Application of a voltage across a piezoelectric crystal causes the crystal either contract or expand depending upon the polarity of the voltage.

A 3D ultrasound image may be formed by moving a sequential linear array in the direction perpendicular to the array.

A single continuous-wave ultrasound transducer can be used for the measurements of blood velocity through Doppler effects, as the same transducer can be used to launch an ultrasound beam and to receive the echo signals.

When an ultrasound beam propagates from medium 1 into medium 2, it has 30% reflection from the interface. When another ultrasound beam propagates in the opposite direction from medium 2 into medium 1, the reflection from this interface is

When an ultrasound beam is focused tighter, the depth of focus becomes larger.

Ultrasound imaging is an ionizing approach with certain radiation risk.

When an ultrasound wave propagates through a 10-cm thick medium, the molecules in the medium may just move very short distances (a few tenths of a nanometer) about a fixed mean position.

Microbubbles may be used as contrast agents for ultrasound detection.

When an ultrasound beam propagates from medium 1 into medium 2, it has 50% reflection. Assume medium 1 has an acoustic impedance of 1 MRayl. The impedance of medium 2 is:

When an ultrasound echo signal is reduced by 20 dB relative to the incident beam, the echo intensity is 20% of that of the incident beam.