Recent Improvement of Medical Optical Fibre Pressure and Temperature Sensors

This investigation describes a detailed analysis of the fabrication and testing of optical fibre pressure and temperature sensors (OFPTS). The optical sensor of this research is based on an extrinsic Fabry-Perot interferometer (EFPI) with integrated fibre Bragg grating (FBG) for simultaneous pressure and temperature measurements. The sensor is fabricated exclusively in glass and with a small diameter of 0.2 mm, making it suitable for volume-restricted bio-medical applications. Diaphragm shrinking techniques based on polishing, hydrofluoric (HF) acid and femtosecond (FS) laser micro-machining are described and analysed. The presented sensors were examined carefully and demonstrated a pressure sensitivity in the range of sp = 2-10 nm/kPa and a resolution of better than ΔP = 10 Pa protect (0.1 cm H2O). A static pressure test in 38 cm H2O shows no drift of the sensor in a six-day period. Additionally, a dynamic pressure analysis demonstrated that the OFPTS never exceeded a drift of more than 130 Pa (1.3 cm H2O) in a 12-h measurement, carried out in a cardiovascular simulator. The temperature sensitivity is given by k = 10.7 pm/K, which results in a temperature resolution of better than ΔT = 0.1 K. Since the temperature sensing element is placed close to the pressure sensing element, the pressure sensor is insensitive to temperature changes.

Investigation on dynamic calibration for an optical-fiber solids concentration probe in gas-solid two-phase flows

This paper presents a review and analysis of the research that has been carried out on dynamic calibration for optical-fiber solids concentration probes. An introduction to the optical-fiber solids concentration probe was given. Different calibration methods of optical-fiber solids concentration probes reported in the literature were reviewed. In addition, a reflection-type optical-fiber solids concentration probe was uniquely calibrated at nearly full range of the solids concentration from 0 to packed bed concentration. The effects of particle properties (particle size, sphericity and color) on the calibration results were comprehensively investigated. The results show that the output voltage has a tendency to increase with the decreasing particle size, and the effect of particle color on calibration result is more predominant than that of sphericity.

Correcting for spatial-resolution degradation mechanisms in OFDR via inline auxiliary points

The spatial resolution of OFDR is normally degraded by the laser phase noise, deviations from linear frequency scan and acoustic noise in the fibers. A method for mitigating these degradation mechanisms, without using an auxiliary interferometer, via inline auxiliary points, is presented and demonstrated experimentally. Auxiliary points are points that are a priori known to have (spatial) impulse reflectivities. Their responses are used for compensating the phase deviations that degrade the response of points that are further away from the source.

SNAP: fabrication of long coupled microresonator chains with sub-angstrom precision

Based on the recently-introduced Surface Nanoscale Axial Photonics (SNAP) platform, we demonstrate a chain of 30 coupled SNAP microresonators spaced by 50 micron along an optical fiber, which is fabricated with the precision of 0.7 angstrom and a standard deviation of 0.12 angstrom in effective microresonator radius. To the best of our knowledge, this result surpasses those achieved in other super-low-loss photonic technologies developed to date by two orders of magnitude. The chain exhibits bandgaps in both the discrete and continuous spectrum in excellent agreement with theory. The developed method enables robust fabrication of SNAP devices with sub-angstrom precision.

Performance of large aperture tapered fiber phase conjugate mirror with high pulse energy and 1-kHz repetition rate

A large aperture fused silica tapered fiber phase conjugate mirror is presented with a maximum 70% stimulated Brillouin scattering (SBS) reflectivity, which is obtained with 1 kHz repetition rate, 15 ns pulse width and 38 mJ input pulse energy. To the best of our knowledge, this is the highest SBS reflectivity ever reported by using optical fiber as a phase conjugate mirror for such high pulse repetition rate (1 kHz) and several tens of millijoule (mJ) input pulse energy. The influences of fiber end surface quality and pump pulse widths on SBS reflectivity are investigated experimentally. The results show that finer fiber end surface quality and longer input pulse widths are preferred for obtaining higher SBS reflectivity with higher input pulse energy. Double passing amplification experiments are also performed. 52 mJ pulse energy is achieved at 1 kHz repetition rate, with a reflected SBS pulse width of 1.5 ns and a M(2) factor of 2.3. The corresponding peak power reaches 34.6 MW. Obvious beam quality improvement is observed.

Ellipsometry with randomly varying polarization states

We show that, under the right conditions, one can make highly accurate polarization-based measurements without knowing the absolute polarization state of the probing light field. It is shown that light, passed through a randomly varying birefringent material has a well-defined orbit on the Poincar sphere, which we term a generalized polarization state, that is preserved. Changes to the generalized polarization state can then be used in place of the absolute polarization states that make up the generalized state, to measure the change in polarization due to a sample under investigation. We illustrate the usefulness of this analysis approach by demonstrating fiber-based ellipsometry, where the polarization state of the probe light is unknown, and, yet, the ellipsometric angles of the investigated sample (Ψ and Δ) are obtained with an accuracy comparable to that of conventional ellipsometry instruments by measuring changes to the generalized polarization state.

