# Shared Flashcard Set

## Details

Understanding Ultrasound Physics/Edelman Ch 19 Part 1
Understanding Ultrasound Physics - Part One
66
Medical
Professional
09/27/2010

## Additional Medical Flashcards

Term
 The frequency of sound changes when the sound source and the receiver move closer together or further apart. What is this called?
Definition
 Doppler ShiftDoppler Frequency
Term
 What is doppler shift used to measure
Definition
 Velocity of Blood Flow
Term
 As sound approaches a receiver, what seems to happen to its frequency/pitch?
Definition
 Increases
Term
 As sound departs a receiver, what seems to happen to its frequency/pitch?
Definition
 Decreases
Term
 Demodulation
Definition
 The process of extracting low doppler frequency from the higher transducer frequency
Term
 What is the doppler shift range?
Definition
 20Hz - 20,000Hz (20kHz)
Term
 If the transmitted signal is 5,000,000 Hz and the received signal is 5,003,000 Hz, what is the doppler shift? Which direction is the blood moving?
Definition
 3,000Hz (positive, so...)Toward Transducer
Term
 When RBCs move toward the transducer, is the doppler shift negative or positive?
Definition
 Positive
Term
 When RBCs move away from the transducer, is the doppler shift negative or positive?
Definition
 Negative
Term
 Speed
Definition
 This is purely a magnitude, indicating the distance traveled
Term
 Velocity
Definition
 This is magnitude, indicating the distance traveled, and the direction traveled
Term
 Speed is reported in what units?
Definition
 cm/s (any distance divided by time)
Term
 Doppler provides a (quantitative|qualitative) measurement
Definition
 Quantitative
Term
 Spectral Doppler (Color Flow) provides a (quantitative|qualitative) measurement
Definition
 Qualitative
Term
 The ideal transducer angle (angle correction/cosine) for taking doppler measurements is what?
Definition
 0 - 60 Degrees(0 or 180 degrees is ideal)
Term
 What is the relationship between doppler shift and blood flow velocity?
Definition
 Directly Related
Term
 Why is there a "2" in the doppler shift equation?
Definition
Term
 What is the relationship between doppler shift and transducer frequency?
Definition
 Directly Related
Term
 When blood flow is ___ to the sound beam, the entire doppler shift is measured, making the velocity measurement 100% accurate
Definition
 Parallel(0 or 180 Degrees)
Term
 When blood flow is ___ to the sound beam, the no doppler shift is measured, making the velocity measurement 0% accurate
Definition
 Perpendicular(90 Degrees)
Term
 The % of true velocity that is measured depends on the ___ of the angle between the sound beam and the direction of flow
Definition
 Cosine
Term
 A Doppler system that measure the presence of blood flow without distinguishing its direction is called what?
Definition
 Nondirectional Doppler
Term
 A ___ doppler shift indicates flow ___ the transducer whereas a ___ doppler shift represents flow ___ the transducer
Definition
 + / towards- / away from
Term
 A doppler system that measures the presence of blood flow and its direction is called what?
Definition
 Bidirectional Doppler
Term
 Nondirectional doppler uses how many speakers?
Definition
 1
Term
 Bidirectional doppler uses how many speakers?
Definition
 2 (one for flow in each direction)
Term
 When flow toward the transducer is displayed graphically, above the baseline, and flow moving away from the transducer is shown below the baseline, what is this called?
Definition
Term
 When assessing adjacent artery and veins with doppler, how can we determine which is which?
Definition
 The artery & vein will each be heard from a different speaker. The arterial signal will have a higher velocity.
Term
 How many crystals are needed for continuous wave doppler?
Definition
 Two - one for transmitting, one for receiving
Term
 What is the greatest advantage of continuous wave doppler?
Definition
 Its ability to accurately measure very high velocities
Term
 What is the primary disadvantage of continuous wave doppler?
Definition
 Range Ambiguity - its inability to determine the exact location of the moving RBCs
Term
 With continuous wave doppler, at which part of the beam are velocities measured?
Definition
 Velocities are measured along the entire beam
Term
 Another disadvantage of continuous wave doppler is its lack of ___: doppler shifts from deeper RBCs may be incorrectly interpreted as having been created by ___ RBCs
Definition
 TGCFewer
Term
