Ultrasound

Question 1

What is ultrasound imaging

Answer 1

A short pulse of mechanical energy is delivered to the tissue

Question 2

How do you generate an ultrasound

Answer 2

Ultrasound waves are generated in piezoelectric materials in the transducer

Question 3

How do you detect an ultrasound

Answer 3

Piezoelectric effect it is reversible

Piezoelectric elements generate ultrasound and detect the echoes

Question 4

What is the human hearing range and ultrasound range?

Answer 4

15-20kHz

2.5-40MHz

Question 5

How does ultrasound differ from other imaging methods?

Answer 5

1. Ultrasound beam is non-ionizing longitudinal waves (unlike electromagnetic waves)
2. The single is recorded in reflection rather than transmit toon mode (unlike X-ray)

Question 6

What is the speed of sound in tissue?

Answer 6

1540 m/s or 1.54mm/us

Question 7

Do ultrasounds move faster or slower in bone?

Answer 7

Faster in bone but have longer wave length!

Question 8

Bulk modulus B

Answer 8

Is a measure of stiffness of a medium and it’s resistance to being compressed

SI unit is Pa

Question 9

What is the density of
Air
Fat
Soft tissue

Answer 9

1.2 kg/m3
924
1050

Question 10

Maximum amplitude, A, also coincides with the compression peak

Answer 10

A is proportional to p

I is proportional to A2

Question 11

Ultrasound interactions are determined by

Answer 11

Acoustic properties of the matter (or medium)

Question 12

As ultrasound energy properties through the medium, interaction include;

Answer 12

Reflection and refraction: boundary interaction

Scattering and absorption: tissue interactions

Question 13

Types of reflection

Answer 13

1. Specular or mirror reflection
   - happens when it strikes a smooth boundary
2. Non-specular reflection
   - irregular boundary

Question 14

Speckle

Answer 14

The noisy textured background in ultrasound images

Question 15

Transmission and refraction

Answer 15

The unreflected ultrasound passes on as a transmission beam

Question 16

Refraction

Answer 16

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

Question 17

What are the process that produce attenuation

Answer 17

1. Absorption by tissue
   - main mechanism for the reduction in the beam intensity
2. Beam divergence
   - by reflecting or scattering

Question 18

Acoustic absorption (or attenuation) coefficient a

Answer 18

Is a measure of power loss in the sound wave

Is proportional to frequency

Question 19

Intensity half value thickness HVL

Answer 19

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

Question 20

Ultrasound transducer

Answer 20

A device which converts one form of energy to another

Piezoelectric crystals made up the production and detection system of transducer

Question 21

Echo display modes

Answer 21

A mode (a for amplitude)
B mode (b for brightness)
C mode (m for motion)

Question 22

Ultrasound pulse

Answer 22

It typically 2-3 wavelengths long

The length of the pulse is called the spatial pulse length SPL

Question 23

Pulse duration

Answer 23

PD is a measure of the tome period of the pulse

Question 24

Duty factor

Answer 24

Is the percentage measurement of the time that the pulse occupies in the transmit receive cycle

Question 25

Spatial resolution

Answer 25

Resolution is measured as the minimum distance between objects which can be distinguished in the image

Question 26

Ultrasound transducer resolution is described in terms of

Answer 26

1. Axial - Rx, is measured in the direction parallel to the beam 2. Lateral - is governed by the beam width - it decreases with increasing beam width - it increases with frequency

Question 27

Doppler imaging

Answer 27

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