During a routine abdominal check-up, a doctor performs an ultrasound scan on a patient. The process involves placing a probe on the skin after applying a thin layer of gel. Answer the following questions based on this procedure.
(i) List, in the correct order, the main steps that take place from the moment the probe emits sound waves to the appearance of an image on the monitor.
(ii) Explain the role of reflection of sound in producing the image.
(iii) State why a gel is applied between the probe and the skin, and describe what might happen to the image quality if the gel were omitted.
(iv) The doctor notices small bright spots on the screen that correspond to interfaces inside the body. Explain how differences in acoustic impedance at boundaries give rise to these spots.