Dissemination of an optical frequency comb over fiber with 3 × 10(-18) fractional accuracy

We demonstrate that the structure of an optical frequency comb transferred over several km of fiber can be preserved at a level compatible with the best optical frequency references currently available. Using an optical phase detection technique we measure the noise introduced by the fiber link and suppress it by stabilizing the optical path length. The measured fractional frequency stability of the transferred optical modes is 2 × 10(-18) at a few thousand seconds and the mode spacing stability after optical-microwave conversion is better than 4 × 10(-17) over the same time scale.

Enhancing long-term stability of the optoelectronic oscillator with a probe-injected fiber delay monitoring mechanism

Optoelectronic oscillators (OEOs), based on optical fiber loops to act as a high-Q cavity, are capable of generating stable radio-frequencies (RF). The long-term frequency stability of the OEO is then limited by the cavity variation that is mainly induced by temperature sensitivity of the optical fiber. In order to actively stabilize the OEO cavity, we employ the technique of RF transfer over optical fibers. We propose and experimentally demonstrate a dual-loop-OEO scheme to enhance the long-term stability with an injected probe signal to monitor the phase variation in the fiber loops. The experimental results show that the resulting spread-spectrum signal is useful in monitoring the fiber delay without observable interference. The relationships between the measured frequency and the monitored delay are theoretically and numerically discussed. We also estimate the long-term stability of the proposed OEO scheme with the cavity phase correction. The corrected result shows the long-term frequency stability of the proposed OEO is within 8.4×10(-8) at one day.

Characterization of a fiber-optic displacement sensor for measurements in high-intensity focused ultrasound fields

A fiber-optic sensor is presented that is capable of measuring the particle displacement in high-intensity focused ultrasound (HIFU) fields. For this probe, a secondary calibration was performed, and the resulting complex frequency response is discussed. As a first practical application, the setup was used to measure the pressure in the field of a weakly focusing ultrasound transducer. The result is compared with that of a membrane hydrophone measurement. The feasibility of measurements in HIFU fields is demonstrated by means of measurements of the spatial distribution of the peak particle velocity within the focus of a HIFU transducer and of the dependence of the peak values on the acoustical power level.

Performance assessment of novel side firing safe tips for endodontic applications

During root canal or periodontal treatment, directing laser energy onto the walls of the root canal is essential for effective disinfection. This study assessed the performance of four different fiber modifications that have increased lateral emission, including three designs with safe tips to reduce irradiation directed toward the root apex. Free-running pulsed infrared lasers (Nd:YAG, Er:YAG, and Er,Cr:YSGG) and a diode laser (980 nm) were used in combination with plain ended (forward emitting) laser fibers; conical laser fibers, side firing honeycomb pattern fibers without a safe end; honeycomb fibers with silver coated ends, conical fibers with selectively abraded tips, and selectively abraded honeycomb fibers with silver coated tips (20 fibers for each laser type). Laser emissions forward and laterally were measured, and digital photographs and thermally sensitive paper used to record the emission profiles. Thermochromic dyes painted onto the root surface of an extracted tooth were used to explore the distribution of laser energy with different tips designs. All three safe tipped ends gave reduced emissions in the forward direction (range 17-59%), but had similar lateral emission characteristics. Fiber designs with reduced forward emission may be useful for various dental laser procedures.

Exact error rate analysis of equal gain and selection diversity for coherent free-space optical systems on strong turbulence channels

Exact error rate performances are studied for coherent free-space optical communication systems under strong turbulence with diversity reception. Equal gain and selection diversity are considered as practical schemes to mitigate turbulence. The exact bit-error rate for binary phase-shift keying and outage probability are developed for equal gain diversity. Analytical expressions are obtained for the bit-error rate of differential phase-shift keying and asynchronous frequency-shift keying, as well as for outage probability using selection diversity. Furthermore, we provide the closed-form expressions of diversity order and coding gain with both diversity receptions. The analytical results are verified by computer simulations and are suitable for rapid error rates calculation.

A simple and reliable method to determine LP(11) cutoff wavelength of bend insensitive fiber

We present a simple and reliable method based on the spectral splice loss measurement to determine the cutoff wavelength of bend insensitive fiber.

Long wavelength fluorescence lifetime standards for front-face fluorometry

With the increased development and use of fluorescence lifetime-based sensors, fiber optic sensors, fluorescence lifetime imaging microscopy (FLIM), and plate and array readers, , calibration standards are essential to ensure the proper function of these devices and accurate results. For many devices that utilize a "front face excitation" geometry where the excitation is nearly coaxial with the direction of emission, scattering-based lifetime standards are problematic and fluorescent lifetime standards are necessary. As more long wavelength (red and near-infrared) fluorophores are used to avoid background autofluorescence, the lack of lifetime standards in this wavelength range has only become more apparent . We describe an approach to developing lifetime standards in any wavelength range, based on Förster resonance energy transfer (FRET). These standards are bright, highly reproducible, have a broad decrease in observed lifetime, and an emission wavelength in the red to near infrared making them well suited for the laboratory and field applications as well. This basic approach can be extended to produce lifetime standards for other wavelength regimes.

