Echocardiography Flashcards
Frequency
Number of cycles per second (ranges between 2.0 and 10 MHz in clinical ultrasonography)
Under what circumstances does amplitude diminish?
Diminishes w/ distance from sound source
The peak of an ultrasound wave is called:
Compression (of particles of medium)
The trough of an ultrasound wave is called:
Rarefaction (of particles of medium)
Wavelength
Length between two peaks of sine wave
What does amplitude measure?
Measure tissue compression
Propagation velocity
Speed of ultrasound wave within tissue
What limits how fast sound waves can travel through a medium?
The speed of sound through that medium
How can we determine distance of an object via ultrasound?
Consider the time required for the sound wave to travel from transducer to the object and back as well as the speed of sound through that medium to determine distance traveled (d = V x T/2)
Distance =
V x T/2
What happens when you apply pressure to a pizoelectric crystal?
It vibrates at a frequency of the voltage that pressure causes it to emit.
How many crystals are on a linear ultrasound array?
64-128
What all is in an array of pizoelectric crystals?
From L --> R Dampening material Pizoelectric crystal Acoustic lens Face plate
T/F: Pizoelectric crystals stop ringing when the pressure on them is released.
False, they keep ringing at the same frequency
Purpose of face plate on array?
Improves conductance of ultrasound form transducer to tissue
What five types of impedance are there in ultrasounds?
Reflection Refraction Absorption Scatter Acoustic impedance
What type of impedance occurs at the interface of tissue 1 and tissue 2?
Acoustic impedance
What type of impedance never reaches tissue 2?
Reflection
What is refraction?
The deflection of the ultrasound beam as it travels from one tissue type to the other
What causes absorption?
Difference in heat between beam and tissue 2
What is scattering?
Occurs when an ultrasound wave strikes a structure that is less than one wavelength in lateral dimension, such as an RBC.
What is acoustic impedance?
The resistance that an ultrasound wave meets when traveling through tissue
Acoustic impedance =
tissue density x propagation velocity
What do we do to protect against all that impedance?
Use a coupling gel!
Which approach of linear array results in a cross-sectional view of the needle? Therefore, which is more ideal for viewing?
Out-of-plane approach = cross-sectional
In-plane approach = optimal
Relationship between near field of linear array and frequency?
As frequency increases, near field lengthens.
Name of columnar portion of ultrasound beam?
Near field
Name of diverging segment of the beam?
Far field
When transducer frequency increases, what happens to angle of divergence?
Decreases
Explain the Doppler effect.
As the source of sound gets closer to you, there is an increase in frequency and the wavelengths are more compressed, so you believe it to get higher and higher. Just the opposite happens when it gets farther from you, so you perceive it to be lower.
Determination of the relative velocity and direction of blood flow depends on:
Doppler effect
Doppler shift (magnitude of change in frequency) is proportional to:
velocity of moving target
Conditions of optimal doppler effect?
Signal is parallel to the flow pathway because the element moves away from the sound source; work to make your signal parallel
Accurate measurement of blood flow velocity utilizing the Doppler effect requires alignment of interrogating beam:
parallel to the direction of blood flow
Pulsed wave Doppler:
the interrogating beam is emitted in short bursts; the returning echoes are received by the same transducer
How does pulsed wave Doppler ensure proper area of interest?
Time gate the return signals and only accept echo information that took as long as you expected to get back
Which doppler method accurately measures high-peak-blood-flow velocities d/t aortic stenosis?
Continuous-wave doppler
Which doppler method can you use to make an estimate of vessel diameter?
Gated doppler
Velocity (from continuous) x cross-sectional area (from gated) =
Flow
T/F: US waves travel poorly through air.
True
T/F: US waves are nearly completely reflected by tissues such as bone, calcium deposits, or metal.
True
Echo shadowing
Any object that lies beneath a dense object will not be imaged because the US will be so severely reflected
Why does increasing frequency decrease depth of tissue penetration?
An increased frequency increases absorption and scattering.
How does increased frequency relate to resolution?
Directly proportional
Speed of transmission of US beams in water:
4080; same as bone!!!
Of blood?
1484
Of muscle?
1580
Depth of penetration is directly proportional to:
Wavelength, because the higher the wavelength, the lower the frequency
Four types of ultrasound resolution:
Axial
Lateral (horizonal and vertical)
Temporal
Contrast
Contrast =
How much is this element reflected?
How do we compensate for the fact that the deeper the tissue, the greater the attenuation (weakening) of the signal?
Time-Gain compensation (TGC); Turning the Gain up improves your view
T/F: signal strength and tissue depth are inversely proportional to each other.
True
Is transthoracic echocardiography more common periop or preop? Used to?
Preop; can image the heart and all the great vessels
How many orientations are appropriate to use in TTE?
