For some critical applications, the location of fiber Bragg gratings (FBGs) in draw tower grating (DTG) arrays needs to be determined to sub-mm accuracy; for example, successful packaging of the FBGs in mm scale packages. The DTG manufacturing process leaves no external visible identification marks on the fiber, hence location needs to be determined prior to packaging. This work presents an automated fiber marking system that can accurately locate the positions of the FBGs within +/- 0.1 mm. The simple, low cost, and automated system avoids manual fiber handling and allows accurate packaging of the FBGs for sensing applications. (C) 2014 Society of Photo-Optical Instrumentation Engineers (SPIE)

Distributed pressure sensing arrays fabricated from fiber Bragg gratings have been demonstrated for real-time monitoring of the dynamic subsurface pressures beneath water waves in a wave tank. Two sensing arrays were used to monitor horizontal and vertical pressures in the tank as periodic wave trains passed overhead. The horizontal and vertical arrays contained 90 and 35 sensing elements, respectively, spaced at 1-cm intervals allowing highly accurate spatial resolution to be achieved in both orientations. The wave tank paddle was programmed to generate wave-trains varying from ~5 to 30-cm peak-to-trough and the pressures measured using the fiber optic array were validated using commercial piezo-electric pressure sensors and video image analysis. The length and sensor separation of the fiber optic sensing array can be varied to suit the location under test, and the fiber optic elements make the devices inherently resistant to corrosion and electromagnetic interference.

The lower gastrointestinal tract has been referred to as the 'Dark Continent' of the human body because it is so hard to access without resorting to a surgeon's blade. In response to an unmet clinical need we have developed a fibre optic manometry catheter that is now in clinical use across Australia and New Zealand. The unparalleled detail of colonic activity that these devices provide is being hailed as ground breaking by global experts. In this paper we present the design and clinical application of the catheters, and also some of the (sometimes surprising) requirements of our clinical colleagues.

Graduated compression bandaging of the lower limbs is the primary therapy for venous leg ulcers with its efficacy believed to be predominantly dependent on the amount and the distribution of the compressive pressure applied. There has been on-going demand for an ideal sensor to facilitate in-vivo monitoring of the sub-bandage pressure. Several methods and devices have been reported but each has its limitations, such as bulkiness, low tolerance to movement, susceptible to thermal noise and single point sensing. An optical fiber force sensor is demonstrated, consisting of two arrays of fiber Bragg grating (FBG) entwined in a double helix form and packaged with contact-force sensitivity. This sensor array has inherent temperature immunity and is capable of real-time, distributed sensing of sub-bandage pressure. The calibration results of the sensor array, as well as the validation human trial results, are presented.

BACKGROUND:Manometry is commonly used for diagnosis of esophageal and anorectal motility disorders. In the colon, manometry is a useful tool, but clinical application remains uncertain. This uncertainty is partly based on the belief that manometry cannot reliably detect non-occluding colonic contractions and, therefore, cannot identify reliable markers of dysmotility. This study tests the ability of manometry to record pressure signals in response to non-lumen-occluding changes in diameter, at different rates of wall movement and with content of different viscosities.METHODS:A numerical model was built to investigate pressure changes caused by localized, non-lumen-occluding reductions in diameter, similar to those caused by contraction of the gut wall. A mechanical model, consisting of a sealed pressure vessel which could produce localized reductions in luminal diameter, was used to validate the model using luminal segments formed from; (i) natural latex; and (ii) sections of rabbit proximal colon. Fluids with viscosities ranging from 1 to 6800 mPa s(-1) and luminal contraction rates over the range 5-20 mmHg s(-1) were studied.KEY RESULTS:Manometry recorded non-occluding reductions in diameter, provided that they occurred with sufficiently viscous content. The measured signal was linearly dependent on the rate of reduction in luminal diameter and also increased with increasing viscosity of content (R(2) = 0.62 and 0.96 for 880 and 1760 mPa s(-1), respectively).CONCLUSIONS & INFERENCES:Manometry reliably registers non-occluding contractions in the presence of viscous content, and is therefore a viable tool for measuring colonic motility. Interpretation of colonic manometric data, and definitions based on manometric results, must consider the viscosity of luminal content.

