Ultrafast laser surgery probe for sub-surface ablation to enable biomaterial injection in vocal folds

Creation of sub-epithelial voids within scarred vocal folds via ultrafast laser ablation may help in localization of injectable therapeutic biomaterials towards an improved treatment for vocal fold scarring. Several ultrafast laser surgery probes have been developed for precise ablation of surface tissues; however, these probes lack the tight beam focusing required for sub-surface ablation in highly scattering tissues such as vocal folds. Here, we present a miniaturized ultrafast laser surgery probe designed to perform sub-epithelial ablation in vocal folds. The requirement of high numerical aperture for sub-surface ablation, in addition to the small form factor and side-firing architecture required for clinical use, made for a challenging optical design. An Inhibited Coupling guiding Kagome hollow core photonic crystal fiber delivered micro-Joule level ultrashort pulses from a high repetition rate fiber laser towards a custom-built miniaturized objective, producing a 1/e2 focal beam radius of 1.12 ± 0.10 μm and covering a 46 × 46 μm2 scan area. The probe could deliver up to 3.8 μJ pulses to the tissue surface at 40% transmission efficiency through the entire system, providing significantly higher fluences at the focal plane than were required for sub-epithelial ablation. To assess surgical performance, we performed ablation studies on freshly excised porcine hemi-larynges and found that large area sub-epithelial voids could be created within vocal folds by mechanically translating the probe tip across the tissue surface using external stages. Finally, injection of a model biomaterial into a 1 × 2 mm2 void created 114 ± 30 μm beneath the vocal fold epithelium surface indicated improved localization when compared to direct injection into the tissue without a void, suggesting that our probe may be useful for pre-clinical evaluation of injectable therapeutic biomaterials for vocal fold scarring therapy. With future developments, the surgical system presented here may enable treatment of vocal fold scarring in a clinical setting.

Ultrafast laser surgery probe with a calcium fluoride miniaturized objective for bone ablation

We present a miniaturized ultrafast laser surgery probe with improved miniaturized optics to deliver higher peak powers and enable higher surgical speeds than previously possible. A custom-built miniaturized CaF2 objective showed no evidence of the strong multiphoton absorption observed in our previous ZnS-based probe, enabling higher laser power delivery to the tissue surface for ablation. A Kagome fiber delivered ultrashort pulses from a high repetition rate fiber laser to the objective, producing a focal beam radius of 1.96 μm and covering a 90×90 μm2 scan area. The probe delivered the maximum available fiber laser power, providing fluences >6 J/cm2 at the tissue surface at 53% transmission efficiency. We characterized the probe's performance through a parametric ablation study on bovine cortical bone and defined optimal operating parameters for surgery using an experimental- and simulation-based approach. The entire opto-mechanical system, enclosed within a 5-mm diameter housing with a 2.6-mm diameter probe tip, achieved material removal rates >0.1 mm3/min, however removal rates were ultimately limited by the available laser power. Towards a next generation surgery probe, we simulated maximum material removal rates when using a higher power fiber laser and found that removal rates >2 mm3/min could be attained through appropriate selection of laser surgery parameters. With future development, the device presented here can serve as a precise surgical tool with clinically viable speeds for delicate applications such as spinal decompression surgeries.

Hyperspectral imaging for simultaneous measurements of two FRET biosensors in pancreatic β-cells

Fluorescent protein (FP) biosensors based on Förster resonance energy transfer (FRET) are commonly used to study molecular processes in living cells. There are FP-FRET biosensors for many cellular molecules, but it remains difficult to perform simultaneous measurements of multiple biosensors. The overlapping emission spectra of the commonly used FPs, including CFP/YFP and GFP/RFP make dual FRET measurements challenging. In addition, a snapshot imaging modality is required for simultaneous imaging. The Image Mapping Spectrometer (IMS) is a snapshot hyperspectral imaging system that collects high resolution spectral data and can be used to overcome these challenges. We have previously demonstrated the IMS’s capabilities for simultaneously imaging GFP and CFP/YFP-based biosensors in pancreatic β-cells. Here, we demonstrate a further capability of the IMS to image simultaneously two FRET biosensors with a single excitation band, one for cAMP and the other for Caspase-3. We use these measurements to measure simultaneously cAMP signaling and Caspase-3 activation in pancreatic β-cells during oxidative stress and hyperglycemia, which are essential components in the pathology of diabetes.

