Imaging Of Biological Tissues Research Articles

Analytic method to optimize aperture design in focal modulation microscopy

Focal modulation microscopy (FMM) has been demonstrated more effective than confocal microscopy for imaging of thick biological tissues. To improve its penetration depth further, we propose a simple analytical method to enlarge the modulation depth, the unique property of FMM directly linked to its signal-to-noise ratio. The modulation depth increases as the excitation intensity of the binary phase aperture status is pushed further away from the focal region of the detection optics, thereby creating a dark region in the focal volume, which we call maximally flat crater (MFC). By direct algebraic manipulation, MFCs are achieved for both scalar and vector diffraction optics. Numerical results show that the modulation depth from MFC is very close to the maximum values, with a small difference less than 3% for the same number of subapertures. Applications of bifocus produced by MFC apertures are also discussed.

Advanced Fiber Soliton Sources for Nonlinear Deep Tissue Imaging in Biophotonics

Optical imaging plays a major role in both basic biological research and clinical diagnostics, providing noninvasive or minimally invasive microscopic imaging capability to investigate biological tissues. Optical image acquisition through significant depths of biological tissues, however, presents a major challenge since tissue is extremely heterogeneous and the strong scattering of the various tissue components has restricted high-resolution optical imaging to superficial layers. Multiphoton microscopy (MPM) has significantly extended the penetration depth of high-resolution optical imaging, particularly for in vivo applications. Multiphoton imaging critically depends on ultrafast technologies, particularly pulsed excitation sources. In this paper, the basics of deep tissue MPM and its improvements utilizing soliton self-frequency shift (SSFS) are reviewed. Wavelength tunable, high-energy soliton generation through SSFS in large-mode-area (LMA) fibers and photonic crystal rods is presented. The application of these solitons to MPM enables noninvasive imaging in biological tissues with unprecedented depth. The main characteristics of the excitation source for deep tissue MPM, such as wavelength, pulse energy, and repetition rate, are discussed.

Elasticity imaging of biological soft tissue using a combined finite element and non-linear optimization method

A novel material reconstruction method combining finite element (FE)-based direct inverse method and non-linear optimization algorithm is proposed for elasticity imaging of biological soft tissue. The biological soft tissue is represented using Neo-Hookean hyperelastic model. The FE-based direct inverse method provides an estimation of material parameter distribution which serves as the initial guess of the Levenberg–Marquardt optimization algorithm. Direct calculation of Jacobian matrix is proposed to improve the computational efficiency of the combined algorithm. Computer simulation demonstrated that the material parameters of soft tissue can be determined rapidly and accurately within a small tolerance using the proposed method. Our experimental results on a human lower leg demonstrated the clinical viability of this method.

GPU acceleration of nonlinear diffusion tensor estimation using CUDA and MPI

Diffusion MRI is a non-invasive magnetic resonance technique and has been increasingly used in imaging neuroscience. It is currently the only method capable of depicting the complex structure of white matter of the brain in vivo. One of the most popular techniques is diffusion tensor imaging (DTI) which is commonly used clinically to produce in vivo images of biological tissues with local microstructural characteristics such as water diffusion. Diffusion tensor maps are usually computed on a voxel-by-voxel basis by fitting the signal intensities of diffusion weighted images as a function of their corresponding data acquisition parameters (b-matrices). This processing is computation-intensive and time-consuming which can constraint the clinical practice of DTI. This study presents the application of using high performance GPU clusters in addition to CPUs for diffusion tensor estimation by accelerating the multivariate non-linear regression. The results are tested using both simulated and clinical diffusion datasets and show significant performance gain in tensor fitting. The proposed GPU implementation framework can significantly reduce the processing time of DTI data especially for the datasets with high spatial and temporal resolution, and hence further promote the clinical use of DTI. It also can be used to accelerate statistical analysis of DTI where Monte Carlo simulations are employed, be readily applied to quantitative assessment of DTI using bootstrap analysis, robust diffusion tensor estimation and should be applicable to other MR imaging techniques that use univariate or multivariate regression to fit MRI data to a model.

