Ultrasound Flashcards
What is a combo of A and B scan
Standard echographs
Ocular ultrasound indications
Opaque ocular media: Opacified K, hyphema, hypopyon, mitosis, lens opacities, persistent pupillary membrane, vitreal hemes.
Intra ocular foreign bodies
Clear ocular media: Iris lesions, CB lesions, ONH abnormality
Tumors
Choroid or retinal detachment
Orbital ultrasound indication
Exophthalmos Enophthalmos Globe displacement Ptosis Lid retraction Lid swelling Periorbital mass Motility disturbance/diplopia Periorbital pain
Contraindications to ultrasound
No absolute contraindications.
Extra care should be taken following surgeries or open wounds.
Ophthalmic ultrasounds use which frequencies
8-10MHz.
Relationship between frequencies, penetrance and resolution.
As you increase the Hz, the resolution increases. Penetrance decreases.
What system is used to get the ultrasound
Pulse echo system using a crystal component in the transducer. Creates vibrations that are converted into electrical impulses that are amplified. Displayed in real time.
Angle of incidence is ____ to the angle of reflection
Equal
Smooth straight interfaces reflect all the wave. This is called
Specular reflection
Irregular and small surfaces cause part of the echo to be
Scattered.
Sound velocity through solid vs liquid media
Travels quicker through solid than liquid
How to minimize absorption
Absorption is converted to heat. Minimize by performing on K.
Refraction
Same as light rays. Medium to high index causes sound/light to bend towards the perpendicular.
Absorption and refraction are minimal at interfaces that are
Reflective and regularly structures.
You want them to be minimal or else they will reduce beam strength.
Shadowing can be caused by
Strong reflective surfaces- air, FB, calcifications.
B scans offer __ and ___ representation of ocular or orbital structures
Topographical and qualitative
An oscillating sound beam is emitted from the probe the direction of which is indicated by
The mark on the probe tip. Either superior or nasal.
Increasing the gain
Decreases the resolution. Allows weaker signals to be displayed- more scatter and nice.
Decreasing the gain
Increases resolution. Only strong signals appear.
What gazes to take pics of when the marker is superior
ONH/PP
Nasal
Temporal
What gazes to take pics of when the marker is nasal
ONH/PP
Superior
Inferior
If the marker is nasal, the upper part of the screen is
Nasal
A scan offers a ____ representation of the ocular structures
Quantitative. Gives a number
A scan is best used for determining
Tissue texture, internal structures, density and dimension of lesion.
How to apply B scan vs A scan
B scan- can be applied to K (proparacaine, without gel) or to lid (no proparacaine, with gel)
A scan- applied only to K with proparacaine and no gel. Do not indent K surface.
For A scans, what is the optimum gain for tissue differentiation
Tissue sensitivity gain setting.
A scans are vital component of
Calculations in determining intraocular lens implant before cataract surgery.
Normal axial length
22-24.5