Improvement and analysis of a micro Raman probe

A micro Raman probe (MRP) with a 600 microm diameter, which we previously reported as the narrowest achieved to date, was further improved by introducing high-quality optical filters and a collecting lens at the tip. We fabricated the MRP with a high collection efficiency, a wider collection wavelength, and a high signal-to-noise ratio. We compared two types of probes: one with a lens-tipped end and one with a flat tip. We experimentally tested the performance of these MRPs to evaluate the detection properties defined by parameters such as the optical purity against inherent Raman background noise due to optical fibers, the sensitivity, and the viewing area. Finally, we demonstrated their effectiveness in measurements of standard Raman samples and applied them to measurements of plastic and human skin samples in situ.

Development of calibration techniques for ultrasonic hydrophone probes in the frequency range from 1 to 100 MHz

The primary objective of this work was to develop and optimize the calibration techniques for ultrasonic hydrophone probes used in acoustic field measurements up to 100 MHz. A dependable, 100 MHz calibration method was necessary to examine the behavior of a sub-millimeter spatial resolution fiber optic (FO) sensor and assess the need for such a sensor as an alternative tool for high frequency characterization of ultrasound fields. Also, it was of interest to investigate the feasibility of using FO probes in high intensity fields such as those employed in HIFU (high intensity focused ultrasound) applications. In addition to the development and validation of a novel, 100 MHz calibration technique the innovative elements of this research include implementation and testing of a prototype FO sensor with an active diameter of about 10 microm that exhibits uniform sensitivity over the considered frequency range and does not require any spatial averaging corrections up to about 75 MHz. The results of the calibration measurements are presented and it is shown that the optimized calibration technique allows the sensitivity of the hydrophone probes to be determined as a virtually continuous function of frequency and is also well suited to verify the uniformity of the FO sensor frequency response. As anticipated, the overall uncertainty of the calibration was dependent on frequency and determined to be about +/-12% (+/-1 dB) up to 40 MHz, +/-20% (+/-1.5 dB) from 40 to 60 MHz and +/-25% (+/-2dB) from 60 to 100 MHz. The outcome of this research indicates that once fully developed and calibrated, the combined acousto-optic system will constitute a universal reference tool in the wide, 100 MHz bandwidth.

Optical frequency combs generated by four-wave mixing in optical fibers for astrophysical spectrometer calibration and metrology

Optical frequency combs generated by multiple four-wave mixing in short and highly nonlinear optical fibers are proposed for use as high precision frequency markers, calibration of astrophysical spectrometers, broadband spectroscopy and metrology. Implementations can involve two optical frequency standards as input lasers, or one standard and a second laser phase-locked to it using a stable microwave reference oscillator. Energy and momentum conservation required by the parametric generation assures phase coherence among comb frequencies, while fibers with short lengths can avoid linewidth broadening and stimulated Brillouin scattering. In contrast to combs from mode-locked lasers or microcavities, the absence of a resonator allows large tuning of the frequency spacing from tens of gigahertz to beyond teraHertz.

Hollow fiber optics with improved durability for high-peak-power pulses of Q-switched Nd:YAG lasers

To improve the damage threshold of hollow optical waveguides for transmitting Q-switched Nd:YAG laser pulses, we optimize the metallization processes for the inner coating of fibers. For silver-coated hollow fiber as the base, second, and third Nd:YAG lasers, drying silver films at a moderate temperature and with inert gas flow is found to be effective. By using this drying process, the resistance to high-peak-power optical pulse radiation is drastically improved for fibers fabricated with and without the sensitizing process. The maximum peak power transmitted in the fiber is greater than 20 MW. To improve the energy threshold of aluminum-coated hollow fibers for the fourth and fifth harmonics of Nd:YAG lasers, a thin silver film is added between the aluminum film and the glass substrate to increase adhesion of the aluminum coating. By using this primer layer, the power threshold improves to 3 MW for the fourth harmonics of a Q-switched Nd:YAG laser light.

Neurofiberscopic biopsy of tumors of the pineal region and posterior third ventricle: indications, technique, complications, and results

OBJECTIVE

Evaluation of results of the neurofiberscopic biopsy of tumors of the pineal region and posterior third ventricle.

METHODS

From 2001 to 2004, 23 patients (mean age, 30.6 yr) with tumors located in the pineal region or posterior third ventricle underwent neurofiberscopic biopsy with simultaneous third ventriculostomy. The procedure was indicated for verification of the histological diagnosis of the neoplasm, which was planned to be treated by radiotherapy and/or chemotherapy without open surgery (eight patients), establishment of the pathological diagnosis for further choice of the most appropriate treatment strategy (11 patients), differentiation of the recurrent neoplasm and radiation necrosis (two patients), and decompression of the large tumor-associated cyst (two patients). In six previously shunted patients, substitution of the ventriculoperitoneal shunt on the third ventricle stoma was performed.

RESULTS

There was no postoperative mortality or permanent morbidity. In all cases, the obtained tissue sample was sufficient for pathological diagnosis. Transient postoperative complications included fever (15 patients), nausea and vomiting (three patients), and diplopia (one patient). On the long-term follow-up, delayed third ventricular stoma failure caused by tumor regrowth and scar formation was found in one patient, and dissemination of the malignant glioma through the subarachnoid space was found in another patient.

CONCLUSION

Neurofiberscopic biopsy represents a useful method for sampling of tumors of the pineal region and posterior third ventricle, which can be effectively used in both previously shunted and shunt-free patients.

