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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. ^[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.

A B-mode ultrasound scan maps echo strength to displayed brightness and assembles multiple pulse-echo ultrasound lines into a spatial image. Each echo's location is inferred from beam direction and return time using an assumed sound speed. ^[ref]

A bright point represents a strong received echo, not a direct measurement of tissue density. Acoustic impedance contrasts, propagation losses and the instrument's display mapping all affect brightness. A moving image consists of repeated spatial frames; in an M-mode ultrasound scan, the second display axis instead tracks time along one beam.

An M-mode ultrasound scan repeatedly samples one pulse-echo ultrasound beam and places successive depth profiles alongside one another in time. Depth is one display axis and acquisition time the other; echo strength controls brightness. This makes motion along the selected line visible. ^[ref]

A stationary interface traces a line at constant depth; an oscillating interface traces a varying depth. Converting echo delay to depth still assumes a sound speed and a return path. This display records one beam over time, whereas a B-mode ultrasound scan combines beam lines across space.

In pulse-echo ultrasound, a transducer emits a pulse and records returning echoes. For a straight round-trip path in a medium of assumed sound speed $c$, an echo delay $t$ gives depth $z=ct/2$. Reflections depend on acoustic-impedance changes, while attenuation, scattering and propagation geometry affect the received amplitude.

An A-mode ultrasound scan displays echo amplitude against inferred depth along one beam. A B-mode ultrasound scan maps received amplitude to brightness and assembles many beam directions or translated beam lines into a spatial image. An M-mode ultrasound scan repeats one beam line and displays its depth profile versus time, making motion along that line visible. Thus the display axes and acquisition pattern differ even when the pulse-echo principle is shared.

For a pulse lasting ${\tau }_p$, a simple axial-separation estimate is $c{\tau }_p/2$. Lateral resolution depends on aperture, wavelength, focusing and depth. Shorter pulses and broader bandwidth can improve axial resolution; an assumed sound speed or a multiple-reflection path can instead misplace an echo. Brightness is not a direct universal map of composition.

Doppler ultrasound uses frequency or pulse-to-pulse phase changes from moving scatterers. In a simple backscatter geometry, $\Delta f\simeq 2f_{0}v\cos \theta /c$. Inferring speed requires the beam-to-motion angle; pulsed sampling can alias frequencies, and an unknown angle leaves a velocity-projection ambiguity. This describes generic acoustic acquisition rather than a clinical diagnosis.