4-5
What all can be visualized in the longitudinal parasternal TTE view?
RV outflow tract Proximal aorta/aortic valve Anterior ventricular septum LV w/ mitral valve Inferoposterior wall of LV
Which TTE positions are optimal for viewing all four chambers of the heart?
Apical or subcostal
The characteristic “candy cane aorta” is seen in long or short axis suprasternal position?
Longitudinal suprasternal position = “candy cane”
Echocardiography display format where an US wave is sent along a single scan line, and the depths and intensities at which echoes occur are represented on the screen as a line graph.
A-mode, the simplest form of interpretation
Echocardiography display format used to demonstrate changes along a single scan line
M-mode; motion mode
Variables in A-mode?
Distance to tissue boundary
Amplitude of reflected waves
Used to determine axial length of eye
A-mode; amplitude mode
Variables in M-mode?
Distance to tissue boundary
Amplitude of reflected waves
Time on x-axis
Interference of motion
Used to assess rapidly moving parts of the heart
M-mode
Used to give 2D “slices” of tissue by summation of returns from multiple scan lines
B-mode; brightness mode
Variables of B-mode?
2D representation of “slice” of tissue
Amplitude of reflected waves
Time
Motion
Used for anatomic diagnosis and ultrasound-guided invasive procedures
B-mode
Occurs when frequency of sound waves is altered if either the reflector or receiver is moving relative to the other
Doppler shift
Used to assess velocity of tissue movement or flow
Doppler shift
By whats means can Doppler be used to assess difference between venous and arterial flow while placing CVP?
Doppler shift
Variables in Doppler shift?
Velocity of flow
Direction of flow
Specular:
of or like a mirror
T/F: US returning from an object has an increased amplitude for weak reflection and a decreased amplitude for strong specular reflectance.
False; US returning from an object has an increased amplitude for strong specular reflectance.
Second generation contrast echocardiography uses:
Low solubility flurocarbon gas: Optison, SonoVue
Stabilizes bubbles, increases duration of contrast effect
First generation contrast echo used:
air
Third generation contrast echo will add what to low solubility gas?
Polymer shell
We use contrast echo to determine:
how well blood flows through heart
If you inject your patient’s RA with agitated saline during contrast echo and their LA is opacified almost immediately after their RA is, what can you assume?
There is a large right-to-left shunt d/t patent foramen ovale
What type of echo might we use to identify a patent foramen ovale in a patient?
Constrast echo
Describe the echo probe:
A gastroscope mounted with a multiplane transducer at the distal end
Just proximal to the distal tip of the echo probe is the:
deflection area
Possible movements of echo probe?
Anterior/posterior, right/left
Two types of TEE adult probes? Typical size?
Biplaner and uniplaner, typically 10-14 mm
Pediatric TEE size?
4 mm
In TEE, wavelength is a function of:
thickness of pizoelectric crystal in probe
Phased array TEE:
A more modern TEE that uses electronically linked smaller crystals to act as one large crystal. Advantages when it comes to producing, focusing, and steering the ultrasound beam
How does phased array TEE allow a 3 cm probe to sweep out into 8 cm of area?
It energizes the crystals in sequences and causes waves to move out so that the wavefront has an angle to its source.
Does phased array TEE energize its crystals individually or in sequences?
In sequences, producing an angle that allows for a “pie sweep” of an area
How do you steer a linear phased array?
Manipulate the time of firing (the order in which these elements fire) of the individual elements
How can you image a volume of tissue with phased array TEE?
Scan from left to right and back with the phased array
Phased excitation of the transducers in phased array TEE can produce:
a focused beam w/ high resolution at a smaller point
Crystals are sequentially fired from the outer edge to the middle of the array = concave wave that converges at a certain distance from the transducer before it diverges again
The focal distance from the transducer is a function of:
time delay between firing crystals from the edge to the middle of the array
In phased array TEE, what is produced when all transducer elements are fired simultaneously?
Compound wave sound pulse that travels perpendicular to the transducer face
In phased array TEE, what is produced when there is a sequence of firing from first element to last element?
Compound wave direction
In phased array TEE, what is produced when there is a sequence of firing from outer elements to inner elements?
Electronic focused array
T/F: electronic focuses array is a compound wave.
That appears to be false in the pictures.
T/F: images produces in the far field of a focused beam will be of lower quality than those produced in the far field of an unfocused beam.
True
T/F: images produces in the near field of a focused beam will be of lower quality than those produced in the far field of an unfocused beam.
False; will be improved.
Possible movements of TEE probe in esophagus?
Withdraw/advance
Turn right/left
How do you change scanning angles in TEE?
Rotate the probe forward and back
Possible movements of TEE tip?
