Imaging Of Biological Tissues Research Articles

Plasmonic nanoantenna hydrophones.

Ultrasound is a valuable biomedical imaging modality and diagnostic tool. Here we theoretically demonstrate that a single dipole plasmonic nanoantenna can be used as an optical hydrophone for MHz-range ultrasound. The nanoantenna is tuned to operate on a high-order plasmon mode, which provides an increased sensitivity to ultrasound in contrast to the usual approach of using the fundamental dipolar plasmon resonance. Plasmonic nanoantenna hydrophones may be useful for ultrasonic imaging of biological cells, cancer tissues or small blood vessels, as well as for Brillouin spectroscopy at the nanoscale.

Gram-Schmidt orthonormalization for retrieval of amplitude images under sinusoidal patterns of illumination.

Structured illumination using sinusoidal patterns has been used for optical imaging of biological tissues in biomedical research, and of horticultural products in food quality evaluation. Implementation of structured-illumination imaging relies on retrieval of amplitude images, which is conventionally achieved by a phase-shifting technique that requires collecting a minimum of three phase-shifted images. In this study, we have proposed Gram-Schmidt orthonormalization (GSO) to retrieve amplitude component (AC) images using only two phase-shifted images. We have proposed two forms of GSO implementation, and prior to GSO processing, we eliminated the direct component (DC) background by subtracting a DC image we recovered using a spiral phase function (SPF) in the Fourier space. We demonstrated the GSO methods through numerical simulations and application examples of detection of bruise defects in apples by structured-illumination reflectance imaging (SIRI). GSO performed comparably to conventional three-phase-based demodulation. It is simple, fast and effective for amplitude retrieval and requires no prior phase information, which could facilitate fast implementation of structured-illumination imaging.

Recent applications of phthalocyanines and naphthalocyanines for imaging and therapy.

With high extinction coefficients and long absorption wavelengths in the near infrared region, phthalocyanines (Pcs) and naphthalocyanines (Ncs) are well-suited for optical imaging and phototherapies in biological tissues. Pcs and Ncs have been used in a range of theranostic applications. Peripheral and axial substituents can be introduced to Pcs and Ncs for chemical modification. Seamless metal chelation of Pcs or Ncs can expand their possibilities as medical therapeutic and imaging agents. Nanoparticulate approaches enable unique ways to deliver Pcs and Ncs to target tissues and improve their solubility, biocompatibility, biodistribution and stability. Herein, we highlight some recent Pc or Nc nanoscale systems for theranostic applications. WIREs Nanomed Nanobiotechnol 2017, 9:e1420. doi: 10.1002/wnan.1420 For further resources related to this article, please visit the WIREs website.

High-energy proton imaging for biomedical applications.

The charged particle community is looking for techniques exploiting proton interactions instead of X-ray absorption for creating images of human tissue. Due to multiple Coulomb scattering inside the measured object it has shown to be highly non-trivial to achieve sufficient spatial resolution. We present imaging of biological tissue with a proton microscope. This device relies on magnetic optics, distinguishing it from most published proton imaging methods. For these methods reducing the data acquisition time to a clinically acceptable level has turned out to be challenging. In a proton microscope, data acquisition and processing are much simpler. This device even allows imaging in real time. The primary medical application will be image guidance in proton radiosurgery. Proton images demonstrating the potential for this application are presented. Tomographic reconstructions are included to raise awareness of the possibility of high-resolution proton tomography using magneto-optics.

Grueneisen relaxation photoacoustic microscopy in vivo.

Grueneisen relaxation photoacoustic microscopy (GR-PAM) can achieve optically defined axial resolution, but it has been limited to ex vivo demonstrations so far. Here, we present the first in vivo image of a mouse brain acquired with GR-PAM. To induce the GR effect, an intensity-modulated continuous-wave laser was employed to heat absorbing objects. In phantom experiments, an axial resolution of 12.5 μm was achieved, which is sixfold better than the value achieved by conventional optical-resolution PAM. This axial-resolution improvement was further demonstrated by imaging a mouse brain in vivo, where significantly narrower axial profiles of blood vessels were observed. The in vivo demonstration of GR-PAM shows the potential of this modality for label-free and high-resolution anatomical and functional imaging of biological tissues.