Infrared and Raman Imaging for Characterizing Complex Biological Materials: A Comparative Morpho-Spectroscopic Study of Colon Tissue

Complementary diagnostic methods to conventional histopathology are currently being investigated for developing rapid and objective molecular-level understanding of various disorders, especially cancers. Spectral histopathology using vibrational spectroscopic imaging has been put in the frontline as potentially promising in this regard as it provides a "spectral fingerprint" of the biochemical composition of cells and tissues. In order to ascertain the feasible conditions of vibrational spectroscopic methods for tissue-imaging analysis, vibrational multimodal imaging (infrared transmission, infrared-attenuated total reflection, and Raman imaging) of the same colon tissue has been implemented. The spectral images acquired were subjected to multivariate clustering analysis in order to identify on a molecular level the constituent histological organization of the colon tissue such as the epithelium, connective tissue, etc., by comparing the cluster images with the histological reference images. Based on this study, a comparative analysis of important factors involved in the vibrational multimodal imaging approaches such as image resolution, time constraints, their advantages and limitations, and their applicability to biological tissues has been carried out. Out of the three different vibrational imaging modalities tested, infrared-attenuated total reflection mode of imaging appears to provide a good compromise between the tissue histology and the time constraints in achieving similar image contrast to that of Raman imaging at an approximately 33-fold faster measurement time. The present study demonstrates the advantages, the limitations of the important parameters involved in vibrational multimodal imaging approaches, and their potential application toward imaging of biological tissues.

A Multi-Similarity Fusion Feature–Point Matching Approach for Measuring Internal Deformation Fields Using Magnetic Resonance Volumetric Images of Biological Tissues

A Multi-Similarity Fusion Feature–Point Matching Approach for Measuring Internal Deformation Fields Using Magnetic Resonance Volumetric Images of Biological Tissues

Low-Bremsstrahlung X-Ray Source Using a Low-Voltage High-Current-Density Nanostructured Field Emission Cathode and a Transmission Anode for Markerless Soft Tissue Imaging

We report the design, fabrication, and proof-of-concept characterization of an X-ray generator for improved X-ray absorption imaging that uses a nanostructured field emission cathode as the electron source and a microstructured transmission anode as the X-ray generating structure. Field emission cathodes consume less power, respond faster, and tolerate lower vacuum than the thermionic cathodes used in conventional X-ray generators. The use of a transmission anode, instead of a conventional reflection anode, allows filtering of the background radiation (bremsstrahlung) while allowing efficient generation of X-ray at lower voltages by exciting atomic shell transitions, resulting in emission of X-ray with narrow spectral linewidth for sharper imaging of biological tissue. The fabricated field emission cathode contains arrays of self-aligned and gated silicon field emitters. The field emission cathodes turn on at bias voltages as low as 25 V, and their gates transmit almost 100% of the electrons to the anode. The cathodes produce per-emitter electron currents in excess of $2~\mu $ A (current density >2 A/cm $^{2}$ ) at a bias voltage of 80 V. A desktop rig is built to generate X-ray with a field emission cathode and transmission anode. Using the facility, we obtained X-ray absorption images of several objects. The images clearly show details under $500~\mu $ m in size, as well as soft tissue and fine bone structures without using contrast agents. [2014-0087]

Role of optical coherence tomography in posterior segment eye disorders: A review of two cases

Optical Coherence Tomography produces high resolution tomographic in in vivo imaging of biological tissues. The study reviews OCT images of two patients with varied retinal pathologies to determine its usefulness in aiding evaluation and management of retinal diseases. The patients were imaged using OCT conventional fundus photography and angiography. A case each of premacular haemorrhage and idiopathic polypoidal choroidal vasculopathy, are presented highlighting the merits of OCT. OCT establishes the accurate diagnosis of retinal diseases and in monitoring response to therapy. It is complementary to clinical techniques of direct and indirect ophthalmoscopy, conventional fundus photography, fluorescein and indocyanine green angiography thus should be made readily available for use in the evaluation of retinal disorders to enhance their management.

Role of Optical Coherence Tomography as a Diagnostic Tool in Macular Diseases

Back ground: Optimal coherence tomography (OCT) is a non contactnon invasive newer diagnostic tool that can perform tomography cross sectional imaging of biological tissues with <10 micron axial resolution using light waves near infrared beam. Methodology: Hospital based study conducted on 50 patients having macular diseases who attended DR RSPR Govt. regional eye hospital, Visakhapatnam. Each patient underwent a complete ophthalmic examination including best corrected visual acuity slit lamp biomicroscopy, IOP recording and fundus evaluation by indirect Opthalmoscopy with+90 D lens. In addition fundus photographs were taken. Routine blood examination and urine examination were done. Then the patients were subjected to evaluation of posterior segment by OCT. Results: Of the 50 cases on whom the OCT was done, majority (32%) were diabetic macular Oedema, followed by central serous Retinopathy (24%) and Epiretinal membrane was seen in 10% cases. Among the study participants, 7 patients presented with macular holes. Two patients had full thickness macular holes and five patients had lamellar holes. Conclusion: Diagnosis is confirmed by OCT gives additional information regarding pathological presentation, so help in the management.It may beneficially impact the visual disability by diagnosing a disease at an earlier stage.