Quality assessment of confocal microscopy slide-based systems: Instability

BACKGROUND

All slide-based fluorescence cytometry detections systems basically include an excitation light source, intermediate optics, and a detection device (CCD or PMT). Occasionally, this equipment becomes unstable, generating unreliable and inferior data.

METHODS

A number of tests have been devised to evaluate equipment performance and instability. The following four instability tests are described: galvanometer scanning, stage drift, correct wavelength spectral detection, and long-term laser power.

RESULTS

Quality assurance tests revealed that a confocal microscope can become unstable in the following parameters, yielding inaccurate data: laser power, PMTs functionality, spectrophotometer accuracy, galvanometer scanning and laser stability, and stage drift. Long-term laser power stability has been observed to vary greatly.

CONCLUSIONS

Confocal systems can become unstable in the following parameters: long-term laser power, galvanometer scanning, spectrophotometer accuracy, and stage stability. Instability in any of these parameters will affect image quality. Laser power fluctuations result from either a defective Acousto-optic tunable filter or improper heat dissipation. Spectrophotometer instability will generate unreliable spectra data, extra light reflections, and poor image quality. Galvanometer scanning instability yields poor image quality while microscope stage drift results in a sample going out of the plane of focus. With minor modifications, these tests may be applicable to other slide-based systems.

Standard reference material 2036 near-infrared reflection wavelength standard

Standard Reference Material 2036 (SRM 2036) is a certified transfer standard intended for the verification and calibration of the wavelength/wavenumber scale of near-infrared (NIR) spectrometers operating in diffuse or trans-reflectance mode. SRM 2036 Near-Infrared Wavelength/Wavenumber Reflection Standard is a combination of a rare earth oxide glass of a composition similar to that of SRM 2035 Near-Infrared Transmission Wavelength/Wavenumber Standard and SRM 2065 Ultraviolet-Visible-Near-Infrared Transmission Wavelength/Wavenumber Standard, but is in physical contact with a piece of sintered poly(tetrafluoroethylene) (PTFE). The combination of glass contacted with a nearly ideal diffusely reflecting backing provides reflection-absorption bands that range from 15% R to 40% R. SRM 2036 is certified for the 10% band fraction air wavelength centroid location, (10%)B, of seven bands spanning the spectral region from 975 nm to 1946 nm. It is also certified for the vacuum wavenumber (10%)B of the same seven bands in the spectral region from 10 300 cm(-1) to 5130 cm(-1) at 8 cm(-1) resolution. Informational values are provided for the locations of thirteen additional bands from 334 nm to 804 nm.

Comparison of methods for transfer of calibration models in near-infared spectroscopy: a case study based on correcting path length differences using fiber-optic transmittance probes in in-line near-infrared spectroscopy

This article addresses problems related to transfer of calibration models due to variations in distance between the transmittance fiber-optic probes. The data have been generated using a mixture design and measured at five different probe distances. A number of techniques reported in the literature have been compared. These include multiplicative scatter correction (MSC), path length correction (PLC), finite impulse response (FIR), orthogonal signal correction (OSC), piecewise direct standardization (PDS), and robust calibration. The quality of the predictions was expressed in terms of root mean square error of prediction (RMSEP). Robust calibration gave good calibration transfer results, while the other methods did not give acceptable results.

Use of a multiseparation fiber optic probe for the optical diagnosis of breast cancer

We explore the effects of the illumination and collection geometry on optical spectroscopic diagnosis of breast cancer. Fluorescence and diffuse reflectance spectroscopy in the UV-visible spectral range are made with a multiseparation probe at three illumination-collection separations of 735, 980, and 1225 microm, respectively, from 13 malignant and 34 nonmalignant breast tissues. Statistical analysis is carried out on two types of data inputs: (1) the fluorescence and diffuse reflectance spectra recorded at each of the three illumination-collection separations and (2) the integrated fluorescence (at each excitation wavelength) or diffuse reflectance over the entire spectrum at all three illumination-collection separations. The results show that using the integrated fluorescence intensities recorded at a single excitation wavelength at all three illumination-collection separations can discriminate malignant from nonmalignant breast tissues with similar classification accuracy to that using spectral data measured at several excitation wavelengths with a single illumination-collection separation. These findings have significant implications with respect to the design of an optical system for breast cancer diagnosis. Examining the intensity attenuation at a single wavelength rather than spectral intensities at multiple wavelengths can significantly reduce the measurement and data processing time in a clinical setting as well as the cost and complexity of the optical system.

Fibered confocal fluorescence microscopy (Cell-viZio) facilitates extended imaging in the field of microcirculation. A comparison with intravital microscopy

This study investigated the capability of fibered confocal fluorescence microscopy (FCFM) to provide in vivo microvascular observations. FCFM is specifically designed for in vivo in situ observation thanks to a probe composed of a fiber bundle and micro-optics having a diameter as small as 650 microm. In the first part of the study, we compared the main characteristics of FCFM with those of intravital fluorescence microscopy (IFM). A mouse cremaster preparation was used as a common basis to allow for imaging with both modalities. We discussed the feasibility of obtaining quantitative measurements usually provided by IFM in the context of FCFM: morphometry, capillary permeability, functional capillary density, vasoconstriction and dilation effects. In addition, the possibility to visualize fluorescent red blood cells or leukocytes was also evaluated. Phototoxicity issues and limitations of FCFM were also discussed. We showed that FCFM allows observations and measurements usually provided by IFM and that the real-time capability of the system, as well as the flexibility and small diameter of the optical probe enable micro-invasiveness and can extend imaging capabilities for in vivo in situ observations when compared to IFM.

