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At least 631 records · Page 35Linked to original sources
PubMed2005

Breath ammonia testing for diagnosis of hepatic encephalopathy.

Measurement of arterial ammonia has been used as a diagnostic test for hepatic encephalopathy, but obtaining an arterial specimen is an invasive procedure. The aim of this study was to evaluate the ability of a minimally invasive, highly sensitive optical sensing device to detect ammonia in the breath of patients with end-stage liver disease and to evaluate the correlation of breath ammonia levels, arterial ammonia levels, and psychometric testing. Fifteen subjects with liver cirrhosis and clinical evidence of hepatic encephalopathy underwent mini-mental status examination, number connection test, focused neurological examination, and arterial ammonia testing. On the same day, breath ammonia testing was performed using an apparatus that consists of a sensor (a thin membrane embedded with a pH-sensitive dye) attached to a fiberoptic apparatus that detects optical absorption. Helicobacter pylori testing was performed using the 14C urea breath test. A positive correlation was found between arterial ammonia level and time to complete the number connection test (r = 0.31, P = 0.03). However, a negative correlation was found between breath ammonia level and number connection testing (r = -0.55, P = 0.03). Furthermore, no correlation was found between breath and arterial ammonia levels (r = -0.005, P = 0.98). There is a significant correlation between the trailmaking test and arterial ammonia levels in patients with cirrhosis. However, no correlation was found between breath and arterial ammonia levels using the fiberoptic ammonia sensor apparatus in this small study.

Ammonia↗
PubMed1983

Comparison of two methods of marking the visual axis on the cornea during radial keratotomy.

We compared two methods of marking the visual axis on the cornea during radial keratotomy surgery in 34 eyes of patients participating in the National Eye Institute Prospective Evaluation of Radial Keratotomy. The locations of the corneal light reflections produced by an optical centering device and by the operating microscope filament were identical in 18 eyes, overlapped partially or touched in ten eyes, and were separate in the remaining six eyes. The two corneal marks in this last group were close enough to make little practical difference. The two methods can be used interchangeably in clinical practice.

Cornea↗
PubMed1990

[Extended application potential for Esser's speech-color image transformation in the phoniatrics clinic: initial report].

The SFT system developed by Esser is an electronic device primarily used for visualizing speech sounds in the therapy of severely hearing-impaired patients. This paper discusses first results in the diagnostic and therapeutic application of the SFT on persons with no hearing handicap. The range of application includes the articulation, its malfunctions, speech coordination and voice functions. Observations have shown that SFT representation supplementary to listener judgement permits a clear description of a series of features from the categories mentioned above. Phonetic disorders, speech coordination and certain voice functions can thus also be compared and documented directly. Its application as an optical feedback device in the course of articulatory and voice therapy as well as the adjustment of the SFT system to certain fields of application are discussed.

Articulation Disorders↗
PubMed1995

Visual performance effects and user acceptance of the M43A1 aviation protective mask frontserts.

BACKGROUND: The initial M43 aviation protective mask was fielded without provisions for optical corrective devices. Contact lenses, an interim solution, were not entirely acceptable since a small segment of the population could not be fitted adequately with contacts. This study evaluated visual performance affects and user acceptance of the M43A1 mask with frontsert correction modifications. METHODS: The investigation was divided into three phases: 1) a helicopter simulator evaluation designed to experimentally test the suitability of the M43A1 frontserts, both in single vision and bifocal forms, for use in the aviation environment; 2) a static cockpit evaluation, designed to identify aircraft-specific problems with the frontsert system; and 3) an inflight evaluation to examine the stability and usability of the frontserts under actual flight conditions. The subjects were 30 U.S. Army aviators (28 men and 2 women). RESULTS: Objective data from flight simulation evaluations suggested there were no significant differences between flight performance with and without the mask, despite refractive status. Subjective data from static and flight evaluations reflected positive user acceptance of the new mask and frontserts. Problems may exist in smaller cockpits (OH-58 A/C, D), but evidence suggested that this may have been an artifact resulting from testing the mask while wearing protective body armor. CONCLUSIONS: Within the range of flight conditions and profiles examined, the M43A1 frontsert system meets U.S. Army aviation needs for optical correction when mission requirements dictate flying with chemical-biological protective masks.

