Ascans

Ascans, often written as A-scans, refer to one-dimensional depth profiles obtained by scanning techniques that plot signal amplitude as a function of depth or time. The term is used across several disciplines to describe a foundational depth-measuring trace, typically produced by pulsed ultrasound or similar time-domain methods. An A-scan highlights interfaces within a medium as peaks in the trace, enabling estimation of distances or layer thicknesses when sound velocity is known.

In ophthalmology, A-scan ultrasound biometry employs high-frequency sound waves to measure the axial length of the eye. A transducer emits pulses that reflect from corneal, lens, and retinal interfaces; the resulting trace shows spikes at those interfaces, and the time delays are converted into distances. This measurement is critical for selecting the appropriate intraocular lens power in cataract surgery. Many modern devices integrate A-scans with two-dimensional B-scan imaging or other modalities.

Beyond ophthalmology, A-scans are used in dental imaging, industrial non-destructive testing, and materials science to assess layer thicknesses, detect interfaces, or determine material properties. The accuracy of an A-scan depends on factors such as transducer frequency, coupling quality, and the assumed propagation speed of the medium.

Terminology varies by field; the plural Ascans is commonly used informally to refer to multiple A-scan traces. In professional contexts, the preferred term is often A-scan or A-mode, and it may be contrasted with B-scan, which provides two-dimensional cross-sectional images. See also A-scan, B-scan, ultrasound biometry.