Morphometrics Show Sam Francis’s Painted Forms Are Statistically Similar to Cells in Biological Tissues

The paintings of the abstract expressionist artist Sam Francis contain vivid biomorphic forms. One influence for Francis may have been microscopic images of biological tissues he observed in premedical courses prior to becoming an artist. Using two morphometric measurements common in cell biology, the authors show that forms in Francis’s paintings are statistically similar to cells in biological tissues that resemble his paintings. This study highlights specific similarities between forms in Francis’s paintings and biology. It also presents a novel application of biological morphometrics that could help clarify the creative process and psychological appeal of Francis and other “organic” artists.

Retroreflective-type Janus microspheres as a novel contrast agent for enhanced optical coherence tomography.

Optical coherence tomography (OCT) is a well-developed technology that utilizes near-infrared light to reconstruct three-dimensional images of biological tissues with micrometer resolution. Improvements of the imaging contrast of the OCT technique are able to further widen its extensive biomedical applications. In this study, Janus microspheres were developed and used as a positive contrast agent for enhanced OCT imaging. Phantom and ex vivo liver tissue experiments as well as in vivo animal tests were conducted, which validated that Janus microspheres, as a novel type of OCT tracer, were very effective in improving the OCT imaging contrast. Working principle and SEM image of Janus microsphere (top). Enhanced OCT imaging (bottom) of Janus microspheres in zebrafish stomach (blue dash line) and sinusoids (green arrows) of nude liver.

An edge-on charge-transfer design for energy-resolved x-ray detection

As an x-ray beam goes through the human body, it will collect important information via interaction with tissues. Since this interaction is energy-sensitive, the state-of-the-art spectral CT technologies provide higher quality images of biological tissues with x-ray energy information (or spectral information). With existing energy-integrating technologies, a large fraction of energy information is ignored in the x-ray detection process. Although the recently proposed photon-counting technology promises to achieve higher image quality at a lower radiation dose, it suffers from limitations in counting rate, performance uniformity, and fabrication cost. In this paper, we focus on an alternative approach to resolve the energy distribution of transmitted x-ray photons. First, we analyze the x-ray attenuation in a silicon substrate and describe a linear approximation model for x-ray detection. Then, we design an edge-on architecture based on the proposed energy-resolving model. In our design, the x-ray-photon-induced charges are transferred sequentially resembling the working process of a CCD camera. Finally, we numerically evaluate the linear approximation of x-ray attenuation and derive the energy distribution of x-ray photons. Our simulation results show that the proposed energy-sensing approach is feasible and has the potential to complement the photon-counting technology.

Adaptive Basis Scan by Wavelet Prediction for Single-Pixel Imaging

Single-pixel camera imaging is an emerging paradigm that allows high-quality images to be provided by a device only equipped with a single point detector. A single-pixel camera is an experimental setup able to measure the inner product of the scene under view—the image—with any user-defined pattern. Postprocessing a sequence of point measurements obtained with different patterns permits to recover spatial information, as it has been demonstrated by state-of-the-art approaches belonging to the compressed sensing framework. In this paper, a new framework for the choice of the patterns is proposed together with a simple and efficient image recovery scheme. Our goal is to overcome the computationally demanding $\ell _1$ -minimization of the compressed sensing. We propose to choose patterns among a wavelet basis in an adaptive fashion, which essentially relies onto the prediction of the significant wavelet coefficients’ location. More precisely, we adopt a multiresolution strategy that exploits the set of measurements acquired at coarse scales to predict the set of measurements to be performed at a finer scale. Prediction is based on a fast cubic interpolation in the image domain. A general formalism is given so that any kind of wavelets can be used, which enables one to adjust the wavelet to the type of images related to the desired application. Both simulated and experimental results demonstrate the ability of our technique to reconstruct biomedical images with improved quality compared with compressive-sensing-based recovery. Application to the real-time fluorescence imaging of biological tissues could benefit from the proposed method.

