80 Critical Care Echo
80.1 What this covers
- Physics
- Artifacts
- Doppler
80.2 Learning objectives
- Physics
- Artifacts
- Doppler
- Normal Anatomy
- Flows
- LV Outflow
- RV Outflow
80.3 Bottom line / summary
- Parameters controlled by settings on the machine
- In addition to these settings, there are post processing and preprocessing settings to adjust the display.
- Intercept angle angle between US beam and direction of travel.
- Cos(theta) amount understimate
- PRF pulse <what?> frequency - determines maximum velocity (get nyquist effect if things are moving faster signal aliasing)
80.4 Approach
- power output (higher higher amplitude reflected signals. Limited by safety. Bone heats faster than fat)
- gain (displayed amplitude of received signals, analogous to turning up the volume)
- Time-gain compensation (differential adjustment of gain along length of ultrasound beam; allows for correction of loss to attenuation in certain tissues)
- Depth (how long the machine waits before sending the next signal; increase depth decreases frame rate and maximal display area)
- Dynamic range and compression (amplitude range; larger dynamic range more shades of grey)
80.5 Red flags / when to escalate
- TODO: List red flags that require urgent escalation.
80.6 Common pitfalls
- TODO: Capture common errors or missed steps.
80.7 References
TODO: Add landmark references or guideline citations.
80.8 Source notes
80.8.1 Critical Care Echo
81 Critical Care Echo
81.1 Physics
Parameters controlled by settings on the machine
- power output (higher = higher amplitude reflected signals. Limited by safety. Bone heats faster than fat)
- gain (displayed amplitude of received signals, analogous to turning up the volume)
- Time-gain compensation (differential adjustment of gain along length of ultrasound beam; allows for correction of loss to attenuation in certain tissues)
- Depth (how long the machine waits before sending the next signal; increase depth decreases frame rate and maximal display area)
- Dynamic range and compression (amplitude range; larger dynamic range = more shades of grey)
In addition to these settings, there are post processing and preprocessing settings to adjust the display.
81.2 Artifacts
- suboptimal image quality - usually poor tissue penetration (either poor contact, habits, tissue char)
- Acoustic shadowing - decreased info behind specular reflector
- reverberations - between two strong parallel reflectors
- beam width - superimposition of structures within the beam profile
- lateral resolution - the apparent width increases as depth of the object increases due to refractions in the tissue
- range ambiguoity - echo from the previous pulse reaches transducer on the next cycle (results in superimposed second, deeper image)
81.3 Doppler
Intercept angle = angle between US beam and direction of travel. Cos(theta) = amount understimate
PRF = pulse <what?> frequency - determines maximum velocity (get nyquist effect if things are moving faster = signal aliasing)
- Continuous wave doppler: continuous transmission, receive info from length of the beam so all you get is the distribution of velocities along the beam and no depth resolution.
- Pulsed doppler - pulses are timed, so that the movement at a specific depth is recorded.
Spectral analysis = display doppler velocity data vs time (scale = amplitude). This is the usual presentation in e.g. as in M-mode.
(Note: M-mode has much higher sampling rates - 1800 per second - so can image fast moving structures better)
Color Doppler Flow imaging: on 2d mode, doppler interspersed over the area of interest. This means that the frame rate has to drop (drops more for a larger area of color). Things to adjust on color doppler to optimize:
- color scale (represent the range of velocities across the maximum number of colors)
- velocity range (within nyquist limit at that depth)
- zero the baseline position on the color scale and set variance.
Tissue Doppler: compared to flow of fluids, all moves in the same direction (so spectral analysis does not have a filled waveform).
81.4 Normal Anatomy
3 types of movement:
- translation (movement of an aspect of the heart)
- rotation (circular motion around long axis)
- torsion (unequal rotational motion around Apex vs base.
Nomenclature:
- windows = where the probe is placed on the body
- view = the image plane (either long axis, short axis, four chamber, or two chamber.
81.4.1 Flows
81.4.1.1 LV Outflow
Obtained from apical view
81.4.1.2 RV Outflow
Parasternal short or “RV outflow view”
81.4.1.3 LV Inflow
- E = early diastolic peak velocity
- A = late diastolic peak as a result of atrial kick.
Typically assessed from apical window.