Practice exam Module 1 & 2

Question 1

2 + 2 + 2 = 6 marks
A) An Ultrasound wave travelling in soft tissue has a frequency of 7.5MHz. At the velocity of sound assumed for soft tissue in diagnostic ultrasound imaging, the wavelength of the wave is closest to;
a) 0.21um
b) 0.43um
c) 0.21m
d)0.43mm

B) The period of a 5.8MHz ultrasound wave is closest to;

a) 0.34us
b) 0.18us
c) 0.34ms
d) 0.18ms

C) As ultrasound wave frequency increases

a) Attenuation decreases and depth of penetration decreases.
b) Attenuation increases and depth of penetration decreases
c) Attenuation decreases and depth of penetration increases
d) Attenuation increases and depth of penetration increases.

Answer 1

A) = c) 0.21mm
B) = b) 0.18us
C) = b) Attenuation increases and the depth of penetration decreases.

Question 2

2 + 2 +2 + 2 = 8 marks
The decibel and reflection coefficient
A 4.3MHz ultrasound pulse is transmitted through 5.7cm is soft tissue and then incident on a layer of fat. Answer the following questions relating to this situation.

A) The attenuation loss in dB due to the passage of the pulse through the soft tissue down to, but just before entering, the layer of fat is closest to;

a) 5.2 dB
b) 8.7dB
c) 17.5 dB
d) 33.1dB

B) The reflection coefficient at the soft tissue, fat interface is closest to

a) 0.00523
b) 0.00938
c) 0.01724
d) 0.03219

C) The reflective loss in dB is closest to

a) 8.1dB
b) 12.7dB
c) 22.5dB
d) 41.3 dB

D) The total loss in dB when the pulse has returned to the surface is closest to;

a) 29.7 dB
b) 57.3 dB
c) 78.4dB
d) 145.6dB

Answer 2

A - c) 7.5dB
B - a) 0.00523
C - c) 22.5dB
D - b) 57.3dB

Question 3

2 + 2 +2 +2 = 8 marks
Transducer elements, focusing and steering.

A) The production of an ultrasound pulse by the transducer occurs by means of;

a) The inverse piezo-electric effect and voltage change produced by distortion of the crystal.
b) The inverse piezo-electric effect and crystal distortion caused by the applied voltage.
c) The piezo-electric effect and voltage change produced by distortion of the crystal.
d) The piezo-electric effect and crystal distortion caused by the applied voltage.

B) An ultrasound echo pulse is detected by means of;

a) The inverse piezo-electric effect and voltage change produced by distortion of the crystal.
b) The inverse piezo-electric effect and crystal distortion caused by the applied voltage.
c) The piezo-electric effect and voltage change produced by distortion of the crystal.
d) The piezo-electric effect and crystal distortion caused by the applied voltage.

C) Electronic focusing is achieved by;

a) Firing outside elements first so that the pulses arrive at the focal point simultaneously.
b) Firing outside elements first so that the pulses arrive at the focal point as soon as possible.
c) Firing inside elements first so that the pulses arrive at the focal point simultaneously.
d) Firing inside elements first so that the pulses arrive at the focal point as soon as possible.

D) Electronic steering of the beam to the right of centre occurs;

a) Firing right side elements first so that pulses arrive arrive at the focal point as soon as possible
b) Firing right side elements first so that pulses arrive arrive at the focal point simultaneously.
c) Firing left side elements first so that pulses arrive arrive at the focal point as soon as possible.
d) Firing left side elements first so that pulses arrive arrive at the focal point simultaneously.

Answer 3

A) - b) The inverse piezo-electric effect and crystal distortion caused by the applied voltage.
B) - c) The piezo-electric effect and voltage change produced by distortion of the crystal.
C) - a) Firing outside elements first so that the pulses arrive at the focal point simultaneously.
D) - d) Firing left side elements first so that pulses arrive arrive at the focal point simultaneously.

Question 4

2 + 2 = 4 marks
Frame rate calculation
Calculate the frame rate for a real time B Mode imaging system using a 7.2MHz transducer, with a single focal zone, 310 scan lines and a depth of field of 5.1cm.
A) The maximum pulse repetition frequency for this depth is closest to;
a) 50.6KHz
b) 32.5 KHz
c) 24.2 KHz
d) 15.2 KHz

B) The coresponding frame rate is closest to;

a) 48.2 Hz
b) 55.6 Hz
c) 59.1 Hz
d) 63.4 Hz

Answer 4

A) d) 15.2 KHz

B) a) 48.2 Hz

Question 5

2 + 2 + 3 +2 = 9 marks
Display shape, echo location
Describe briefly the characteristics of real time B Mode scanning for a convex array transducer in terms of;
1. The shape of the display.
2. The position orientation and sequence of successive scan lines.
3. The two parameters on which echo depth determination is based.
4. How the position of the echo source is determined.

Answer 5

1. A convex array transducer has a sector shape display that has an initial profile of the same size as the convex transducer face, which then broadens with axial distance. This is different to a phased array that has a similar shape, but the initial display profile originates at a point.
2. Scan lines that populate the entire width of the beam are depicted as N Number of scan lines. The sequence of this transducer follows an order where only one scan line can be acquired at once, as the information from the first scan line must be emitted and received before the next successive scan line. Each scan line is adjacent to the next with the scan line direction a function of axial depth into the patient and away from the transducer.
3. The two parameters that determine echo depth are
   - Speed of the ultrasound wave, assumed to be 1540m/s in soft tissue. This fluctuates as the ultrasound eave moves through the different soft tissues of a patient however the average is assumed to calculate echo depth.
   - the echo time, which specifies the length of time taken for the wave to be emitted and then reflected back to the transducer (round trip time)
4. The position of the echo source can be identified in terms of it’s axial depth and lateral position in the patient. The chief determinant of axial depth is the echo time, factoring in wave speed. The determinant of lateral position is the echos position with respect to the scan line/line of site upon which it originated.

Question 6

1 + 1 + 1 = 3 marks
Simple beam model

In the simple beam model compare the characteristics of a weakly focused beam and a strongly focused beam in terms of;

1. The position of the focus relative to the transducer
2. The focal width
3. The degree of divergence beyond the focus.

Answer 6

Weakly focused beam

1. The position of the focus relative to the transducer is further away.
2. The focal width is near equivalent in dimensions to the aperture size (little convergence)
3. The degree of divergence beyond the focus is minimal, meaning that the beam profile divergence demonstrates little change.

Strongly focused beam.

1. The position of the focus relative to the transducer is closer.
2. The focal width is significantly more narrow.
3. The degree of divergence beyond the focus is large, much greater than the weakly focused beam.

Question 7

2 + 2 + 2 = 6 marks
Apodisation

In a multi element array with electronic focusing, give and explanation of apodisation in terms of;

i) The general definition of apodisation as applied in diagnostic ultrasound.
ii) The characteristics of apodisation as usually applied in diagnostic ultrasound
iii) The advantage obtained when apodisation is applied in diagnostic ultrasound.

Answer 7

i) Apodisation refers to the process of modulating the magnitude of applied voltage across transducer elements, in order to centralise the intensity distribution to the main beam and mitigate the occurrence of side lobes.
ii) On transmission and reception of echoes the machine de-emphasises the contribution of the outer transducer elements
iii) Apodisation is advantageous as it suppresses the presence of side lobes. This is clinically useful as it lessens the effect of the scanned object being displayed to the left and right of it’s true location by the sidelobes, resulting in a more accurate image.