2.0 - Clinical role of echo

Question 1

What is sound, compression and rarefaction, frequency, wavelength, propagation velocity and amplitude?

What are their units of measurement?

Answer 1

Sound:
Longitudinal mechanical wave which requires the presence of particles.

Compression:
Area within a sound wave where there is higher pressure (particles are closer together)

Rarefaction:
Area within a sound wave where there is lower pressure (particles are further apart).

Frequency:
Number of cycles/waves per second (Hz or MHz).
1000 cycles/s = 1kHz. 1,000,000 cycles/s = 1MHz

Wavelength:
Distance between two waves.
Measured in metres.

Propagation velocity:
Speed the wave travels through the medium, Measured in m/s.

Amplitude:
Strength of the wave (baseline to peak), Measured in dB.

Question 2

How are wavelength, propagation velocity and frequency related?

Answer 2

Velocity = Wavelength X Frequency.

Question 3

How is resolution affected by frequency?

Answer 3

higher frequency = shorter wavelength = high resolution but lower depth

Question 4

What are the propagation velocities in the body and the frequencies of ultrasound?

Answer 4

Soft tissue = 1540m/s
Blood = 1570m/s
Air = 330m/s
Fat = 1450m/s
Muscle = 1580m/s
Bone = 3500m/s

Question 5

What is specular reflection?

Answer 5

Reflection in one direction which occurs when the reflector is large and smooth (e.g. chambers, valves and vessels).

Angle-dependent.

Question 6

What is backscatter reflection?

Answer 6

Reflection in multiple direction.
Occurs when the reflector is small and rough (e.g. RBCs).

Angle-independent.

Rayleigh scatter is backscatter which is equal in all directions (e.g. RBCs)

Question 7

What is the difference between reflection and refraction?

Answer 7

Reflection - Change in direction of the US towards the transducer

Refraction - Change in direction of the US away from the transducer at the boundary of different tissues with different acoustic impedance.

Question 8

What is acoustic impedance and acoustic impedance mismatch?

Answer 8

The resistance to US transmission.

Mismatch occurs when US crosses the boundary between tissues with different acoustic impedances, and the energy is reflected back to the transducer.

Gel decreases acoustic impedance mismatch
Hyperinflated lungs increase acoustic impedance mismatch.

Question 9

What is attenuation?

Answer 9

Loss of energy as ultrasound travels through a medium.

Measured in dB.

Higher the depth = higher attenuation due to reflection, scatter and absorption.

Question 10

What is half intensity depth?

Answer 10

Depth where the intensity of the US has decreased by 50%.

HID (soft tissue) = 6/f

Question 11

What is the piezo-electric effect?

Answer 11

Conversion of mechanical energy to electrical energy and vice versa.

AC current (electrical energy) to crystal = deformation and crystal oscillation.

Oscillation = generates mechanical US energy which is transmitted through body.

Reflected mechanical US energy from the body causes the piezoelectric crystals to oscillate which generates electrical energy which is detected by the transducer.

Question 12

What are the parts of the ultrasound transducer?

Answer 12

Transducers transmit and receive ultrasound.

Acoustic lens:
- Focusses the ultrasound = less scatter = increased resolution.

Matching layer:
- Reduces the impedance between the piezoelectric crystals and the body to decrease reflection.

Piezoelectric crystals:
- Convert ultrasound to electrical energy and vice versa (2D transducers have 128 and 3D transducers have 1000s).

Backing layer:
- Absorbs ultrasound energy to decrease reverberation/ringing of piezoelectric elements.
- Supresses the vibrations of the crystals allowing waves to be sent out in shorter pulses which improves resolution.

Wire:
- Transmits information.

Case:
- Insulation and protection from interference.

Question 13

How do transducers transmit and receive ultrasound to create images?

Answer 13

Transducer transmits short bursts of ultrasound energy, waits, receives the ultrasound energy, and repeats. A small percentage of the ultrasound energy is reflected at interfaces and the transducer calculates the time between the ultrasound being sent and returned. It uses the time, and the propagation velocity, to calculate the distance between the transducer and the reflector. It uses the signal intensity to generate an image.

Question 14

What are the differences between 2D and 3D transducers?

Answer 14

2D - single plane of ultrasound waves.

