B-Scan UltrasonographyBy

Mohamed Abdel-AzizM.Sc.,Egy.Fellowship,ICO

INTRODUCTION

-Ophthalmic ultrasonography is a safe, noninvasive

diagnostic tool that provides instant feedback for

the evaluation of various ophthalmic disorders.

-Diagnostic ophthalmic ultrasonography is most useful

in the presence of opaque ocular media caused by

corneal opacities, anterior chamber opacities, cata-

racts,or vitreous hemorrhage.

-Intraocular tumors are routinely documented,

measured, and differentiated by ultrasonographic

techniques

BASIC PHYSICS

-The maximum range of human hearing includes sound

frequencies from 15 to about 20,000 waves,or cycles,

per second.

-Ultrasound is an acoustic wave with a frequency

above the audible range .

-Frequencies currently used in ophthalmic ultrasound

machines range from 8 to 80 MHz, compared with 2 to 6

MHz typically used in other fields of diagnostic

ultrasound.

-The use of higher frequencies allows for increased

resolution, which is essential in the evaluation of small

ophthalmic structures.

-Echoes are produced when ultrasound waves

encounter an interface between two materials have

different acoustic impedances.

-The greater the difference in impedance, the more

sound will be reflected rather than transmitted.

An ultrasound unit is composed of four basic

elements:

the pulser, the receiver, and the display unit are all

contained within the same chassis and connected to the

transducer, located at the tip of the probe by an

electrically shielded cable.

-The pulser produces electric pulse at a rate of 1000

pulses per second. Each pulse excites the electrodes of

the piezo-electric crystal of the transducer, generating

sound waves.

-The returning echoes are received by the transducer

and transformed into electric signals.

- These signals are processed in the receiver and

demodulator, and then displayed on the screen of the

display unit.

POSTERIOR

OCULAR SEGMENT

IMAGING

-The eye can be likened to a face of the clock, where

the top is 12 o'clock, the right side is 3 o'clock, the

bottom is 6 o'clock, and the left side is 9 o'clock.

-These points of reference are the same whether

one is performing anterior or posterior ocular segment

imaging, or scanning the right or the left eye.

WAYS TO IMAGING

THE EYE

For the posterior ocular segment and orbit, there

are three ways to imaging the eye:

axial, transverse, and longitudinal views.

Axial scan : provides a pleasing, generally

understandable Picture.

1-Horizontal axial views allow simultaneous

imaging of the lens, optic nerve, and the macula.

In this view, the tip of the probe is placed at the

center of the cornea, with the marker positioned

toward the nasal side of the eye. Thus, the top of

the scan is the nasal side, while the bottom is the

temporal side.

views provide simultaneous imaging of Vertical axial -2

the lens and the optic nerve.

In this view, the tip of the probe is placed at the center of

the cornea, with the marker positioned toward the

superior side of the eye. Thus, the top of the scan is the

superior side, while the bottom is the inferior side.

-One can twist the probe 45 degrees to the right or 45

of the oblique axial views degrees to the left to obtain

eye. Similar to vertical axial views, the marker is always

positioned at the superior side.

-Furthermore, one can obtain an axial view of the eye

just above or below the level of the optic nerve head, as

well as immediately to the right or to the left of it. These

of the eye.axial views -paraare termed

provide a lateral sweep of one Transverse views :-

quadrant of the fundus.

- There are as many transverse views as there are

hours in a clock.

views, the tip of the probe is horizontal transverse -

placed on the sclera below the cornea pointing up to

view the superior fundus, or on the sclera above the

cornea pointing down to view the inferior fundus. Like

the horizontal axial view, the marker is always positioned

of the eye. Thus, the top of the scan is at the nasal side

the nasal side, while the bottom is the temporal side.

views, the tip of the probe is vertical transverse -

placed on the sclera nasal to the cornea pointing toward

the opposite side of the eye to view the temporal fundus.

Alternatively, the probe is placed on the sclera temporal

to the cornea pointing toward the opposite side to view

marker . Like the vertical axial view, the fundusthe nasal

side of the eye. is always positioned at the superior

Hence, the top of the scan is the superior side, while the

bottom is the inferior side.

-In both horizontal and vertical transverse views, one

can point the probe toward the back of the eye (posterior

to the equator) to obtain a more posterior transverse

view of the fundus.

-Alternatively, one can point the probe toward the front

(anterior to the equator) to obtain a more peripheral

transverse view of the fundus.

views are essentially diagonal Oblique transverse

transverse views of the eye. Similar to vertical

transverse views, the marker is always positioned at the

superior side.

posterior -provide an anteriorLongitudinal views -

sweep of a specific meridian of the fundus.

-There are as many longitudinal views as there are

hours in a clock.

-In this view, the tip of the probe is placed on the sclera

next to the cornea pointing toward the opposite side of

the eye.

-Here, the marker is always positioned toward the

limbus. Thus, the top of the scan is the anterior

peripheral side, while the bottom is the posterior side

close to the optic nerve..

one can shift the probe away from the limbus to obtain a

more peripheral longitudinal view of a particular meridian

of the fundus

EXAMPLES OF B-

SCAN PICTURES

(A) Fresh vitreous hemorrhage. Longitudinal B-scan showing diffuse low-to-medium

reflective opacities in the vitreous cavity (arrowheads).

(B) Organized vitreous hemorrhage. Note pseudomembranous surfaces (arrowhead)

within the vitreous cavity representing the organization of blood.

.(D) Thickened PVD (arrowheads). B-scan axial view. Note lack of attachment at the optic nerve.

Total open funnel retinal detachment.(A) B-scan at low gain (49 dB) shows open funnel configuration and optic disc attachment. (B) A-scan shows 100% peak corresponding to the RD.

PVD Retinal DetachmentEchogenicity : Low-medium High

Change with gain (dB): Disappears with low gain Visible with low gain

Mobility : High Low

Optic disc attachment : Present or absent Always present

(C) Serous choroidal detachment. B-scan shows two choroidal detachments (arrowheads) with subchoroidal serous fluid (SF).(D)Hemorrhagic choroidal detachment. Note appositional or kissing choroidaldetachment (arrowheads) with dense opacities in the suprachoroidal space indicative of subchoroidal hemorrhage (SH).

Retinoblastoma with calcification. Fundus photograph (A). Transverse B-scans demonstrate a large, domeshaped lesion with marked internal calcification. High gain showing the lesional boundaries (B, arrows). Low gain showing internal calcification causing shadowing of the orbit (C, arrow).