IMAGING OF 3-D DIELECTRIC OBJECTS USING FAR-FIELD HOLOGRAPHIC MICROWAVE IMAGING TECHNIQUE

This paper describes the working principle of a three-dimensional (3-D) holographic microwave imaging (HMI) method for imaging small inclusion embedded in a dielectric object. Using published dielectric properties of various materials, a 3-D mathematical model is developed under the MATLAB environment to validate the HMI on various dielectric objects. Results indicate that the 3-D HMI has an ability to produce a 3-D image and detect small inclusions embedded within a dielectric object. Several potential applications of the 3-D HMI method includes biological tissues imaging, security screening and packaged food evaluation.

Shack-Hartmann wavefront sensing using interferometric focusing of light onto guide-stars

Optical microscopy provides noninvasive imaging of biological tissues at subcellular level. The optical aberrations induced by the inhomogeneous refractive index of biological samples limits the resolution and can decrease the penetration depth. To compensate refractive aberrations, adaptive optics with Shack-Hartmann wavefront sensing has been used in microscopes. Wavefront measurement requires light from a guide-star inside of the sample. The scattering effect limits the intensity of the guide-star, hence reducing the signal to noise ratio of the wavefront measurement. In this paper, we demonstrate the use of interferometric focusing of excitation light onto a guide-star embedded deeply in tissue to increase its fluorescent intensity, thus overcoming the excitation signal loss caused by scattering. With interferometric focusing, we more than doubled the signal to noise ratio of the laser guide-star through scattering tissue as well as potentially extend the imaging depth through using AO microscopy.

A Compact X-ray Generator Using a Nanostructured Field Emission Cathode and a Microstructured Transmission Anode

We report the design, fabrication, and preliminary characterization of a compact X-ray generator for improved X-ray absorption imaging that uses a nanostructured field emission cathode (FEC) as the electron source and a microstructured transmission anode as the X-ray generating element. FECs consume less power, respond faster, and tolerate lower vacuum than thermionic cathodes used in conventional X-ray generators. The use of a transmission anode, instead of a conventional reflection anode, allows filtering of the background radiation (brems strahlung) while allowing efficient generation of X-rays at lower voltages by exciting atomic shell transitions, resulting in emission of X-rays with narrow spectral linewidth for sharper imaging of biological tissue. The fabricated FEC contains arrays of self-aligned, gated field emitters that turn on at bias voltages under 30 V and transmit 99.5% of the electrons to the anode. The FEC emits a maximum current of 1.2 μA per field emitter (588 μA total array current) at a bias voltage of 85 V. A facility is built and tested to generate X-rays with an FEC and a transmission anode. Using the facility, we obtained an X-ray absorption image of an ex-vivos ample that clearly shows softtissue and fine bone structures.

Image-Based Procedure for Biostructure Modeling

For high-resolution medical images, an image-based procedure is developed in strong form to perform microstructure analysis. Consider heterogeneous biomaterials such as bone tissue with porous composition—the associated microscopic cell problems and homogenized mechanical properties have been derived through the asymptotic homogenization to correlate the hierarchy in the macroscale and microscale. Nevertheless, for bioimages with highly irregular geometry, the process of model reconstruction by the traditional mesh-based methods unavoidably encounters issues such as mesh dependency and mesh distortion. Upon using the level set technique for model reconstruction, images of biological tissue showing complex topology can be identified and segmented into different phases effectively, such as the solid skeleton and pores in bone materials. In particular, the employment of the strong form collocation method takes advantage of point discretization and constitutes a seamlessly computational framework for solving level set equations and microscopic cell problems. The application to microstructure modeling of trabecular bone was demonstrated. The extension of the image-based biomaterial modeling includes prediction of bone fracture, bone remodeling process, and design of bone-implant systems.

Photoacoustic correlation signal-to-noise ratio enhancement by coherent averaging and optical waveform optimization

Photoacoustic (PA) imaging of biological tissues using laser diodes instead of conventional Q-switched pulsed systems provides an attractive alternative for biomedical applications. However, the relatively low energy of laser diodes operating in the pulsed regime, results in generation of very weak acoustic waves, and low signal-to-noise ratio (SNR) of the detected signals. This problem can be addressed if optical excitation is modulated using custom waveforms and correlation processing is employed to increase SNR through signal compression. This work investigates the effect of the parameters of the modulation waveform on the resulting correlation signal and offers a practical means for optimizing PA signal detection. The advantage of coherent signal averaging is demonstrated using theoretical analysis and a numerical model of PA generation. It was shown that an additional 5-10 dB of SNR can be gained through waveform engineering by adjusting the parameters and profile of optical modulation waveforms.

