterstic of a good scan areCorneal echo is seen as a tall single peakAqueous chamber does not produce any echoAnte. And post. lens capsule produce tall echoesVitreous cavity produce few or no echoesRetina produce tall, sharply rising echoes with no staircase at the originOrbital fat produce medium to low echoes

Interpretation Initial spike represents vibrations at the probe tip and has no clinical significance.Cornea and lens surface produce tall spikes.Base line represent the vitreous cavity which is characterized by absence of echo spikes in normal conditions. The presence of blip in this area needs evaluation to rule out a pathological condition.Retinal spike is straight ,high rising echo spike perpendicular to baseline.Choroidal spike seen between retinal and scleral spike Scleral spikes are difficult to differentiate from choroidal spikes.

Vitreous floaters

Vit hemorrhage with PVD

A)PVD with sub vitreal bloodB) R D- SINGLE,STEEPLY RISING, HIGH AND THICK SPIKE

R D with subretinal hemorrage

B- SCAN

FOUR TRANSVERSE SCANS

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

NORMAL GLOBE REVEALS TWO ECHOGRAPHIC AREAS, SEPERATED BY AN ECHO FREE AREA.

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LENS: Oval highly reflective structure .

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.

ORBIT -highly reflective due to orbital fat.

Opacities produce dots or short lines

Membranous lesions produce an echogenic line

Description of a lesionLocation in relation to easly demonstrable landmarks e.g optic disc or lensExtent both anteroposterior and lateralDimension in case of tumour or solid lesionShape and configuration-point like ,membrane like or a mass lesionInternal reflectivity-whether echolucent , low , medium or highly refractileStructure-solid or cystic,regular or irregularDegree of sound attenution ,if anyMobility

DIAGNOSISDescribe the features and correlate it 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

ASTEROID HYALOSIS( seen as bright round sinals)

Asteroid hyalosis:

Calcium soaps produce bright point like echos

VITREOUS HAEMORRHAGE( seen as small white echoes)

To detect extent, density, location and cause

Fresh haemorrhage shows dots or lines

Old haemorrhage the dots gets brighter

POSTERIOR VITREOUS DETACHMENT

The detached posterior vitreous is seen as undulating membranous lesion in front of retinochoroidal layer 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

ENDOPHTHLMITIS

IMAGE SHOWS PLENTY OF INTRAGEL ECHOES (ARROWHEAD)ALONG WITH A THICK LAYER OF ECHOES ALONG GLOBE WALL (ARROW)

RETINAL DETACHMENT

B scan showing a high reflective smooth membrane attached to the O.D

THE CONFIGURATION IS CONVEX AND ECHOES ARE UNIFORMLY BRIGHT

d

EXUDATIVE RETINAL DETACHMENT two b scan images demonstrating shifting fluid in an eye .1st imae in supine position shows a total detachment with equal elevation of retina above and below the optic disc . 2nd image taken in erect position shows that fluid has shifted inferiorly and the superior retina apper attached

CLOSED FUNNEL RD WITH RETINAL CYST axial b scan shows long standing RD and retinal cyst formation(arrow head)

CHOROIDAL DETACHMENT ( smooth ,dome shaped,membranes structure not inserting to O.D)

THERE IS NO ECHOES BEHIND MEMBRANE CONFIRMING THAT IT IS A SEROUS CHOROIDAL DETACHMENT

RETINOBLASTOMA ( irregular echogenic mass in vitreous cavity)

Size of the tumour

Shows irregular configuration

Calcification shows high internal reflectivity

Collar button or mushroom shape.Large tumours shows acoustic hallowing CHOROIDAL MELANOMA

OSTEOMA

POSTERIOR STAPHYLOMA

SHALLOW EXCAVATION OF POSTIRIOR POLE

COLOBOMA OF THE CHOROID AND DISC

EXCAVATION OF POSTERIOR POLE BUT IN CONTRAST TO POSTERIOR STAPHYLOMA,ITS EDGES ARE SHARP

NANOPHTHALMOS

IMAGE SHOWS REDUCED AXIAL LENGTH

INTRA OCULAR FOREIGN BODY

Localization and extent of intraocular damage

Metallic foreign bodies produce very high bright signalShadow present posterior to the foreign body

POSTERIORLY DISLOCATED LENS images shows a linear structure (arrow)in the post vit. With high reflectivity

CUPPED DISC

MACULAR EDEMA

PERSISTENT HYALOIDAL VESSEL

PERSISTENT FETAL VASCULATURE IMAGE SHOWING A SMALL EYEBALL AND ATHICK MEMBRANE( ARROW)EXTENDING FROM LENS TO O.D.

RETINOPATHY OF PREMATUIRITY IMAGE SHOWS A CLUMP OF HIGH REFLECTIVE ECHOES SUGGESTIVE OF FIBROVASCULAR TISSUE (ARROW)pulling up the retina in a concave configuration s/o stage 4 ROP

SCLERITIS

Thickening in hyperopic and nanopthalmic eyes

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

MCQs / Cases1. A patient presents with bilateral granulomatous panuveitis with hazy fundus view due to cataract. No Hx of trauma. B scan picture is given below:

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A. What is the probe position?Axial B. What do the arrow head and arrow show?Retinal detachmentChoroidal thickeningC. Probable diagnosis?VOGT-KOYANAGI-HARADA DISEASE(V-K-H)9/17/201694

2. Describe the following A-scan

Ans Immersion technique A-scan9/17/201695

3.what you say about these A-scans?

Ans Artifacts By IOL (Reverberations)9/17/201696

4. Diagnosis?

9/17/201697AnsHypotonic eye with choroidal thickening

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