Super-resolution computational saturated absorption microscopy.

Imaging beyond the diffraction limit barrier has attracted wide attention due to the ability to resolve previously hidden image features. Of the various super-resolution microscopy techniques available, a particularly simple method called saturated excitation microscopy (SAX) requires only simple modification of a laser scanning microscope: The illumination beam power is sinusoidally modulated and driven into saturation. SAX images are extracted from the harmonics of the modulation frequency and exhibit improved spatial resolution. Unfortunately, this elegant strategy is hindered by the incursion of shot noise that prevents high-resolution imaging in many realistic scenarios. Here, we demonstrate a technique for super-resolution imaging that we call computational saturated absorption (CSA) in which a joint deconvolution is applied to a set of images with diversity in spatial frequency support among the point spread functions (PSFs) used in the image formation with saturated laser scanning fluorescence microscopy. CSA microscopy allows access to the high spatial frequency diversity in a set of saturated effective PSFs, while avoiding image degradation from shot noise.

Single-pixel fluorescent diffraction tomography.

Optical diffraction tomography (ODT) is an indispensable tool for studying objects in three dimensions. Until now, ODT has been limited to coherent light because spatial phase information is required to solve the inverse scattering problem. We introduce a method that enables ODT to be applied to imaging incoherent contrast mechanisms such as fluorescent emission. Our strategy mimics the coherent scattering process with two spatially coherent illumination beams. The interferometric illumination pattern encodes spatial phase in temporal variations of the fluorescent emission, thereby allowing incoherent fluorescent emission to mimic the behavior of coherent illumination. The temporal variations permit recovery of the spatial distribution of fluorescent emission with an inverse scattering model. Simulations and experiments demonstrate isotropic resolution in the 3D reconstruction of a fluorescent object.

Spatial frequency modulated imaging in coherent anti-Stokes Raman microscopy.

For sparse samples or in the presence of ambient light, the signal-to-noise ratio (SNR) performance of single-point-scanning coherent anti-Stokes Raman scattering (CARS) images is not optimized. As an improvement, we propose replacing the conventional CARS focus-point illumination with a periodically structured focus line while continuing to collect the transmitted CARS intensity on a single detector. The object information along the illuminated line is obtained by numerically processing the CARS signal recorded for various periods of the structured focus line. We demonstrate experimentally the feasibility of this spatial frequency modulated imaging (SPIFI) in CARS (SPIFI-CARS) and SHG (SPIFI-SHG) and identify situations where its SNR is better than that of the single-point-scanning approach.

Hyperspectral imaging in the spatial frequency domain with a supercontinuum source.

We introduce a method for quantitative hyperspectral optical imaging in the spatial frequency domain (hs-SFDI) to image tissue absorption (µa) and reduced scattering (µs') parameters over a broad spectral range. The hs-SFDI utilizes principles of spatial scanning of the spectrally dispersed output of a supercontinuum laser that is sinusoidally projected onto the tissue using a digital micromirror device. A scientific complementary metal-oxide-semiconductor camera is used for capturing images that are demodulated and analyzed using SFDI computational models. The hs-SFDI performance is validated using tissue-simulating phantoms over a range of µa and µs' values. Quantitative hs-SFDI images are obtained from an ex-vivo beef sample to spatially resolve concentrations of oxy-, deoxy-, and met-hemoglobin, as well as water and fat fractions. Our results demonstrate that the hs-SFDI can quantitatively image tissue optical properties with 1000 spectral bins in the 580- to 950-nm range over a wide, scalable field of view. With an average accuracy of 6.7% and 12.3% in µa and µs', respectively, compared to conventional methods, hs-SFDI offers a promising approach for quantitative hyperspectral tissue optical imaging.

Compressive Raman imaging with spatial frequency modulated illumination.

We report a line scanning imaging modality of compressive Raman technology with spatial frequency modulated illumination using a single pixel detector. We demonstrate the imaging and classification of three different chemical species at line scan rates of 40 Hz.

Fourier computed tomographic imaging of two dimensional fluorescent objects.

We introduce a new form of tomographic imaging that is particularly advantageous for a new class of super-resolution optical imaging methods. Our tomographic method, Fourier Computed Tomography (FCT), operates in a conjugate domain relative to conventional computed tomography techniques. FCT is the first optical tomography method that records complex projections of the object spatial frequency distribution. From these spatial frequency projections, the spatial slice theorem is derived, which is used to build a tomographic imaging reconstruction algorithm. FCT enables enhancement of spatial frequency support along a single spatial direction to be isotropic in the entire transverse spatial frequency domain.

Single pixel quantitative phase imaging with spatial frequency projections.

We introduce a new single pixel imaging technique that automatically co-registers quantitative phase and incoherent image modalities through the simultaneous acquisition of identical object spatial frequency information. The technique consists of using a time varying groove density diffraction grating to produce a reference and scan beam. The interference between the beams produce time varying spatial frequencies in the sample. The collected light on a single pixel detector produces a time trace that allows easy recovery of coherent and incoherent contrast mechanisms. We derive theory for the quantitative phase and show excellent agreement with experimental data and numeric model. Additionally, we derive a general theory of single pixel quantitative phase theory that can be applied broadly to general methods that use a sequence of modulated light patterns for single pixel phase imaging.

Nipah virus infection in dogs, Malaysia, 1999.

The 1999 outbreak of Nipah virus encephalitis in humans and pigs in Peninsular Malaysia ended with the evacuation of humans and culling of pigs in the epidemic area. Serologic screening showed that, in the absence of infected pigs, dogs were not a secondary reservoir for Nipah virus.

Bat Nipah virus, Thailand.

Surveillance for Nipah virus (NV) was conducted in Thailand's bat population. Immunoglobulin G antibodies to NV were detected with enzyme immunoassay in 82 of 1,304 bats. NV RNA was found in bat saliva and urine. These data suggest the persistence of NV infection in Thai bats.