Diffuse correlation spectroscopy is a widely used optical technique for recovery of blood flow. Its applications have included monitoring of ischemia, blood flow in tumors, and cerebral blood flow. Recently, several variants on this technology have been developed with potential to enhance sensitivity to deep tissues, increase signal-to-noise ratio, and lower costs. Here, we employ diffuse correlation spectroscopy, speckle contrast optical spectroscopy, and interferometric diffusing wave spectroscopy concurrently to measure in vivo and in vitro flow. The results elucidate the advantages and disadvantages of each modality and will aid researchers in selecting a blood flow monitoring method for specific applications.
The current fluorescence image-guided surgery technique does not provide accurate estimates of target depth and
transverse margins of fluorescing tumors. We adapted Spatial Frequency Domain Fluorescence Diffuse Optical Tomography to rapidly acquire the depth and transverse margins of fluorescent inclusions in a turbid media in two steps. First, we derive estimates of depth from normalized fluorescence responses to the spatially modulated light patterns. Second, using the estimated depth, we reconstruct the transverse margin in the target plane. We demonstrate the performance of our instrumentation and approach using a series of phantom experiments.
SignificanceCerebral metabolic rate of oxygen (CMRO2) consumption is a key physiological variable that characterizes brain metabolism in a steady state and during functional activation.AimWe aim to develop a minimally invasive optical technique for real-time measurement of CMRO2 concurrently with cerebral blood flow (CBF).ApproachWe 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.ResultsThe method enables computation and tracking of CMRO2 during functional activation with high temporal resolution (∼7 Hz). In contrast to other approaches, our assessment of CMRO2 does not require measurements of CBF or hemoglobin oxygen saturation.ConclusionsThe independent records of intravascular and extravascular partial pressures of oxygen, CBF, and CMRO2 provide information about the physiological events that accompany neuronal activation, creating opportunities for dynamic quantification of brain metabolism.
SignificanceRapid 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.AimWe 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.ApproachSpatial 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.ResultsSingle 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 ∼30 % error from true margins.ConclusionsThe 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.
We present a novel method for real-time measurement of the oxygen (pO2) gradients between intra- and extra-vascular compartments in rat brain cortex during functional activation. This information, obtained in parallel with measurements of cerebral blood flow (CBF), permits determination of absolute cerebral metabolic rate of oxygen (CMRO2). The timing of pO2, CBF, and CMRO2 responses is captured with high temporal resolution (~7 Hz). We discuss these results in the context of physiological models that connect oxidative metabolism to neuronal activation.
We present a biomedical application of Digital Micro-mirror technologies by adapting the DLP4500 module for quasi real-time intraoperative tumor imaging. Fluorescence image guided surgery has been increasingly popular due to its ability to inform surgeons about tumor boundaries in real-time. We have extended this technique to provide 3D tomographic images of a tumor, by adapting a DLP4500 device to illuminate the surgical field with spatially modulated near-infrared (NIR) light. We combine the digital micro-mirror device (DMD) with two simultaneously triggered CMOS cameras to realize a spatial frequency domain imaging system. Spatial frequency domain imaging utilizes sinusoidally modulated illumination at different spatial frequencies and three different phases; corresponding signals are readily demodulated, and analyzed to derive a 3D fluorescence image. Our DMD device is commercially modified and equipped with high-power (5W) NIR diode laser. We present a brief discussion of data acquisition using DLP4500 module, and corrections for spatial inhomogeneity and gamma adjust in order to create linear/desired sinusoidal illumination of NIR light. We discuss results from a tissue phantom study and in-vivo experiments.
Surgical resection is the most effective treatment strategy for solid tumors, but complete removal of the tumor is critical for post-surgical recovery/long-term survival and is dependent on correct identification of the tumor margin and accurate excision of microscopic residual tumor in the surgical field. Fluorescence image guided surgery is an emerging technique that has shown promise for intraoperative location of tumors and tumor margins. Current versions of such intraoperative fluorescence imaging, however, are generally limited to 2D near-surface images, i.e., without information about tumor depth. Here we present an intraoperative fluorescence imaging system for 3D volumetric imaging of tumors; the system uses spatial frequency domain diffuse optical tomography with an analytic inversion reconstruction method. The new instrument can derive depth-sensitive 3D tumor images at depths up to 1 cm, and it employs compact epi-imaging and illumination suitable for the operating room, with quasi-real-time image reconstruction for surgical visualization. We present experimental results with FDA-approved Indocynanine Green using an extensive array of tissue phantoms and in a pilot in-vivo study.
Surgery is the most effective treatment strategy for solid tumors. Intraoperative imaging of tumors helps detect tumor margins and establish the most appropriate surgical margins. Endoscopic surgery is a standard of care procedure for the resection of tumors, and is applicable for a wide range of solid tumors. While several imaging methodologies can be used for intraoperative imaging, optical imaging is promising for clinical application because it can detect microscopic disease, is minimally invasive, is inexpensive, does not require advance training for surgeons and can provide real-time images. Fluorescence from an injected contrast agent (Indo-cyanine green, ICG) has been effectively used for the identification of tumors in humans. In this study, we adapt a commercially available endoscope for intraoperative imaging of solid tumors. Our instrument utilizes light from a near-infrared 780nm LED to illuminate the surgical field of view and two CCD cameras for imaging the reflected fluorescence as well as the background tissue. We show that our instrument can simultaneously image fluorescence from the tumor as well as the background tissue. We characterize our instrument in tissue simulating phantoms, with tumor simulating ‘targets’.
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