Miniature fiber-optic multiphoton microscopy system using frequency-doubled femtosecond Er-doped fiber laser.

We report on a miniature fiber-optic multiphoton microscopy (MPM) system based on a frequency-doubled femtosecond Er-doped fiber laser. The femtosecond pulses from the laser source are delivered to the miniature fiber-optic probe at 1.58 µm wavelength, where a standard single mode fiber is used for delivery without the need of free-space dispersion compensation components. The beam is frequency-doubled inside the probe by a periodically poled MgO:LiNbO3 crystal. Frequency-doubled pulses at 786 nm with a maximum power of 80 mW and a pulsewidth of 150 fs are obtained and applied to excite intrinsic signals from tissues. A MEMS scanner, a miniature objective, and a multimode collection fiber are further used to make the probe compact. The miniature fiber-optic MPM system is highly portable and robust. Ex vivo multiphoton imaging of mammalian skins demonstrates the capability of the system in imaging biological tissues. The results show that the miniature fiber-optic MPM system using frequency-doubled femtosecond fiber laser can potentially bring the MPM imaging for clinical applications.

Tutorial on photoacoustic tomography.

Photoacoustic tomography (PAT) has become one of the fastest growing fields in biomedical optics. Unlike pure optical imaging, such as confocal microscopy and two-photon microscopy, PAT employs acoustic detection to image optical absorption contrast with high-resolution deep into scattering tissue. So far, PAT has been widely used for multiscale anatomical, functional, and molecular imaging of biological tissues. We focus on PAT’s basic principles, major implementations, imaging contrasts, and recent applications.

Investigation of the Impact of Desorption Electrospray Ionization Sprayer Geometry on Its Performance in Imaging of Biological Tissue.

In this study, the impact of sprayer design and geometry on performance in desorption electrospray ionization mass spectrometry (DESI-MS) is assessed, as the sprayer is thought to be a major source of variability. Absolute intensity repeatability, spectral composition, and classification accuracy for biological tissues are considered. Marked differences in tissue analysis performance are seen between the commercially available and a lab-built sprayer. These are thought to be associated with the geometry of the solvent capillary and the resulting shape of the primary electrospray. Experiments with a sprayer with a fixed solvent capillary position show that capillary orientation has a crucial impact on tissue complex lipid signal and can lead to an almost complete loss of signal. Absolute intensity repeatability is compared for five lab-built sprayers using pork liver sections. Repeatability ranges from 1 to 224% for individual sprayers and peaks of different spectral abundance. Between sprayers, repeatability is 16%, 9%, 23%, and 34% for high, medium, low, and very low abundance peaks, respectively. To assess the impact of sprayer variability on tissue classification using multivariate statistical tools, nine human colorectal adenocarcinoma sections are analyzed with three lab-built sprayers, and classification accuracy for adenocarcinoma versus the surrounding stroma is assessed. It ranges from 80.7 to 94.5% between the three sprayers and is 86.5% overall. The presented results confirm that the sprayer setup needs to be closely controlled to obtain reliable data, and a new sprayer setup with a fixed solvent capillary geometry should be developed.

Corrigendum: Laser spectrometry for multi-elemental imaging of biological tissues.

Scientific Reports 4: Article number: 6065; 10.1038/srep06065published online: August142014; updated: April222016 In this Article, B. Busser is incorrectly affiliated with ‘Institut Lumiere Matiere, UMR5306 Universite Lyon 1-CNRS, Universite de Lyon 69622 Villeurbanne cedex, France’. The correct affiliation is listed below: Universite Joseph Fourier, Inserm U823, IAB, F-38000 Grenoble, France

Motion-free endoscopic system for brain imaging at variable focal depth using liquid crystal lenses.