Kagome fiber based ultrafast laser microsurgery probe delivering micro-Joule pulse energies

We present the development of a 5 mm, piezo-actuated, ultrafast laser scalpel for fast tissue microsurgery. Delivery of micro-Joules level energies to the tissue was made possible by a large, 31 μm, air-cored inhibited-coupling Kagome fiber. We overcome the fiber's low NA by using lenses made of high refractive index ZnS, which produced an optimal focusing condition with 0.23 NA objective. The optical design achieved a focused laser spot size of 4.5 μm diameter covering a 75 × 75 μm2 scan area in a miniaturized setting. The probe could deliver the maximum available laser power, achieving an average fluence of 7.8 J/cm2 on the tissue surface at 62% transmission efficiency. Such fluences could produce uninterrupted, 40 μm deep cuts at translational speeds of up to 5 mm/s along the tissue. We predicted that the best combination of speed and coverage exists at 8 mm/s for our conditions. The onset of nonlinear absorption in ZnS, however, limited the probe's energy delivery capabilities to 1.4 μJ for linear operation at 1.5 picosecond pulse-widths of our fiber laser. Alternatives like broadband CaF2 crystals should mitigate such nonlinear limiting behavior. Improved opto-mechanical design and appropriate material selection should allow substantially higher fluence delivery and propel such Kagome fiber-based scalpels towards clinical translation.

Design and fabrication of a miniature objective consisting of high refractive index zinc sulfide lenses for laser surgery

A miniature laser ablation probe relying on an optical fiber to deliver light requires a high coupling efficiency objective with sufficient magnification in order to provide adequate power and field for surgery. A diffraction-limited optical design is presented that utilizes high refractive index zinc sulfide to meet specifications while reducing the miniature objective down to two lenses. The design has a hypercentric conjugate plane on the fiber side and is telecentric on the tissue end. Two versions of the objective were built on a diamond lathe-a traditional cylindrical design and a custom-tapered mount. Both received an antireflective coating. The objectives performed as designed in terms of observable resolution and field of view as measured by imaging a 1951 USAF resolution target. The slanted edge technique was used to find Strehl ratios of 0.75 and 0.78, respectively, indicating nearly diffraction-limited performance. Finally, preliminary ablation experiments indicated threshold fluence of gold film was comparable to similar reported probes.

Introduction to the bio-optics: design and application

The "Bio-Optics: Design and Application" symposium, held on April 12-15, 2015, in Vancouver, BC, was an important step in a continuous journey to closely connect technological design advancement and biomedical applications. The symposium presented a broad range of innovations in diagnostic devices, endoscopy, optical microscopy, optical coherence tomography, multi-modal imaging, and highlighted specific applications including cancer diagnostics, detection of infectious disease and point of care, as well as microsurgery treatment.

Confocal foveated endomicroscope for the detection of esophageal carcinoma

By mimicking the variable resolution of the human eye, a newly designed foveated endomicroscopic objective shows the potential to improve current endoscopic based techniques of identifying abnormal tissue in the esophagus and colon. The prototype miniature foveated objective is imaged with a confocal microscope to provide large field of view images combined with a high resolution central region to rapidly observe morphological structures associated with cancer development in a mouse model.

Low-Cost Disposable Cartridge for Performing a White Blood Cell Count and Partial Differential at the Point-of-Care

Being able to perform a white blood cell (WBC) count and differential is a crucial laboratory test for basic diagnostic practices. In this paper, we demonstrate proof of concept results for a disposable cartridge that could be used to perform a WBC count and 3-part differential at the point-of-care. The cartridge is composed of a glass slide, a layer of transfer tape, and a glass cover slip and incorporates acridine orange for cell staining and sub-type differentiation; the stained blood is then imaged, and image analysis techniques return a WBC count and 3-part differential. The cartridge was tested on a laboratory microscope with 3 normal samples, and had promising results with 85.7% of images resulting in a WBC count with ±15% of the true value. Further, the 3-part differential concentrations determined using the disposable cartridge had strong correlations with the true concentrations (R² values of 0.9986, 0.9421, and 0.6942 for granulocytes, lymphocytes, and monocytes, respectively). Preliminary designs for a low-cost, portable microscope have been created and are currently being prototyped.

