Photoacoustic Measurement of Localized Optical Dichroism in Chiral Crystals

In this communication, we present a novel method to measure local optical dichroism (OD) in opaque crystal powder suspensions using photoacoustic (PA) effect. Our method is based upon the novel...

Light-emitting diode-based transcranial photoacoustic measurement of sagittal sinus oxyhemoglobin saturation in hypoxic neonatal piglets

We present a light-emitting diode (LED)-based transcranial photoacoustic measurement (LED-trPA) of oxyhemoglobin (HbO2) saturation at superior sagittal sinus (SSS) in hypoxic neonatal piglets. The optimal LED imaging wavelengths and frame averaging scheme were determined based on in vivo characterization of transcranial sensitivity. Based on the framework (690/850 nm with >20 frame averaging), graded hypoxia was successfully identified in neonatal piglets in vivo with less than 10.0 % of root mean squared error (RMSE). This preclinical study suggests the feasibility of a rapid, cost-effective, and safe LED-trPA monitoring of perinatal hypoxia-ischemia and prompt interventions for clinical use.

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 compared the photoacoustic measurement of sagittal sinus So2 against that measured directly by blood sampling over a wide range of conditions. Systemic hypoxia was produced by decreasing inspired oxygen stepwise (i.e., 100, 21, 19, 17, 15, 14, 13, 12, 11, and 10%) with and 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 O2 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 discriminating So2 <30% showed an area under the curve of 0.84 for the pooled group data, and 0.87, 0.91, and 0.92 for hypoxia alone, hypoxia plus unilateral occlusion, and hypoxia plus bilateral occlusion subgroups, respectively. The detection precision in this critical range 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 validate the capability of photoacoustic sensing technology to accurately monitor sagittal sinus So2 noninvasively over a wide range and support its use for early detection of neonatal hypoxia-ischemia. NEW & NOTEWORTHY We present data to validate the noninvasive photoacoustic measurement of sagittal sinus oxyhemoglobin saturation. In particular, this paper demonstrates the robustness of this methodology during a wide range of hemodynamic and physiological changes induced by the stepwise decrease of fractional inspired oxygen to produce hypoxia and by unilateral and bilateral ligation of the common carotid arteries preceding hypoxia to produce hypoxia-ischemia. This technique may be useful for diagnosing risk of neonatal hypoxic-ischemic encephalopathy.