Week 1: B-mode imaging

Question 1

What is B-mode imaging?

Answer 1

Cross sectional image of organ & tissue boundaries, constructed from echoes, generated by reflection of US at tissue boundaries & scattering from irregularities within tissues

Question 2

What are the B-Mode imaging variables

Answer 2

1. Range of the target

2. Direction of the target from active area of transducer (position and orientation)

Question 3

What is US?

Answer 3

• high frequency (f) sounds waves (MHz)
• mechanical vibration through a medium
• internal structure, function & amplitude; motion (BF)

Question 4

How is an US image produced?

Answer 4

1. US pulses are transmitted into the body
2. US is reflected or scattered back by surfaces in the body (structures) –> US waves returning detecter by the probe.
3. Time taken for pulse to go & return = depth of target ( assuming C is constant)
4. Brightness of image –> relates to amplitude (Z) or returning US

Question 5

Transducer f changes (dependent on?)

Answer 5

• depth

* properties I.e. density and stiffness

Question 6

What’s the relationship in f and ATTENUATION

Answer 6

• Lower f US waves penetrate further due to attenuation

* Higher f waves attenuated more quickly than low f

Question 7

What’s the relationship with ATTENUATION and AMPLITUDE. And what ways is it presented

Answer 7

Attenuation- a reduction in amplitude if signal
ABSORPTION –> as waves pass through, some is converted to heat
SCATTERING –> when waves come into contact w/ a smaller target - waves become scattered over large angle e.g. blood

Question 8

What is Attenunation?

Answer 8

US is attenuated when passing through a medium w/ several mechanisms, a reduction in amplitude due to distance/depth

Question 9

How is attenuation measured?

Answer 9

dBcm-1 MHz-1

Question 10

When echoes from small scatters with sample volume come together to crease random fluctuation in the image brightness. What is this..?

Answer 10

Speckle

Question 11

Constructive interference

Answer 11

2 seperate waves in phase meeting at the crest, creating a larger resultant wave w/ > amplitude

Question 12

Destructive interference

Answer 12

when the 2 waves are out of phase i.e. the crest of 1 meets with trough of the other. Producing reduced amplitude or cancel each other out.

Question 13

What does brightness at certain points relate to?

Answer 13

• boundaries & amplitude; types of material

- amplitude of the returning echo

Question 14

What is intensity of a reflected wave dependent on?

Answer 14

• (@boundary) acoustic impedance (z) of material p/side

Question 15

What is acoustic impedance (Z)?

Answer 15

• property of the tissue (dependent on C)

- number of resistance on US beam encounters w/ passing through a medium or tissue

Question 16

What is Z dependent on?

Answer 16

• density of tissue (kg. m) K.

- C (m/s)

Question 17

What does returning echo amplitude dependent on?

Answer 17

• change in Z at interface

Question 18

What US controls govern the brightness of image point

Answer 18

• Gain
• TGC
• output power
• DR/compression
• Grey scale map

Question 19

What is Pulse repetition frequency (PRF)?

Answer 19

of pulses transmitted p/sec

Question 20

Why do we only want 1 pulse in flight at a time for PRF

Answer 20

To avoid range ambiguity

Question 21

PRF equation

Answer 21

PRF max = C/ 2R

C = Speed of sound
( R = depth)

Question 22

What is Frame rate (FR)?

Answer 22

of images created p/sec

Question 23

Max FR given by:

Answer 23

FR = C/ 2RN PRF/N

```
N = # of scan lines
(R = depth)
~~~

Question 24

What happens if theres double scan lines

Answer 24

Reduced FR (halved)

Question 25

When looking at moving structure. What do you need to do to FR?

Answer 25

Increase it.

Question 26

Resolution

Answer 26

Identify 2 objects close to eachother - axial and lateral

Question 27

Contrast Res

Answer 27

Able to differentiate 2 objects w/ similar reflective properties

Question 28

Temporal Res

Answer 28

Identify 2 events at a time

Question 29

What does sensitivity relate to?

Answer 29

Penetration

Question 30

How can the user optimise these features?

Answer 30

- compromise between axial res and penetration - selected f - compromise between lateral res and FR - # scan lines - selection of appropriate gain & amplitude compression

Question 31

Describe this picture....

Answer 31

* Transmitted US is back scattered from moving blood cells | * The recieved US is unchanged due to velocity of blood cells

Question 32

Intensity (I) or reflected wave at a boundary depends on...... each side of the boundary

Answer 32

Acoustic impedance (z) of the material

Question 33

What is the attenuation coefficient for muscle?

Answer 33

0.57 dB cm-1 MHz-1

Question 34

What property has the greatest attentunation coefficient?

Answer 34

Bone (22dBcm-1 MHz -1)

Question 35

Describe the image....

Answer 35

* US transmitted is back scattered from moving blood cells | * Recieved US is however, changed due to the velocity of the blood cells.

Question 36

Why is resolution important?

Answer 36

For high quality image production

Question 37

What information does Colour flow imaging (CFI) show?

Answer 37

- BF direction, mean velocity in relation to US beam

Question 38

In CFI. What does red and blue colours indicate?

Answer 38

RED/YELLOW -blood travelling towards the transducer | BLUE - blood is travelling away

Question 39

Detected Doppler Shift Frequency (Fd) = ...... and received frequency (Fr)

Answer 39

transmitted frequency (Ft)

Question 40

What is the Doppler Shift Frequency dependent of?

Answer 40

- frequency (Ft) - C (as it passes through tissue) - Velocity of blood - angle of insonation (variation of orientation of vessel or probe)

Question 41

Explain this picture...

Answer 41

- Scan lines are sampled several times (sent and recieved) - Recieved echoes are displayed at increased depth - moving further away from the transducer. - Vertical line corresponds with fixed depth - Amplitude changes when crossing the vertical line - The change in amplitude of recieved echoes contains the doppler shift and is extracted by demodulation

Question 42

3-16 pulses

Answer 42

number of pulses required with CFI

Question 43

What does the displayed colour depend on?

Answer 43

angle of insonation

Question 44

Alternation angle of insonation. Can be altered by adjusting the orientation of the probe to get highest Doppler Shift Frequecny.

Answer 44

How would you get angle of insonation on higher or lower body limbs that are parallel to skin

Question 45

When would you get the highest Doppler shift f?

Answer 45

When vessel and beam are aligned.

Question 46

Whay governs for velocity?

Answer 46

Angle of insonation between beam path and BF direction

Question 47

What's the true and no velocities values?

Answer 47

True = 0 degree angle | No velocity detected = 90 degree angle

Question 48

Angle of insonation of US beam relative to ROI, are greatest when echoes produced with ..... approaching ....

Answer 48

Angle of incidence | Angle of reflection

Question 49

What happens if angle of insonation is more than 60 degree angle?

Answer 49

More chance for velocity error measurements

Question 50

What does Angle correction cursor do in relation to velocity measures?

Answer 50

The correct placement is important enabling measurements of angle of insonation so velocity measurements can be obtained

Question 51

At what percentage on the graph are velocity error measurements likely to occur?

Answer 51

5% error in velocity measurement ( ~10-20) angle of insonation

Question 52

When would the transducer f change?

Answer 52

with; 1) depth 2) tissue properties e.g. density and stiffness

Question 53

In CFI with the principle of angle of insonation, when are echoes greater relave to the tissues and organs?

Answer 53

When angle of incidence approaches the angle of reflection

Question 54

What unit is Z presented?

Answer 54

kg m−2 s−1 or Rayl