Describing Sound Waves
Energy
Define Spatial Pulse Length
SPL is the distance that a pulse occupies in space from the start to the end of a pulse
Acoustic energy that interacts with human tissues
Bioeffects
longitudinal resolution
What are the units for lateral resolution?
length (mm)
Name the three Acoustic Variables
Pressure, Density, Distance
Is Pulse Repetition Period adjustable?
Yes. When the sonographer adjusts the scan depth of view, the PRP is also altered
Which type of intensity risks thermal bioeffects?
SPTA
A pulse's time-of-flight is 26 microseconds. How deep was the reflector?
2cm (13 microseconds per 1cm)
What part of the beam is Azimuthal resolution the best?
At the focus (Azimuthal = Lateral resolution)
Period and frequency are both determined by what?
Sound source only, not the medium
Duty factor = (Pulse duration divided by what?) x 100
DF (%) = (PD/ PRP) x 100
Which probe would create a deeper focus?
small diameter, low frequency
large diameter, high frequency
small diameter, high frequency
large diameter, low frequency
large diameter, high frequency
A soundwave strikes a boundary with normal incidence. The impedances of the two media are identical. What percentage of sound is refracted?
0% (Refraction cannot occur with normal incidence)
What type of frequency (high or low) has the best range resolution?
High frequency
Medium 1 has a density of 9 and a stiffness of 6. Medium 2 has a density of 8 and a stiffness of 6. In which medium will sound travel SLOWER?
Medium 1. Since both have same stiffness, the medium with the greater density has the lower propagation speed
By changing the imaging depth, which of the following does the operator also change? (choose 3):
PRF, DF, Speed, PRP, Amplitude, SPL
PRF
DF
PRP
Which type of probe would create the most divergence?
small diameter, low frequency
small diameter, high frequency
large diameter, low frequency
large diameter, high frequency
small diameter, low frequency
Refraction occurs only if what two conditions are satisfied?
1. oblique incidence
2. different propagation speed of the two media
Which type of focusing is adjustable or can create multiple focuses?
Phased array (electronic focusing)
If intensity remains the same while the power is doubled, what has happened to the beam area?
Doubled. Intensity = power/area. If intensity is unchanged, then what ever happens to power must also happen to area
Going from a 3MHz transducer to a 6MHz transducer, if image depth is the same, what happens to wavelength? (increase, decrease, stays the same)
decreases. higher freq = smaller wavelength
What principle or law explains why a sound beam created by a disc-shaped crystal is hourglass shaped?
Huygens' Principle: Large elements have millions of tiny sound sources with V shaped wavelets. These waves interfere (constructive and destructive) to combine to create the hourglass shape
A PW transducer has a resonant frequency of 5MHz. The lowest freq. is 2MHz and the highest is 8MHz. What is the bandwidth?
6MHz
8MHz-2MHz= 6MHz
The sensitivity of a transducer that create short duration pulses is likely to be (greater than, less than, or equal to) that of transducers that create long pulses
less than