A great read just popped out of my alerts: Microcontroller USB interfacing with MATLAB GUI for low cost medical ultrasound scanners . Interesting, if one is to interface a probe with MATLAB ;)

Other interesting articles:

• http://sci-hub.io/10.1109/ULTSYM.2015.0517 for a full fledge Smartphone Probe - awesome work too !
• Development of an embedded system and MATLAB-based GUI for online acquisition and analysis of ECG signal
• Integrating hardware and software for the development of microcontroller-based systems
• Design of a USB based multichannel, low cost data acquisition system using PIC microcontroller
• Low-cost USB interface for operant research using Arduino and Visual Basic

Another awesome read: Development of a wide band front endecho sounder receiver circuit - Master Thesis of Jatin Sharma. There's everything, from VHDL to schematics.