 Simultaneous anatomic imaging and doppler imaging is called what?
Definition
 Duplex Imaging
Term
 A transducer which contains only two crystals and no backing material is called what?
Definition
 Dedicated Continuous Wave(Pedoff)
Term
 Which kind of transducer offers these advantages:- higher sensitivity- high quality factor- narrow bandwidth- undampened signal strength
Definition
 Dedicated Continuous Wave(Pedoff)
Term
 How many crystals are needed for pulsed wave doppler?
Definition
 One - alternates between transmit & receive
Term
 With pulsed wave doppler, at which part of the beam are velocities measured?
Definition
 Gate Sample Volume
Term
 What is the greatest advantage of pulsed wave doppler?
Definition
 Ability to select the exact location to assess - Range Resolution/Specificity- Freedom from Range Ambiguity Artifact
Term
 What is the primary disadvantage of pulsed wave doppler?
Definition
 Inaccurate measurement of high velocity signals (aliasing)
Term
 What is it called when high velocity flow in one direction is displayed as traveling in the opposite direction?
Definition
 Aliasing
Term
 Which kind of transducer offers these advantages:- low quality factor- low sensitivity- wide bandwidth pulses
Definition
 Pulsed Wave Doppler Transducers
Term
 Can pulsed wave doppler transducers produce images as well?
Definition
 Yes
Term
 Aliasing only occurs with what type of doppler?
Definition
 Pulsed Wave Doppler
Term
 This is the highest doppler frequency or velocity that can be measured without the appearance of aliasing
Definition
 Nyquist Limit
Term
 Half the PRF is also called what?
Definition
 Nyquist Limit
Term
 The Nyquist Limit is measured in what units?
Definition
 Hz
Term
 Deeper sample volumes create more ___
Definition
 Aliasing
Term
 The sampling rate of pulsed wave doppler is the ___
Definition
 PRF
Term
 Will the following result in more or less aliasing?- slower blood velocity- lower transducer frequency- shallow gate
Definition
 Less Aliasing
Term
 Will the following result in more or less aliasing?- faster blood velocity- higher transducer frequency- deep gate
Definition
 More Aliasing
Term
 What happens to the PRF/Nyquist Limit when the sample volume gate is shallow?
Definition
 High PRF/Nyquist Limit
Term
 What happens to the PRF/Nyquist Limit when the sample volume gate is deep?
Definition
 Low PRF/Nyquist Limit
Term
 What type of transducers create more aliasing?
Definition
 High Frequency Transducers
Term
 What type of transducer is less likely to create doppler shifts that exceed the Nyquist Limit?
Definition
 Low Frequency Transducers
Term
 These 5 techniques can be used to avoid what?1. Adjust scale to maximum2. Use lower freq transducer3. Use shallower sample volume gate4. Use CW Doppler5. Adjust baseline (appearance only)
Definition
 Aliasing
Term
 What is an advantage of adjusting doppler scale to its maximum?
Definition
 Doing so increases PRF & Nyquist Limit to maximum values, thus reducing the chances of aliasing
Term
 What is a disadvantage of adjusting doppler scale to its maximum?
Definition
 1. Higher PRF reduces sensitivity to low velocities2. Aliasing can still occur
Term
 What is an advantage of selecting a lower frequency transducer?
Definition
 Lower doppler shifts are less likely to exceed the Nyquist Limit and alias
Term
 What is a disadvantage of selecting a lower frequency transducer?
Definition
 Nothing significant, although lower quality grayscale anatomical images can occur during duplex imaging
Term
 What is an advantage of using a shallower sample volume gate?
Definition
 The PRF/Nyquist Limit increases, reducing the chances of aliasing
Term
 What is a disadvantage of using a shallower sample volume gate?
Definition
 Nothing really, although in some cases the sonographer may be unable to adjust the view to allow for a shallower sample volume gate
Term
 What is an advantage of using CW doppler?
Definition
 Aliasing never happens with CW
Term
 What is a disadvantage of using CW doppler?
Definition
 Range Ambiguity - the entire beam is measured
Term
 What is an advantage of using baseline shift?
Definition
 High velocity flows are displayed in the proper direction. Although no more accurate, it is more pleasing to the eye
Term
 What is a disadvantage of using baseline shift?
Definition
 1. Nothing changes other than visual appearance - audio signal will still come from the wrong speaker2. Aliasing can still occur
Supporting users have an ad free experience!