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Chapter 4
describing pulsed waves
| Question | Answer |
|---|---|
| What are the 5 parameters that describe pulsed sound? | Pulsed duration, pulse repetition period, pulsed repetition frequency, duty factor and spatial pulse length |
| In diagnostic ultrasound, what cannot create anatomic images? | Continuous wave sound |
| Imaging systems produce _____ ______ or _____, of acoustic energy to create every picture of anatomy. | Short bursts or pulses |
| What is a pulsed sound? | is a collection of cycles that travel together. |
| What must a pulse have? | A beginning and an end |
| What is a pulse made of? | An individual cycle and moves as a single unit. |
| What two components does a pulsed ultrasound have? | Transmit, talking or "on" time and receive, listening, or "off" time |
| Each particular transducer emits what? | a pulse with a fixed duration |
| What is pulse duration? | Pulse duration is the actual time from the start of a pulse to the end of that pulse. |
| Does pulse duration send out a transmit or receive? | Transmit |
| Units of pulse duration are reported in what unit? | Units of time such as microseconds |
| Pulsed duration is is determined by? | Sound source only |
| Is pulsed duration adjustable? | No |
| how is pulse duration proportional to the number of cycles in the pulse? directly or inversely | directly |
| how is pulse duration proportional to period? directly or inversely? | directly |
| what two characteristics create pulses of long duration? | many cycles in the pulse, or individual cycles with long periods |
| what two characteristics create pulses of short duration? | few cycles in the pulse, or individual cycles with short periods |
| In clinical imaging, a pulse typically has how many cycles? | 2 to 4 cycles |
| which pulses are desirable for imaging and why? | short pulses because the create images of greater accuracy |
| what is spatial pulse length? | spatial pulse length is the distance that a pulse occupies in space from the start to the end of a pulse |
| what are the units of SPL? | units of distance |
| what is SPL determined by? | both sound source and the meduim |
| Is SPL adjustable? if so, why? | no |
| How is spatial pulse length proportional to wavelength? | directly |
| How is spatial pulse length proportional to frequency? | inversely |
| How is spatial pulse length proportional to the number of cycles in the pulse? | directly |
| while pulse duration is the time that a pulse is on, spatial pulse length is the _______ of the pulse end to end. | distance |
| what are 2 characteristics to create long pulses of spatial pulse length? | many cycles in the pulse and cycles with longer longer wavelengths |
| what are 2 characteristics to create short pulses of spatial pulse length? | fewer cycles in the pulse and cycles with shorter wavelengths |
| define pulse repetition period. | pulse repetition period is the time from the start of one pulse to the start of the next pulse |
| what are the units of PRP? | units of time |
| what is PRP determined by? | sound source only |
| Is PRP adjustable? If so, why? | it is adjustable because the sonographer can adjust the depth of view |
| when the system is imaging shallow, the time from one pulse to another is? | short |
| when the system is imaging deeply, the time from one pulse to another is? | longer |
| what is depth of view? | depth of view describes the maximum distance in to the body that an ultrasound system is imaging. |
| how are pulse repetition period and imaging depth related? | directly |
| as depth of view increases, pulse repetition period ________ | increases |
| as depth of view decreases, pulse repetition period ________ | decreases |
| what are the two components of the pulse repetition period? | transmit time or "on" time, and receive time or "off" time |
| the transmit time is called _____________ | pulsed duration |
| with deeper imaging, the listening time and the pulse repetition period | lengthen |
| with shallower imaging, the listening time and the pulse repetition period | shorten |
| when is the only time the listening time portion is altered? | when the sonographer changes the depth of the image |
| what is pulse repetition frequency (PRF)? | pulsed repetition frequency is the number of pulses that an ultrasound system transmits into the body each second |
| what are the units of pulse repetition frequency? | units of Hz (hertz) |
| what is PRF determined by? | sound source only |
| Is PRF adjustable? If so, why? | It is adjustable because the sonographer can alter the depth |
| how are pulse repetition frequency and depth related? | inversely |
| as depth of view increases, pulse repetition __________ | decreases |
| as depth of view decreases, pulse repetition __________ | increases |
| when imaging shallow, the pulse repetition is? | high |
| when imaging deep, the pulse repetition is? | low |
| how are pulse repetition period and pulse repetition frequency related? | inversely or reciprocal |