Diagnostic catheters based on fiber Bragg gratings (FBG's) are proving to be highly effective for measurement of the muscular activity associated with peristalsis in the human gut. The primary muscular contractions that generate peristalsis are circumferential in nature; however, it has long been known that there is also a component of longitudinal contractility present, acting in harmony with the circumferential component to improve the overall efficiency of material movement. While detection of the circumferential contractions has been possible using solid state, hydraulic, and pneumatic sensor arrays in the oesophagus and anorectum, there have been relatively few reports on the measurement or inference of longitudinal contractions in humans. This is partly due to the lack of a viable recording technique suitable for real-time in-vivo measurement of this type of activity over extended lengths of the gut. We report on the development of, and latest results from, catheter based sensors capable of detecting both forms of muscular activity. Results from validation trials of both circumferential and longitudinal FBG catheters during simultaneous recording and video analysis in lengths of excised mammalian colon are given. Preliminary data from human clinical trials in patients with functional gastrointestinal disorders of the colon are also presented demonstrating the ability of the fiber optic catheter technology to provide high resolution data from the complex and convoluted regions of the human gut below the stomach.

In this paper the feasibility study of an optical fiber Bragg grating (FBG) based chemical sensor is presented. A previously developed FBG pressure sensor was modified by enveloping the grating regions with polymer sleeves. When in contact with different chemical solvents, the polymers react with different degrees of swelling which change the force exerted on the underlying FBG, modulating the grating period and subsequently shifting the Bragg wavelength. The characteristic rates of change of the Bragg wavelength can then be examined to identify the chemical being measured. Preliminary experimental results of measuring different chemicals with the FBG sensor are presented and discussed.

A miniature FBG pressure sensor is reported. Two optical fibers containing FBG arrays are twisted together and the sensing elements are enclosed in a specially designed structure to detect variations in the ambient pressure. It provides an overall diameter of ~1 mm which is extremely beneficial for the studies of peristalsis in the gastrointestinal tract and flow in the vascular system. The static and dynamic responses of the miniature catheter were calibrated and the results are presented.

Diagnostic catheters based on fibre Bragg gratings (FBG's) are proving to be highly effective for measurement of the muscular activity associated with motility in the human gut. While the primary muscular contractions that generate peristalsis are circumferential in nature, it has long been known that there is also a component of longitudinal contractility present, acting in harmony with the circumferential component to improve the overall efficiency of material movement. We report the detection of longitudinal motion in mammalian intestine using an FBG technique that should be viable for similar detection in humans. The longitudinal sensors have been combined with our previously reported FBG pressure sensing elements to form a composite catheter that allows the relative phase between the two components to be detected. The catheter output has been validated using video mapping in an ex‐vivo rabbit ileum preparation. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The precise location of Bragg gratings written into optical fibre during the drawing process provides an accurate method of inferring variations in draw velocity and hence any potential subtle variations in fibre characteristics.

Diagnostic catheters based on fibre Bragg gratings (FBG's) are proving to be highly effective for measurement of the muscular activity associated with peristalsis in the human gut. The primary muscular contractions that generate peristalsis are circumferential in nature; however, it has long been known that there is also a component of longitudinal contractility present, acting in harmony with the circumferential component to improve the overall efficiency of material movement. To date, there have been relatively few reports on the measurement or inference of longitudinal contractions in humans and all have been limited to detection at a single location only. This is due to the lack of a viable recording technique suitable for real-time in-vivo measurement of this type of activity over extended lengths of the gut. We report the detection of longitudinal motion in lengths of excised mammalian colon using an FBG technique that should be viable for similar detection in humans. The longitudinal sensors have been combined with our previously reported FBG pressure sensing elements to form a composite catheter that allows the relative phase between the two components to be detected. The catheter output has been validated using digital video mapping in an ex-vivo animal preparation using lengths of rabbit ileum.

The design of a fibre Bragg grating based manometry catheter for in-vivo diagnostics in the human colon is presented. The design is based on a device initially developed for use in the oesophagus, but in this instance, longer sensing lengths and increased flexibility were required to facilitate colonoscopic placement of the device and to allow access to the convoluted regions of this complex organ. The catheter design adopted allows the number of sensing regions to be increased to cover extended lengths of the colon whilst maintaining high flexibility and the close axial spacing necessary to accurately record pertinent features of peristalsis. Catheters with 72 sensing regions with an axial spacing of 1 cm have been assembled and used in-vivo to record peristaltic contractions in the human colon over a 24hr period. The close axial spacing of the pressure sensors has, for the first time, identified the complex nature of propagating sequences in both antegrade (towards the anus) and retrograde (away from the anus) directions in the colon. The potential to miss propagating sequences at wider sensor spacings is discussed and the resultant need for close axial spacing of sensors is proposed.