3D - multiple planes of ultrasound waves, generate images with a higher spatial resolution but lower temporal resolution.

Question 15

What are the differences between linear array and phased array transducers?

Answer 15

Linear array:
- Organise elements in a straight line
- Generate a rectangular image
- Narrower width
- Lower depth
- Higher frequency = higher resolution
- Paediatric echo.

Phased array:
- Organise elements in a curved line
- Generate a sector shaped image
- Wider width
- Higher depth
- Lower frequency = lower resolution
- Adult echo.

Question 16

What are the Fresnel and Fraunhofer zones and what are their characteristics?

Answer 16

Fresnel zone:
- Near zone
- Cylindrical
- Narrow, high intensity, high resolution, and the length is dependent on the frequency.

Fraunhofer zone:
- Far zone
- Diverse.
- Wide, low intensity and low resolution.

Question 17

How is the near zone affected in image optimisation?

Answer 17

Higher frequency and wider transducer diameter = greater the near zone depth therefore a higher resolution.

Question 18

What are side lobes?

Answer 18

Low intensity secondary ultrasound signals outside of the primary ultrasound beam.

Also known as grating artefact.

They’re secondary to energy which travels at different angles to the primary ultrasound pathway and which is reflected by strong reflectors outside of the primary ultrasound beam. This is due to diffraction.

Question 19

What is beam steering and what are the beam steering methods?

Answer 19

Methods to direct and focus the US beam.

Mechanical steering - physically moving the ultrasound transducer. Rotating transducers involve rotating the transducer to sweep the beam through an area. Wobbling transducers involve a transducer on a motor which rocks back and forward to steer the beam.

Electronic steering - controlling the timing of electrical energy delivered to the piezoelectric crystals in the transducer.

These include:
- Linear array transducers - simultaneously activate elements in the transducer to steer the beam in a linear direction.
- Phased array transducers use time delays to sequentially activate different elements in the transducer to steer the beam at different angles.
- Curvilinear array transducers

Question 20

What is focusing and what are the transducer focusing methods?

Answer 20

Focussing the US narrows the US in the near zone so increases the resolution. But it widens the US in the far zone so decreases the resolution. Focussing the ultrasound will not affect the near zone length.

Fixed focusing involves using a fixed point and fixed time delays (limited to known low depths).

Dynamic receive focusing involves introducing time delays to adjust the returning ultrasound at different depths to increase the resolution and improve the image quality. A shorter time delay is required for echos at higher depths and a longer time delay is required for echos at lower depths.

Question 21

What is the focus position?

Answer 21

The depth with the highest resolution.

The transducer uses electronic focusing methods, in which the timing of sent and returned signals are adjusted, to improve the image quality.

Dual focus uses two focus positions simultaneously or sequentially to increase resolution at two positions, visualising near and far structures.

Question 22

What is the role of intracardiac echo?

Answer 22

Visualises the heart from within.
- High resolution and allows assessment of cardiac anatomy and physiology and real time guidance for cardiac procedures (e.g. EP and structural interventions).

Question 23

What is broadband imaging?

Answer 23

Uses a transducer which transmit and receive US with a variety of frequencies.

Broadband allows a high frequency variety, high resolution, high depth, improved tissue differentiation.

Question 24

What is harmonic imaging?

Answer 24

The reflected ultrasound includes ultrasound at the frequency of the original ultrasound and harmonics (multiples of the original ultrasound frequency).

Second harmonic imaging filters the returning ultrasound to remove the original frequency to generate an image using the second harmonics only. The increased frequencies increase the resolution.

Harmonic imaging decreases noise and artefact and increases the image resolution and quality, particularly for far field structures

Question 25

What are M-mode and curved M-mode and what are their advantages?

Answer 25

M-mode:
- Movement along one line.
- Narrow zone so the PRF, and therefore frame rate, are high.
- High temporal resolution so improves the assessment of fast moving structures (e.g. valves).

CAMM: (curved anatomical m-mode)
- Utilises M-mode and 2D to allow the M-mode line to follow the shape the structure to improve the anatomical and physiological assessment of the structure.

Question 26

What are the pulse repetition frequency, frame rate and scan lines per second?

