ULTRASONOGRAPHY LECTURE II_2

Important characteristics of sound waves that influence sonography.

Key Wave Properties

Sound waves with frequencies above the human hearing range, used in medical imaging.

Ultrasound

A branch of physics that studies sound and sound waves.

Acoustics

2 ways to define sound

Experiential and Physical

Sound as perceived through the human auditory system.

Experiential

Propagation of pressure variations through a medium from a sound source to a listener.

Physical

A form of energy causing mechanical disturbances through molecular vibrations in a medium.

Sound

Also refers to mechanical wave that travels to a medium

Sound

A type of mechanical wave where molecules vibrate parallel to the direction of wave travel.

Longitudinal or Compressed Wave

A type of mechanical wave where molecules vibrate perpendicular to the direction of the wave propagation.

Transverse or Shear wave

True or False. Sound does not require a medium with molecules to travel and cannot propagate through a vacuum.

False

Acoustic Variables includes

pressure, density, and particle motion that characterize sound.

A sound wave that travels in a sinusoidal form.

Ultrasound Wave

A type of ultrasound wave characterized by compression and rarefaction.

Longitudinal Wave

Regions of high pressure in a sound wave.

Compression

Regions of low pressure in a sound wave.

Rarefaction

The number of cycles per second, measured in Hertz (Hz)

Frequency

Ultrasound Imaging Frequency Range

2-20 MHz

Relationship of Frequency and Resolution

Lower frequency allows for higher penetration but lower resolution. (Direct with Resolution, Inverse with Penetration)

The time taken for a sound wave to complete one cycle, measured in seconds or microseconds.

Period (T)

Period Formula

Period= 1/Frequency (MHz)

Relationship of Frequency and Period

Frequency Increases, Period Decreases (Inverse)

The distance over which one cycle of a sound wave occurs. It is also the length of cycle.

Wavelength

The speed at which a sound wave travels through a medium (cm/sec), is influenced by density and stiffness or elasticity.

Propagation Velocity

Propagation velocity of Soft tissue

1540

Propagation velocity of Bone

4080

Propagation Velocity slowest in?

Air/Gas

Propagation Velocity Fastest in?

Solids

Propagation Velocity Formula

Velocity=wavelength x frequency

The strength or intensity of a sound wave affects image brightness in ultrasound. It is also the wave's height and the image's brightness.

Amplitude

Relationship of amplitude with brightness of the image

Amplitude Increases, Brightness of an image Increases (Direct)

Relationship of amplitude with Depth

Amplitude Decreases, Depth Increases (Inverse)

The rate at which energy is transmitted into the body, measured in watts (W). It varies over Time and Space.

Power (energy)

Unit of Power (energy)

W, mW

Unit of Frequency

Hertz (Hz)

Unit of Period (T)

sec, ms, us

Intensity of sound measures in

bel or decibel (dB)

The amount of energy passing through a specified area per second.

Intensity (energy per second)

True or False. Intensity of wave is proportional to the amplitude of the wave square.

True

The amount of force applied over a specific area, measured in Pascals (Pa), Megapascal.

Pressure

Relationship of pressure or force and volume of sound waves or intensity

Directly Proportional because these two deals with power

Relationship of pressure and Area

Inversely Proportional