= A-mode ultrasound scan
{c}
An <A-mode ultrasound scan> plots the returning echo amplitude along one <pulse-echo ultrasound> beam. With assumed <sound speed> $c$, echo delay $\tau$ is converted to depth by $z=c\tau/2$; the factor two accounts for outward and return travel. Peaks mark reflecting interfaces along that line. <Ultrasound Theory Module by FAMUS>[The origin of the ultrasound image; Ultrasound modes, A–Mode]{ref}
The horizontal coordinate is depth inferred from travel time, while the vertical coordinate is signal amplitude. An <A-mode ultrasound scan> therefore provides a one-dimensional depth profile rather than the spatial cross-section assembled by a <B-mode ultrasound scan>.
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