Adult↗
PubMed2004

Detection and staging of esophageal cancers.

PURPOSE OF REVIEW: Technology for detection and staging of esophageal cancer has made significant strides advances in the past 2 years. These advances have led to the enhanced selection of appropriate treatments for esophageal cancer. Cancers that are discovered at an early stage can be treated with endoscopic therapy, whereas advanced cancers are primarily treated with chemotherapy and radiation. RECENT FINDINGS: Detection of esophageal cancer can be enhanced by two major mechanisms: one is by enhancing the lesion, which has typically been done using vital dyes and the other is by changing the method of imaging of the lesion, which has been accomplished by the use of several technologies including fluorescence and optical coherence tomography. Neither of these techniques has been proven, but some investigators have been able to use them to enhance cancer detection. Similar technologies have been applied to staging esophageal cancer. The optical imaging devices also have the potential to stage mucosa-based malignancy. The use of positron emission tomography has been the most recent development that may have application for advanced cancer. Endoscopic ultrasonography has also been improved in resolution and ability to perform fine needle aspiration. The most significant development for staging early cancers is mucosal resection. Finally, by using mucosal resection techniques, the depth of tumor invasion can be established by histology, which allows gastroenterologists to treat early cancers with greater confidence regarding rates of metastatic disease. SUMMARY: Early detection of esophageal cancer can be enhanced by the use of vital dyes for mucosal staining, but the advancement of novel optical diagnostic strategies may be more suitable for clinical use. The primary advantage of these new staging methods is to clearly identify early stage cancer that potentially can be treated without traditional surgical resection techniques. More advanced cancers can be staged with positron emission tomography, but definitive studies demonstrating its role are still lacking.

Journal Article↗
PubMed2001

Real-time optical coherence tomography for minimally invasive imaging of prostate ablation.

OBJECTIVE: Numerous ablation techniques have been developed to alleviate urethral obstruction and improve urodynamics in benign prostatic hyperplasia. Most techniques, however, rely on visual observation of surface changes for ablation end points. The feasibility of using real-time optical coherence tomography (OCT) for minimally invasive imaging to guide and monitor prostate resection is demonstrated with representative techniques of laser and radiofrequency ablation. Empiric comparisons of ablation dynamics are made, and the use of OCT as a high-resolution, subsurface modality for image guidance is evaluated. MATERIALS AND METHODS: Optical coherence tomography is a high-resolution, high-speed near-infrared imaging technique analogous to ultrasound imaging, except that reflections of light are detected rather than sound. High-speed OCT is used to image the dynamic process of laser and radiofrequency ablation of in vitro human prostate tissue. OCT images of ablation sites are compared with corresponding histology. RESULTS: Based on comparisons between OCT images and corresponding histology, OCT imaged transurethral prostate tissue morphology, including urethral sinuses and submucosal glands. Real-time OCT imaging provided rapid feedback and control of ablation dynamics. The compact and portable OCT technology is amenable to minimally invasive beam-delivery devices. CONCLUSIONS: Optical coherence tomography offers a minimally invasive means of assessing transurethral prostate morphology. Real-time OCT has the potential to provide image guidance of prostate resection for many of the existing surgical treatments directed at alleviating urethral obstruction associated with benign prostatic hyperplasia.

Catheter Ablation↗
PubMed2003

Assessment of an in situ temporal calibration method for time-resolved optical tomography.

A 32-channel time-resolved optical imaging device is developed at University College London to produce functional images of the neonatal brain and the female breast. Reconstruction of images using time-resolved measurements of transmitted light requires careful calibration of the temporal characteristics of the measurement system. Since they can often vary over a period of time, it is desirable to evaluate these characteristics immediately after, or prior to, the acquisition of image data. A calibration technique is investigated that is based on the measurement of light back-reflected from the surface of the object being imaged. This is facilitated by coupling each detector channel with an individual source fiber. A Monte Carlo model is employed to investigate the influence of the optical properties of the object on the back-reflected signal. The results of simulations indicate that their influence may be small enough to be ignored in some cases, or could be largely accounted for by a small adjustment to the calibrated data. The effectiveness of the method is briefly demonstrated by imaging a solid object with tissue-equivalent optical properties.

