7.2.11
Ultrasound Imaging
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Acoustic Impedance and Attenuation
Reflection at a boundary between materials depends upon the difference in Z. The reflected intensity increases with increasing difference in acoustic impedance.

Acoustic impedance
- Acoustic impedance (more accurately specific acoustic impedance) of a material (Z) = density x velocity of sound in the material.

Comparative attenuation
- Bone has approximately 4x the impedance of muscle, and 10 000x the impedance of air.
- Ultrasound will also be attenuated by the material it is propagating through.
- The attenuation depends upon the frequency of the sound.
A and B Scans
There are two types of ultrasound scans:

A scans
- A-scans are similar to traditional echo-sounding techniques.
- Distances between layers in the body can be easily measured.

B scans
- For a B-scan, the position and orientation of the transducer are used to provide an image of a section of the body.
- The transducer is moved by the operator to provide information from these different positions.
Advantages and Disadvantages of Ultrasound
Ultrasound can be a very helpful medical imaging device however, it cannot be used effectively in all situations.

Advantages of ultrasound
- Ultrasound gives accurate information about the distance of layers of tissue from the time taken for reflection to happen.
- Ultrasound is non-ionising so is safe for soft tissue.
- Ultrasound can give information on the density of material from how intense the reflection is.
- Ultrasound is safe for use on pregnant mothers.

Disadvantages of ultrasound
- The resolution is not as high as when an X-ray is used.
- Due to the difference in acoustic impedance ultrasound will not produce an image from organs with large amounts of gas, like the lungs.
- We are not aware of the long-term effects of ultrasound on soft tissue or on a fetus.
1Physical Quantities & Units
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8Superposition
9Thermal Physics
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14Modern Physics
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1Physical Quantities & Units
1.1Physical Quantities & Units
2Kinematics
3Dynamics
3.1Momentum & Newton's Laws of Motion
3.2Non-Uniform Motion
3.3Linear Momentum & Conservation
4Force, Density & Pressure
4.1Force, Density & Pressure
4.1.1Fields4.1.2Force in Uniform Fields4.1.3Friction4.1.4Buoyancy4.1.5Terminal Speed4.1.6End of Topic Test - Acceleration Due to Gravity4.1.7Centre of Mass4.1.8Forces & Equilibrium4.1.9End of Topic Test - Scalars & Vectors4.1.10Moments4.1.11End of Topic Test - Moments & Centre of Mass4.1.12Density4.1.13Pressure
5Work, Energy & Power
6Deformation of Solids
7Waves
7.1Simple Harmonic Motion
7.2Waves
7.2.1Progressive Waves7.2.2Intensity of Waves7.2.3Wave Speed & Phase Difference7.2.4Longitudinal & Transverse Waves7.2.5End of Topic Test - Progressive Waves7.2.6Electromagnetic Waves7.2.7Doppler Effect7.2.8Sound Waves7.2.9Measuring Sound Waves7.2.10End of Topic Test - Waves7.2.11Ultrasound Imaging7.2.12Ultrasound Imaging 2
8Superposition
9Thermal Physics
9.1Circular Motion
9.2Thermal Physics
9.2.1Temperature9.2.2Measuring Temperature9.2.3Ideal Gas Law9.2.4Ideal Gases9.2.5Boyle's Law & Charles' Law9.2.6Molecular Kinetic Theory Model9.2.7Molecular Kinetic Theory Model 29.2.8Thermal Energy Transfer9.2.9Thermal Energy Transfer Experiments9.2.10End of Topic Test - Thermal Energy & Ideal Gases9.2.11First Law of Thermodynamics
10Communication
10.1Communication Channels
10.2Digital Communication
11Electric Fields
11.1Electric Fields
12Current Electricity
12.1Current Electricity
12.1.1Basics of Electricity12.1.2Mean Drift Velocity12.1.3Current-Voltage Characteristics12.1.4End of Topic Test - Basics of Electricity12.1.5Resistivity12.1.6End of Topic Test - Resistivity & Superconductors12.1.7Power and Conservation12.1.8Microphones12.1.9Components12.1.10Relays12.1.11Strain Gauges
13Magnetic Fields
13.1Magnetic Fields
14Modern Physics
14.1Quantum Physics
14.1.1The Photoelectric Effect14.1.2The Photoelectric Effect Explanation14.1.3End of Topic Test - The Photoelectric Effect14.1.4Collisions of Electrons with Atoms14.1.5Energy Levels & Photon Emission14.1.6Wave-Particle Duality14.1.7End of Topic Test - Absorption & Emission14.1.8Band Theory14.1.9Diagnostic X-Rays14.1.10X-Ray Image Processing14.1.11Absorption of X-Rays14.1.12CT Scanners
14.2Nuclear Physics
14.2.1Rutherford Scattering14.2.2Atomic Model14.2.3Isotopes14.2.4Stable & Unstable Nuclei14.2.5A-A* (AO3/4) - Stable & Unstable Nuclei14.2.6Alpha & Beta Radiation14.2.7Gamma Radiation14.2.8Particles, Antiparticles & Photons14.2.9Quarks & Antiquarks14.2.10Particle Interactions14.2.11Radioactive Decay14.2.12Half Life14.2.13End of Topic Test - Radioactivity14.2.14Nuclear Instability14.2.15Mass & Energy14.2.16Binding Energy14.2.17A-A* (AO3/4) - Nuclear Fusion
Practice questions on Ultrasound Imaging
Can you answer these? Test yourself with free interactive practice on Seneca — used by over 10 million students.
- 1What is the equation for the acoustic impedance?Multiple choice
- 2
- 3Two types of ultrasound techniques:Fill in the list
- 4
- 5Why is ultrasound NOT as good as an X-ray?Multiple choice
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