I was under the naive impression that the acoustic impedance mismatch across the skull/cranial-fluid/brain means that not enough ultrasound would go through for

I was under the naive impression that the acoustic impedance mismatch across the skull/cranial-fluid/brain means that not enough ultrasound would go through for useful imaging. Is that not as big a deal, or is the problems somehow circumvented? EDIT: Here’s what the article says about this: > "Current high-resolution brain–machine interfaces use electrode arrays that require brain surgery, which includes opening the dura, the strong fibrous membrane between the skull and the brain, and implanting the electrodes directly into the brain. But ultrasound signals can pass through the dura and brain non-invasively. Only a small, ultrasound-transparent window needs to be implanted in the skull; this surgery is significantly less invasive than that required for implanting electrodes," says Andersen. > Though this research was carried out in non-human primates, a collaboration is in the works with Dr. Charles Liu, a neurosurgeon at USC, to study the technology with human volunteers who, because of traumatic brain injuries, have had a piece of skull removed. Because ultrasound waves can pass unaffected through these "acoustic windows," it will be possible to study how well functional ultrasound can measure and decode brain activity in these individuals.