Biocompatibility of a physiological pressure sensor

A newly developed fiber optic micropressure sensor was evaluated for biocompatibility using the International Organization for Standardization (ISO) test standard 10993-6. The test material and an inert control (fused silica glass) were tested in New Zealand white rabbits. Four test specimens were implanted in the paravertebral muscles on one side of the spine about 2-5 cm from the mid-line and parallel to the spinal column. Similarly, four control specimens were implanted on the opposite side. The implantation periods were 1, 4, and 12 weeks to ensure a steady state biological tissue response. Four animals were tested at each time period. Macroscopic and microscopic observations were performed to compare the biological reactions between the test and control materials. There was an inflammatory reaction at 1 week which subsided at 4 weeks. There was fibrous tissue growth near the implant that also decreased over time. Most importantly, there was no significant difference in the biological response between the test and control materials. Therefore, we conclude that the pressure microsensor is biocompatible.

Current trends in ureteroscopy

The advances of technology are having substantial ramifications in medicine and in urology, in particular. This article discusses these advances and explores current trends in ureteroscopy.

Techniques of ureteroscopy

The flexible ureteroscope has revolutionized the diagnosis and treatment of the entire upper urinary tract. Endoscopic tools have evolved, providing the surgeon with the armamentarium necessary to treat many different pathologic processes. Almost all renal calculi can be treated with retrograde ureteroscopy. The fragility of these new endoscopes is a concern, and great care must be taken when using them. With good technique and proper use of instruments, their working life can be extended.

Minimally invasive surgery: only as good as the picture

BACKGROUND

In minimally invasive surgery, there is increased reliance on real-time 2-dimensional images. The fibre-optic light lead is one of the most frequently damaged elements of the 'imaging chain', leading to a poor quality picture.

METHODS

Light leads with a honeycomb projection were connected to a light source and the resulting beam directed at a sheet of paper. Darkened sectors with diminished or absent light transmission were recorded.

RESULTS

All suitable light leads in routine use were examined. A mean of 22.2% (SD 7.8%) of the projection had diminished or absent light transmission.

CONCLUSION

Sub-optimal endoscopic equipment was in routine use.

Ureteroscopes: flexible, rigid, and semirigid

Since its introduction, the ureteroscope has undergone significant improvements. Using the currently available rigid, semirigid, and flexible ureteroscopes and working instruments, urologists can diagnose and treat lesions throughout the upper urinary tract. Over the past 25 years, the ureteroscope in combination with shock wave lithotripsy has transformed the diagnosis and treatment of more than 90% of upper urinary tract pathology from an open to an endourologic procedure. With endoscope manufacturers continually incorporating new technology into their ureteroscopes, future models will undoubtedly provide better optics, increased durability, and improved capabilities, resulting in greater success when urologists perform endoscopic forays into the upper urinary tract.

Advanced intrarenal ureteroscopic procedures

The role of flexible ureteroscopy in the management of intrarenal pathology has undergone a dramatic evolution, powered by improvements in flexible ureteroscope design; deflection and image quality; diversification of small, disposable instrumentation; and the use of holmium laser lithotripsy. This article reviews the application of flexible ureteroscopy for advanced intrarenal procedures.

Evaluation of a new fiber-optic pressure recording system for cardiovascular measurements in mice

We have tested a new fiber-optic pressure recording system, Samba, with a thin fiber [outer diameter (OD) = 0.25 mm] and a pressure sensor (length and OD = 0.42 mm) attached to the end. The accuracy of the system tested in vitro was good, with a coefficient of variation of 2.54% at 100 mmHg. The drift was <0.45 mmHg/h, and the temperature sensitivity was approximately 0.07 mmHg/1 degrees C between 22 and 37 degrees C. The frequency response characteristics were similar to a 1.4-Fr Millar catheter (0-200 Hz). Introduction of the Samba sensor from the right carotid artery into the left ventricle in six mice caused no drop in mean aortic pressure, whereas introduction of a 1.4-Fr Millar catheter (OD = 0.47 mm; n = 6) caused a pressure drop from 91.6 +/- 9.2 to 65.1 +/- 6.2 mmHg; P < 0.05. Thus the Samba sensor system may represent a new alternative to assess hemodynamic variables in the murine cardiovascular system.

