Physical Properties of Diagnostic Ultrasound - Ultrasound Beam - Medical Science Assignment Help

Assignment Task

Question 1 
a) For a 7.5 MHz ultrasound beam of intensity 23.0 mW cm- 2 traveling in soft tissue, calculate: i. The particle displacement amplitude. 
ii. The particle velocity amplitude. 
iii. The acoustic pressure amplitude. 
b) For the three different amplitude values you have found above, briefly state how  these values compare, and whether this is what you would expect. 

Question 2 
a) An ultrasound pulse suffers a -35 dB change when passing through an 8 cm thickness of soft tissue.  Find the following values if the original transmitted intensity into the tissue was 50 mWcm-2 
i. The final intensity. 
ii. The ratio of the final pulse amplitude to the initial pulse amplitude.
b) An ultrasound pulse traveling in soft tissue has normal incidence on a layer of muscle.  i. Calculate the reflection and transmission coefficients 
ii. Express the reflective loss in deciBels 

Question 3 
a) An ultrasound beam traveling in soft tissue is incident upon a layer of fat, striking the boundary at an  angle of 70o to the boundary. Calculate the change in direction between the incident beam and the  transmitted beam. 
b) Explain what is meant by the term Critical Angle and provide clear specifications of the critical angle  for a soft tissue / fat interface. 

Question 4  
A 5 MHz transducer is constructed with a crystal of diameter 11.0 mm, and has a curved surface to focus  the beam at a depth of 55 mm. Make the necessary calculations to complete the following: - 
a. Draw the effective beam profile for the focussed transducer, also showing the theoretical and  effective beam profiles for the corresponding plane transducer for comparison. 
b. Sketch a graph of the central axis intensity along the beam, indicating the estimated positions of  maxima and minima. 
c. Classify the focussing capability of the transducer. 

Question 5  
A 5 MHz phased array transducer consists of fifteen 1.4 mm wide piezoelectric elements with a 0.1 mm  gap between each element. Delay lines are used to both focus and steer the ultrasound beam in soft  tissue. The elements are each 15 mm long and are mechanically focussed in the elevation direction. 
a. Sketch the theoretical and effective lateral beam profiles if all elements are pulsed simultaneously,  included calculated dimensions of the beam divergence and the near field length.  
b. Calculate the time delay between firing the central and outer elements, if the effective radius of  curvature of the ultrasound wavefront is 50 mm, and the beam is directed along the transducer axis or  “un-steered” (ie perpendicular to the transducer face). 
c. Calculate the time delay between each end element and the central element if the beam is steered  10o away from the transducer axis and the focal depth is 45 mm, as measured along the axis of the  transducer.

Question 6  
a. Write brief notes to explain the piezo-electric effect and its role in generating a pulse of ultrasound.  b. What is the importance of the piezo-electric crystal thickness?  
c. Briefly explain how the ultrasound beam is steered through the field of view in a linear array  transducer. 

Question 7  
a. Write brief notes to explain the pulse-echo principle and how it is used in M-mode imaging. b. Describe the role and operation of the TGC in a B-mode imaging system.  

Question 8  
Write brief notes to describe the presentation of the following B-mode artefacts and explain the  underlying physics.  
i. Acoustic enhancement  
ii. Mirror image artefact 
iii. Presentation Assignments should be presented as a word document, using appropriate maths font.  Required diagrams and sketches may be hand drawn, scanned and saved in jpeg format and then pasted  into the document. Your answers to written questions should be succinct and well directed to address  the question asked.

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