What is the difference between acoustic imaging, acoustic micro imaging, and scanning acoustic microscopy?

None. They are synonyms for the same non-destructive inspection technique. The acronyms AMI, SAM and C-SAM® are also frequently used and stand for Acoustic Micro Imaging, Scanning Acoustic Microscopy and C-mode Scanning Acoustic Microscopy, respectively. The term "ultrasonic testing" is sometimes used to describe this technique as well, but can also be used in reference to macro systems designed for inspecting larger items, such as structural components of vehicles or aircraft, using lower frequencies. The term "Sonoscan testing" is often used as another synonym for acoustic micro imaging. Sonoscan® and C-SAM® are registered trademarks of Sonoscan Inc., the inventor of this inspection technology and a primary provider of acoustic microscopy systems.