Physics

Question 1

Resolution

Answer 1

Smaller wave length greater frequncy greater resolution

Velocity = freq x wavelength

Ability to distinguish between 2 points

Question 2

Specular reflection

Answer 2

Tissue reflection to probe improved when 90 degree angle perpendicular, if off angle then less returned

Question 3

Scattering

Answer 3

Reflection from ultrasound beam strikes structure smaller than wavelength of transmitted beam, causes scattering of returning energy

Red blood cells, cause speckle texture

Question 4

Attenuation

Answer 4

Total amount of energy lost as wave travels through patient

Absorbed, reflected, scattered

Mostly converted to heat
Most affects high frequency waves with small wave length, affected at faster rate
So reduces penetration

Question 5

Balancing axial resolution and penetration

Answer 5

Higher frequency of waves
smaller wavelength
Better axial resolution
But poor penetration due to attenuation (absorption)

Selecting frequency of ultrasound beam

Question 6

Temporal Resolution (frame rate) vs. Lateral Resolution

Answer 6

Sector size (depth and angle)
line density (sector angle - spacing apart of ultrasound beam lines across sector width)
Frame rate how long to complete image from averaging between lines

high line density good lateral resolution but lowers frame rate

Question 7

TGC time gain compensation (sliding dials)

Answer 7

Signal affected by attenuation
Helps Creates even image

Question 8

Acoustic shadowing

Answer 8

Structure reflects all of ultrasound beam back creates area of shadow/dropout
(Rib or prosthetic valve)

Question 9

Refraction

Answer 9

Ultrasound beam deviates from normal path as passing through tissues.

Shows incorrect position of structures
(Ghost aortic valve)

Question 10

Range Ambiguity

Answer 10

Shows structure far away / farfield

Extra flection by structure as travelling back to probe hits underside of previous structure so travels back to original structure then all way back to probe, time delay makes look further away

(Diaphragm, pericardium or pericardial effusion)

Question 11

Pizoelectric effect / Ultrasound Beam transmission

Answer 11

Allows transformation of electrical energy (ultrasound beam) into mechanical/kinetic energy then back to electrical signal

Mechanical longitudinal wave created by propagation (compression decompression = rare fraction)

Question 12

Nyquist Limit

Answer 12

Half pulse frequency (PW signal)

Maximum Doppler shift accurately measured before aliasing

Question 13

Amplitude, Period , Frequency, Wavelength, Velocity

Answer 13

Amplitude: intensity of signal at defined point

Period: time duration peak to peak

Frequency: waves/cycles per second

Wavelength: distance signal travels per cycle

Velocity: how quickly travels through medium (determined by medium)

Question 14

Ultrasound Frequency
Nyquist Limit
Velocitys in soft tissue, blood, bone

Answer 14

Ultrasound Frequency: >20Hz
Nyquist Limit: 50-70 cm/s
Velocity in Air/gas: 330m/s
Velocity in soft tissue: 1540m/s
Velocity in blood: 1560m/s
Velocity in bone: >4000m/s

Question 15

High Frequency (resolution vs. Penetration)

Answer 15

Higher frequency improves axial and lateral resolution
But poor penetration due to loss from attenuation (absorption)

Question 16

Harmonic Imaging

Answer 16

Used 2nd reflected ultrasound frequency for higher resolution and fewer artefact

E.g. send 2.5MHz receive at 5MHz

Question 17

Transducer frequncy

Answer 17

Adult 2-4Hz
Children 5-7Hz