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SPI Chapter 4
Describing Pulsed Waves
| Question | Answer |
|---|---|
| What are the 5 Parameters of to describe pulsed sound? | Pulse Duration, Pulse Repetition Period, Pulse Repetition Frequency, Duty Factor, Spatial Pulse Length |
| What are pulses? | a collection of cycles that travel together and is acoustic energy that creates pictures |
| What must a pulse have? | a beginning and an end |
| What two components does pulse ultrasound have? | "on" and "off" time |
| What is pulse duration? | the time from the start of a pulse to the end of that pulse |
| What are the units for pulse duration? | units of time |
| What are the typical values of pulsed duration? | 0.3 to 2.0 microseconds |
| What is pulse duration determined by? | sound source |
| Is pulse duration adjustable by the sonographer? | No |
| What does pulse duration identifies? | "on" time |
| Pulse duration is equal to | = # cycles x period (micro. sec.) |
| What is pulse duration directly proportional to? | period |
| What is pulse duration inversely proportional to? | frequency |
| What is the number of cycles in the pulse directly proportional to? | Pulse duration |
| What is the formula for pulse duration? | pulse duration (micro sec.) = # cycles/frequency (MHz) |
| What two characteristics create pulses of long duration? | many cycles in a pulse or individual cycles with long periods |
| What two characteristics create pulses of short duration? | few cycles in a pulse or individual cycles with short periods |
| How many pulse cycles does a pulse typically contain? | 2 to 4 cycles |
| Which type of pulse is more desirable for imaging? | Shorter duration because they obtain greater accuracy |
| What is spatial pulse length? | distance from the start to the end of a pulse |
| What are the units for spatial pulse length? | units of distance, mm |
| What are the typical values in soft tissue for spatial pulse length? | 0.1 to 1.0 mm |
| What is spatial pulse length determined by? | both the source and the medium |
| Is spatial pulse length adjustable by the sonographer? | No |
| What is the formula for spatial pulse length? | spatial pulse length (mm) = #cycles x wavelength (mm) |
| What is spatial pulse length directly proportional to? | #cycles in a pulse |
| What wavelength directly proportional to? | spatial pulse length |
| What is spatial pulse length inversely proportional to? | frequency |
| What are two characteristics to create long pulses? | many cycles in the pulse and cycles with longer wavelengths |
| What are two characteristics to create short pulses? | fewer cycles in the pulse and cycles with shorter wavelengths |
| What is pulse repetition period? | the time from the start of one pulse to the start of the next pulse |
| What does pulse repetition period consist of? | one "on" time and one "off" time |
| What are the units of pulse repetition period? | units of time (mili sec.) |
| What are the typical values for pulse repetition period? | 100 micro sec. to 1 mili sec. |
| What is pulse repetition period determined by? | sound source and imaging depth |
| Is pulse repetition period adjustable by the sonographer? | Yes |
| What is PRP unrelated to? | period |
| What is PRP directly related to? | depth of view |
| What is depth of view? | the maximum distance into the body that an ultrasound system is imaging (markers alongside the image) |
| Is depth of view controlled by the sonographer? | Yes |
| What is another word for transmit time? | pulse duration |
| Why can pulse duration not be adjusted by the sonographer? | because it is a characteristic of the transducer and has a fixed value |
| When does the transducer receive reflections from in the body? | "off" time/listening time |
| When the sonographer adjusts the imaging depth, what else do they only alter at the same time? | the listening time |
| What is pulse repetition frequency? | number of pulses that an ultrasound system transmit into the body each second |
| What are the units of pulse repetition frequency? | Hz (per second0 |
| What are the typical values of pulse repetition frequency? | 1,000 to 10,000 hertz |
| What is the pulse repetition frequency determined by? | sound source |
| Is pulse repetition frequency adjustable by the sonographer? | Yes |
| What is PRF unrelated to? | frequency |
| What is PRF directly related to? | depth of view |
| What is PRF inversely related to? | depth of view |
| What relationship does PRP and PRF have? | inversely related/reciprocals |
| Can two waves have identical PRFs, even if their PRPs are different? | No, that does not exists |
| Can two waves have identical PRFs, even if their frequencies are different? | True. Frequency and PRF are unrelated |
| Can two waves have identical PRFs, even if their periods are different? | True. Period and PRF are unrelated |
| Is PRF and PRF determined only by the imaging depth? | Yes |
| What is Duty Factor? | percentage or fraction of time |
| What are the units of duty factor? | None, it is a percentage |
| What are the typical values of duty factor? | 0.2% to 0.5% |
| What is duty factor determined by? | sound source |
| Is duty factor adjustable by the sonographer? | Yes |
| What is duty factor inversely related to? | Image depth |
| What is the formula for duty factor? | duty factor (%) = pulse duration/PRP x 100 |
| What is the maximum value for duty factor? | 1 or 100% |
| What is the minimum value for duty factor? | 0 % |
| How does the sonographer change duty factor? | when the sonographer alters imaging depth |
| What does shallow imaging consists of? | less listening, shorter PRP, higher PRF, higher duty factor |
| What does deep imaging consists of? | more listening, longer PRP, lower PRF, lower duty factor |
| If all other factors remain unchanged, what happens to the duty factor when the PRF increases? | increases |
| If all other factors remain unchanged, what happens to the duty factor when imaging increases? | decreases |
| If all other factors remain unchanged, what happens to the duty factor when the PRP increases? | decreases |
| If all other factors remain unchanged, what happens to the duty factor when the sonographer uses a new transducer with a longer pulse duration? | increases |
| When adjusting image depth, what else changes? | the PRP, PRF, and duty factor |
| What can not be changed by the sonographer? | the pulse duration and spatial pulse length |
| What are the parameters that describe both pulsed and continuous waves? | the period, frequency, wavelength, and speed |
| What does continuous wave both consists of? | both "on" and "off" time |
| The speed of a 5 MHz continuous wave is 18 km/sec. The wave is then pulsed with a duty factor of 0.5. Calculate the new speed? | 1.8 km/sec. Propagation speed for pulsed and continuous wave sound is the same in this case, it depends only upon the medium |
| What is the duty factor if the pulse duration is 1 micro. sec., and the PRP is 1 ms? | 0.001 or 10^-3 |
| What is the duty factor if the pulse duration is 1ms, and the PRP is 1 sec.? | 0.001 or 0.1% |
Created by:
Lazacha
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