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study material ph 2
| Question | Answer |
|---|---|
| Pulse duration units | Micro seconds |
| Pulse duration formula | number cycles in pulse times period or number of cycles in pulse/frequency |
| Aka Pulse duration | “on time”,”talk time”, “transmit time” |
| Pulse duration is determined by | the sound source |
| Is pulse duration adjustable | no |
| Pulse durations is related to the number of_____ in the pulse | cycles |
| Pulse duration is/is not directly related to period | is |
| Pulse duration is __________ to the frequency | proportional |
| This sends out a sound wave and then turns off to listen. Listens till first wave returns before sending out another one (that way is knows where the wave comes from, how deep it comes from and where to put it on our image) | pulse sound |
| The units for this is time (ex. Microsecond) and it is the actual time from start to end of a pulse | pulse duration |
| Which type of pulse is more desirable in diagnostic US? | short pulses and short pulse lengths gives better images |
| Spatial pulse length aka | distance |
| Spatial pulse length is determined by – | both the source and the medium |
| Spatial pulse length determines what? | the longitudinal resolution (image quality) |
| Formula for spatial pulse length | Spl(mm)=number of cycles time wavelength |
| To make shorter pulse duration you have to have | few cycles or cycles with shorter periods |
| To make short spatial pulse length you have to have | few cycles or short wavelength (so use high F) |
| Spatial Pulse length definition | distance that a pulse occupies in space/distance from the beginning of pulse to end of pulse. |
| Spatial pulse length is ________ proportional to the number of cycles | directly |
| Spatial pulse length is directly proportional to? | wavelength |
| You want a ____ spl | high |
| There is a 3 MHz and 5 MHz transducers both with 5 cycles. Which will have the greatest spatial pulse length? | 3Mhz because ^F v wavelength and the v the F the ^ the wavelength |
| The lower frequency the longer wavelength, thus longer the | spatial pulse length |
| Spatial pulse length increases when the | Number of cycles increase or the wavelength increases |
| Is spatial pulse length adjustable | no |
| What do you need to do since you cannot adjust SPL | get a new transducer |
| Spl is inversely proportional to | F |
| What is PRP | the time from the start of one pule to the start of a next pulse |
| AKA pulse repetition period | pulse duration and receive time |
| Can Pulse repletion period be changed by sonographer | yes (by adjusting depth but this is not the same as pulse duration) |
| Pulse repetition period is generally________ times longer than pulse duration. | 100 to 1000 |
| As imaging depth increases | PR period increases (its having to listen longer) |
| As imaging depth decreases | the PR period decreases |
| PRP is ______ to period. | unrelated |
| PRP is just related to | depth |
| When you decrease it means going? | shallow |
| Which of these four values for PRF would have the longest PRP 2 kHz, 4000Hz, 6 Hz, or 1 kHz? | ^ Hz (^PRPvORF) |
| Four pulses have PRP’s as listed. Which of the following waves has the Highest PRF? 8s, 80 ms,5ms,or 400 ks? | 5 ms (^ high PRF = v short PRP) |
| Which of the following pulses with PRF’s listed has shortest PRP 12 KHz, 20 KHz, 6000 Hz, or 1 KHz? | 20 KHZ (short PRP=high PRF) |
| Four wave have PRP’s as listed. Which has the lowest PRF 8s, 80 microseconds, 800 nannseconds, or 800 ms? | 8 s (low PRF=high (long) PRP) |
| The _____ is the percentage or fraction of time that the system is transmitting a pulse. | duty factor |
| If the max value of system is 1. to 100 percent this is a _____ system. | continuous wave |
| If the minimum value is 0.0 to 0 % than this is a _____system. – | trx is silent system is off |
| Formula for duty factor (%) | pulse duration (sec)/pulse repetition period (sec) |
| Duty factor and ____ are buds | PRF as DF ^ PRF ^ |
| If you are sending out a lot of pulses, there is a lot of | talk time and high DF (higher % of talk time) |
| In clinical imaging (pulsed US), | the ______ ranges from .001 to .01 (0.1% to 1%) |
| The _______ adjust the maximum imaging depth and thereby determines the PR period. Therefor the operator ______ changes the duty factor while adjusting image depth. | operator, indirectly |
| What is Duty Factor determined by | the sound source |
| Is duty factor adjustable by the sonographer? | yes by changing the depth |
| This is inversely related to imaging depth? | duty factor |
| When PFR increases________ increases. | duty factor |
| Imaging depth decreases duty factor_______ | increases |
| Pulse repetition period increases, the duty factor | decreases |
