Answer Happy

spectrum. Explain what spectral broadening is and give two possible causes of spectral broadening. 2. Blood Flow Velocity Measurement (600 words maximum) Doppler Angle Draw a labelled diagram showing the patient's surface, a linear transducer, a scan line approximately perpendicular to the patient's surface and a blood vessel at an angle to the surface. On this diagram, show the Doppler angle. Give a written definition of the Doppler angle based on this diagram. The Doppler angle is normally chosen so that it lies between about 30' and 60'. Consider a scenario in which the sonographer has set a Doppler angle of 63 (that is, above the normal permissible range). In this case the system measures the Doppler shift to be 1553.0 Hz and the blood flow velocity is determined to be 43.9 cm/s with a transducer frequency of 6 MHz. However, the sonographer has, unknowingly, set the Doppler angle cursor 3 too low. du. Calculate (i) the true blood flow velocity at the true Doppler angle of 66' for this case and (ii) the percentage by which the velocity value determined is in error relative to the true velocity value? Aliasing Given a blood flow velocity of 55 cm/s, a Doppler angle of 52", and a transducer frequency of 7 MHz, calculate the Doppler shift frequency that would be found under the given conditions. If the pulse repetition frequency is 5.9 kHz, state the Nyquist limit frequency. Can spectral Doppler imaging be carried out without aliasing in the present case? Explain why or why not. if aliasing did occur, draw a diagram describing its appearance in spectral Doppler imaging. Give three possible methods for alleviating aliasing artefacts (excluding base-line shifting). 3. Beam Focusing and Steering (600 words maximum) The ultrasound beam may be focused to a point electronically and also steered to provide a beam angle which is not perpendicular to the patient's surface. Both focusing and steering of the beam is achieved by manducar alements