Optically-sectioned two-shot structured illumination microscopy with Hilbert-Huang processing

We introduce a fast, simple, adaptive and experimentally robust method for reconstructing background-rejected optically-sectioned images using two-shot structured illumination microscopy. Our innovative data demodulation method needs two grid-illumination images mutually phase shifted by π (half a grid period) but precise phase displacement between two frames is not required. Upon frames subtraction the input pattern with increased grid modulation is obtained. The first demodulation stage comprises two-dimensional data processing based on the empirical mode decomposition for the object spatial frequency selection (noise reduction and bias term removal). The second stage consists in calculating high contrast image using the two-dimensional spiral Hilbert transform. Our algorithm effectiveness is compared with the results calculated for the same input data using structured-illumination (SIM) and HiLo microscopy methods. The input data were collected for studying highly scattering tissue samples in reflectance mode. Results of our approach compare very favorably with SIM and HiLo techniques.

Toward a low-cost compact array microscopy platform for detection of tuberculosis

This paper describes the development of a microscope array capable of imaging separate fields of view without the need for opto-mechanical scanning components. This microscope array can be integrated with array illuminating optics, a full frame digital single lens reflex (DSLR) camera, and automated algorithms for the detection of Mycobacterium tuberculosis (MTB). The entire array will fit within the area of a typical sputum smear. A custom miniature objective has been designed for this microscope array that has a numerical aperture of 0.5, optical resolution of 0.63 μm, and a field of view that is 0.54 mm in diameter. A single prototype miniature objective of this design has been built, and images are presented demonstrating its imaging performance. Images are sufficiently high quality for diagnostic use. When fully integrated, this device has the potential to significantly improve performance compared to conventional microscopy systems and to enable more effective diagnosis of tuberculosis at the point of care.

Improving spatial resolution of a fiber bundle optical biopsy system

To reduce the number of invasive tissue biopsies and needle aspirations performed during cancer screenings, endo-microscopes can be used to image tissue in vivo. However, when optical fiber bundles are used to transmit the image, the resolution of such systems is limited by undersampling due to the spacing of the bundle's individual fibers for a given field of view. We propose a method to increase the sampling of an optical biopsy system and thereby improve the system's resolution. The method involves taking several images, shifting the object and fiber bundle slightly relative to each other from one image to the next. Multiple shifting patterns were evaluated to determine which provided the greatest increase in resolution. The shifted images are later realigned and recombined by a custom algorithm. By combining four shifted images of a USAF resolution target, we were able to measure an improvement in the resolution of the system from approximately 3.9 μm to 2.2 μm. When tested on cultured cells, a visible increase in detail was detectable. This technique can provide the basis for improving the diagnostic abilities of optical biopsy systems.

Modeling and optimization for a prismatic snapshot imaging polarimeter

Thin birefringent prisms placed near an image plane introduce sinusoidal fringes onto a 2D polarized scene making possible a snapshot imaging polarimeter, which encodes polarization information into the modulation of the fringes. This approach was introduced by Oka and Kaneko [Opt. Express 11, 1510 (2003)], who analyzed the instrument through the Mueller calculus. We show that the plane-wave assumption adopted in the Mueller theory can introduce unnecessary error in a polarimeter design. To directly take prism effects such as beam splitting and deviating into accounts we introduce a geometric imaging model, which allows for a versatile simulation of the birefringent prisms and provides a means for optimization. A calcite visible system is investigated as an example, which essentially shows how each design parameter affects the overall image quality and how to modify the polarimeter design to optimize overall performance. The approach is applicable to any prismatic imaging polarimeter with different prism materials and different working wavelengths.

High birefringence of the yttrium vanadate crystal in the middle wavelength infrared

A high birefringence of over 0.21 for the yttrium vanadate (YVO4) crystal in the middle wavelength infrared (i.e., 3-5 microm) was measured. A Fourier transform infrared spectrometer was employed in the channel spectra technique to obtain the measurements.

Optical imaging of cervical pre-cancers with structured illumination: an integrated approach

OBJECTIVE

Structured illumination microscopy is an inexpensive alternative to confocal microscopy that allows optical sectioning at a sub-cellular resolution. However, its application in imaging biological tissue has been limited by inadequate contrast present in them especially in reflectance imaging. Novel, optically active contrast agents like gold nanoparticles and quantum dots targeted against biomarkers of cancer can be integrated with structured illumination to image both the morphological and biochemical changes associated with epithelial pre-cancers.

