Chapter 8 Flashcards
You are given 5 substances: backing material, PZT, matching layer, gel, and skin, whose impedance have been measured. Unfortunately, the labels identifying the impedance of each substance have fallen off these materials. There are five labels, indicating impedances of 0.8 mrayls, 1.9 mrayls, 1.6 mrayls, 2.0 mrayls and 1.0 mrayls. If the impedance of the backing material is 1.9 mryals, what are the impedances of soft tissue, matching layer, gel, and PZT? Why?
The impedance of the substances are: PZT- 2 mrayls Matching layer- 1.6 mrayls Gel- 1.0 mrayls Skin- 0.8 mrayls The impedance of the active element is similar to that of the backing material. To optimize the efficiency of sound energy transfer between the transducer and the body, the impedances of the materials along the path from the PZT to the skin will decrease in order; the highest impedance will be that of the PZT, then the matching layer, then gel, and finally the skin.
Pulse length is _________ related to pulse duration.
Directly
Q-factor is ____________ related to bandwidth
Inversely
Pulse duration is __________ related to bandwidth.
Inversely
The sensitivity of transducers that create short duration pulses is likely to be _________ that of transducers that create long pulses.
Less than
All of the following correctly describe an imaging transducer except: High sensitivity Low Q Wide bandwidth Damped
High sensitivity.
High sensitivity does not describe imaging transducers. Imaging transducers have a low sensitivity.
T or F. Shorter duration events (such as dampened pulses) are more likely to be wide bandwidth.
True
What occurs when a PZT crystal’s temperature is elevated above the Curie point?
When PZT’s temperature exceeds the Curie’s point, the PZT is depolarized. The crystal’s piezoelectric properties are lost forever and the transducer is ruined.
T or F. The acoustic impedance of the matching layer is approximately the same as the acoustic impedance of skin.
False.
The impedance of the matching layer is greater than the impedance of the skin.
T or F. Imaging transducers are usually of high rather than low bandwidth
True.
Imaging transducers are high or wide bandwidth (broadband).
T or F. A very high Q factor transducer is used more often in diagnostic imaging transducers than a low Q factor.
False.
Imaging transducers are low Q
T or F. A pulse with a long pulse duration is likely to have a narrow bandwidth.
True
Longer events tend to have a narrow bandwidth. Shorter events tend to have wider bandwidth.
T or F. The damping material in a transducer increases the sensitivity.
False.
Damping reduces sensitivity
T or F. The damping material in a transducer increases the pulse length.
False
Damping shortens pulse length
T or F. The damping material in a transducer decreases the pulse duration
True
Damping decreases pulse duration
T or F. The damping material in a transducer improves the system’s lateral resolution
False
Damping does not affect lateral resolution
T or F. The damping material in a transducer improves the system’s longitudinal resolution
True
Damping improves longitudinal resolution
T or F. The damping material in a transducer decreases the bandwidth
False
Damping increases bandwidth
T or F. The damping material in a transducer decreases the quality factor.
True
Damping decreases the Q factor
T or F. If the frequency of the electrical excitation voltage of a pulsed wave transducer is 6 MHz, then the operating frequency of the transducers 6 MHz.
False
With pulsed wave transducers, the frequency of sound is not determined by the electrical signal.
T or F. If the pulse repetition frequency of a transducer is increased, then the frequency of sound produced by the transducer remains the same.
True
Frequency and pulse repetition frequency are not related
T or F. The diameter of the active element of a transducer helps to determine the frequency of the sound that the transducer creates.
False
The diameter of the active element does not determine the frequency of sound created by the transducer
T or F. If the frequency of the electrical excitation voltage of a continuous wave transducer is 6 MHz, the the operating frequency of the transducer is 6 MHz
True
The frequency of the electrical voltage and the frequency of the sound beam are identical with continuous wave transducers.
T or F. Two piezoelectric crystals are made from the same material. The thicker crystal will make a pulsed transducer with a higher frequency.
False
Thicker active elements create sound with lower frequency, not higher.
T or F. Two piezoelectric crystals are made from the same material. The thicker crystal will make a continuous wave transducer with a low frequency.
False.
With a continuous wave transducer, active element thickness does not determine the sound beam’s frequency.
T or F. The normal propagation speed in piezoelectric material is about 3 to 5 times greater than that in in soft tissue.
True.
Sound travels much faster in PZT than in soft tissue
The impedance of a transducer active element is 1,900,000 rayls, and the impedance of the skin is 1,400,000 rayls. What is an acceptable impedance for the matching layer.
1,726,000 rayls
The impedance of the matching layer is between that of the active element and the skin.
Which of the following crystals will produce sound with the lowest frequency?
Thick with a low speed.
Sound with the lowest frequency is produced by a thick active element in which sound travels slowly
Which type of transducer has a greater Q factor: therapeutic or imaging?
Therapeutic transducers have a higher Q factor than imaging transducers
Which type of transducer has a greater bandwidth: continuous wave or imaging?
Imaging transducers have a wider bandwidth than continuous wave transducers.
Which type of transducer has more backing material: therapeutic or imaging?
Imaging transducers use more backing material than therapeutic transducers
In an imaging transducer, what is the purpose of attaching the backing material to the PZT?
Improve image quality
A pulsed-wave transducer has a resonant frequency of 5 MHz. The lowest frequency in the pulse is 2 MHz and the highest is 8 MHz. What is the bandwidth?
6 MHz
Bandwidth is the range of frequencies found in a pulse.
8 MHz- 2 MHz= 6 MHz
For the transducer described in question 25, what is the main frequency?
5 Mhz