View of Normal Human Skin In Vivo as Observed Using Fluorescent Fiber-Optic Confocal Microscopic Imaging

Fluorescence confocal scanning laser microscopy, using a miniaturized handheld scanner, was performed to visualize the microscopic architecture of normal human epidermis in vivo. Fluorescein sodium (approximately 20 microL of 0.2% wt/vol) was administered via intradermal injection to normal skin on the volar forearm of 22 patients. The skin was imaged continuously from 1 to 15 min after injection. Fluorescein was excited at 488 nm and the fluorescent emission was detected at > 505 nm. In each subject, a series of images was collected at increasing depth, from superficial stratum corneum to papillary dermis. Features observed in confocal images were compared to those seen in hematoxylin- and eosin-stained sections of skin. The confocal images demonstrated the architecture of superficial skin in the horizontal plane. There was a transition in keratinocyte size, shape, and morphology with progressive imaging into the deeper epidermal layers. Superficial dermis and microscopic capillaries with blood flow were easily observed. The morphologic patterns associated with the major cell types of the epidermis were consistent with those known from conventional histology. We report the ability of in vivo fluorescence point scanning laser confocal microscopy to produce real-time, high-resolution images of the microscopic architecture of normal human epidermis using a noninvasive imaging technology.

Structure and process quality illustrated by fibreoptic intubation: analysis of 1612 cases

The purpose of this investigation was the description of structure and process quality based on the analysis of 1612 fibreoptic intubations. We evaluated all fibreoptic intubations (nasotracheal in awake patients and orotracheal in anaesthetised patients) from a previously described database over a period of 2 years. We assessed structure quality by evaluating the distribution of the fibreoptic intubations across all staff anaesthetists, and process quality by analysing the number of attempts, the time required, the cases where we had to switch to conventional intubation and the complications. In all, 955 nasotracheal and 657 orotracheal intubations were evaluated. Almost all anaesthetists performed at least 15 nasotracheal and 10 orotracheal intubations. The success rate was 85.2% at the first attempt. Within 3 min, 93.9% of all fibreoptic intubations were successfully completed. In 24 cases, fibreoptic intubation was abandoned. Severe nasal bleeding as a major complication occurred in 1.3% of the nasotracheal intubations.

von Frey hairs: new materials for a new design

von Frey filaments are widely used in pain research. Conventionally, they are made of synthetic fibres. This plastic material is susceptible to changes in humidity and temperature, and such filaments do not keep their calibration. Filaments made of optical glass fibres are highly elastic and do not suffer these problems. Their optical properties can be used to make thin fibres more visible.

Clinical evaluation of the InnerSpace fibreoptic intracranial pressure monitoring device

OBJECTIVE

The aim of this study is the clinical evaluation of the intraparenchymal ICP monitor InnerSpace OPX 100.

METHODS

Sixty-four Inner Space OPX 100 transducers in 51 patients with severe head injury (42), intracranial spontaneous bleeding (6) or hypoxia (3) were studied. The transducer was placed in the frontal white matter. Thirty-nine patients received one catheter, eleven patients two catheters and one patient three catheters. The study period ranged from 10 hours-25 days; total study time was 421.5 days (mean duration 6.6 days).

RESULTS

In nine cases (14.1%) an inadequate location of the ICP transducer was found, but the accuracy of the measurement was not influenced. Dislocation of the transducer occurred in eight cases (12.5%) due to inadequate handling. A failed transducer was observed in four cases (6.3%) because of a damaged optical fibre (1) or inadequate handling (3). In one patient (1.9%) a minor local infection developed. In eleven cases (17%) a haematoma around the ICP sensor was observed. Six haematomas were small; five haematomas were larger than 1 cm in diameter. In two patients a large frontal haematoma developed after exchange of the transducer. Operative evacuation was necessary in both cases. Zero shift was below 2 mmHg in all catheters.

CONCLUSION

It is concluded that the InnerSpace intraparenchymal ICP monitor is a reliable device: the rate of catheter related intracerebral haematomas, however, is not acceptable. This could be improved by a better fixation of the catheter in the burr hole in order to avoid micromovements of the transducer.

Fiber optic pressure sensor for biomedical applications

In vivo measurement of blood pressure is critical in many settings, including patient care, medical research, and control of cardiovascular assist and replacement devices. This article describes a pressure sensor based on fiber optic, white light interferometry. An optical interference filter formed between the end face of an optical fiber and the sensing diaphragm selectively reflects a wavelength component. A low cost, thin film optical wedge interferometer placed at the output end detects the wavelength of the reflected signal, which represents a unique cavity length of the interference filter directly related to the diaphragm deflection and, therefore, pressure. Several key features of this sensing scheme include low drift, high accuracy, and insensitivity to light loss factors along the length of the optical fiber. This fiber optic pressure sensor promises significant advances as a medical monitoring tool, a research instrument, and a component of cardiovascular assist and replacement devices. A prototype pressure gauge has been built, and the feasibility of the optical approach verified. Experimental results of the prototype gauge for resolution, repeatability, and drift and a preliminary design for a high resolution, low drift, miniature fiber optic pressure probe are presented herein.