Answer 26

PRF - The number of pulses (transmitted by the transducer) per second, measured in Hz.

Frame rate - Number of frames (images) per second, measured in fps.

Scan lines per frame - Number of beams (lines) required to form an image (frame).

Question 27

What is the relationship between depth and width and PRF and frame rate, and what are their effects on resolution?

Answer 27

Lower depth = shorter distance between the transducer and the sample volume = shorter period of time to transmit and receive the ultrasound = therefore higher PRF.

Narrower the sector width + lower the image depth = fewer number of scan lines = shorter period of time to create a frame therefore higher frame rate.

A higher PRF and frame rate = higher temporal resolution and lower spatial resolution.

Question 28

What is parallel processing?

Answer 28

3D transducers can parallel process by processing the scan lines simultaneously not sequentially.

Parallel processing increases the number of scan lines acquired and processed, increasing the FR, increasing the temporal (and spatial) resolution.

Question 29

What is temporal resolution?

Answer 29

Temporal resolution (FR) is the ability to discriminate between events close in time. The narrower the width and the lower the depth, the higher the temporal resolution.

Question 30

What is spatial resolution?

Answer 30

Spatial resolution is the ability to discriminate between structure close in space. The types of spatial resolution are lateral (azimuthal), axial and elevation.

Question 31

What is axial resolution?

Answer 31

Axial resolution is the ability to differentiate between structures on the same axis of the ultrasound. The higher the frequency and the shorter the pulse duration, the higher the axial resolution.

Question 32

What is Lateral (azimuthal) resolution?

Answer 32

Lateral (azimuthal) resolution is the ability to differentiate between structures parallel to one another but perpendicular to the ultrasound. The narrower the ultrasound beam (optimised by focussing the ultrasound) and the lower the gain, the higher the lateral resolution.

Question 33

What is elevation resolution?

Answer 33

Elevation resolution is the ability to differentiate between structures with different depths in the elevation direction (z axis), perpendicular to the axial and lateral directions.

Question 34

What is greyscale compression (dynamic range) and what is its effect on the image?

Answer 34

Greyscale compression (dynamic range) adjusts the number of shades of grey in the image to adjust the contrast.

The higher the dynamic range, the higher the number of shades of grey, the lower the contrast, the higher the resolution.

A low dynamic range in used in patients with a high BMI.

Question 35

What is artefact and what are the 5 types?

Answer 35

The presence of structures on the image but the absence in the heart or vice versa.

Acoustic shadowing:
- Due to the presence of a highly echo reflective structure (e.g. prosthetic mechanical valve) which blocks ultrasound penetration which causes echo dropout (black) in the far field zone.

Reverberation:
- Due to the ultrasound bouncing multiple times between two strong specular reflectors. This delays the return of the ultrasound to the transducer so it misinterprets the location of the structure to be further from the transducer than it truly is. This causes “ghost” images which move with the true structure.

Beam width:
- Due to the machine being unable to differentiate if the returning ultrasound signal is from the centre or the edge of the ultrasound beam. Therefore, highly reflective structures at the edge of the beam in the heart are present at the centre of the beam on the image. Focussing the beam minimises beam width artefacts.

Side lobe:
- Due to side lobe beams (extra beams at the side of the primary beam). Therefore, structures outside of the beam in the heart are present at the centre of the beam on the image. Focussing the beam minimises side lobe artefacts.

Question 36

What are the factors affecting image quality?

Answer 36

• Optimisation (width and depth)
• Frequency (wavelength)
• PRF, FR and lines
• Characteristics of structures (propagation velocity, acoustic impedance, acoustic impedance mismatch, attenuation)
• Reflection and scatter
• Focusing and steering
• Spatial resolution (axial, lateral, elevation)
• Temporal resolution
• Artefacts (shadowing, reverberation, side lobe, beam widths)
• Signal to noise ratio.

Question 37

What are the functions of the 9 echo machine controls for image optimisation?

Answer 37

Transmit power:
- Level of US energy transmitted to the patient.
- Lowest transmit power setting should be used to minimise the risk of mechanical or thermal effects.

Overall gain:
- Level of signal amplification of the received US energy to increase the brightness of the image.
- Overall gain: increases the gain of the whole image
- TGCs which increase the gains for part of the image.
- Increases the intensity of low-level signals but increases noise and decreases lateral resolution.

