Physics - Ch. 5 Imaging Motion and Flow With Principle 1

Which state of matters classify as fluids?

liquids and solids

Which states of matter "flow"?

gases and liquids

Viscosity units

poise or kg/m-s

Volumetric Flow Rate (Q)

The volume of blood passing a point per unit of time

Volumetric Flow Rate units

milliliters per second (mL/s)

Volumetric Flow Rate formula

Q (mL/s) = Pressure difference (dyne/cm²) / Resistance to flow (poise)

What situation is Poiseuille's Law used for?

calculate steady flow in long, straight tubes

If pressure difference increases, flow rate ____________.

increases

If diameter of the tube increases, flow rate ____________.

increases

If viscosity of the tube increases, flow rate _____________.

decreases

If length of the tube increases, flow rate _____________.

decreases

Poiseuille's Equation:

Q = ΔPπr^4/8Lη

Q(mL s) = ∆P(dyne /cm2) × π × d4 (cm 4) / 128 × L (cm) × η (poise)

The volumetric flow rate in a tube is determined by ______________ difference and _____________.

pressure; resistance

With parabolic flow, the average flow speed across the vessel is equal to....

one half the maximum flow speed (center)

Is forward net flow still maintained with turbulent flow?

yes

Continuity Rule

Blood is neither created nor destroyed as it flows through a vessel SO... volumetric flow rate must be constant proximal, within, and distal to a stenosis

Bernoulli Effect

A drop in pressure associated with high flow speed at a stenosis

Absolute Doppler effect

for light

Relative Doppler effect

sound waves

f Dop =

f received - f transmitted

or

1/c

Doppler effect is caused by a change in ______________, caused by motion relative to the observer.

wavelength

As relative motion increases the Doppler effect _____________.

increases

What is the relationship between velocity and distance traveled for the doppler effect?

proportional: higher velocity implies a greater distance traveled

The relative distance change is a percentage of the ________________.

wavelength

Anything which results in a greater distance will result in a greater....

percent change in wavelength

Which three situations can affect the Doppler effect?

moving source

moving receiver

moving reflector

The change in frequency of the Doppler shift is caused by....

motion

If scatterer speed increases, the Doppler shift ____________.

increases

If source frequency increases, the Doppler shift _____________.

increases

Are Doppler shift and flow speed proportional?

yes

What type of flow information can Doppler Ultrasound provide?

presence of flow, direction of flow, speed of flow, character of flow

Form of presentation of Doppler information:

audible sounds, strip-chart recording, spectral display, color Doppler display

What happens to our velocity values as we get closer to 90 degrees?

they get less accurate

Signal processor uses a mathematical technique called __________________ to produce color Doppler.

autocorrelation

Is color Doppler angle dependent?

yes

The power of the Doppler shift is determined by the __________________ of the moving scatterers.

concentration

Is power Doppler angle dependent?

nope

Does power Doppler alias?

nope - but that also means there's no flow speed or character information

Which is more sensitive to flow, color or power Doppler?

power

What separates forward and reverse Doppler shift voltages?

A phase quadrature detector

Fast Fourier Transformation

digitization of spectral sample

The vertical axis on spectral display represents...

Doppler shift frequency

The horizontal axis on spectral display represents...

time

What indicates flow conditions downstream?

the relationship between peak systolic and end diastolic flow speeds

What does the Pulser determine:

PW, CW, or high PRF

PW -> gate size and depth

Doppler scale -> low PRF or high PRF

Can we steer with CW?

Naur unless it is pulsed

Do RBC's travel at the same speed and at the same angle?

no - so the machine calculates and entire RANGE of frequency shifts known as a SPECTRUM

How do we obtain bi-directional Doppler?

Reflectors coming back are both from stationary and moving structures -> Doppler removes the stationary ones -> Quadrature detection -> Zero-crossing detection -> Bidirectional Doppler

PW and CW Dynamic Range values:

PW = 140 dB

CW = 160 dB

there is a HUGE dynamic range

RBC's are _______ (high/low) level echos.

low

Wall Filter Theory

clutter is slower than blood resulting in low frequency shifts

___________ ___________ affects what wall filter setting should be used.

operating frequency

f Dop is proportional to f ___

fo (observer)

If the saturation of wall filters is set too low, _____________ __________ will occur.

electronic clutter

What are the 3 quantities of spectral Doppler on a 2D display?

1. Frequency on the vertical axis (converted to velocity per the Doppler equation)

2. Time on the horizontal axis (Sweep speed)

3.Amplitude/brightness

How are frequency and amplitude related?

they aren't

Frequency shift is dictated by the....

