ABSTRACT
Significance: Cerebral metabolic rate of oxygen ( CMRO 2 ) consumption is a key physiological variable that characterizes brain metabolism in a steady state and during functional activation. Aim: We aim to develop a minimally invasive optical technique for real-time measurement of CMRO 2 concurrently with cerebral blood flow (CBF). Approach: We used a pair of macromolecular phosphorescent probes with nonoverlapping optical spectra, which were localized in the intra- and extravascular compartments of the brain tissue, thus providing a readout of oxygen gradients between these two compartments. In parallel, we measured CBF using laser speckle contrast imaging. Results: The method enables computation and tracking of CMRO 2 during functional activation with high temporal resolution ( â¼ 7 Hz ). In contrast to other approaches, our assessment of CMRO 2 does not require measurements of CBF or hemoglobin oxygen saturation. Conclusions: The independent records of intravascular and extravascular partial pressures of oxygen, CBF, and CMRO 2 provide information about the physiological events that accompany neuronal activation, creating opportunities for dynamic quantification of brain metabolism.
ABSTRACT
Significance: Rapid estimation of the depth and margins of fluorescence targets buried below the tissue surface could improve upon current image-guided surgery techniques for tumor resection. Aim: We describe algorithms and instrumentation that permit rapid estimation of the depth and transverse margins of fluorescence target(s) in turbid media; the work aims to introduce, experimentally demonstrate, and characterize the methodology. Approach: Spatial frequency domain fluorescence diffuse optical tomography (SFD-FDOT) technique is adapted for rapid and computationally inexpensive estimation of fluorophore target depth and lateral margins. The algorithm utilizes the variation of diffuse fluorescence intensity with respect to spatial-modulation-frequency to compute target depth. The lateral margins are determined via analytical inversion of the data using depth information obtained from the first step. We characterize method performance using fluorescent contrast targets embedded in tissue-simulating phantoms. Results: Single and multiple targets with significant lateral size were imaged at varying depths as deep as 1 cm. Phantom data analysis showed good depth-sensitivity, and the reconstructed transverse margins were mostly within â¼30 % error from true margins. Conclusions: The study suggests that the rapid SFD-FDOT approach could be useful in resection surgery and, more broadly, as a first step in more rigorous SFD-FDOT reconstructions. The experiments permit evaluation of current limitations.