Time gain control (TGC):
- Depth compensation control
- Compensates for the attenuation of the ultrasound at greater depths.
- Increases the gain of far field signals to create a uniform level of brightness for the image.

Reject:
- filters out low-amplitude echos often associated with noise or weak signals.

Logarithmic compression:
- A method of audio processing
- Adjusts the dynamic range of the audio so quiet sounds are louder and louder sounds are quieter.
- Rejecting logarithmic compression maintains the raw dynamic range of the audio.

Greyscale compression (dynamic range):
- A method of visual processing
- Adjusts the number of shades of grey in the image to adjust the contrast.
- Higher dynamic range = higher number of shades of grey = lower contrast = higher resolution.

Pre-processing, processing and post-processing:
- Involves processing the image before, during and after image acquisition.

Question 38

Why is ultrasound gel used?

Answer 38

• Fills the air between the transducer and the skin
• Minimises the acoustic impedance mismatch to maximise ultrasound transmission.
• But gel increases infection risk.

Question 39

What are spatial and temporal smoothing?

Answer 39

A filter is added decrease noise and motion artefacts and increase image quality and uniformity over space and time respectively.

Question 40

How are patients positioned to optimise the images?

Answer 40

• Left lateral decubitus position for the parasternal and apical views
• Supine position for the subcostal and suprasternal views.

Question 41

How are probes manipulated to optimise the images?

Answer 41

Sweeping:
- Movement on the short axis up and down

Sliding:
- Movement on the long axis left and right

Rotating:
- Clockwise and counter clockwise

Tilting:
Movement in the short axis forwards and backwards. e.g. anterior and posterior

Rocking:
- Movement in the long axis side to side. e.g. medial and lateral.

Question 42

How are echo machine controls adjusted to optimise the images?

Answer 42

Adjust:
- Depth
- Sector width
- Focusing the ultrasound
- Gain and TGC
- Greyscale compression
- CFD box size
- CWD and PWD scale

Question 43

What are the standard and non-standard TTE views?

Answer 43

PLAX
RV inflow
RV outflow
PSAX (AV, MV, basal, mid and apical levels)
A4C
A5C
A2C
A3C
Subcostal
Suprasternal.

Non-standard views:
- High parasternal view (assess the Asc.Ao)
- Subcostal SAX (if the PSAX is suboptimal)
- Modified subcostal (hepatic vein, Abd.Ao)
- Right parasternal view (right lateral decubitus position, Asc.Ao & AS)

Question 44

How are images stored and displayed?

Answer 44

• Data is acquired, processed and stored.
• At the transducer, the returning echo signal is processed via amplification, TGC and filtering.
• At the scan converter, the ultrasound signal is converted to a digital signal and the video signal is converted to a rectangular signal.
• Post-processing - stored in a digital format and/or undergoes digital to analogue processing to create a video signal to be shown on the monitor and/or stored in a videotape or archived on optical discs or hard drives.
• Archiving offers high data storage, fast data transfer and post-processing.
• The display devices and display controls are adjusted to allow image analysis.

Question 45

What are the considerations of image storage and display?

Answer 45

Digital Imaging and Communications in Medicine (DICOM) standardises data storage, allowing data to be transferred between systems.

Data compression decreases file size for storage and transfer but maintains image quality for analysis.

There is the ability to choose the type and number of cardiac cycles, time based or ECG based image acquisition, the ability to review acquired loop and the ability to adjust and quantify images retrospectively

Question 46

What frequency is audible? What is the frequency of ultrasound?

Answer 46

Audible frequency: 20-20,000Hz
Ultrasound frequency: >20,000Hz (2MHz)

Question 47

What is the frequency range use in echo?

Answer 47

Typically 2–5 MHz.

Can be as high as 45 MHz.

Question 48

What is the difference between specular reflection and backscatter?

Answer 48

Specular reflection:
Reflection in one direction which occurs when the reflector is large and smooth (e.g. chambers, valves and vessels).

Angle-dependent.

Backscatter:
Reflection in multiple direction.
Occurs when the reflector is small and rough (e.g. RBCs).

Angle-independent.

