2. INTRODUCTION
B-scan also known as brightness scan is a simple, non
invasive tool for diagnosing lesions of the posterior segment
of the eyeball with the help of ultrasound waves.
B-scan provides the topographic information of shape,
location ,extension ,mobility , and gross estimation of
thickness of the tissue.
Sound waves pass through opaque tissue and expose the
ominous tumours behind the globe, retinal detachment etc
3.
4. HISTORY
The concept of sound waves in ophthalmology was applied only in
20th century . In 1956, Mundt and Hughes were the first to use A-
scan technique for detecting ocular diseases. In 1958, Baum and
greenwood developed a B-scanner for the eye and orbit.
Coleman and his collaborators perfected a B-scan immersion unit
that incorporated both A-mode and M-mode .Bronson then
developed the first commercially available handheld contact
scanner and introduced a rapid scanning technique.
Ossoinig extensively worked to the effect by standardizing A-scan
then developing B-scan.
5. INSTRUMENTATION
Ultrasound waves exhibits frequencies above 20kHz which is
not audible to humans . Ultrasound is an acoustic wave in
which compression and rarefactions occur because changes
in density within solid and fluid substances. Ophthalmic
ultrasound ranges frequencies ranges from 8 to 10 mHz.
Higher frequency > shorter wavelength> lesser depth of
penetration >better resolution [ophthalmic use]
4 basic components of B-scan [ a pulser, a transducer,a
receiver and a display system]
6. CONTI….
An electric pulse is applied to piezoelectric crystal , which in
turn generates a short pulse of ultrasound energy . This
energy transverses a known path in the eye at 1500 m/sec .
As the applied pulse voltage is varied in polarity , the
piezoelectric crystal expands and contract rapidly and
ultrasonic vibrations result .since electrical energy is
converted into sound energy , crystal is acting as transducer .
The ultrasonic pulse is partially reflected at various tissues
due to acoustic properties . When the sound energy returns to
the crystal it is converted back to electrical energy as the
duration of pulse is very small the same crystal transmit and
receive the pulse.
7.
8. PROCEDURE
Explain the procedure to the patient .
Positioning the patient : B-scan is performed with patient
reclining or supine position , certain ocular conditions require
sitting position [eg air bubble in the anterior chamber, to
demonstrate shifting fluid in exudative retinal detachment]
Usually the scan is performed with eyelids closed , using a
coupling jelly over the probe . In case the eyelids need to be
open while performing the scan then topical anesthesia is a
must.
Probe orientation :
9. CONTI…..
The transducer probe always has a marker [ dot, line ,or logo ]
3 basic probe is present axial ,transverse , and longitudinal
Longitudinal scan: the probe is place such that the marker is
perpendicular to limbus. Hence the beam scans across a
single meridian at any given clock hour . The oriented
meridian is the one exactly opposite to the meridian in which
the probe is placed eg if the probe is placed at 6 o clock
meridian the picture is displayed at 12 0 clock meridian.
Transverse scan : the probe is placed such that the marker is
parallel to limbus . This orientation is useful for lateral extent
of a leision. Depending on the orientation of the probe marker
, transverse scans can be horizontal, vertical or oblique
10. CONTI……
Axial scan : in this method the patient is asked to fix at primary
gaze and the probe is placed on the position of centre of the
cornea . The sound beam transverses posterior through the
centre of the lens , intersecting the optic nerve in its path . This
position is useful to evaluate the macular region, axial length,
and position of lesions in relation to the lens and optic nerve .
11. CONTI….
the sensitivity control should also varied during the
examination procedure. The sensitivity control allows the
examiner to estimate the relative acoustic densities of various
tissues . If a particular ocular structure has high acoustic
density then it will reflect sound waves even atlow sensitivity
settings .
12. INDICATIONS
An Ultrasound B scan can be done in a variety of situations .
The ,most frequently ordered conditions are given below
Choroidal metastasis
13.
14. Opaque ocular
media
Clear ocular
media
Intraocular
foreign bodies
Orbital lesions
Anterior segment AS Detection
/localization
Tumours
Corneal opacity Iris lesions Orbital foreign
bodies
Hyphema/hypopy
on
Ciliary body
lesions
Muscle
inflammation
Miotic pupil PS
Cataract tumours
Pupillary/reteroart
icular membrane
Choroidal
detachment
Posterior segment Rd, posterior
uveitis
Vitreous
haemorrhages
Optic disc
abnormalities