Surgical video systems

Surgical video systems (SVSs), which typically consist of a video camera attached to an optical endoscope, a video processor, a light source, and a video monitor, are now being used to perform a significant number of minimally invasive surgical procedures. SVSs offer several advantages (e.g., multiple viewer visualization of the surgical site, increased clinician comfort) over nonvideo systems and have increased the practicality and convenience of minimally invasive surgery (MIS). Currently, SVSs are used by hospitals in their general, obstetric/gynecologic, orthopedic, thoracic, and urologic procedures, as well as in other specialties for which MIS is feasible. In this study, we evaluated 19 SVSs from 10 manufacturers, focusing on their use in laparoscopic applications in general surgery. We based our ratings on the usefulness of each system's video performance and features in helping clinicians provide safe and efficacious laparoscopic surgery. We rated 18 of the systems Acceptable because of their overall good performance and features. We rated 1 system Conditionally Acceptable because, compared with the other evaluated systems, this SVS presents a greater risk of thermal injury resulting from excessive heating at the distal tip of the laparoscope. Readers should be aware that our test results, conclusions, and ratings apply only to the specific systems and components tested in this Evaluation. In addition, although our discussion focuses on the laparoscopic application of SVSs, much of the information in this study also applies to other MIS applications, and the evaluated devices can be used in a variety of surgical procedures. To help hospitals gain the perspectives necessary to assess the appropriateness of specific SVSs to ensure that the needs of their patients, as well as the expectations of their clinicians, will be satisfied, we have included a Selection and Purchasing Guide that can be used as a supplement to our Evaluation findings. We have also included a Glossary of relevant terminology and the supplementary article, "Fiberoptic Illumination Systems and the Risk of Burns or Fire during Endoscopic Procedures," which addresses a safety concern with the use of these devices. While we made every effort to present the most current information, readers should recognize that this is a rapidly evolving technology, and developments occurring after our study was complete may not be reflected in the text. For additional information on topics related to this study, refer to the following Health Devices articles: (1) our Guidance Article, "Surgical Video Systems Used in Laparoscopy," 24(1), January 1995, which serves as an introduction to SVS terminology and includes a discussion of the significance of many SVS specifications; (2) our Evaluation, "Video Colonoscope Systems," 23(5), May 1994, which includes a detailed overview of video endoscopic applications and technology; and (3) our Evaluations of laparoscopic insufflators (21[5], May 1992, and 24[7], July 1995), which address issues related to the creation of a viewing and working space inside the peritoneal cavity to facilitate visualization in laparoscopic procedures.

Effects of a modified Q-switched Nd-YAG laser on human vascular tissue: an ex vivo study

RATIONALE AND OBJECTIVES

Relatively disappointing results with continuous-wave lasers stimulated us to evaluate pulsed lasers for interventional radiology. In this article, we describe our efforts to assess the effects of this technology ex vivo.

METHODS

We modified a Q-switched yttrium aluminum garnet (Nd-YAG) laser to emit pulses of 300 mJ maximum with a 20-Hz repetition rate, at 1064 nm, and with a duration that ranged from 300 ns to 2.3 microseconds. The lengthening of the pulse duration by a factor of 100 (compared with the conventional nanosecond Q-switched Nd-YAG laser) and the ability to define it exactly were obtained by controlling the opening and closing of the Pockels cell electronically. Lengthening the pulse duration made it possible to reduce peak power while conserving the same total energy. In this way, high energy was transmitted through thin optical fibers.

RESULTS

One hundred fifty millijoules with 2-microsecond pulses, 140 mJ with 1-microsecond pulses, and 100 mJ with 500-ns pulses were transmitted through a 300-micron silica-polymer fiber. The transmission coefficient was identical for the three pulse durations. Ex vivo irradiation experiments were performed on human atheromatous arteries in saline solution using a 300-micron diameter optical fiber. Craters were easily obtained. Their depth and width were related to maximum energy transmission and irradiation time. No carbonization occurred and no destruction of the optical fiber was observed.

CONCLUSION

A modified Q-switched Nd-YAG laser can transmit high-energy pulses through thin optical fibers without damaging them and can destroy human atheroma in an ex vivo setting.

Endoscopic release of the carpal tunnel: a randomized prospective multicenter study

A 10-center randomized prospective multicenter study of endoscopic release of the carpal tunnel was carried out. Surgery was performed with a new device for transecting the transverse carpal ligament while control hands were treated with conventional open surgery. There were 122 patients in the study; 25 had carpal tunnel surgery on both hands and 97 had surgery on one hand. Of the surgical procedures, 65 were in the control group and 82 were in the device group. The endoscopic device was coupled to a fiberoptic light and a video camera. A trigger-activated blade was used to incise the transverse carpal ligament. After surgery, the best predictors of return to work and to activities of daily living were strength and tenderness variables. For patients in the device group with one affected hand, the median time for return to work was 21 1/2 days less than that for the control group. Two patients treated with the endoscopic device required reoperation by open surgical decompression; only one of these had incomplete release with the device. Two patients in the device group experienced transient ulnar neurapraxia.

The anatomic range of examination by fibreoptic rectosigmoidoscopy (60 centimetres)

The purpose of the study was to investigate the anatomic location of the flexible rectosigmoidoscope (60 cm) when introduced as far as technically possible. One hundred and forty-nine consecutive patients referred for double-contrast enema (DCE) were examined with rectosigmoidoscopy before the radiologic examination, and CO2 was used for insufflation. A plain abdominal film was taken to locate the tip of the instrument when 60 cm or as much as possible of the instrument had been introduced. The sigmoid loop was passed and the tip of the scope located in the ascending colon or at the left flexure in 99 (66%) of the patients, and in a further 27 (18%) the upper part of the sigmoid colon was reached. The sigmoid colon had been passed in 71%, 80%, and 44% when 60, 50, and 40 cm of the instrument was introduced, respectively. DCE could be performed at the same session as the rectosigmoidoscopy, as CO2 was quickly absorbed. In the vast majority of patients the sigmoid colon can be inspected with a rectosigmoidoscope.