Rayleigh scatter is backscatter which is equal in all directions (e.g. RBCs)

Question 49

What is the relationship between PRF, FR, scan lines per frame, field of view and depth?

Answer 49

???

Question 50

How does parallel processing influence frame rate and image quality?

Answer 50

Parallel processing is used to speed up image acquisition and improve image quality. It involves dividing the imaging workload across multiple processing units or algorithms to handle different parts of the echocardiographic data simultaneously.

How Parallel Processing Works in TTE

Beamforming:
- US system sends out sound waves (beams) and detects the echoes reflected by heart tissues.
- Parallel processing allows the system to send and process multiple beams simultaneously = increased data collection speed.

Real-Time Image Construction:
- Allows for faster construction of the US image by analysing multiple echoes at once.
This is useful for Doppler imaging and color flow mapping, where detailed velocity and flow information is needed.

3D and 4D Imaging:
For advanced techniques like 3D echocardiography or real-time 4D imaging, parallel processing is essential. It enables the system to handle the enormous amount of data required for volumetric visualization.

Frame Rate:
- Improved Temporal Resolution: Parallel processing reduces the time required to generate each frame, allowing for higher frame rates. This is critical in echocardiography, where fast-moving structures like heart valves and chambers need to be visualized in real time.
- Better Real-Time Assessment: High frame rates enhance the ability to assess dynamic cardiac functions, such as valve motion or blood flow patterns.

Image Quality:
- Enhanced Spatial Resolution: By efficiently processing more lines of ultrasound data simultaneously, parallel processing can produce sharper and more detailed images.
- Improved Doppler Sensitivity: Parallel processing improves the accuracy of spectral and color Doppler imaging by handling complex calculations faster and more precisely.
- Reduced Artifacts: The simultaneous processing of data can minimize common ultrasound artifacts and enhance clarity.
Practical Benefits of Parallel Processing in TTE
- Efficient Workflow: Faster imaging reduces the time required for patient examinations.
- Dynamic Assessments: Provides clearer visualization of rapid cardiac events (e.g., during stress echocardiography).
Advanced Capabilities: Supports emerging techniques like myocardial strain imaging and speckle tracking for detailed cardiac analysis.

In summary, parallel processing allows for faster imaging, higher frame rates, and improved visualization of cardiac structures and functions.

Question 51

What is the difference between greyscale and dynamic range?

Answer 51

Greyscale:
- The shades of grey from black to white.
- The shade of grey (brightness) is related to the amplitude.

Dynamic range:
- The range between the brightest and darkest signals that the system displays.
- A higher dynamic range means the system can capture finer details in both very bright and very dark areas simultaneously.
- Important in visualizing subtle differences in tissue density or echogenicity.
- A wide dynamic range allows the system to distinguish between structures with small differences in reflectivity, such as cardiac tissues and blood flow.

Question 52

What are the 3 types of spatial resolution?

Answer 52

• Lateral (azimuthal)
• Axial
• Elevation

Question 53

What are the limiting factors for detecting small targets?

Answer 53

Spatial resolution:
- Ability to distinguish between separate structures.
- Axial - depends on wavelength and pulse length
- Lateral - depends on beam width (narrower = better resolution but decreased depth)
- Elevation - thickness of image plane. Poor elevational resolution can cause small targets to blend with surrounding tissues

Frequency:
- higher = increased resolution but limited depth

Acoustic windows and patient factors:
- Ribs, lungs, thick chest wall limits quality
- Obesity, chest deformations, scarring
- Lung interference, eg COPD can obscure small targets.

Signal to noise ratio (SNR):
- small targets produce weaker echos which can be lost if this ratio is low.
- Factors affecting SNR: depth of target, high attenuation, suboptimal gain settings.

Temporal resolution:
- Ability to detect motion over time
- Low frame rates may cause small or rapidly moving targets, such as vegetations or thrombi, to appear blurred or missed entirely

Artefact:
- Reverberation, shadowing, side-lobe.

Operator:
- skill level and experience.

Dynamic range and post-processing:
- Narrower dynamic range supress subtle echo’s making smaller targets harder to see
- Post-processing - poor optimisation of contrast and filtering can obscure or falsely enhance small targets.

