Chap 4 Lvl 2 Flashcards
What is a pulsed wave?
A mode that turns the transmitter on and off periodically to reduce range ambiguity.
Pulsed wave refers to PW Doppler, color Doppler, 2D imaging, 3D imaging, and M-mode.
Define an acoustic beam.
A single transducer event in a specific direction and the associated echoes.
The term ‘acoustic line’ is sometimes used, but ‘beam’ is more appropriate as it implies three dimensions.
What is a receive beam?
A returning echo from an impulse
What is frame time?
The time required to generate an image
Also referred to as scan time, acoustic scan time, or acoustic frame time.
What is the frame rate?
The reciprocal of the frame time, equivalent to the number of images generated per second.
A better name for this parameter is the frame frequency, which indicates the reciprocal nature with respect to the frame time.
True or False: The sampling rate is also referred to as sampling frequency.
True
This term provides a more intuitive understanding of the parameter.
Fill in the blank: The frame rate is equivalent to the number of images generated per _______.
second
What governs the maximum frequency detectable in sampling?
The Nyquist criterion.
This criterion is discussed in detail in Chapter 6, Part I.
What is a characteristic of non-scanned modalities?
Non-scanned modalities transmute in the same direction repeatedly over time
These modalities transmit energy in a consistent direction.
How does the transmit power in non-scanned modalities relate to thermal bioeffects?
Transmit power is limited by the rate of thermal bioeffects
Thermal bioeffects refer to damage caused by excessive heat in tissues.
Name commonly used non-scanned ultrasound modalities.
Commonly used modalities include:
* CW Doppler
* PW Doppler
* M-mode
* A-mode (almost extinct)
CW stands for Continuous Wave and PW stands for Pulsed Wave.
What new approach has been created for non-scanned modalities in recent years?
A new approach for generating 2D and 3D images using plane waves or diverging waves
This development adds complexity to the classification of non-scanned modalities.
What was a simple criterion to determine if an ultrasound modality was scanned or non-scanned?
The presence or absence of an image
This criterion is no longer a definitive differentiator due to advancements in technology.
Fill in the blank: A non-scanned modality is when each successive transmit is in the same direction as the _______.
previous transmit
This definition emphasizes the repetitive nature of non-scanned modalities.
What is the purpose of scanned modalities?
Images are ‘built up’ over time
Scanned modalities involve the accumulation of data over a period to generate a complete image.
What is the benefit of parallel processing in scanned modalities?
Reduces the time needed to generate a frame
Parallel processing allows for faster image generation by transmitting wider beams sequentially.
True or False: Conventional sequential imaging uses wider beams than parallel processing.
False
Conventional sequential imaging typically utilizes narrower beams compared to the wider beams used in parallel processing.
What is the characteristic of a typical 2-D pulse?
A few cycles with a very large amplitude
2-D pulses are used in imaging techniques.
How does the amplitude of a typical pulsed wave (PW) Doppler pulse compare to a 2-D pulse?
Smaller amplitude with many cycles
PW Doppler pulses are used to measure velocities.
What is the nature of a continuous wave (CW) Doppler wave?
Continuous with an even lower amplitude
CW Doppler is used for continuous monitoring of blood flow.
What control allows the user to determine the number of cycles in a pulsed wave Doppler pulse?
Sample volume (gate) size
This control is crucial for optimizing Doppler measurements.
Fill in the blank: The typical 2-D pulse has a few cycles but a very large _______.
amplitude
True or False: The CW Doppler wave has a higher amplitude than the PW Doppler pulse.
False
CW Doppler waves generally have lower amplitude than PW Doppler pulses.
What is the relationship between Pulse Repetition Period (PRP) and imaging depth?
PRP is dependent on the imaging depth; increasing imaging depth increases the PRP
As the time to and from the target increases, the PRP lengthens.
What is the assumed propagation velocity for ultrasound machines?
1540 m/s
This value is used to calculate the maximum achievable PRP.
How does imaging depth affect Pulse Repetition Frequency (PRF)?
Imaging depth is inverse to prf so as imaging depth increases, prf decreases
PRF is the reciprocal of PRP.
Fill in the blank: The maximum achievable PRP is dependent only on the _______.
imaging depth
True or False: An increase in imaging depth will decrease the Pulse Repetition Period (PRP).
