Ray tracing of optically modified fiber tips. 2: laser scalpels

Cone-shaped optical fiber tip for cost-effective digital lensless holographic microscopy

In this work, the development and application of a cost-effective and robust digital lensless holographic microscopy (DLHM) system is presented. In the simple architecture of DLHM based on a point source and a digital camera, the production of the former is introduced by means of an engineered step-index optical fiber with a cone-shaped end tip. The conventional and regularly expensive point source in DLHM is produced by means of a high-numerical-aperture microscope objective and a metallic wavelength-sized pinhole. The proposed replacement renders to DLHM additional simplicity of building, in addition to mechanical stability and robustness, and further reduces the cost of the microscope. The simplified cost-effective DLHM architecture is utilized for imaging resolution test targets and samples of human blood and pond water, revealing competitive mechanical stability and trustable phase images of the imaged specimens.

Analytical study of the numerical aperture of cone-shaped optical fibers: A tool for tailored designs

In this work, a set of analytical expressions to tailor the numerical aperture of cone-shaped step optical fibers is proposed. The expressions are derived from the geometrical study of light-ray tracing at the cone-shaped tip of a regular step-index optical fiber. Analysis of the different physical phenomena that can take place at the tip of the fiber led to numerical apertures ranging from 0 to 1.5 which can be achieved via a variety of cone angles, providing great versatility in the design of light sources or light collecting devices based on step-index optical fibers.

A monolithic microsphere-fiber probe for spatially resolved Raman spectroscopy: Application to head and neck squamous cell carcinomas

The ability to identify precise cancer margins in vivo during a surgical excision is critical to the well-being of the patient. Decreased operative time has been linked to shorter patient recovery time, and there are risks associated with removing either too much or too little tissue from the surgical site. The more rapidly and accurately a surgeon can identify and excise diseased tissue, the better the prognosis for the patient. To this end, we investigate both malignant and healthy oral cavity tissue using the Raman spectroscopy, with a monolithic microsphere-fiber probe. Our results indicate that this probe has decreased the size of the analyzed area by more than an order of magnitude, as compared to a conventional fiber reflection probe. Scanning the probe across the tissues reveals variations in the Raman spectra that enable us to differentiate between malignant and healthy tissues. Consequently, we anticipate that the high spatial resolution afforded by the probe will permit us to identify tumor margins in detail, thereby optimizing tissue removal and improving patient outcomes.

Fiberoptic microneedles: novel optical diffusers for interstitial delivery of therapeutic light

BACKGROUND AND OBJECTIVES

Photothermal therapies have limited efficacy and application due to the poor penetration depth of light inside tissue. In earlier work, we described the development of novel fiberoptic microneedles to provide a means to mechanically penetrate dermal tissue and deliver light directly into a localized target area.This paper presents an alternate fiberoptic microneedle design with the capability of delivering more diffuse, but therapeutically useful photothermal energy. Laser lipolysis is envisioned as a future clinical application for this design.

MATERIALS AND METHODS

A novel fiberoptic microneedle was developed using hydrofluoric acid etching of optical fiber to permit diffuse optical delivery. Microneedles etched for 10, 30, and 50 minutes, and an optical fiber control were compared with three techniques. First, red light delivery from the microneedles was evaluated by imaging the reflectance of the light from a white paper.Second, spatial temperature distribution of the paper in response to near-IR light (1,064 nm, 1 W CW) was recorded using infrared thermography. Third, ex vivo adipose tissue response during 1,064 nm, (5 W CW)irradiation was recorded with bright field microscopy.

RESULTS

Acid etching exposed a 3 mm length of the fiber core, allowing circumferential delivery of light along this length. Increasing etching time decreased microneedle diameter, resulting in increased uniformity of red and 1,064 nm light delivery along the microneedle axis. For equivalent total energy delivery, thinner microneedles reduced carbonization in the adipose tissue experiments.

CONCLUSIONS

We developed novel microscale optical diffusers that provided a more homogeneous light distribution from their surfaces, and compared performance to a flat-cleaved fiber, a device currently utilized in clinical practice. These fiberoptic microneedles can potentially enhance clinical laser procedures by providing direct delivery of diffuse light to target chromophores, while minimizing undesirable photothermal damage in adjacent, non-target tissue.

Nd:YAG laser and tracheobronchial metallic stents: an experimental in vitro study

STUDY DESIGN/MATERIALS AND METHODS

The aim of this experimental study was to investigate the effect of Nd:YAG laser on metallic tracheobronchial stents, because Nd:YAG laser could be used for resection of tumourous tissue growing through stent meshes (Strecker-, Palmaz-, Wallstent).

STUDY DESIGN/MATERIALS AND METHODS

An in vitro worst-case-model was used to investigate the effects of different types of laser application on metallic stents: non-contact application, and contact application with bare fibres and with hemispherical sapphires.

RESULTS

In the non-contact method and with bare fibres stent destruction occurred at power settings exceeding 10 W, whereas in the contact method with hemispherical sapphires power settings of 20 W were possible without stent damage.

Laser light delivery systems for medical applications

For medical applications, the choice of a delivery system will be governed by the characteristics of the laser system on the one hand and the tissue application on the other. The most important parts are the beam guide and the target optics. Most lasers have wavelengths in the visible and near-infrared and can be transported by silica fibres. For the mid- and far-IR other fibre materials or hollow waveguides are used. At the end of the waveguide or fibre, an optically active component is present to direct the beam and to control the power density on the target tissue. The laser beam can be delivered either by focusing handpieces and scanning devices to treat superficial areas or through microscopes, endoscopes and flexible fibres to treat areas almost anywhere inside the human body. The characteristics of the delivery systems can be determined looking at beam properties, transmission and thermal properties. The delivery of continuous wave or pulsed laser energy, contact or non-contact, will determine the contribution of optical, thermal and mechanical effects to the tissue. The practical use of laser delivery systems is illustrated by various clinical applications.

Lifetime testing of sapphire and sculpted silica fiber scalpels

BACKGROUND AND OBJECTIVE

Sapphire and sculpted silica fiber scalpels were evaluated for performance as they aged. Performance was determined by measuring their useful lifetime, forward transmission, incision depth, and the thermal coagulation thickness at the sides and bottom of the incision. STUDY DESIGN/MATERIALS, AND METHODS: Aging was performed with a chicken breast model. Performance measurements were made at periodic intervals. Sapphire scalpels were cooled with air or saline.

RESULTS

The air-cooled, frosted sapphire scalpels had the longest useful lifetime, whereas the saline-cooled, frosted sapphire scalpels had the shortest. Aging deteriorated the forward transmission of the sculpted silica fiber scalpels the most. Little difference was found between the averages of all incision measurements. Two of the saline-cooled, frosted sapphire scalpels fractured during the aging process.

CONCLUSION

Aging influences the scalpel lifetime, but there was no evidence that the aging process significantly affected the incision size.

Ray tracing of optically modified fiber tips. 1: spherical probes

The beam profiles and spatial irradiance distributions of modified fiber tips mainly used in laser angioplasty have been calculated by ray tracing assuming a uniform spatial combined with a weighted angular irradiance distribution. The computations were compared to paraxial theory and to measurements in air and in water. For ball-shaped fibers and hemispherical probes, made of either silica or sapphire, the position of the maximum irradiance in front of the probe in water did not coincide with the calculated paraxial focal point. The maximum irradiance increase was limited by internal backward reflections and by beam divergence. It is expected that beam focusing is minimal when optically modified fiber tips are in contact with tissue. Ray tracing is useful for optimizing the design of optically modified fiber tips when paraxial theory cannot be applied.