Ultrasounds Physics and Artifacts Basics

Ultrasounds Physics and Artifacts Basics

Ultrasounds Physics and Artifacts Basics

Alain Giroux, DVM, MSc, DACVR

1-Ultrasound Characteristics

a) Sound wave: propagating variation of acoustic variables in a medium.

-Acoustic Variables: pressure; density; temperature; particle motion

b) Sound properties:

-Source (transducer) determined:


–Amplitude (US console) and intensity (US console)

-Medium determined:

–Propagation speed

-Source and medium determined:


c) Frequency:

-Unit: Hertz (Hz): one cycle per second

-Megahertz (MHz): 1 million Hertz
-Infrasound: less than 20 Hz
-Ultrasound: above 20000 Hz

-Veterinary medical ultrasound: 3 to 12 MHz

d) Wavelength:

-Length in between wave cycles (mm)

e) Propagation speed:

-Speed of sound wave: meter per second (m/s)

-Different in Air, liquid, solid.

-Speed in soft tissue: 1540 m/s

-Why important? Because US equipment assumes this speed in calculating depth location of structures.

-Propagation Speed X Density = Impedance

-High reflection occurs when large difference in tissue impedance and propagation speed.

2-Diagnostics Ultrasound Characteristics

a)Pulse-echo: Ultrasound is sent as pulses.

Each pulse contains small number of waves

As illustrated on figure.

distance and location

b) Attenuation (dB):

–Decreased in intensity as it travels in soft tissues

–Absorption (conversion into heat)


–Scattering: Image generation (specular scattering)

3-Ultrasound Equipment


-Converts bi-directionnaly electric energy into ultrasound energy.

-Piezoelectricity: PZT materials (ceramics, quartz) are deformed by applied voltage and causes changes of pressure that propagates as a sound pulses.

-Transducers construction: Single element or linear-array made of piezocomposites.

b) Type of transducers:

–MechanicalRotating or oscillating single or array of elementsin acoustic coupling liquid.

–Sequenced and phased array


4-Ultrasound Settings

a) Gain: sometimes identified as decibel dB.

b) Time gain compensation (TGC)-also called: Near field gain, far field gain; multiple field gain; STC: surface time compensation

c) Depth:

-Depth/range; zoom; magnification

d) Mode:

-Brightness (B); Motion (M); Doppler (D); various combination of modes

e) Measurements:

-Mark, Trace; enter; Set

f) Probe; transducers

g) Focus: in phased array-Focal Zones; manual focus

5-Ultrasound Artifacts:

a) Acoustic shadowing:

-Reduction of the echo amplitude from reflectors that is located beyond a strongly reflecting or attenuating structure.

b) Acoustic enhancement:

-Increased brightness (echo amplitude) of structures (reflectors) located beyond a low-attenuating structure.

c) Refraction (edge shadowing):

-Change in direction of sound when it encounters a round surface. Echoes from the structure beyond the surface are decreased in amplitude.

d) Mirror image:

-Structures of one side of strong reflector presented on other side of the reflectors. Decreased brightness and synchronized movement of structures.

Video segment

e) Improper gain:

-Part of a structure and of the image is falsely decreased in amplitude due to erroneous TGC setting.Video segment

f) Section thickness:

-Portion of a round shape structure wall or outer lining is projected falsely inside its lumen.

Video segment