Dineshbabu Duraibabu

Differential in vivo urodynamic measurement in a single thin catheter based on two optical fiber pressure sensors

Abstract. Urodynamic analysis is the predominant method for evaluating dysfunctions in the lower urinary tract. The exam measures the pressure during the filling and voiding process of the bladder and is mainly interested in the contraction of the bladder muscles. The data arising out of these pressure measurements enables the urologist to arrive at a precise diagnosis and prescribe an adequate treatment. A technique based on two optical fiber pressure and temperature sensors with a resolution of better than 0.1  cm H2O (∼10  Pa), a stability better than 1  cm H2O/hour, and a diameter of 0.2 mm in a miniature catheter with a diameter of only 5 Fr (1.67 mm), was used. This technique was tested in vivo on four patients with a real-time urodynamic measurement system. The optical system presented showed a very good correlation to two commercially available medical reference sensors. Furthermore, the optical urodynamic system demonstrated a higher dynamic and better sensitivity to detect small obstructions than both pre-existing medical systems currently in use in the urodynamic field.

Femtosecond-Laser-Based Inscription Technique for Post-Fiber-Bragg Grating Inscription in an Extrinsic Fabry–Perot Interferometer Pressure Sensor

In this paper, a novel fiber Bragg grating inscription technique based on a femtosecond laser is presented. The grating was inscribed in close proximity to the tip of an extrinsic Fabry-Perot interferometer (EFPI)-based optical fiber pressure sensor. This therefore represents an optical fiber pressure and temperature sensor (OFPTS) for simultaneous pressure and temperature measurement for use in exactly the same physical location. The temperature measurement can also be used to compensate thermal drift in the EFPI sensor. The Bragg wavelength can be tailored precisely to any given wavelength in the optical spectrum and the degree of reflection can be adjusted to suit the FPI spectrum. The OFPTS has a diameter of 200 μm and is fully biocompatible. Furthermore, the sensor shows a high stability after grating inscription, of better than 0.5% in 20 min. The small size and high stability makes the sensor especially interesting for volume restricted areas, like blood vessels or the brain.

Novel FBG femtosecond laser inscription method for improved FPI sensors for medical applications

A novel fibre Bragg grating (FBG) post-inscription technique using a femto second laser (FSL), used to modify an optical fibre pressure sensor (OFPS) based on an extrinsic Fabry Perot Interferometer (EFPI) is presented. The resultant sensor is an optical fibre pressure and temperature sensor (OFPTS), able to measure temperature and pressure simultaneously in precisely the same location within the optical fibre. Hence the temperature measurement can be used to accurately compensate any thermal fluctuations in the pressure measurements, leading to an improved long term stability. The Bragg-wavelength can be tailored to coincide with any part of the Fabry-Perot Interferometer (FPI) spectrum (e.g. define the FBG at a valley of the FPI spectrum). We use a modified femtosecond laser, point-by-point inscription method for precise and controlled placement of the fibre Bragg grating. Our technique can be readily adapted to commercial production methods for optical fibre sensors as it greatly mitigates the alignment problems associated with femtosecond laser inscription of gratings in optical fibres. The sensor presented in this paper is entirely fabricated with quartz glass, which makes it fully bio-compatible and can be used for biomedical application. The sensors achieved a high sensitivity of 1.3 nm over kPa resulting in a resolution of ~ 1mmHg and a temperature sensitivity of ~ 10.7pm over K. After the inscription, the sensors still demonstrated a stability of better than 0.1% in 30min. The small diameter of only 200μm allows biomedical in-vivo application in volume restricted areas (e.g. blood vessels or the brain) for simultaneous temperature and pressure measurements.

Novel diaphragm microfabrication techniques for high-sensitivity biomedical fiber optic Fabry-Perot interferometric sensors

In this paper new algorithms and procedures are reported which enable miniaturization and optimization of the thickness of a diaphragm for an all-glass extrinsic Fabry-Perot interferometer (EFPI)-based pressure sensor. Diaphragm etching improves the EFPI sensors ability to detect relatively small changes in pressure (0.1mmHg) and the resulting sensor exhibits excellent stability over time (drift < 1 mmHg / hour) for measurement in air and liquid. The diaphragm etching procedure involves fiber polishing followed by etching in hydrofluoric (HF) acid. An additional Ion-beam etching technique was investigated separately to compare with the HF-etching technique. A sensitivity better than 10 10 nm/kPa, which provides a pressure resolution of 0.05mmHg, is achieved by reducing the EFPI diaphragm thickness down to less than 2μm for the miniature pressure sensor used in this investigation (overall diameter of 200μm). The techniques reported is also applicable for the fabrication of high sensitivity sensors using a smaller fiber diameter e.g. 80μm.

