Sorrell Chapter 2 Flashcards
Frequency range of human hearing
20,000 Hz to 20Hz
Frequency range of cardiac ultrasound probes.
1 to 12 MHz
The velocity of sound transmission in soft tissue
1.54 km/s or 1,540M/s
Gain
The degree of amplification of the returning sound signal
Intensity
Distribution of power within an area, analogous to loudness
Attenuation
The net loss of ultrasound energy during propagation
Absorption
The transfer of ultrasound energy to the tissue during the propagation
Acoustic impedance
Product of tissue density and the velocity of sound.
Formula for estimating attenuation
0.5dB/cm/MHz
Dead time
the time in between pulses that the echograph is not emitting ultrasound
Duty factor
a unitless number between 0 and 1 representing the fraction of time that the transducer is emitting ultrasound
Far filed
the diverging conical portion of the beam beyond the near field
frequency
number of cycles per second, measured in Hz
Half layer value
the distance a ultrasound beam penetrates into a medium before its intensity has attenuated to half the original value
near field
the proximal cylindrical shaped portion of the ultrasound beam before divergence begins to occur
period
the time required to complete one cycle, usual expressed in microseconds
Power
rate of transfer over time of acoustic energy from the propagating wave to the medium, measured in watts
pulse
burst or packet of emitted ultrasound of finite duration containing a fixed number of cycles traveling together
pulse length
the physical length or distance that a pulse occupies in spaced, usually expressed in mm.
pulse repetition
the rate at which pulses are emitted from the transducer, usually measured over a period of 1 second.
wavelength
distance measurement of one cycle of ultrasound wave
Specular reflectors
large targets like pericardium, endocardium, and valves
scattered reflectors
created by small targets, only small portion of ultrasound is reflected back such as myocardium (Rayleigh scatterer.)
In M mode the pulse repetition rate is ____ compared to 2D
lower. More pulses/s needed to create 90 degree sector of 2D. Temporal resolution much better for M-Mode.
In 2D echo, two sweeps of the ultrasound constitute …
1 frame