| which of these four values foras depth of view increases pulse repetition __________ would have the longest pulse repetition period? A. 2 kHz B. 4,000 Hz C. 6 Hz D. 1 kHz | C. 6 Hz. pulse repetition period is the reciprocal of pulse repetition frequency. this choice has the lowest pulse repetition frequency and, thus, the longest pulse repetition period. |
| four pulses have pulse repetition periods as listed below. which of the following four waves has the highest pulse repetition frequency? A. 8 s B. 80 ms C. 5 ms D.400 ks | C. 5 ms. the pulse with the shortest pulse duration will have the highest pulse repetition period. |
| which of these four pulses with PRFs listed below has the shortest pulse repetition period? A. 12 kHz B. 6,000 Hz C. 20 kHz D. 1 kHz | c. 20 kHz. Pulse repetition period is the reciprocal pf pulse repetition frequency. this answer has the highest pulse repetition frequency and , thus, the shortest pulse repetition period |
| four waves have pulse repetition periods as listed below. which of the following has the lowest pulse repetition frequency? A. 8 s B. 80 μs C. 8000 ns D. 800 ms | A. 8 s. the pulse with the longest pulse duration will have the lowest pulse repetition frequency |
| true or false. two waves can have identical pulse repetition frequencies, even if their pulse repetition periods are different. | false. tow waves can never have identical PRFs if their PRPare different |
| true or false. two waves can have identical PRFs, even if their periods are different. | true. period and pulse repetition frequency are unrelated |
| true or false. two waves canhave identical PRFs , even if their frequencies are different. | true. frequency and pulse repetition frequency are unrelated. |
| true or false. PRF and pulse repetition period are determined only by the imaging depth. | true. this is a very important comcept. |
| what is duty factor? | duty factor is the percentage or fraction of time that a system transmits a pulse |
| what are the units of duty factor? | none |
| what are the typical values of duty factor? | ranges from 0.002-0.005 or 0.2%-0.5% |
| how is duty factor determined? | sound source |
| is duty factor adjustable? If so, why? | it is adjustable because the sonographer can change the depth of view |
| what is the maximum value for for duty factor? | 1 or 100% |
| what is the minimum value for duty factor? | 0% |
| true or false. duty factor changes when the sonographer alters the imaging depth. | true |
| what happens to the pulse duration or transmit time as image depth increases? | it remains constant while listening time is prolonged. |
| what happens to the duty factor during deeper imaging? | it decreases |
| if all the factors remain unchanged, what happens to the duty factor [increases, decreases, remains the same] when the pulse repetition frequency increases? | increases |
| if all the factors remain unchanged, what happens to the duty factor [increases, decreases, remains the same] when imaging depth increases? | decreases |
| if all the factors remain unchanged, what happens to the duty factor [increases, decreases, remains the same] when the pulse repetition periods increases? | decreases |
| if all the factors remain unchanged, what happens to the duty factor [increases, decreases, remains the same] when the sonographer uses a new transducer with a longer pulse duration? | increases |
| what is the duty factor if the pulse duration is 1 μs abd the pulse repetition period is 1 ms? A. 100% B. 0.1 C. 0.01 D. 0.001 | D |
| which if the following terms does not belong with the others? A. high duty factor B. shallow imaging C. low PRF D. short pulse repetition period | C. Low PRF is associated with deep imaging. the other three choices are all associated with shallow imaging |
| which of the following terms does not belong with the others? A. low duty factor B. shallow imaging C. low PRF D. long pulse repetition period | B. shallowing imaging does not belong. the others three choices are associated with deep imaging |
| what happens when you adjust the imaging depth? | it changes the pulse repetition period, pulse repetition frequency, and duty factor |
| _________ is the time from the start of a pulse to the end of that pulse. | pulse duration |
| ________ is the time from the start of a pulse to the start of the next pulse. | pulse repetition period |
| pulse repetition frequency is the reciprocal of ___________ | pulse repetition period |
| by changing the imaging depth, which of the following does the operator also change (more than 1 may be correct)? A. PRF B. duty factor C. propagation speed D. PRP E. amplitude F. spatial pulse length | A. PRF, B. duty factor, D. PRP |
| the speed pf a 5MHz continuous wave is 1.8 km/sec. the wave is then pulsed with a duty facot of 0.5. calculate the new propagation speed. | the propagation speed for pulsed and continuous wave sound is the same.; in this case 1.8 km/s. it depends only upon the meduim through which the sound travels |
| what is the duty factor if the pulse duration is 1 millisecond, and the pulse repetition period is 1 second? | the duty factor is 0.001 or 0.01%, 0.001 divided by 1.0=0.001 |
Created by:
april.angelico