We present a motion-free system for microendoscopic imaging of biological tissues at variable focal depths. Fixed gradient index and electrically tunable liquid crystal lenses (TLCL) were used to build the imaging optical probe. The design of the TLCL enables polarization-independent and relatively low-voltage operation, significantly improving the energy efficiency of the system. A focal shift of approximately 74±3µm could be achieved by electrically controlling the TLCL using the driving frequency at a constant voltage. The potential of the system was tested by imaging neurons and spines in thick adult mouse brain sections and in vivo, in the adult mouse brain at different focal planes. Our results indicate that the developed system may enable depth-variable imaging of morpho-functional properties of neural circuitries in freely moving animals and can be used to investigate the functioning of these circuitries under normal and pathological conditions.

Electrical conductivity and permittivity maps of brain tissues derived from water content based on T1 -weighted acquisition.

To develop an electrical properties tomography (EPT) technique that can provide in vivo electrical conductivity and permittivity images of biological tissue without performing complex-valued radiofrequency field measurements. Electrical conductivity and permittivity images are modeled as a monotonic function of tissues' water content (W) under the principle of Maxwell's mixture theory. Water content maps are estimated from two spin-echo images having different repetition times (TRs). For the modeling functions, physically measured parameters (electrical properties, water content, and T1 ) of brain cerebrospinal fluid (CSF), gray matter, and white matter are used as landmark literature references. The formulations are validated by a developed electrolyte-protein phantom and by human brain studies at 3 Tesla (T). The electrical properties (EPs) of the phantom estimated by the proposed method match well with the values measured on the bench. The conductivity and permittivity maps from all experiments show uncompromised spatial resolution without boundary artifacts and higher contrast when compared with water content maps. Human brain and phantom EP images suggest that water content is a dominating factor in determining the electrical properties of tissues. Despite possible literature inaccuracies, the proposed method offers EP maps that can provide complementary information to current approaches, to facilitate EPT scans in clinical applications. Magn Reson Med 77:1094-1103, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Magnetoacoustic tomography with magnetic induction for biological tissue imaging: numerical modelling and simulations

Abstract Many imaging techniques are playing an increasingly significant role in clinical diagnosis. In the last years especially noninvasive electrical conductivity imaging methods have been investigated. Magnetoacoustic tomography with magnetic induction (MAT-MI) combines favourable contrast of electromagnetic tomography with good spatial resolution of sonography. In this paper a finite element model of MAT-MI forward problem has been presented. The reconstruction of the Lorentz force distribution has been performed with the help of a time reversal algorithm.

Nonresonant, femtosecond laser vaporization and electrospray post-ionization mass spectrometry as a tool for biological tissue imaging

An ambient mass spectrometry imaging (MSI) source is demonstrated with both high spatial and mass resolution that enables measurement of the compositional heterogeneity within a biological tissue sample. The source is based on nonresonant, femtosecond laser electrospray mass spectrometry (LEMS) coupled to a quadrupole time-of-flight (QTOF) mass analyzer. No matrix deposition and minimal sample preparation is necessary for the source. The laser, translation stage, and mass spectrometer are synchronized and controlled using a customized user interface. Single or multiple laser shots may be applied to each pixel. A scanning rate of 2.0s per pixel is achieved. Measurement of a patterned ink film indicates the potential of LEMS for ambient imaging with a lateral resolution of ∼60μm. Metabolites including sugar, anthocyanins and other small metabolites were successfully mapped from plant samples without oversampling using a spot size of 60×70μm2. Molecular identification of the detected analytes from the tissue was enabled by accurate mass measurement in conjunction with tandem mass spectrometry. Statistical analysis, non-negative matrix factorization and principle component analysis, were applied to the imaging data to extract regions with distinct and/or correlated spectral profiles.

Photoswitching Near-Infrared Fluorescence from Polymer Nanoparticles Catapults Signals over the Region of Noises and Interferences for Enhanced Sensitivity.