We report the design and use of multi-channel fibre Bragg grating based manometry catheters with pressure sensors spaced at 1 cm intervals along its axis. The catheters have been tested in-vivo in both the human oesophagus and colon and have been shown to provide analogous results to commercially available solid state pressure sensors. The advantage of using fibre gratings comes from the ability to extend the number of sensor elements without increasing the diameter or complexity of the catheter or data acquisition system. We present our progress towards the fabrication of a manometry catheter suitable for recording manometric data along the full length of the human colon. Results from early phase equivalence testing and recent in-vivo trials in the human oesophagus and colon are presented. The colonic recordings were taken in basal and post-prandial periods of 2.5 hours each. The close axial spacing of the pressure sensors has identified the complex nature of propagating sequences in the colon in both antegrade (towards the anus) and retrograde (away from the anus) for the first time. By sub-sampling the data using data from sensors 7 cm apart the potential to misrepresent propagating sequences at wider sensor spacings is demonstrated and proposed as a potential reason why correlation between peristaltic abnormalities recorded using traditional catheters, with 7.5-10 cm spaced sensors, and actual patient symptoms remains elusive.

Fiber optic catheters for the diagnosis of gastrointestinal motility disorders are demonstrated in-vitro and in-vivo. Single element catheters have been verified against existing solid state catheters and a multi-element catheter has been demonstrated for localized and full esophageal monitoring. The multi-element catheter consists of a series of closely spaced pressure sensors that pick up the peristaltic wave traveling along the gastrointestinal (GI) tract. The sensors are spaced on a 10 mm pitch allowing a full interpolated image of intraluminal pressure to be generated. Details are given of in-vivo trials of a 32-element catheter in the human oesophagus and the suitability of similar catheters for clinical evaluation in other regions of the human digestive tract is discussed. The fiber optic catheter is significantly smaller and more flexible than similar commercially available devices making intubation easier and improving patient tolerance during diagnostic procedures.

We report the design and operation of an optical fibre manometry catheter for measuring variation in pressure in the oesophagus during peristalsis. Catheters of this kind are used to help diagnose oesophageal disorders by recording the muscular contractions of the oesophageal wall in patients having difficulty swallowing. Traditional oesophageal catheters consist of an array of recording sites enabling pressure measurement from multiple locations along the the oesophagus. However, these catheters tend to be bulky or complex to operate whereas our optical equivalent uses a series of Fibre Bragg Grating (FBG) pressure sensors on a single fibre;, significantly reducing complexity and allowing the catheter diameter to be minimised. The data from each FBG was recorded using a solid state spectrometer in which the reflected peaks each covered a number of pixels of the spectrometer. This has enabled the FBG peaks to be tracked in wavelength with sub-nanometre precision resulting in pressure sensitivities of less than 1 mmHg. Results from a clinical trial carried out on 10 healthy subjects will be presented. For the trial, each subject was simultaneously intubated with the optical catheter and a commercially available solid-state catheter. Back-to-back readings were taken from both devices during a series of controlled water swallows. Ten swallows were recorded with the catheters sensors positioned in proximal, mid, and distal regions of the oesophagus and the data analysed statistically. The fibre optic device accurately picked up the dynamic variations in pressure, and can react at least as fast as the solid state device.

Fibre Bragg grating based pressure sensing catheters for the diagnosis of gastrointestinal motility disorders are presented. These catheters have been successfully trialled under controlled clinical conditions and results from in-vivo trials are given.

The design and clinical performance of fiber Bragg grating based pressure sensing catheters for the diagnosis of gastrointestinal motility disorders are presented. The fiber optic design allows catheters with multiple sensing regions but small overall diameters to be fabricated, which is advantageous for nasal intubation into patients. The fiber optic catheters have been compared to a commercially available solid-state device both in-vitro and in-vivo, and results demonstrate that they are suitable for diagnosis of gastrointestinal motility disorders.