Echo Made Easy - Chapter 1 Flashcards
What are the two phases of a sound wave?
Each wave consists of a peak and a trough. The peak coincides with an adjacent group of molecules moving towards each other (compression phase). The trough coincides with an adjacent group of molecules moving away from each other (rarefaction phase).
In what unit frequency expressed?
What do kilo- and mega- when applied to this unit?
1 hertz (Hz) = 1 cycle per second
1 kilohertz (KHz) = 103 Hz = 1000 Hz
1 megahertz (MHz) = 106 Hz = 1000000 Hz
How are frequency and wavelength related? (Equation)
Frequency and wavelength are inter-related. Since sound
travels a fixed distance in one second, more the cycles in a
second (greater the frequency), shorter is the wavelength
Velocity = Frequency × Wavelength.
What is the velocity of sound through soft tissue?
1540 m/sec
What is the normal audible range of sound frequencies?
Therefore what is ultrasound?
The normal audible range of sound frequency is 20 Hz to
20 KHz.
Sound with a frequency above what is audible
to the human ear (more than 20 KHz) is known as ultrasound.
How are electricity and ultrasound transformed from one to the other?
How is the pressure-electric effect also known?
Electricity and ultrasound are two different forms of energy that can be transformed from one to the other by special crystals made of ceramic such as barium titanate.
Ultrasound relies on the property of such crystals to transform electrical current of changing voltage into mechanical vibrations or ultrasound waves. This is known as the piezoelectric (pressure-electric) effect
How does an electrical current affect a piezoelectric crystal?
How do reflected ultrasound waves affect a piezoelectric crystal?
When electrical current is passed through a piezoelectric crystal, the crystal vibrates. This generates ultrasound waves which are transmitted through the body by the transducer which houses several such crystals.
Reflected ultrasound waves again distort the piezoelectric crystals and produce an electrical current. These reflected echoes are processed by filtration and amplification into an image.
What are the echo-reflectivities and hence grey-scale shade of each of the following:
- Bone
- Muscle
- Air
- Bone - Reflectivity High, Shade White
- Muscle - Reflectivity Low, Shade Grey
- Air - Reflectivity Nil, Shade Black
How does probe frequency relate to resolution and imaging depth?
Therefore which probes are best for superficial structures?
Since wavelength and frequency are inversely related, the higher the frequency of ultrasound, the shorter the wavelength. The shorter the wavelength, the higher the image resolution and the lower the penetration.
Therefore, high frequency probes (5.0–7.5 MHz) provide better resolution when applied for superficial structures and in children.
How is doppler shift calculated as it relates to initial frequency and velocity?
How is velocity calculated as it relates to doppler shift and initial frequency?
What is applied to correct for the angle between the ultrasound beam and blood flow?
What should the angle be to ensure accurate measurement?
What is the value at 0 degree (i.e. parallel)?
What is the value at 90 degrees (i.e. perpendicular)?
Cosine theta.
Cos 0º is 1.
Cos 90º is 0.
Angle should be less than 20º
Are low or high frequency transducers better for obtaining information by doppler about maximum velocity?
Why?
Since, the original frequency value (2×Fo) is in the denominator
of the velocity equation, it is important to remember that maximum velocity information is obtained using a low frequency (2.5 MHz) transducer.
Which equation can be used to calculated the pressure gradient across a valve?
Δ P = 4 V2
P: pressure gradient (in mm Hg)
V: peak flow velocity (in m/sec)
What is FVI? How is it calculated?
What is spectral broadening (of a spectral trace of velocities) also known as (2)? What does it suggest about blood flow?
Velocities towards the transducer are displayed above the baseline (positive deflection) and velocities away from the transducer are displayed below the baseline (negative deflection).
The returning Doppler signal is a spectral trace of velocity display on a time axis. The area under curve (AUC) of the spectral trace is known as the flow velocity integral (FVI) of that velocity display.
Turbulent blood flow (i.e. stenotic valve) = wide distribution of velocities of RBCs (spectral broadening, high variance, increased band width) = filled in appearance of Doppler signal.
