I skimmed through this paper and found it fascinating that a $10,000+ commercial ultrasound device could be effectively implemented with less than a few hundred dollars. The paper is well-written and effectively demonstrates how to do it. I was astonished by how well balanced and detailed the thesis was, something that I seldom expect from graduate students writing for a masters degree. It is better than many of the thesis papers I have read that were written by PhD candidates!
The OP has admitted to being "an absolute beginner to electronics." This is NOT a project for a beginner, nor is it suitable for most hobbyists with little or no access to research facilities. This is the type of work I would have been asked to help with (and was asked on several occaisions) while employed at the University of Dayton Research Instutute... the electronics and physical construction part of it anyway. The grad student designs the experiment, records the test data, and writes the thesis paper! All the heavy lifting in other words. I helped with what I could.
I like the (future) idea of using either a microprocessor or programmable logic array to control (modulate) the PZT transducer array to vary the focus position and shape of the ultrasonic treatement field. Using a 3D solid-modeling program and a printer to design the concave hemispherical cavity in which to mount the PZT elements was genius! I will forward a link to this paper to the president of my former employer, UES, Inc., since she has PhDs in this area and the company has a biomed division. This could be a seminal paper in how to lower the cost of "medical" equipment used in research.