Doubts about abdominal ultrasonography in dogs with diarrhoea are discussed in Lamb‘s new treatise:
“How Useful is Abdominal Ultrasonography in Dogs With Diarrhoea?” Emma K. Mapletoft, Karin Allenspach, and Chris R. Lamb [pictured here], Journal of Small Animal Practice, epub November 2017.
The authors, at the Royal Veterinary College, UK, report:
“Abdominal ultrasonography had moderate utility in 56 (38%) dogs and no utility in 79 (53%) dogs. Abdominal ultrasonography was considered counterproductive in 10 (7%) dogs because results were either falsely negative or falsely positive.”
BONUS (possibly not related): Here is video of a dog responding to the spoken word “diarrhoea”: