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Examination 

Examination
Chapter:
Examination
Author(s):

Patrizio Lancellotti

and Bernard Cosyns

DOI:
10.1093/med/9780198713623.003.0001
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date: 23 September 2020

  1. 1.1 How to set up the echo machine to optimize your examination

1.1 How to set up the echo machine to optimize your examination

Preparing for the TTE examination

  • Make sure the patient is comfortable/relaxed in a left decubitus position, with the left arm up to open up intercostal spaces and breathing quietly to minimize translation of the heart

  • The echo-room should be:

    • darkened: avoid sunlight for optimal contrast

    • silent: auditory feedback allows optimizing Doppler sample positions

  • A time-aligned ECG of good quality is mandatory for timing of cardiac events

  • Select the appropriate probe according to the patient size

  • Start with cardiac pre-settings (Fig. 1.1.1AB)

Important note:

  • The ultrasound machine needs maintenance for optimal performance

Acoustic power

Controls acoustic energy output

  • More energy → better signal → better image quality (i.e. better signal-to-noise ratio: SNR) (Fig. 1.1.2AB, see also Box 1.1.1)

  • Expressed in decibel [dB] relative to the maximal energy output available on the system (100% output = 0dB; 50% reduction = −6dB)

  • Too much acoustic energy can result in tissue damage due to:

    • Heating: monitored through the ‘thermal index’ (TI should remain below 2)

    • Cavitation (i.e. formation of small gas bubbles with subsequent bubble collapse associated with high pressures/temperatures locally): monitored through the ‘mechanical index’ (MI should remain below 1.9)

Gain

Controls overall amplification of the echo signals

More gain

  • amplifies the echo signal

  • equally amplifies the noise

  • SNR remains identical! (Figs 1.1.3 and 1.1.4, see also Box 1.1.2)

Fig. 1.1.4 Effects of increased gain on 2D image

Fig. 1.1.4
Effects of increased gain on 2D image

Depth gain compensation

Depth-specific amplification of the echo signals to compensate for attenuation

  • Automatic: amplifies signals from deeper structures

  • Manual: allows correction of the automatic compensation (Figs 1.1.5ABC, see also Box 1.1.3)

Fig. 1.1.5 Manual adjustment of depth gain settings. 5A: slider to the right, 5B: neutral, 5C: slider to the left

Fig. 1.1.5
Manual adjustment of depth gain settings. 5A: slider to the right, 5B: neutral, 5C: slider to the left

Transmit frequency

Controls transmit frequency of the transducer (see Box 1.1.4)

Lower frequency (Fig. 1.1.6)

  • Worse spatial resolution

  • Better penetration

Fig. 1.1.6 Effects of changing transmit frequency

Fig. 1.1.6
Effects of changing transmit frequency

Note: Changing the frequency away from the centre frequency of the probe lowers spatial resolution

Lowering transmit frequency will activate harmonic imaging (Fig. 1.1.7)

  • Worse spatial resolution along the image line

  • Better SNR (i.e. less noise)

Fig. 1.1.7 Effects of lowering transmit frequency

Fig. 1.1.7
Effects of lowering transmit frequency

Note: Harmonic imaging increases SNR but reduces intrinsic spatial resolution along the image line. This is particularly relevant when studying small/thin structures (i.e. valve leaflets)

Focal position

Controls the depth at which the ultrasonic (US) beam is focused

Around this region spatial (lateral) resolution is optimal (Fig. 1.1.8, see also Box 1.1.5)

Fig. 1.1.8 Position of the focal point

Fig. 1.1.8
Position of the focal point

Note: The position of the focal point is indicated alongside the sector image (arrow point)

Frame rate

Controls the trade-off between number of lines in a single frame and the number of frames created per second (see also Box 1.1.6)

Higher frame rate will result in less lines in the image and thus worse spatial (lateral) resolution (Fig. 1.1.10)

Fig. 1.1.10 Frame rate and spatial resolution

Fig. 1.1.10
Frame rate and spatial resolution

Fig. 1.1.9 Simulated pressure field of a cardiac transducerWhite horizontal bar = beam width in focal zone when focus point at 50 mm (i.e. left panel) Mark the difference in beam width at larger depth with changing focal position (white circles)

Fig. 1.1.9
Simulated pressure field of a cardiac transducer

White horizontal bar = beam width in focal zone when focus point at 50 mm (i.e. left panel) Mark the difference in beam width at larger depth with changing focal position (white circles)

Focus point deeper: less effective focusing, lateral resolution decreases

Beyond this focus point, beam widens, lateral resolution worsens

Continuous-wave and pulsed-wave Doppler

High-quality/reliable Doppler recordings require:

