Validation of Noninvasive Photoacoustic Measurements of Sagittal Sinus Oxyhemoglobin Saturation in Hypoxic Neonatal Piglets.

We hypothesize that noninvasive photoacoustic imaging can accurately measure cerebral venous oxyhemoglobin saturation (sO2 ) in a neonatal model of hypoxia-ischemia. In neonatal piglets, which have a skull thickness comparable to that of human neonates, we validated the noninvasive photoacoustic measurement of sagittal sinus sO2 against that measured directly by blood sampling. Systemic hypoxia was produced by decreasing inspired oxygen stepwise (i.e., 100, 21, 19, 17, 15, 14, 13, 12, 11, 10%) with or without unilateral or bilateral ligation of the common carotid arteries to enhance hypoxia-ischemia. Transcranial photoacoustic sensing enabled us to detect changes in sagittal sinus sO2 saturation throughout the tested range of 5-80% without physiologically relevant bias. Despite lower cortical perfusion and higher oxygen extraction in groups with carotid occlusion at equivalent inspired oxygen, photoacoustic measurements successfully provided a robust linear correlation that approached the line of identity with direct blood sample measurements. Receiver-operating characteristic analysis for the pooled dataset showed an area under the curve of 0.84, and separate analysis for each group showed excellent areas under the curve of 0.87, 0.91, and 0.92 for hypoxia alone, hypoxia plus unilateral occlusion, and hypoxia plus bilateral occlusion groups, respectively. The detection precision in the critical range of <30% sagittal sinus sO2 was confirmed with sensitivity (87.0%), specificity (86.5%), accuracy (86.8%), positive predictive value (90.5%), and negative predictive value (81.8%) in the combined dataset. These results support the capability of photoacoustic sensing technology to monitor sagittal sinus sO2 noninvasively for early detection of neonatal hypoxia-ischemia.