Ultrasound Flashcards
It is the term that describes sound waves of frequencies exceeding the range of human hearing and their propagation in a medium.
Ultrasound
Medical diagnostic ultrasound is a modality that uses ultrasound energy and the acoustic properties of the body to produce an image from stationary and moving tissues.
This is a mechanic energy that propagates through a continuous, elastic medium by the compression and rarefaction of “particles” that comprise it.
Sound
This is caused by a mechanical deformation induced by an external force, with resultant increase in the pressure of the medium.
Compression
This occurs following compression event -as the backward motion of the “piston” reverses the force, the compressed particles transfer their energy to adjacent particles with a subsequent reduction in the local pressure amplitude.
Rarefaction
Energy propagation occurs as a wave front in the direction of energy travel, known as a what?.
Longitudinal wave
The is the distance between compressions or rarefactions, or between any two points that repeat on the sinusoid always wave of pressure amplitude.
Wavelength
This is the number of times the wave oscillates through one cycle each second.
Frequency
Sound waves with frequencies less than 15 cycles per second (Hz) are called what?.
Infrasound
The range between 15 Hz and 20 kHz comprises what?.
Audible acoustic spectrum
Ultrasound represents the frequency range above how many kHz?
20 kHz
Medical ultrasound uses frequencies in the range of how many MHz?
2 to 10 MHz
With speciliazed ultrasound applications up to 50 MHz.
This is the time duration of one wave cycle.
Period
This is the distance traveled by the wave per unit time and is equal to the wavelength divided by the period.
Speed of sound
This is determined by the ration of the bulk modulus (a measure of the stiffness of a medium and its resistance to being compressed) and the medium.
Wave speed
A highly compressible medium, such as air, has a low speed of sound, while a less compressible medium, such as bone, has a higher speed of sound.
What are the average speed for “soft tissue”, fatty tissue, and air?
Soft tissue = 1,540 m/s
Fatty tissue = 1,450 m/s
Air = 330 m/s
Higher frequency has _______ wavelength.
Shorter or longer?
Shorter
For body parts requiring greater travel distance of sound waves (e.g. abdominal imaging), lower frequency ultrasound is used to image significant depths.
Approximately how many MHz?
3.5 to 5 MHz
For small body parts or organs close to the skin surface (e.g., thyroid, breast), higher frequency ultrasound is selected.
Approximately how many MHz
7.5 to 10 MHz
Most medical imaging applications use ultrasound frequencies in what range?
2 to 10 MHz
Interaction of two or more separate ultrasound beams in a medium can result in what?.
Constructive and/or destructive wave interferences
The amount f constructive or destructive wave interference depends on several factors, but most important are the _________ and ________ of the interacting beams.
Phase (position of the periodic wave with respect to a reference point) and amplitude
The spatial resolution of the ultrasound image and the attenuation of the ultrasound beam energy depend on the ________ and _______, respectively.
Wavelength and frequency
This interference occurs with two ultrasound waves of the same frequency and phase, resulting in a higher amplitude output wave.
Constructive interference
This interference occurs with the waves 180 degrees out-of-phase, resulting in lower amplitude output wave
Destructive interference