Spatio-angular filter (SAF) imaging device for deep interrogation of scattering media.

Optical microscopy is limited to shallow interrogation depths as high-resolution imaging in scattering media is challenging. Current methods require complex and expensive experimental setup or suffer from low resolution. Through gating of photons exiting the scattering media using a restricted numerical aperture (NA) fiber optic plate (FOP), we establish a novel spatio-angular filter imaging device that allows deeper imaging in scattering media. Using dilutions of Intralipid (1-4 v/v%) and a USAF resolution target, it is shown that by reducing the NA of the FOP from 0.55 to 0.17, the interrogation depth improves ~2 times using trans-illumination.

Non-labeled lensless micro-endoscopic approach for cellular imaging through highly scattering media.

We describe an imaging approach based on an optical setup made up of a miniature, lensless, minimally invasive endoscope scanning a sample and matching post processing techniques that enable enhanced imaging capabilities. The two main scopes of this article are that this approach enables imaging beyond highly scattering medium and increases the resolution and signal to noise levels reaching single cell imaging. Our approach has more advantages over ordinary endoscope setups and other imaging techniques. It is not mechanically limited by a lens, the stable but flexible fiber can acquire images over long time periods (unlike current imaging methods such as OCT etc.), and the imaging can be obtained at a certain working distance above the surface, without interference to the imaged object. Fast overlapping scans enlarge the region of interest, enhance signal to noise levels and can also accommodate post-processing, super-resolution algorithms. Here we present that due to the setup properties, the overlapping scans also lead to dramatic enhancement of non-scattered signal to scattered noise. This enables imaging through highly scattering medium. We discuss results obtained from in vitro investigation of weak signals of ARPE cells, rat retina, and scattered signals from polydimethylsiloxane (PDMS) microchannels filled with hemoglobin and covered by intralipids consequently mimicking blood capillaries and the epidermis of human skin. The development of minimally invasive procedures and methodologies for imaging through scattering medium such as tissues can vastly enhance biomedical diagnostic capabilities for imaging internal organs. We thereby propose that our method may be used for such tasks in vivo.

Independent component analysis of broadband near-infrared spectroscopy data acquired on adult human head.

The goal of this study was to investigate the ability of independent component analysis in the time-spectral domain to isolate physiological sources of functional near infrared spectroscopy signals. We apply independent component analysis to the broadband fNIRS data acquired on the human forehead at 650 different wavelengths between 700 nm and 950 nm. To induce cerebral oxygenation changes we use the breath holding paradigm. We found one major independent component during baseline and two major components during exercise. Each independent component corresponds to one oxy-hemoglobin and one deoxy-hemoglobin time courses. The corresponding characteristic spectra of changes in optical absorption suggested that one component represented vasodilation of cerebral arterioles while the delayed component represented the washout of deoxyhemoglobin either in cerebral capillaries and venules or in extra cerebral tissue. We found that both broadband and isolated wavelength data can produce similar independent components.

Optimal quantitation of the cerebral hemodynamic response in functional near-infrared spectroscopy.

We have compared cerebral hemodynamic changes measured by near-infrared spectroscopy (NIRS) with simultaneously acquired BOLD fMRI signals during breath hold challenge in humans. The oxy- and deoxyhemoglobin concentration changes were obtained from the same broadband NIRS data using four different quantitation methods. One method used only two wavelengths (690 nm and 830 nm), and three other methods used broadband data with different spectral fitting algorithms. We found that the broadband techniques employing spectral derivatives were significantly superior to the multi-wavelength methods in terms of the correlation with the BOLD signals. In two cases out of six we found that the time courses of the deoxyhemoglobin changes produced by the two-wavelength method were qualitatively inconsistent with the BOLD fMRI signals.