  1. 1. Proper alignment of the image (i.e. Doppler) line with the flow direction (< 20̊ off-axis) (Fig. 1.1.11, see also Box 1.1.7)

  1. 2. Proper velocity scale (also referred to as Nyquist velocity/PRF) (Fig. 1.1.12AB)

    • Scale too low: aliasing

    • Scale too high: sub-optimal velocity resolution (i.e. smallest difference between two different velocities that can be measured is larger)

Fig. 1.1.12 Doppler velocity scale. A: Adequate, B: Too low (i.e. aliasing)

Fig. 1.1.12
Doppler velocity scale. A: Adequate, B: Too low (i.e. aliasing)

Continuous-wave and pulsed-wave Doppler

Sample position

Controls the position of the sample volume (Fig. 1.1.13ABC, see also Box 1.1.8)

Fig. 1.1.13 Sample position. A: Too high, B: Appropriate C: Too low

Fig. 1.1.13
Sample position. A: Too high, B: Appropriate C: Too low

Sample volume

Controls the size of the sample volume (Fig. 1.1.14ABC)

Fig. 1.1.14 Sample size. A: Too large, B: Appropriate, C: Too small

Fig. 1.1.14
Sample size. A: Too large, B: Appropriate, C: Too small

  • ♦ Small sample volume: good spatial resolution at lower velocity resolution

  • ♦ Large sample volume: good velocity resolution at lower spatial resolution

Continuous-wave and pulsed-wave Doppler: settings

Wall filter

Controls the threshold for velocities displayed in the velocity spectrum (Fig. 1.1.15ABC, Box 1.1.9)

Fig. 1.1.15 Wall filter. A: Too low, B: Appropriate, C: Too high

Fig. 1.1.15
Wall filter. A: Too low, B: Appropriate, C: Too high

Sweep speed

Controls the refresh rate of the velocity spectrum (Fig. 1.1.16AB, Box 1.1.10)

Fig. 1.1.16 Sweep speed. A: 100 mm/s, B: 33 mm/s

Fig. 1.1.16
Sweep speed. A: 100 mm/s, B: 33 mm/s

Colour-flow mapping

Velocity scale

Controls the range of velocities displayed in the colour box (Fig. 1.1.17, Box 1.1.11)

Fig. 1.1.17 Velocity scale

Fig. 1.1.17
Velocity scale

Aliasing

  • ♦ Blue: motion away from transducer

  • ♦ Red: motion towards the transducer

  • ♦ Green: velocity out of range (i.e. aliasing)/large spatial variance (i.e. turbulence)

Colour gain

Controls amplification of the colour Doppler signals (see Box 1.1.12)

Size of colour box

Directly impacts frame rate (Fig. 1.1.18AB, Box 1.1.13)

Fig. 1.1.18 Colour box size. A: Adequate, B: Not optimal

Fig. 1.1.18
Colour box size. A: Adequate, B: Not optimal

Advanced techniques

Myocardial velocity imaging (MVI) (Fig. 1.1.19)

  1. 1. Proper alignment of the image line with the wall motion direction

  2. 2. Proper velocity scale (Nyquist velocity/PRF)

  3. 3. Small sector angles for higher frame rates (optimal > 115 fps)

  4. 4. Adjust sample position, sample size, wall filter, and sweep speed

  5. 5. High-quality ECG required for optimal timings all apply for myocardial PW and colour Doppler analyses (as for blood pool Doppler)

Fig. 1.1.19 Myocardial veIocity imaging

Fig. 1.1.19
Myocardial veIocity imaging

Speckle tracking—2D strain (rate) imaging (Fig. 1.1.20)

  1. 1. Optimize gain settings and focus position

  2. 2. Centre the region of interest

  3. 3. Adjust depth and region of interest size for optimal spatial resolution (MV annulus at the bottom of the image for LV regional function analysis)

  4. 4. Adjust frame rates since specific analysis software often requires specific frame rate settings (optimal 50–90 fps)

  5. 5. High-quality ECG required for automated tracking

Fig. 1.1.20 2D–speckle tracking imaging

Fig. 1.1.20
2D–speckle tracking imaging

3D imaging (Fig. 1.1.21)

  1. 1. Transducer position: a good acoustic window is essential for optimal 3D visualization (difficult because of larger probe size)

  2. 2. Use 2D guidance for centring of the region of interest

  3. 3. Image acquisition during breath hold or quiet respiration

  4. 4. Adjust volume size to optimize volume rate (real time vs stitched images for post-processing)

  5. 5. Adjust gain and avoid drop-out artefacts

  6. 6. Crop, translate, and rotate the 3D volume to visualize the structure of interest