As a very sensitive technique, photoswitchable fluorescence not only gains ultrasensitivity but also imparts many novel and unexpected applications. Applications of near-infrared (NIR) fluorescence have demonstrated low background noises, high tissue-penetrating ability, and an ability to reduce photodamage to live cells. Because of these desired features, NIR-fluorescent dyes have been the premium among fluorescent dyes, and probes with photoswitchable NIR fluorescence are even more desirable for enhanced signal quality in the emerging optical imaging modalities but rarely used because they are extremely challenging to design and construct. Using a spiropyran derivative functioning as both a photoswitch and a fluorophore to launch its periodically modulated red fluorescence excitation energy into a NIR acceptor, we fabricated core-shell polymer nanoparticles exhibiting a photoswitchable fluorescence signal within the biological window (∼700-1000 nm) with a peak maximum of 776 nm. Live cells constantly synthesize new molecules, including fluorescent molecules, and also endocytose exogenous particles, including fluorescent particles. Upon excitation at different wavelengths, these fluorescent species bring about background noises and interferences covering nearly the whole visible region and therefore render many intracellular targets unaddressable. The oscillating NIR fluorescence signal with an on/off ratio of up to 67 that the polymer nanoparticles display is beyond the typical background noises and interferences, thus producing superior sharpness, reliability, and signal-to-noise ratios in cellular imaging. Taking these salient features, we anticipate that these types of nanoparticles will be useful for in vivo imaging of biological tissue and other complex specimens, where two-photon activation and excitation are used in combination with NIR-fluorescence photoswitching.

Reduce the matrix effect in biological tissue imaging using dynamic reactive ionization and gas cluster ion beams.

In the context of a secondary ion mass spectrometry (SIMS) experiment, dynamic reactive ionization (DRI) involves introducing a reactive dopant, HCl, into an Ar gas cluster primary ion beam along with a source of water to enable dissociation of HCl to free protons. This concerted effect, precisely occurring at the impact site of the cluster beam, enhances the protonation of molecular species. Here, the authors apply this methodology to study the hippocampus and cerebellum region of a frozen-hydrated mouse brain section. To determine the degree of enhancement associated with DRI conditions, sequential tissue slices were arranged in a mirrored configuration so that comparable regions of the tissue could be explored. The results show that the protonated lipid species are increased by ∼10-fold, but that the normally prevalent salt adducts are virtually unaffected. This observation is discussed as a novel approach to minimizing SIMS matrix effects in complex materials. Moreover, the chemical images of protonated lipid ions exhibit clearer features in the cerebellum region as compared to images acquired with the pure Ar cluster beam.

High-resolution handheld rigid endomicroscope based on full-field optical coherence tomography.

Full-field optical coherence tomography (FF-OCT) is a powerful tool for nondestructive assessment of biological tissue, i.e., for the structural examination of tissue in depth at a cellular resolution. Mostly known as a microscopy device for ex vivo analysis, FF-OCT has also been adapted to endoscopy setups since it shows good potential for in situ cancer diagnosis and biopsy guidance. Nevertheless, all the attempts to perform endoscopic FF-OCT imaging did not go beyond lab setups. We describe here, to the best of our knowledge, the first handheld FF-OCT endoscope based on a tandem interferometry assembly using incoherent illumination. A common-path passive imaging interferometer at the tip of an optical probe makes it robust and insensitive to environmental perturbations, and a low finesse Fabry-Perot processing interferometer guarantees a compact system. A good resolution (2.7 μm transverse and 6 μm axial) is maintained through the long distance, small diameter relay optics of the probe, and a good signal-to-noise ratio is achieved in a limited 100 ms acquisition time. High-resolution images and a movie of a rat brain slice have been recorded by moving the contact endoscope over the surface of the sample, allowing for tissue microscopic exploration at 20 m under the surface. These promising ex vivo results open new perspectives for in vivo imaging of biological tissue, in particular, in the field of cancer and surgical margin assessment.