Question 54

What can you do to detect smaller targets better?

Answer 54

Use high frequency probes
Optimise gain and depth settings
Utilise harmonic imaging
Contrast enhanced echo
Improve acoustic window
Advanced imaging models - eg speckle tracking or 3D

Question 55

Optimisation of imaging parameters

Answer 55

Frequency (transducer freq.):
- Number of waves per second
- Increase frequency = decrease wavelength
= increase resolution but decrease depth.
Angle of alignment:
- Better alignment = increased signal quality.

Scan angle:
- Width of the beams coverage
- Determines how much of the heart and structures can be seem on one image.
- Affects field of view and image quality.
- Sector width, depth, etc.

Gamma correction:
- Non-linear process which adjusts the brightness and contrast of the images.
- Decreasing gamma = increase contrast of bright signals
- Increasing the gamma = increase contrast of dark signals.

Spatial and temporal smoothing:
- A filter is added decrease noise and motion artefacts and increase image quality and uniformity over space and time respectively.

Question 56

What are the advantages of 3D echo?

Answer 56

• More detailed visualisation of valve anatomy (leaflet morphology, commissures and annulus geometry)
• Improved spatial orientation - useful when planning interventions (TAVI or MVR)
• Captures motion throughout cardiac cycle - timing of abnormality.
• Eliminates geometric assumptions - measures the actual shape and dimensions of cardiac structures, avoiding simplified assumptions.
• Planimetry for valve area - stenosis
• Volume estimations - no geometrical assumptions like biplane Simpsons.
• Regurgitant volumes, VC - severity grading.
• Better tracking for RWMAs.

Clinical Applications of 3D Echo in Valve Pathology:

Mitral Valve Disease:
- Prolapse/Flail Leaflets: Accurate localization of affected scallops for surgical or interventional planning.
- Annuloplasty Planning: Visualizing annular dimensions and saddle shape.
- Stenosis: Direct planimetry of the mitral valve orifice area without geometric assumptions.

Aortic Valve Disease:
- Stenosis: Direct planimetry of the aortic valve area in 3D.
- Regurgitation: Accurate quantification of regurgitant orifice and volume.

Tricuspid and Pulmonary Valves:
- Comprehensive en face views and evaluation of complex valve geometries.

Congenital Valve Anomalies:
- Better visualization of abnormal leaflet configurations (eg BAV) and structural abnormalities

Question 57

What is the relevance of frame/volume rate, cropping and manipulation of viewing plane for optimisation of 3D volume acquisition?

Answer 57

Frame rate:
- High frame rate = accurate dynamic images. Narrow sector width, reduce temporal resolution.
- Low frame rate = increased spatial resolution (detail) but lowers temporal resolution. good for static structures, valve morphology.
- Trade-off between temporal and spatial resolution. High temporal resolution for dynamic studies. High spatial resolution for structural analysis.

Cropping:
- Removal of irrelevant parts of 3D dataset to focus om specific structures.
- Trimming away tissue not need to look at
- Rotational cropping - isolate planes for x sectional analysis.

Manipulation of viewing plane:
- Multi-planar reconstruction - adjust plane to align with structure you’re interested in.

Question 58

What is pixel density and what increases the volume of data?

Answer 58

Pixel density:
- Number of pixels in an image
- Higher = better image quality

Volume of data increases with:
- Higher frame rates
- Larger field of view
- Advanced models - 3D or strain imaging.

Question 59

What is the DICOM standard?

Answer 59

• Universal standard for storing, transmitting, and displaying medical images.
• Ensures compatibility across different imaging systems and workstations.
• Stores both the image and associated metadata (e.g., patient demographics, imaging parameters, and date of acquisition).

Advantages:
Enables seamless integration with Picture Archiving and Communication Systems (PACS).
Facilitates review, comparison, and sharing of echocardiographic studies.

Question 60

What is data compression and why is it needed?

Answer 60

• Echo data files are large so compressing the files saves storage space.

eg JPEG, AVI, etc.

Question 61

What’s the difference between ECG-gated acquisition and continuous recording?

Answer 61

ECG-gated:
- Synchronises image acquisition with cardiac cycle phases. Reduces motion artefacts

Continuous:
- Acquires images without ECG recognition - real time data.