Question n o 1

(g) If the absorption in tissue is given by aa'dB = 0.75 dB-cm'] -MH2'1, calculate the absorption coefficient an in Np-rn" Tad1's. (h) Assume the transducer has a radius of curvature (focal length) of 140 mm and an outer aperture diameter of 120 m. (i) Using the absorption value from part (g) and Eq. (2}, calculate the frequency in MHz that maximises the volume rate of heat deposition. (ii) Calculate the length and width of the focal zone assuming the sound speed in tissue is 1540 m-s". (iii)State an advantage and a disadvantage of using a focal zone of this size for HIFU therapy