METHODS

We modified the optical path of a widefield microscope to implement structured illumination both in reflectance and fluorescence modes. For imaging, we used 25-nm-diameter gold nanoparticles and CdSe quantum dots for reflectance and fluorescence imaging, respectively, to label three-dimensional tissue constructs of SiHa cervical cancer cells. Contrast agents were targeted against the epidermal growth factor receptor (EGFR) using an anti-EGFR monoclonal antibody. Agents targeted with a non-specific IgG antibody served as a control to monitor non-specific labeling.

RESULTS

Our result shows that optically sectioned images taken with structured illumination are very comparable to those obtained using confocal microscopy. Moreover, images of three-dimensional cultures stained with the anti-EGFR agents show significantly more image intensity than those stained with the IgG targeted control.

CONCLUSION

Our findings suggest that the combination of novel optical contrast agents and structured illumination can differentiate neoplastic cells which overexpress EGFR from normal cells in intact tissue. Combining structured illumination microscopy with novel contrast agents can potentially provide a powerful and inexpensive tool to aid in the detection of cervical pre-cancers.

High resolution, molecular-specific, reflectance imaging in optically dense tissue phantoms with structured-illumination

Structured-illumination microscopy delivers confocal-imaging capabilities and may be used for optical sectioning in bio-imaging applications. However, previous structured-illumination implementations are not capable of imaging molecular changes within highly scattering, biological samples in reflectance mode. Here, we present two advances which enable successful structured illumination reflectance microscopy to image molecular changes in epithelial tissue phantoms. First, we present the sine approximation algorithm to improve the ability to reconstruct the in-focus plane when the out-of-focus light is much greater in magnitude. We characterize the dependencies of this algorithm on phase step error, random noise and backscattered out-of-focus contributions. Second, we utilize a molecular-specific reflectance contrast agent based on gold nanoparticles to label disease-related biomarkers and increase the signal and signal-to-noise ratio (SNR) in structured illumination microscopy of biological tissue. Imaging results for multi-layer epithelial cell phantoms with optical properties characteristic of normal and cancerous tissue labeled with nanoparticles targeted against the epidermal growth factor receptor (EGFR) are presented. Structured illumination images reconstructed with the sine approximation algorithm compare favorably to those obtained with a standard confocal microscope; this new technique can be implemented in simple and small imaging platforms for future clinical studies.

Application of the Alvarez-Humphrey concept to the design of a miniaturized scanning microscope

This paper contains two optical designs that utilize the Alvarez- Humphrey surfaces to provide the miniature multi-modal microscope (4M device) with the additional capability of imaging different object depths onto the same image plane. The Alvarez-Humphrey surfaces are a pair of conjugate, rotationally asymmetrical, aspheric surfaces such that, the lateral movement of these surfaces across the optical axis, results in an element of variable optical power. The first design is a direct application of the Alvarez-Humphrey concept to the 4M device. However, due to the inadequate imaging performance and unavailability of space for the actuator due to proximity of the Alvarez Plates, a second design was created. The Separated Alvarez Plate Design is a unique design involving two conjugate pairs of Alvarez-Humphrey surfaces. The lateral movement of the central element changes the optical power. However, due to the symmetry of the system and the incorporation of the theoretical work done on induced aberration correction, this system has far superior performance. It also has adequate space for the actuator due to the separation of the elements.

Realization of refractive microoptics through grayscale lithographic patterning of photosensitive hybrid glass

Refractive microlenses with more than 50 microm sag are fabricated using grayscale lithography. Mechanical assembly features are made simultaneously alongside the microlenses to facilitate high precision assembly of miniature optical systems. The microlens elements are formed using lithographic patterning of photosensitive hybrid sol-gel glass requiring no etch transfer to the substrate material. Grayscale lithography enables the straightforward patterning of aspheric lenses and arbitrary surfaces within the material depth. Lessons learned in the design of a grayscale photomask are described. Characterization of the fabricated lens elements is reported including lens shape, surface quality, and image quality of a complete assembled imaging system.