Multifiber, multiwavelength, fiber optic fluorescence spectrophotometer

A fiberoptic spectrofluorimeter was constructed capable of remote operation of up to 18 biosensors under fully automated, multiplexed control. Excitation and emission wavelengths were separately adjustable, as were optical bandwidths, signal gain, phase, integration time, and illumination duty cycle. Synchronous demodulation was used to enhance signal-to-noise ratio and allow operation under ambient lighting conditions. Detection limit for aqueous sodium-fluorescein was below 1 ng/mL at greater than unity signal-to-noise ratio, with effective sampling volumes less than 0.02 microL. The fluorimeter showed characteristics fiberoptic sampling behavior with asymptotic nonzero signal magnitudes under increasing pathlength conditions.

A fibre optics system for the evaluation of airway pressure in mechanically ventilated patients

OBJECTIVE

The present study was intended to evaluate the "in vivo" endotracheal (ET) tube resistance and respiratory mechanics in mechanically ventilated patients with respiratory failure by using fiber optic catheters.

DESIGN

Two fiber optic catheters, consisting of a thin probe with a pressure transducer on the tip, were used. The first was placed at the proximal side of the ET tube and the second was positioned distally beyond the end. A low compliant air-filled catheter connected to a traditional pressure transducer was placed close to the proximal fiber optic device to compare the pressure values obtained with both systems.

SETTING

The study was performed in the General Intensive Care Unit of Rome "La Sapienza", University Hospital.

PATIENTS AND PARTICIPANTS

Seven patients admitted for the management of acute respiratory failure of different etiologies were included in the protocol. All the patients were intubated and mechanically ventilated for at least 48 h prior to the investigation.

MEASUREMENTS AND RESULTS

The endotracheal tube resistance was obtained both by the end-inspiratory occlusion method and measuring pressure proximally and distally to the ET tube. The measurement of respiratory mechanics was obtained proximally and distally to the ET tube. Different flows and tidal volume changes were performed. The results showed that the fiber optic device gives an adequate evaluation of airway pressure and the possibility for an easy detection of obstructions and/or deformations of the ET tube. The area described by inspiratory and expiratory pressure recorded at both sides of the ET tube showed a positive relationship between the surface and flows while no surface changes were shown when the tidal volumes were modified. Thoraco-pulmonary compliance measured proximally and distally to the ET tube gave rise to a small and statistically insignificant difference.

CONCLUSION

This study confirms that 48 h after the positioning of ET tubes the airflow resistance is significantly higher than might be expected from the "in vitro" data. The presence of the endotracheal tube can interfere with the evaluation of thoraco-pulmonary mechanics, particularly in dynamic conditions. The fiber optic system represents an interesting and simple tool for the evaluation of ET tube resistance and pulmonary mechanics in patients undergoing mechanical ventilation.

Designing a hospital data network for the 21st century

There are many factors to consider when designing a data communications network for the medical center of the 21st century. User requirements are changing and expanding. New technologies for data handling are emerging. The most important factor is that you acquire the available expertise and develop a real-world plan for future data networks. This plan must serve as a guide to implementation of the network strategy. In this way, the hospital can be assured that its capital is being invested wisely.

The Fujinon diagnostic fiber optic hysteroscope. Experience with 1,503 patients

A soft and rigid diagnostic fiber optic hysteroscope (outer diameter, 3.7 mm) was developed. A total of 1,503 women underwent panoramic, televised fiber optic hysteroscopy without cervical dilation. No anesthesia, analgesia or tenaculum was required. No complication was encountered during or after the operation. The procedure is simple, easy and safe, with the operator in a relaxed and comfortable position even when the patient has acute flexion of the uterus. Our clinical results prove that the soft and rigid structure of the fiberscope offers advantages over rigid scopes or conventional fiberscopes with full-length soft, malleable parts.

A new "transducer-tipped" fiber optic catheter for measuring intramuscular pressures

Laboratory and clinical tests were used to determine the efficacy of a new fiber optic "transducer-tipped" catheter for measuring intramuscular pressures. When pressures ranging from 0 to 250 mm Hg were applied by a mercury manometer, the fiber optic system accurately recorded the pressures. In addition, the fiber optic system showed long-term stability by accurately recording the manometer pressure over a 3 day period. The Slit system showed a higher magnitude of hydrostatic pressure artifacts with catheter tip movement as compared to the fiber optic system. The two catheters showed no difference when measuring pressures in pig muscle at rest or when being compressed throughout a range of 0 to 250 mm Hg. In human volunteers, both catheters measured essentially equal pressures at rest, during venous stasis, and during a combination of venous stasis and compression. For long-term assessment, the Slit system required as many as three saline flushes, whereas the fiber optic system measured pressures continuously without manipulation. We conclude that the fiber optic system is as accurate as the Slit catheter for measuring tissue fluid pressures at rest. In addition, the fiber optic system offers distinct advantages over conventional fluid-filled systems for measuring intramuscular pressures due to a lack of hydrostatic pressure artifacts caused by limb position and to the lack of flushing for long-term measurements.