Ultrasound Flashcards
What is ultrasound imaging
A short pulse of mechanical energy is delivered to the tissue
How do you generate an ultrasound
Ultrasound waves are generated in piezoelectric materials in the transducer
How do you detect an ultrasound
Piezoelectric effect it is reversible
Piezoelectric elements generate ultrasound and detect the echoes
What is the human hearing range and ultrasound range?
15-20kHz
2.5-40MHz
How does ultrasound differ from other imaging methods?
- Ultrasound beam is non-ionizing longitudinal waves (unlike electromagnetic waves)
- The single is recorded in reflection rather than transmit toon mode (unlike X-ray)
What is the speed of sound in tissue?
1540 m/s or 1.54mm/us
Do ultrasounds move faster or slower in bone?
Faster in bone but have longer wave length!
Bulk modulus B
Is a measure of stiffness of a medium and it’s resistance to being compressed
SI unit is Pa
What is the density of
Air
Fat
Soft tissue
1.2 kg/m3
924
1050
Maximum amplitude, A, also coincides with the compression peak
A is proportional to p
I is proportional to A2
Ultrasound interactions are determined by
Acoustic properties of the matter (or medium)
As ultrasound energy properties through the medium, interaction include;
Reflection and refraction: boundary interaction
Scattering and absorption: tissue interactions
Types of reflection
- Specular or mirror reflection
- happens when it strikes a smooth boundary - Non-specular reflection
- irregular boundary
Speckle
The noisy textured background in ultrasound images
Transmission and refraction
The unreflected ultrasound passes on as a transmission beam
Refraction
If incident u/s beam strikes a smooth boundary at some oblique angle then the reflected beam is projected at the same angle from the normal
What are the process that produce attenuation
- Absorption by tissue
- main mechanism for the reduction in the beam intensity - Beam divergence
- by reflecting or scattering
Acoustic absorption (or attenuation) coefficient a
Is a measure of power loss in the sound wave
Is proportional to frequency
Intensity half value thickness HVL
The ultrasound half vale thickness is the thickness of tissue over which the incident intensity of the wave is reduced by 50% and in dB scale is a reduction of intensity by 3dB
Ultrasound transducer
A device which converts one form of energy to another
Piezoelectric crystals made up the production and detection system of transducer
Echo display modes
A mode (a for amplitude) B mode (b for brightness) C mode (m for motion)
Ultrasound pulse
It typically 2-3 wavelengths long
The length of the pulse is called the spatial pulse length SPL
Pulse duration
PD is a measure of the tome period of the pulse
Duty factor
Is the percentage measurement of the time that the pulse occupies in the transmit receive cycle
Spatial resolution
Resolution is measured as the minimum distance between objects which can be distinguished in the image
Ultrasound transducer resolution is described in terms of
- Axial
- Rx, is measured in the direction parallel to the beam - Lateral
- is governed by the beam width
- it decreases with increasing beam width
- it increases with frequency
Doppler imaging
Blood velocity can be measured very accurately using Doppler effect
Is the change in frequency of a source of sound as it approaches
Helps diagnose blood clots and blocked arteries