False
Increasing the imaging depth increases the time to and from the target, thereby increasing the PRP.
What is the relationship between PRP and PRF?
PRF is the reciprocal of PRP
This means that as PRP increases, PRF decreases.
What is the first step in the sequence of events for ultrasound imaging?
A pulse is transmitted
This initiates the imaging process.
What occurs at Time 2 in the ultrasound imaging sequence?
Transmit pulse arrives at desired imaging depth
This is the moment when the sound wave reaches the target tissue.
What happens at Time 3 in the ultrasound imaging process?
Echo from desired imaging depth is received back at the transducer
The returning echo provides data for image formation.
What action is taken at Time 4 in the ultrasound imaging sequence?
Another pulse is transmitted, repeating the process
This creates another set of data for imaging.
What is the purpose of the ultrasound imaging sequence?
To create a series of data points for imaging
This helps in forming a visual representation of internal structures.
Fill in the blank: The sequence of events in ultrasound imaging begins with a _______.
[pulse being transmitted]
Acoustic line time (prp) equation
PRP = 13 microsec/cm x imaging depth
Frame time equation
Frame time = Time/Line x #Lines/Frame
Time/line = 13 microseconds/CM
Frame time equation with imaging depth
Frame rate = (13 microsec/cm)(imaging depth/line)(#Lines/Frames)
What is color Doppler in the context of ultrasound imaging?
A non-scanned modality within a packet
How is a color image produced in ultrasound imaging?
By scanning a collection of color packets across the patient
What are the acoustic lines in a color packet?
Non-scanned lines that create a packet
How much more time is required to produce a color scan compared to a standard 2D image?
Considerably more time
What is the formula for calculating color frame time?
color frame time = time/packet line * packet lines / display lines * display lines/frame
What does Wavelength (X) represent in ultrasound?
The distance between successive peaks of a wave
Wavelength is critical for understanding wave propagation.
What does Pulse Duration (PD) refer to?
The time for one pulse to occur
Pulse duration is important for determining image resolution.
Fill in the blank: Pulse Repetition Frequency (PRF) is measured in _______.
Hertz (Hz)
PRF indicates how often pulses are emitted.
What does Duty Factor indicate in ultrasound?
The fraction of time that the system is actively transmitting
It is calculated as PD / PRP.
True or False: The Duty Factor is always less than 1.
True
A duty factor of 1 would mean continuous wave transmission.
What is Frame Rate in ultrasound?
The number of frames displayed per second
Higher frame rates lead to better motion representation.
What is Frame Time?
The time taken to produce one frame
Frame time affects the overall temporal resolution of the ultrasound image.
Formula for PD
PD = P * #cycles
Formula for PRP
PRP = 13microsec * depth
Formula for duty factor
DF = PD/PRP
Foundational drawing for PW
What does bandwidth refer to?
The range of frequencies over which a device can function.
Benefit of wide bandwidth transducers?
They can operate over a wide range of frequencies.
Define bandwidth.
Bandwidth (BW) = maximum frequency - minimum frequency for a specified attenuation rate
What is fractional bandwidth?
Fractional bandwidth = bandwidth / operating frequency
True or False: The fractional bandwidth is commonly used for transducers.
True
What is the quality factor (Q)?
Q = 1 / fractional bandwidth
True or False: A broader bandwidth is always better.
False
What advantage does greater bandwidth provide?
Flexibility in operating at different frequencies
What is frequency agility?
The ability to operate at different frequencies suited for the modality and specific patient
What is dynamic frequency tuning?
A technique that uses wide bandwidth in transmit and sliding receive filters to produce images.
What does dynamic frequency tuning achieve in imaging?
It produces higher frequency echoes for near field images and lower frequency echoes for far field images.
True or False: Dynamic frequency tuning does not utilize wide bandwidth.
False
What is the role of sliding receive filters in dynamic frequency tuning?
They adjust to allow different frequency echoes to be processed for imaging.
What types of echoes are produced in the near field and far field using dynamic frequency tuning?
Higher frequency echoes for near field and lower frequency echoes for far field.
What imaging technique is associated with dynamic frequency tuning?
Harmonic Imaging
