Diagnostic Ultrasound
A-scan and B-scan basics — indications, technique, and recognizing common echo patterns.
A-Scan and B-Scan Basics
Why sound — when cataract, corneal opacity, or vitreous hemorrhage block the view, ultrasound images what light can't reach. Sound needs a continuous medium: coupling gel or immersion fluid, never an air gap.
A-scan — one-dimensional amplitude spikes along a single beam; each spike is an interface (cornea, lens surfaces, retina). Used for axial length and for characterizing lesion reflectivity.
B-scan — the probe sweeps to build a two-dimensional cross-section of the globe and orbit, performed through closed lids with gel. Screens for retinal detachment, tumors, and posterior foreign bodies.
Technique notes — orient the probe marker deliberately, examine in multiple gaze positions, and adjust gain: high gain shows weak echoes (vitreous opacities), low gain isolates strong ones (retina, calcification).