CSN025 Physical Principles of Ultrasound assignment

Solution.pdf

You are assisting a QUT colleague, Anthony, design an experiment. He has determined that the speed of sound in material A is 1500 m/s. Please assist Anthony select a new material (material B) in which the speed of sound will provide a critical angle of greater than 40 degrees. The experiment is designed so the ultrasound beam with first pass through material A to reach material B. What is the desired speed of sound in material B? 

Question 2 (3 marks) 

There are two ultrasound machines (UM1 and UM2) in the department. It has been calculated for one of these machines(UM1) that the brightest echo on display has an intensity of 7.0mW.cm-2 and the echo just visible on the screen has an intensity of 2.0 x 10-8 mW.cm-2 . 

a) Determine the dynamic range for UM1? (3 marks) 

1 

Question 3 (2 marks) 

The acoustic impedance difference between material A and B is 0.25. The acoustic impedance of A is 1.25 Rayls. Determine the percentage refection at the A/B interface? 

Question 4 (2 marks) 

Complete the table below after determining the attenuation coefficient for material A and B. This is for 10 MHz beam. 

Material Attenuation 

Coefficient 

Distance Travelled Decibel Loss 

A 10cm 8 dB B 8 cm 8 dB 

Question 5 ( 6 marks) 

A 4 MHz beam is transmitted as demonstrated below: 

a) For Fig 1.below, if the initial (transmitted) intensity was 1000 mWcm-2, what is the final (received) intensity from the Bone/ muscle interface? Assume no losses at the transducer / bone interface. (6 marks) 

Fig. 1 

Bone 

Muscle 

2cm 

1 cm 

2 

Question 6 (2 marks) 

Determine the number of different values possible with a 5 digit binary number? You must show working to get full marks. (2 marks) 

Question 7 (4 marks) 

a) Calculate the ideal acoustic impedance of the matching layer of a transducer whose PZT crystal has an acoustic impedance of 10 Rayls? (Acoustic impedance of soft tissue = 1.2 Rayls) (4 marks) 

Question 8 ( 2 marks) 

A 5 MHz transducer emits 10 cycles in a pulse and has a pulse repetition frequency of 500 Hz. 

(a) What is the pulse repetition period? (1 mark) (b) What is the pulse duration? (1 mark) 

(2 marks) 

Question 9 (2 marks) 

A trainee sonographer states that to image deeper structures we should always increase the frequency of our beam and try to image through bone as it has a higher acoustic impedance 

Do you agree with this statement(s)? (YES/NO) 

Provide (brief, in point form) justification to support your conclusion. 

(2 marks). 

3 

Some formula and values that may be useful, there may be others 

α of fat = 0.63 dB cm-1 MHz -1 

α of bone=20 dB cm-1 MHz -1 

α of water=0.0022 dB cm-1 MHz -1 

α of muscle=0.52 dB cm-1 MHz -1 

Z of water = 1.48 Rayls Z of fat = 1.38 Rayls 

Z of bone = 7.8 Rayls Z of muscle= 1.7 Rayls 

v of fat = 1450 m/s v of blood = 1570 m/s 

= 

× ? ???0 

? ???dB 

log10 II R 

= ? 

??ZZ ZZ 2 

2 +- 1 1 ? ??2 

T = 1 – R sin θ = vv 1 2at the critical angle 

PRP = PRF 1 PD = nT 

T = 1/ f SPL = nλ 

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