Application of high-intensity focused ultrasound to the study of mild traumatic brain injury

Though intrinsically of much higher frequency than open-field blast overpressures, high-intensity focused ultrasound (HIFU) pulse trains can be frequency modulated to produce a radiation pressure having a similar form. In this study, 1.5-MHz HIFU pulse trains of 1-ms duration were applied to intact skulls of mice invivo and resulted in blood-brain barrier disruption and immune responses (astrocyte reactivity and microglial activation). Analyses of variance indicated that 24h after HIFU exposure, staining density for glial fibrillary acidic protein was elevated in the parietal and temporal regions of the cerebral cortex, corpus callosum and hippocampus, and staining density for the microglial marker, ionized calcium binding adaptor molecule, was elevated 2 and 24h after exposure in the corpus callosum and hippocampus (all statistical test results, p<0.05). HIFU shows promise for the study of some bio-effect aspects of blast-related, non-impact mild traumatic brain injuries in animals.