Doppler equation

Amplitude of the signal is determined by....

the scattering properties of the RBC's

Dead time

the roundtrip propagation time

When does listening start?

listening does not start until 13μsec x the depth to the gate - no earlier echoes are recorded

Does PW Doppler have any range ambiguity?

yes - it has some range ambiguity bc its not perfect

Can CW Doppler alias?

no

Nyquist criterion formula

(f Dop max) = PRF / 2

aka aliasing occurs when the frequency shift is greater than PRF / 2

__________ (high/low) frequency Doppler shifts cause aliasing.

High

Using the Doppler equation, what does high frequency Doppler shift do?

higher velocity flow, higher fo, lower, propagation velocity and angles closer to 0 and 180 degrees, deeper imaging, longer PRP, lower PRF

"True" or "Doppler" aliasing

you can not increase the scale high enough, "wrapping" around

Aliasing units

cm/s and m/s

Display aliasing

can be unwrapped by changing the baseline, not true alias but display alias

Decreasing the scale _____________ (increases/deceases) PRF and _______________ the PRP adding "dead time"

decreases; increases

What to do if aliasing continues after the scale is increased?

1. Use a lower frequency transducer

2. Find a view that has a shallower depth for the gate

3. Use CW Doppler

4. Use HPRF

Maximum Detectable Velocity equation

Rearranging the Doppler equation and adding the Nyquist

V (max) = c X PRF / 4 X f o cosθ

Nyquist Sampling Limit

Require PRF = 2 x Doppler Frequency

If there is a 3kHz Doppler signal, need _____ kHz PRF to sample.

6

The Maximum Doppler frequency that can be sampled is...

1/2 the PRF - more than that aliasing will occur

If PRF = 8 kHz, the max Doppler frequency is _____ kHz

4

Ambiguous gate location characteristics:

may be no blood flow there, signals are weaker, more attenuation from deeper depths, phased transducers are focused at the gate, decreasing the intensity for the ambiguous gate locations

HPRF

Compromise of both PW and CW - uses ambiguous gates above and below to pick up signals - used for DEEP structures and to prevent aliasing velocities

How does HPRF use range ambiguity?

to increase the max detectable velocity without aliasing, at the expense of some range resolution

samples above and below

Doing what automatically activates HPRF?

increasing the Doppler scale high enough or the depth deep enough

Differenced in gating technique: HPRF, CW, PW, color Doppler

Do most systems have separate controls for the color wall filters?

no, most set the color wall filters as a percentage of the color scale (10%)

As a result of increasing the color scales, the wall filters also increase, resulting in less ability to visualize _______ (higher/lower) velocity flow.

lower

What does the number at the top of the color bar indicate?

The highest detectable mean velocity towards the transducer is 63.6 cm/sec - encoded as red towards yellow

What does the number in the middle of the color bar indicate?

The black band vaguely represents that signals detected in this range are not likely to be visualized as a result of wall filtering

What does the number at the bottom of the color bar indicate?

The highest detectable mean velocity away from the transduceris 63.6 cm/sec - encoded as blue towards aqua

Color persistence

a technique in which frames are "averaged"over time

Is color averaging an equal weighting of each frame? If not, what is it an average of?

no - rather a heavier weighting of the latest frames, and less weighting of earlier frames (increases sensitivity)

How does color persistence affect short duration events vs long duration?

can make short duration events completely disappear, while making longer duration events persist even longer than reality

Color priority

a thresholding technique which allows the user to determine above what grayscale level 2-D data is presented and below which color data is presented

Round Trip Effect

the structure is moving as it reflects the wave back to the transducer, there is a doubling effect -> we should expect to see a factor of 2 in the Doppler shift equation

Doppler equation with no angle effects (yet)

f Dop = 2 f o v / c

Doppler equation assuming 1540 m/s

f Dop = 2 f o v / c = f o v / 770 m/s

cos (90)

0

DO we want to interrogate small RBC's with a high or low frequency probe?

high

Do we really even image BRC's?

no, we image constructive interference of spherical waves from multiple blood cells (increasing signal strength)

What is responsible for blood reflection?

changes in cell concentration

Rouleaux flow

occurs when RBC's aggregate -> low flow state

Doppler angle is critical to determine:

1. Flow direction

2. Assess Doppler measurement accuracy

3. Minimize Doppler error sources

4. Assess likelihood of artifact related issues, like spectral broadening

Insonification angle

measure between flow and line of observation

Which insonification angle will produce high frequency reflections? Low?

0 degrees; 180 degrees