| As pulse duration increases, the duty factor increases and – | need a new transducer |
| By adjusting the imaging depth the operator changes? | PRP, PRF, and DF |
| If all other factors remain unchanged, what happens to the duty factor when the PRF increases? Does it increase, decrease, or remain the same? | increases (PRF and DF are buds) |
| If all other factors remain unchanged, what happens to the duty factor when the imaging depth increases? Increases, decreases, or remains the same? | decreases (deeper we go the fewer pulses fo out, less talk time, so % of talk time or % of time on drops |
| If all other factors remain unchanged, what happens to the duty factor when the PRP increases? Increases, decreases, or remains the same? | decreases (DF has one friend (PRF). Since PRF and PRP are opposite, so are DF and PRF) |
| 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, decreases, or stays the same? | increases (if we go from 2 to 3 cycles its talking more) |
| What is the duty factor if the pulse duration is 1 micro second and the PRP is 1 ms? 100%, 0.1, 0.01, or 0.001? | 0.001 PD/PRP |
| This is the ability to image correctly? | resolution |
| What is the ability to distinguish two structures that are close to each other front to back and/or parallel to or along the main axis | LARRD |
| T/F. The shorter the pulse the better the LARRD resolution | true |
| LARRD resolution is determined by | spatial pulse length (medium and sound source (also short pulse duration)) |
| As frequency increases, the numerical value of the _________ resolution decreases. | LARRD |
| We have better LAARD resolution and higher quality images with ______ frequency transducers? | high |
| The smaller the number, the ______ the axial resolution. | better |
| Is LARRD resolution adjustable? | no |
| Since the SPL for the Trx is fixed, the sonographer ______ change the axial resolution. | cannot |
| What is the formula for LARRD? | SPL/2 |
| In soft tissue formula for LARRD? | .77 time number of cycles in pulse/f(MHz) |
| The shorter the pulse, the _____ the number, the better the picture quality. | smaller |
| For best axial resolution we want | short pulses and short pulse durations |
| The higher the frequency you use, the _____ the wavelength that is used_ | shorter |
| Short pulses have less_____ and fewer cycles in the pulse. | ringing |
| Shorter pulses and shorter pulse lengths shows | exactly what is going on in the body |
| A pulse is short if there are _____ cycles in the pulse. | fewer |
| How do we reduce ringing | with dampening of the crystal |
| A pulse is short if each cycle in the pulse has a _____wavelength. | short |
| Shorter wavelengths are characteristic of _______ frequency sound | higher |
| Pulses made of higher frequency cycles have _________ ______ resolution | superior axial |
| Superior axial resolution is associated with | shorter spatial pulse length, shorter pulse duration, high f and shorter wavelength, fewer cycles/pulse (less ringing), and a lower numerical number |
| Which of the following tranducers has the poorest axial resolution?1.7 MHz and 4 cyc/pulse, 2.6 MHz and 3 cyc/pulse, 1.7 MHz and 5 cyc/pulse, or 2.6 MHz and 2 cyc/pulse | 1.7 and 5 cyc/pulse (low freq many cycles) |
| Which tranducers has the best axial resolution? 1.7 MHz and 4 cyc/pulse, 2.6 MHz and 3 cyc/pulse, 1.7 MHz and 5 cyc/pulse, or 2.6 MHz and 2 cyc/pulse | 2.6 MHZ cyc/pulse (higher freq, shorter cycles) |
| The ______ is the range or difference between the highest and lowest frequency emitted from the transducer. | bandwidth |
| The smaller the bandwidth, the _____ exact the frequency emitted by the tranducer. | more |
| An ultrasound pulse containing frequencies in a small range around the main frequency is said to have a ______ bandwidth | narrow |
| The process of ______ increases the range of frequencies present in any pulse. | damping |
| Resonant frequency AKA | main, center, primary, natural |
| Main frequency is 3 MHZ with a frequency range of (1 | 5MHz) what is the bandwidth? |
| We want a ______ frequency and a ______bandwidth. | low, wide |
| Q factor = | resonant frequency/bandwidth |
| The Q factor has what kind of unit | none it is unitless |
| How is a PZT created? | by heating to 360 C or 680 F (curie pt) |
| What determines the Frequency of the pulsed US? | thickness of the PZT and the speed of sound in the PZT |
| Thickness of the the PZT equals ____ of the wavelength of sound in the crystal | 1/2 |
| Crystal thick= | low freq (beer mug) |
| Crystal thin= | high freq (wine glass) |
| T/F.A very high Q factor transducer is used more often in diagnostic imaging transducers than a low Q factor | False we use a low Q factor |
| T/F. The damping material in a transducer decreases the bandwidth. | False it increases the bandwidth |