A method for operative quantitative interpretation of multispectral images of biological tissues

A method for operative retrieval of spatial distributions of biophysical parameters of a biological tissue by using a multispectral image of it has been developed. The method is based on multiple regressions between linearly independent components of the diffuse reflection spectrum of the tissue and unknown parameters. Possibilities of the method are illustrated by an example of determining biophysical parameters of the skin (concentrations of melanin, hemoglobin and bilirubin, blood oxygenation, and scattering coefficient of the tissue). Examples of quantitative interpretation of the experimental data are presented.

In vivo photoacoustic imaging of breast cancer tumor with HER2-targeted nanodiamonds.

Radiation-damaged nanodiamonds (NDs) are ideal optical contrast agents for photoacoustic (PA) imaging in biological tissues due to their good biocompatibility and high optical absorbance in the near-infrared (NIR) range. Acid treated NDs are oxidized to form carboxyl groups on the surface, functionalized with polyethylene glycol (PEG) and human epidermal growth factor receptor 2 (HER2) targeting ligand for breast cancer tumor imaging. Because of the specific binding of the ligand conjugated NDs to the HER2-overexpressing murine breast cancer cells (4T1.2 neu), the tumor tissues are significantly delineated from the surrounding normal tissue at wavelength of 820 nm under the PA imaging modality. Moreover, HER2 targeted NDs (HER2-PEG-NDs) result in higher accumulation in HER2 positive breast tumors as compared to non-targeted NDs after intravenous injection (i.v.). Longer retention time of HER-PEG-NDs is observed in HER2 overexpressing tumor model than that in negative tumor model (4T1.2). This demonstrates that targeting moiety conjugated NDs have great potential for the sensitive detection of cancer tumors and provide an attractive delivery strategy for anti-cancer drugs.

3D static elastography at the micrometer scale using Full Field OCT

Full-Field OCT (FF-OCT) is able to image biological tissues in 3D with micrometer resolution. In this study we add elastographic contrast to the FF-OCT modality. By combining FF-OCT with elastography, we create a virtual palpation map at the micrometer scale. We present here a proof of concept on multi-layer phantoms and preliminary results on ex vivo biological samples such as porcine cornea, human breast tissues and rat heart. The 3D digital volume correlation that is used in connection with the 3D stack of images allows to access to the full 3D strain tensor and to reveal stiffness anisotropy.

Measurement depth enhancement in terahertz imaging of biological tissues

We demonstrate the use of a THz penetration-enhancing agent (THz-PEA) to enhance the terahertz (THz) wave penetration depth in tissues. The THz-PEA is a biocompatible material having absorption lower than that of water, and it is easily absorbed into tissues. When using glycerol as a THz-PEA, the peak value of the THz signal which was transmitted through the fresh tissue and reflected by a metal target, was almost doubled compared to that of tissue without glycerol. THz time-of-flight imaging (B-scan) was used to display the sequential glycerol delivery images. Enhancement of the penetration depth was confirmed after an artificial tumor was located below fresh skin. We thus concluded that the THz-PEA technique can potentially be employed to enhance the image contrast of the abnormal lesions below the skin.

A cost-efficient frequency-domain photoacoustic imaging system

Photoacoustic (PA) imaging techniques have recently attracted much attention and can be used for noninvasive imaging of biological tissues. Most PA imaging systems in research laboratories use the time domain method with expensive nanosecond pulsed lasers that are not affordable for most educational laboratories. Using an intensity modulated light source to excite PA signals is an alternative technique, known as the frequency domain method, with a much lower cost. In this paper, we describe a simple frequency domain PA system and demonstrate its imaging capability. The system provides opportunities not only to observe PA signals in tissue phantoms, but also to acquire hands-on skills in PA signal detection. It also provides opportunities to explore the underlying mechanisms of the PA effect.

Enhancement of Gauss–Newton Inversion Method for Biological Tissue Imaging

The multiplicatively regularized Gauss-Newton inversion (GNI) algorithm is enhanced and utilized to obtain complex permittivity profiles of biological objects-of-interest. The microwave scattering data is acquired using a microwave tomography system comprised of 24 co-resident antennas immersed into a saltwater matching fluid. Two types of biological targets are imaged: ex vivo bovine legs and in vivo human forearms. Four different forms of the GNI algorithm are implemented: a blind inversion, a balanced inversion, a shape-and-location inversion, and a novel balanced shape-and-location inversion. The latter three techniques incorporate typical permittivity values of biological tissues as prior information to enhance the reconstructions. In those images obtained using the balanced shape-and-location reconstruction algorithm, the various parts of the tissue being imaged are clearly distinguishable. The reconstructed permittivity values in the bovine leg images agree with those obtained via direct measurement using a dielectric probe. The reconstructed images of the human forearms qualitatively agree with magnetic resonance imaging images, as well as with the expected dielectric values obtained from the literature.