I am sorry if mentioning this study can confuse someone. I could not find better that explicitly says that US penetrate human bone. Study was performing in vitro, that’s not on the living man. And also interfering with blood cloth in the brain is matter of neurosurgeons not physios. So, let’s keep our profession. In almost every book for electrotherapy there could be found contraindication for using US on aria of the head and front of the neck. But I find similar debate on this topic few times that’s why I posted this answers.