| T/F. The damping material in a transducer improves the systems range resolution. | true also called LARRD |
| 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?1,200,000,1.400,000,1.725.000. Or 1.950.000 | 1726,000 Rayls |
| Which of the following crystals will produce sound with the lowest frequency? Thin with a low speed, thin with a high speed, thick with a low speed, or thick with a high speed | thick with a low speed |
| Which type of transducer has a greater Q factor? Therapeutic or imaging | therapeutic |
| In an imaging transducer, what is the purpose of attaching the backing material to the PZT? Increasing the bandwidth, decreases the q factor, improve image quality, or decrease the transducers sensitivity | improve image quality (it does all of these, but its purpose is to do this or we would never get an image) |
| The ability to distinguish two structures lying close together is called | resolution |
| The ability to distinguish two structures lying close together front to back is | LARRD |
| The ability to distinguish two structures close together side by side or perpendicular is called | LATA |
| Axial and lateral resolution are both measured with units of | distance |
| When the number of cycles in the pulse increases , frequeny remains the same, what happens to image quality? | it degrades |
| High frequency trx have best ? | range resolution |
| What is the benefit of choosing a transducer with a large diameter over one with a small diameter? | can focus at greater depths |
| Frequency for Doppler is usually ______ than for imaging | lower |
| Increasing the number of focal zones is a trade off of what | lateral resolution for temporal resolution |
| Decreasing the elevational resolution will give us what | the inability to clearly demonstrate small cystic structures |
| An array tranducer has the ability to | electronically focus and steer the beam |
| What does apodization do | it decreases the side lobes by giving more power to the inner elements |
| Subdicing help to do what | decrease grading lobes |
| This is the measure of beam width perpendicular to the imaging plane | elevational resolution |
| The elevations resolution is determined by – | mechanical focusing that is placed along the width of the array |
| If you use a lower frequency transducer, what is the trade off | decreased spatial resolution for improved penetration |
| Pulsed array is used for | cardiac imaging |
| You can reduce the beamwidth to increase spatial resolution by | focusing |
| In order to focus a sound beam relatively far away from the transducer, it is advantageous to | increase the diameter of the element |
| This represents the best measurement for resolution of modern ultrasound transducers | axial (the worst is elevational) |
| If you want an improved field of view use | a tightly curved transducer |
| Bandwidth is the spectrum of Frequencies emitted by the | pulse way trx |
| The matching layer equals_____ of the wavelength of the center of the frequency of the trx. | 1/4 |
| What does the matching layer do to axial resolution | improves it |
| Axial resolution = | near to far, crispness |
| Slice thickness | elevational resolution |
| A large field of view = | decreased frame rate |
| And smaller field of view = | and higher frame rate |
| Power output = | increased artifacts, brightness, and pt exposure |
| The lateral resolution is best here | at the focus |
| The focus = | 1/2 diameter of the crystal |
| Near zone length formula= | d^2/4wavelength |
| NZL is inversely related to | wavelength |
| NZL is directly related to | the crystals diameter |
| Formula for NZL= | p2f/4c (prop speed) |
| Attenuation is – | frequ/2 if increase frequency you increase attenuation |
| The far zone is | 2x the near zone |
| These are the consequences of using backing materials | decreasing sensitivity, decreased bandwidth, low Q factor |
| Q factor is a | unitless number related to bandwidth |
| Formula for Q factor= | Main freq/bandwidth |
| A wide bandwidth probe probe has a _____ Q factor | low |
| The Q factor directly related to | pulse length |
| A short pulse makes us have a _____ Q factor | low |
| A long pulse makes us have a _____ Q factor | high |
| A narrow bandwidth probe has a _____ Q factor | high |
| Example of a probe with a narrow bandwidth | cw doppler and therapeutic probes |
| What determines the freq of sound produced by the trx? | characteristics of the active element |
| Aka Continuous wave | electrical freq, acoustic freq |
| A pulsed wave has | on and off time |
| What are two characteristics of an element that combine to determine the frequency of sound from pulsed wave trxs | speed of sound in Pzt (inversely related) and thickness of the element |
| The thinner the element the | higher the frequency |
| The thicker the element the | lower the frequency |
Created by:
hseratt