Anteflex, retroflex
Flex to right, flex to left
“Turn TEE probe to right” means:
moving tip of probe clockwise
“Turn TEE probe to left” means:
moving tip of probe counterclockwise
To retroflex the TEE probe, in what direction should you rotate the control wheel?
Counterclockwise
To anteflex the TEE probe, in what direction should you rotate the control wheel?
Clockwise
Which TEE position allows you to see the roundness of the ventricles?
Transverse
When using B-Mode in TEE, the probe is correlated to the anterior or inferior portion of your “slice”?
Inferior
Positions in TEE:
I
II
III
I = basal short-axis II = four chamber long axis III = transgastric short axis
The view in which the RV looks like a crescent and the LV looks like a mushroom is called:
Transgastric short-axis
What TEE angle is especially useful for visualizing IVC and SVC?
Basal long axis
What TEE angle is especially useful for isolating left atrium and ventricle, right atrium and ventricle?
Four chamber short axis
What TEE angle is especially useful for visualizing the aorta?
Transgastric long axis
What adjustment is necessary to visualize all four chambers in four-chamber long axis view?
Retroflexing the probe
What doppler mode can determine SV?
Gated doppler
How is TEE used to determine EF?
Elliptical diameters are measured in four chamber and two chamber views. That is then used to determine LV volume at end-diastole and end-systole, allowing for calculation of EF.
T/F: the Pascal equation can be used to calculate a pressure gradient across any restrictive orifice.
False; the Bernoulli equation can.
Pulsed wave Doppler echocardiogram:
Vertical axis:
Horizontal axis:
Vertical axis: blood flow velocities
Horizontal axis: time
Flow =
product of cross-sectional area of the chamber or vessel through which flow is occurring and velocity of flow
The time-velocity integral is used to calculate:
pulsatile flow
Because SV = TVI x CSA
How to determine volumetric flow:
Combination of area and velocity measurements
If mixed colors of green and yellow show up on a doppler, what does that indicate?
Turbulent flow; common around stenotic valve
What doppler modality presents the spatial relationship between structure and blood flow?
Color flow
Best doppler modality for measuring fast BF velocities?
Continuous wave
Continuous wave doppler measures blood flow velocities up to
7 m/s
Primary disadvantage of continuous wave doppler?
Cannot ID location of peak velocity along ultrasound scan line
Which doppler modality measures BF velocities through pulmonary veins, mitral valve, and in low-flow areas of heart?
Pulse wave doppler
Which doppler modality measures BF velocities through aorta, aortic valve, stenotic valve lesions, regurgitant valvular jets?
Continuous wave
Which doppler modality enhances recognition of valvular abnormalities, aortic dissections, and intracardiac shunts?
Color flow
How does doppler calculate wall thickening during systole?
Compare systolic to diastolic thickness for each segment
Most sensitive method of detecting ischemia?
TEE
Why is TEE so effective in detecting ischemia?
A decrease in ventricular wall motion occurs within seconds after cessation of coronary BF, and the extent of wall motion abnormality relates to the severity of coronary insufficiency to the affected area.
What degree of radial shortening is normal?
> 30%, large degree of wall thickening during systole
What degree of radial shortening determines mild hypokinesis?
10-30%
What degree of radial shortening determines severe hypokinesis?
0-10%
What degree of radial shortening determines akinesis?
0%
Dyskinesis is defined by:
Radial lengthening and wall thinning
Category I of TEE:
These are conditions that are not an immediate threat: heart valve repair, congenital heart surgery, HOCM, endocarditis, acute aortic dissection, aortic aneurysm, etc.
Category II of TEE:
These are conditions that are life-threatening at every second: MI, CAD, air emboli, intracardiac masses, heart valve repair, aneurysm of heart, intracardiac thrombi, pulmonary emboli, heart-lung transplantation, mechanical circulatory support, etc.
Placement of IABP is what category for TEE use?
Category III
Under what surgical circumstances should TEE always be used?
Open heart surgery
Besides open heart surgery, consider using TEE in:
CABG procedures
Transcatheter intracardiac procedures
Critical care application for TEE?
When diagnostic info that is expected to alter management cannot be obtained by TTE, etc.
Non-cardiac surgical application for TEE?
Use when unexplained life-threatening circulatory instability persists despite corrective therapy
T/F: the higher the US frequency, the better the image quality.
T
What is axial resolution?
The minimal separation between two interfaces aligned along a direction perpendicular to a beam
What is elevational resolution?
The ability to determine differences in the thickness of the imaging plane
What does the continuity equation use to determine aortic valve area?
Measurement of flow through LV outflow tract and aortic valve
What view should be used to evaluate mitral stenosis?
Transgastric basal short-axis view
Valvular regurtiation is best identified using:
color-flow doppler spectra
