Put the Probe Here Flashcards
The human ear can pick up frequencies up to _______ Ultrasound machines can produce sound waves with frequencies of ____ to ______
20 kHz 1.5 MHz to 7.5 MHz
In Ultrasound, when the sound wave is emitted by the piezoelectric crystals and reflected back by the material being scanned, what 2 things are being measured and what do they tell the computer?
- The time between the signal impulse and its return : indicates how deeps the structure is. 2. The intensity of the signal: indicates how dense the structure is.
How do piezoelectric crystals work?
They transform electrical oscillations (varying voltages in the electrical current) into mechanical oscillations, which are essentially sound waves. They send out sound waves and receive those that get reflected back, and turn them into electrical impulses.
What causes ultrasound waves to be reflected back to the probe?
Moving between the interfaces of two different media.
In Pulse Wave Doppler, one transducer crystal sends out a signal at a fixed time interval called the __________.
Pulse Repetition Frequency.
The main advantage of Pulse Wave Doppler as compared to Continuous Wave Doppler is: _______. The main disadvantage is: _________.
Advantage: It can measure the doppler shift (velocities) at a specifc point that is set by the echocardiographer, called the sample volume.
Disadvantage: Since PW doppler uses a single crystal to send and receive signals, there is a maximum frequency to the signals that can be sent out (called the “pulse repetition frequency”). Therefore, PW has a maximum velocity that it can reliably measure before it is subject to aliasing.
Define Nyquist Frequency.
- The maximum Doppler shift (or velocity) you can measure with Pulse Wave Doppler.
- Equals half the Pulse Repetition Frequency.
- Doppler shifts above the Nyquist frequency undergo aliasing.
What happens with aliasing?
- Aliasing happens when a velocity (or, doppler shift) being measured by Pulse Wave Doppler exceeds the Nyquist Frequency (half the Pulse Repetition Frequency).
- The result is that the doppler signal (aka velocity jet) appears to be going in the opposite direction.
What is the main advantage and disadvantage with Continuous Wave Doppler?
Advantage: There is no maximum doppler shift that can be measured, and therefore no aliasing.
Disadvantage: It cannot measure jet velocities at a specific point, only the maximum velocity (doppler shift) along the path of the ultrasound wave.
In Colour Doppler, velocities coming towards the probe are coded ____ (colour) and velocities moving away from the probe are coded ______.
Toward: Red
Away from: Blue
Tip: BART (Blue Away, Red Towards)
Tissue Doppler, in general, is used to look at:
Ventricular relaxation and diastolic dysfunction.
One advantage of M-mode over 2-D echo is ________ and it is especially useful when you want to do these two things:
Advantage: It has better resolution.
Especially useful when you want to measure wall thickness and measure things that move in the heart, especially valves.
What’s the name of the equation you use to convert velocities into pressure, and how do you write it?
The simplified Bernoulli Equation:
Delta P = 4V2
Where P is the pressure difference (gradient) along the path you’re measuring.
Eg. you measure a jet velocity to be 2m/s. The pressure differential is 16.
Explain how one uses TR jet velocity to measure PA systolic pressure.
Use the simplified Bernoulli equation to calculate the pressure differential between the RA and RV in systole. Now as long as there’s no pulmonic stenosis (which is rare unless it’s congenital), PA systolic pressure = RV systolic pressure. To determine RV systolic pressure, add the estimated RA pressure to the pressure differential you just calculated. You estimate RA pressure by measuring the IVC’s diameter and inspiratory collapse in the sub-costal view. Table:
What pressures can be estimated with the following doppler velocities?
Peak TR velocity
Peak PR velocity
End-diastolic PR velocity
Peak MR velocity
End-diastolic AR velocity
Pressure gradients accross valves, both peak and mean, are determined using this equation:
The simplified Bernoulli equation.
How is the Continuity Equation written, and what does it mean?
What do we use this equation for in echo?
The Continuity Equation stipulates that the volume of blood flowing into a valve must equal the volume of blood flowing out of a valve.
Flow in = Flow out
aka:
A1 x V1 = A2 x V2
A = area, V = velocity
More accurate to use Velocity Time Integral (VTI) instead of Velocity (V) though
When using the Continuity Equation to determine valve area, why do we trace velocity jets instead of just placing the cursor on the maximum velocity like for TR jet determination?
Because in a pulsatile system like the heart, flow velocities vary during an ejection period, starting off slow, speeding up to reach a maximum, then slowing down again. So it is more accurate to calculate the integral.
When using the Continuity Equation to measure aortic valve area, A1, V1 (before the valve) and V2 (at or after the valve) are measured in which views and with which type of doppler (PW or CW)?
A1: measured, so no doppler used. Parasternal long axis. Measure the LVOT diameter.
V1: Apical view. PW (b/c want the velocity at that particular point)
V2: Apical view. CW (b/c want the max velocity)
Apical view with the velocities b/c need to line up the ultrasound beam with the direction of blood flow to be accurate.
