Echography/Echocardiography Flashcards
(93 cards)
What occurs to amplitude of a sound wave as distance from the sound source increases?
Amplitude (diagonal line) diminishes with distance from the sound source.

What is amplitude in ultrasound a measure of?
tissue compression
Sound waves generated from the pizoelectric crystals in the transducer are transmitted into the surrounding medium at what rate?
proportional to the speed of sound in that medium
What can be determined from the time required of the sound wave to travel from the transducer to the object and back?
distance of object from transducer
Label
What occurs to ultrasound waves as they strike an interface between two different tissue types? (5)
- Specular reflection
- Refraction
- Absorption
- Scatter
- Acoustic impedance
_________ type transducers aid in placement of peripheral lines.
Linear array
In a linear array transducer, what are the near and far fields?
Near field is the columnar portion of the beam.
Far field is the diverging segment.
What MHz is needed to see a baby for instance?
What MHz is needed to see a vessel?
Less MHz, ~3.5
Higher MHz, ~8
Note: See picture to help visualize.
As an object approaches, the apparent frequency increases as object moves toward you. This is known as the _________.
Doppler effect
What are 3 characteristics of the waveforms as an object approaches a person, for example?
increased frequency
increased pitch
compressed wavelength

What are 3 characteristics of the waveforms as an object moves away from a person, for example?
decreased frequency
decreased pitch
elongated wavelength

The movement of red blood cells, frequency transmitted by a tranducer, velocity of RBCs, and speed of ultrasound in blood is known as:
Doppler shift
The doppler shift is directly proportional to the ________.
velocity of the moving target
If the target is stationary, what will frequency reflected (fr) and frequency transmitted (ft) be?
fr = ft
If the target is moving toward the transducer, what will ft and fr be?
fr > ft
Note: r is reflected, t is transmitted.
If the target is moving away from the transducer, what will fr and ft be?
fr < ft
How do you calculate doppler shift?
fr - ft
frequency (reflected - transmitted)
Accurate measurement of blood flow velocity utilizing the Doppler effect requires careful alignment of the interrogating beam __________ to the direct of blood flow.
parallel
What are the two types of Doppler?
_continuous _
pulsed wave
Why were pulsed wave transducers developed?
Continuous wave failed to provide information on distance of target to the transducer.
How does a pulsed wave transducer operate?
The transmitter beam (ft) is emitted in short bursts and the returning echoes (fr) are received by the same transducer.
Because the speed of sound in tissues is nearly constant, the area of interest for pulsed wave Doppler can be selected by what?
time gating the returning signals–only accepting echo information that required the “correct” amount of time to return from the target
What is the main drawback to pulsed wave Doppler?
higher blood flow velocities cannot be accurately measured