Optical fibre pressure and temperature sensor system designed for urodynamic applications

This paper presents an optical fibre pressure and temperature sensor (OFPTS) system, which is adapted for use as a urodynamic pressure measurement system (UPS) for differential pressure measurement with temperature compensation. The OFTPS is based on a Fabry Perot interferometer (FPI), which acts as a pressure sensor and includes an embedded fibre Bragg grating (FBG) for temperature measurement. The sensor system is evaluated in a lower urinary tract (LUT) simulator, which simulates the bladder, rectum and detrusor muscle. The system was benchmarked against a commercially available urodynamic system, at the University Hospital Limerick (UHL) Urology Clinic. Both systems demonstrate a high correlation with a relative pressure variation of less than ±2.8cmH2O for abdominal and ±4cmH2O for vesical pressure. The repetitive measurement of the OFPTS system in the LUT simulator against the commercial system demonstrated the high repeatability. Furthermore, the low fabrication cost makes the OFPTS a potentially interesting instrument for urodynamic and other medical applications.

Novel ultrahigh resolution optical fibre temperature sensor

In this paper a novel patent pending high resolution optical fibre temperature sensor, based on an optical fibre pressure and temperature sensor (OFTPS), which is surrounded by an oil filled chamber, is presented. The OFPTS is based on a Fabry Perot interferometer (FPI) which has an embedded fibre Bragg grating (FBG). The high ratio between the volume of the oil filled outer cavity and the FPIs air filled cavity, results in a highly sensitive temperature sensor. The FBG element of the device can be used for wide range temperature measurements, and combining this capability with the high resolution capability of the FPI/oil cavity results in a wide range and high resolution temperature sensing device. The outer diameter of the sensor is less than 1mm in diameter and can be designed to be even smaller. The sensors temperature response was measured in a range of ΔT = 7K and resulted in a shift in the optical spectrum of ΔλF = 61.42nm. Therefore the Q-point of the reflected optical FPI spectrum is shifting with a sensitivity of sot = 8.77 nm/K . The sensitivity can easily be further increased by changing the oil/air volumetric ratio and therefore adapt the sensor to a wide variety of applications.

An optical fibre sensor for combined point pressure measurement and spatially resolved temperature measurement

In this paper, two optical fibre sensors are presented: 1) based on extrinsic Fabry-Perot Interferometer (EFPI) with Fibre Bragg Grating array and 2) and EFPI sensor with a chirped Fibre Bragg grating (CFBG). The CFBG with EFPI sensor fabrication technique is described and temperature response of both sensors is presented. Such sensors have many potential applications including applications in the aerospace industry and medical industry (e.g. radio frequency thermal ablation of tumors).

Multi FBG Femtosecond laser inscription in FPI based pressure sensors for temperature distribution

We present in this paper an optical fiber pressure and temperature sensor (OFPTS) with multi Fibre Bragg Grating (FBG) array. The sensor based on an extrinsic Fabry Perot interferometer and is fabricated from silica glass. A femtosecond laser (FSL) was used to inscribe multiple FBGs proximately close to the diaphragm, parallel to each other. This concepts allows a chain of FBGs with miniature active length which can be a significant important tool for medical application, like radio frequency ablation (RFA) cancer treatment.

Low drift and high resolution miniature optical fiber combined pressure- and temperature sensor for cardio-vascular and urodynamic applications

The all-glass optical fibre pressure and temperature sensor (OFPTS), present here is a combination of an extrinsic Fabry Perot Interferometer (EFPI) and an fiber Bragg gratings (FBG), which allows a simultaneously measurement of both pressure and temperature. Thermal effects experienced by the EFPI can be compensated by using the FBG. The sensor achieved a pressure measurement resolution of 0.1mmHg with a frame-rate of 100Hz and a low drift rate of < 1 mmHg/hour drift. The sensor has been evaluated using a cardiovascular simulator and additionally has been evaluated in-vivo in a urodynamics application under medical supervision.