Assessment of Cerebral Oxygenation based on Blood Perfusion Maps Obtained from Ultrasonically Tracked Microbubbles*

Monitoring brain oxygenation plays a key role in preventing secondary injuries led by brain ischemia and hypoxia in hydrocephalic patients. However, conventional monitoring techniques are either invasive or inaccurate. A non-invasive and reliable assessment technique would be of great importance for continuous management of brain oxygenation and neurosurgical interventions. Here we use contrast-enhanced ultrasound (CEUS) imaging and ultrasound localization microscopy (ULM) to map the cerebral micro vessels and assess the microvascular blood flow. This procedure involves tracking of lipid-coated micro-bubbles (2-3 μm in diameter) in a coronal section of the brain and using the tracks to generate detailed maps of the cerebral micro- and macro-vessels and measuring the blood velocity in them. A 'cerebral microcirculation parameter (CMC),' is defined as the product of blood vessels concentration and flow velocity to characterize the perfusion in different cerebral sections. In efforts to develop means of measuring the intracranial pressure (ICP) non-invasively, tests involving infant pigs have examined the correlation between CMC of micro- and macro-vessels, ICP, and the invasively-measured cerebral oxygen tension (PbtO2). Results show that the cortical CMC scaled by mean arterial pressure is linearly correlated with the PbtO2 with a correlation coefficient exceeding 0.76. This finding suggests that CMC could be used as an effective non-invasive means for assessing cerebral oxygenation.