What does a scalp ultrasound show on an infant? is it the same as a cranial ultrasound or something different?

Your post is confusing. I would suppose a scalp US can look inside a bruise or other projection on the skull to identify the underlying structure. Cranial ultrasounds are a common way to evaluate the internal waterworks of the brain using the open "soft spot" as an entry point. Someone might use the terms interchangeably but I have never heard of any study labeled that way.

Scalp ultrasound is used to check all the layers of the scalp and its component whereas cranial or transcranial ultrasound is used to primarily check the intracranial (inside the skull, i.e. the brain) vessels. These 2 procedures are serving different purposes.