Principles of 2D and M-Mode Echo Week1

Question 1

What is Attenuation?

Answer 1

Attenuation is reduction in amplitude and intensity of the sound wave as it passes through a medium

Question 2

What are some ways ultrasound can interact with tissue?

Answer 2

Absorption: conversion of ultrasound energy into other forms of energy as it passes through tissue.
Reflection: ultrasound waves encounter a boundary between tissues with different acoustic impedance, causing some of the energy to bounce back towards the transducer.
Refraction: The bending of ultrasound waves as they pass through tissues with varying densities, altering their direction of propagation.
Scattering: Ultrasound scattering involves the random redirection of ultrasound waves by small structures within tissues, contributing to the overall pattern of the ultrasound beam.
Diffraction: Ultrasound diffraction refers to the bending and spreading out of ultrasound waves around obstacles or through small openings, affecting the distribution of energy in the beam.

Question 3

What are the 3 things related to attenuation and where do they sit in the Attenuation coefficient equation?

Answer 3

-AC (Attenuation coefficient of the tissue)/ Properties of the medium
-Frequency (MHZ)
-Distance from the probe (CM)

A=1/2frequency

Total attenuation (dB) = attenuation coefficient (𝜶, dB/cm) × Length (𝒄𝒎) × frequency (𝑴𝑯𝒛)

Put in simple example: For typical soft tissue the attenuation coefficient a is approxiamately 0.5dB/cm/MHZThus for example transmitted ultrasound with a frequency of 3MHZ travelling to a depth of 20cm in soft tissue will be attenuated by:

0.5 x 3 x 20 = 30dB

Question 4

What frequency should you use ?

Answer 4

The highest frequency compatible with the required depth

Question 5

Calculate the total attenuation (dB) if your frequency is 5MHZ, the beam is moving through muscle tissue (1.2), and depth is 10cm

Answer 5

5 x 1.2 x 10 = 60 dB

Question 6

How many times on the way down is an ultrasound beam reduced by and how many times on the way up?

Answer 6

Way down = 100
Way up = 10,000

Question 7

What is an intensity ratio?

What is attenuation?

Answer 7

Intensity Ratio: This represents how much the intensity of the ultrasound beam is reduced as it travels through tissue. It’s the factor by which the intensity decreases. An intensity ratio of 100 means the intensity is reduced to 1/100th of its original value.

So, in simple terms:

The attenuation tells us how much the intensity is reduced (20 dB).
The intensity ratio tells us by what factor the intensity is reduced (100, meaning it’s reduced to 1/100th of its original value).
So, the 20 dB of attenuation results in an intensity reduction of 100 times.

Question 8

What is absorption in terms of ultrasound?
Absorption is determined by 3 main factors, what are they?

Answer 8

Acoustic energy is lost in a medium because it is converted to heat
Determined by-
1.Viscosity of the medium: Increase in viscosity means increased resistance meaning increase in friction
2. Relaxation time of the medium: If relaxation time of the medium is longer then the particles vibrate for longer and the second sound wave must stop the particles and reverse the direction, this requires energy and produces heat.
3. Frequency of the sound: Increase in frequency =increase in particle motion and heat. In addition, increase in relaxation time means particles remain in motion longer, therefore if you double the frequency you double the absorption

Question 9

What are two primary interations responsible for image production?

Answer 9

Reflection & Scatter
Backscatter(speckling) is very important because it givees structures texture

Question 10

The percentage of the sound beam projected to the transducer depends on three variables, What are they?

Answer 10

1.The acoustic properties of the two tissues
2. The angle of incidence
3.The reflecting surface

Question 11

Whats the equation for calculating acoustic impedance

Answer 11

Z=pc
Z= Acoustic impedance kg/m2/secor rayl (a measure of the opposition a material presents to the transmission of sound waves).
P=Tissue density(kg/m3)
C=Propagation of speed (m/s)

Question 12

Why does air have trouble transmitting ultrasound

Answer 12

Although air has a low acoustic impedance, not a high one. It’s this mismatch in impedance between air and tissue that causes significant reflection at the air-tissue interface. Hence the need for gel

Question 13

The amplitude of the sound beam depends on the acoustic impedance between the two materials

Answer 13

R=Z2-Z1
——-
Z2+Z1
R= Reflection amplitude coefficient, which quantifies the amount of ultrasound energy that is reflected at the interface.
Z1 acoustic impedance on the proximal side of the interface
Z2 acoustic impedance on the distal side of the interface

Question 14

Describe Rayleigh Scatters and give an example

Answer 14

Rayleigh
Scatters

• Hits a surface with Dimension of much less than one wavelength.
• Reflect energy equally in all
  directions.(organised scattering)
  Example: Red blood cell (RBC)
  Note: important for spectral Doppler

Question 15

Refraction

Answer 15

Bending of a sound beam ( Transmission with a bend).
A soundwave strikes a boundary between two different tissue types.
(Remember the pencil in water image that looks like its bending)
Two things required for this:
1.Incident sound wave must not be perpendicular
2. Speed of sound must be different on 2 sides of the interface.

Question 16

Snells law

Answer 16

Predicts the direction of a sound beam when diffraction occurs
If its a smaller propergation speed at first then the angle will be larger & if the initial tissue propergation speed is larger, the refraction angle will be smaller

Question 17

What do the characters in snells law mean

Answer 17

The equation is: sin(θi) / sin(θo) = c1 / c2

• θi represents the angle of incidence, which is the angle at which the sound beam enters the interface between two different media.
• θo represents the angle of refraction, which is the angle at which the sound beam changes direction as it passes through the interface.
• c1 is the speed of sound in the first medium.
• c2 is the speed of sound in the second medium.

The equation basically states that the ratio of the sine of the angle of incidence to the sine of the angle of refraction is equal to the ratio of the speed of sound in the first medium to the speed of sound in the second medium. This equation helps predict the direction of the transmitted sound beam when refraction occurs.

Question 18

Why is knowledge of the beam path important in ultrasound?

Answer 18

-Enables accurate image interpretation and artifact recognition.
-Optimizes image acquisition settings for improved diagnostic accuracy.
-Helps identify and mitigate shadowing and attenuation effects.
-Guides precise targeting in interventional procedures, enhancing safety.
-Essential for ensuring effective and safe clinical practice in ultrasound.

Question 19

Why is the critical angle and angles greater than the critical angle important in diagnostic
ultrasound?

Answer 19

-Critical angle and angles greater than it affect ultrasound beam reflection and transmission.
-Understanding these angles helps in optimizing image quality and diagnostic accuracy.
-Critical angle determines when total internal reflection occurs at tissue boundaries.
-Angles greater than critical angle enable visualization of deeper structures through reflection.
-Knowledge of critical angles aids in avoiding artifacts and improving tissue differentiation.
-Overall, critical angles and their implications are essential for effective diagnostic ultrasound imaging.

Question 20

What is a transducer

Answer 20

A transducer is a device used in ultrasound imaging to both emit and receive ultrasound waves. It converts electrical energy into mechanical vibrations (sound waves) and vice versa.

Question 21

whats special materirals is a transducer made of?

Answer 21

Piezoelectric crystals, such as lead zirconate titanate (PZT), are commonly used in ultrasound transducers.
These crystals exhibit the piezoelectric effect, meaning they can expand or contract in response to electrical voltage changes.
When voltage is applied to the crystals, they generate ultrasound waves by vibrating at specific frequencies.
Conversely, when ultrasound waves strike the crystals, they produce electrical signals due to their piezoelectric properties.
PZT and similar materials are chosen for their efficient conversion between electrical and mechanical energy.
This efficiency makes them well-suited for use in ultrasound transducers, enabling the emission and reception of ultrasound waves in medical imaging applications.

Question 22

What is PRP ?

Answer 22

Pulse Repetition Period (PRP) refers to the time interval between the beginning of one pulse and the beginning of the next pulse in ultrasound imaging. It’s a crucial parameter that determines the rate at which ultrasound pulses are emitted and received by the transducer. PRP influences factors such as image depth, frame rate, and penetration depth in ultrasound imaging. A shorter PRP allows for faster image acquisition but may limit penetration depth, while a longer PRP enables deeper imaging but reduces the frame rate. PRP is adjusted based on imaging requirements to optimize image quality and diagnostic accuracy.

Question 23

What is PRF?

Answer 23

Pulse Repetition Frequency. It refers to the number of ultrasound pulses emitted by the transducer per unit of time, typically expressed in Hertz (Hz) or kilohertz (kHz). PRF is closely related to the Pulse Repetition Period (PRP) and is its reciprocal. A higher PRF means that ultrasound pulses are emitted more frequently, which allows for faster image acquisition but may limit penetration depth. Conversely, a lower PRF results in slower image acquisition but enables deeper imaging. PRF is a critical parameter in ultrasound imaging, as it directly affects factors such as frame rate, image quality, and the ability to visualize structures at different depths within the body. Adjusting PRF appropriately is essential to optimize image acquisition and diagnostic accuracy in ultrasound examinations.

Question 24

Key points about attenatuion, absorption, reflection, diffraction, M-Mode

Answer 24

The ultrasound beam undergoes attenuation, a reduction in amplitude and
intensity, when it encounters tissues.
* Attenuation increases with depth and frequency and is a fundamental limitation of
ultrasound.
* Attenuation occurs due to absorption, reflection, scattering, diffraction, and
refraction.
* Absorption converts energy from the sound beam into heat while reflection,
scattering, diffraction, and refraction redirects the beam.
* Reflection and scattering are the primary interactions responsible for ultrasound
production.
* Diffraction and refraction redirect the beam which causes structures to be
displaced or not in view.
* To produce an ultrasound image, a transducer sends out short acoustic pulses
across an image plane which reflect at tissue borders back to the transducer, to
form a virtual image.
* M-mode has better temporal resolution than 2D and provides a single dimensional
image of reflector distance versus time.

Question 25

Advantages and disadvantages of MMode

Answer 25

Advantages:

High temporal resolution, allowing precise assessment of moving structures like heart valves.
Provides real-time visualization of motion along a single axis, useful for measuring cardiac dimensions and wall motion.
Helps in accurate determination of cardiac cycle events such as systole and diastole.
Can detect abnormalities in motion patterns, aiding in diagnosis of cardiac conditions.
Relatively simple and quick to perform, making it suitable for bedside evaluations.
Cost-effective compared to other imaging modalities, making it widely accessible.

Disadvantages:

Limited spatial resolution compared to other imaging modes like 2D or 3D ultrasound.
Only provides information along a single scan line, potentially missing complex motion patterns.
Requires skilled interpretation and operator expertise for accurate diagnosis.
Limited field of view may hinder comprehensive assessment of cardiac structures.
Vulnerable to artifacts such as reverberation or side lobe artifacts, which can distort images.
Not suitable for detailed assessment of complex cardiac anatomy or dynamic structures.