Brain↗
PubMed2001

Narrow-band microcavity waveguides in photonic crystals.

A novel device, formed by a widely spaced periodic array of defects in a photonic bandgap crystal, is studied with the goal of designing a waveguide with a prescribed narrow bandwidth. Tunneling of radiation between the defect sites allows wave propagation along the line of the defects. An analytical study based on the weakly coupled cavity model is performed, and the dispersion relation omega(beta) of the new waveguide is derived. The frequency shift and the band structure of the periodic defect waveguide are linked by an analytic relationship to the distance between the defect sites and therefore can be tuned by varying the latter. Sections of such waveguides can be employed as ultra-narrow-band filters in optical routing devices. Numerical simulations demonstrate the performances of this new device and support the analytical predictions.

Journal Article↗
PubMed2006

Developing nucleic acid-based electrical detection systems.

Development of nucleic acid-based detection systems is the main focus of many research groups and high technology companies. The enormous work done in this field is particularly due to the broad versatility and variety of these sensing devices. From optical to electrical systems, from label-dependent to label-free approaches, from single to multi-analyte and array formats, this wide range of possibilities makes the research field very diversified and competitive. New challenges and requirements for an ideal detector suitable for nucleic acid analysis include high sensitivity and high specificity protocol that can be completed in a relatively short time offering at the same time low detection limit. Moreover, systems that can be miniaturized and automated present a significant advantage over conventional technology, especially if detection is needed in the field. Electrical system technology for nucleic acid-based detection is an enabling mode for making miniaturized to micro- and nanometer scale bio-monitoring devices via the fusion of modern micro- and nanofabrication technology and molecular biotechnology. The electrical biosensors that rely on the conversion of the Watson-Crick base-pair recognition event into a useful electrical signal are advancing rapidly, and recently are receiving much attention as a valuable tool for microbial pathogen detection. Pathogens may pose a serious threat to humans, animal and plants, thus their detection and analysis is a significant element of public health. Although different conventional methods for detection of pathogenic microorganisms and their toxins exist and are currently being applied, improvements of molecular-based detection methodologies have changed these traditional detection techniques and introduced a new era of rapid, miniaturized and automated electrical chip detection technologies into pathogen identification sector. In this review some developments and current directions in nucleic acid-based electrical detection are discussed.

Journal Article↗
PubMed2003

Sounds and silence: an optical topography study of language recognition at birth.

Does the neonate's brain have left hemisphere (LH) dominance for speech? Twelve full-term neonates participated in an optical topography study designed to assess whether the neonate brain responds specifically to linguistic stimuli. Participants were tested with normal infant-directed speech, with the same utterances played in reverse and without auditory stimulation. We used a 24-channel optical topography device to assess changes in the concentration of total hemoglobin in response to auditory stimulation in 12 areas of the right hemisphere and 12 areas of the LH. We found that LH temporal areas showed significantly more activation when infants were exposed to normal speech than to backward speech or silence. We conclude that neonates are born with an LH superiority to process specific properties of speech.

Humans↗
PubMed2000

AC coupled three op-amp biopotential amplifier with active DC suppression.

A three op-amps instrumentation amplifier (I.A) with active dc suppression is presented. dc suppression is achieved by means of a controlled floating source at the input stage, to compensate electrode and op-amps offset voltages. This isolated floating source is built around an optical-isolated device using a general-purpose optocoupler, working as a photovoltaic generator. The proposed circuit has many interesting characteristics regarding simplicity and cost, while preserving common mode rejection ratio (CMRR) and high input impedance characteristics of the classic three op-amps I.A. As an example, a biopotential amplifier with a gain of 80 dB, a lower cutoff frequency of 0.1 Hz, and a dc input range of +/- 8 mV was built and tested. Using general-purpose op-amps, a CMRR of 105 was achieved without trimmings.

Action Potentials↗
PubMed1996

Computer assisted brain surgery for small lesions in the central sensorimotor region.

The capacity of a new optical navigation device is demonstrated by six microsurgical procedures for small subcortical lesions within the central sensorimotor strip. This small series is aimed at less invasive resection in this functionally critical region, independently of primary diagnosis and outcome. Guided by high resolution CT imaging data five brain tumours and one cavernous angioma was selectively located and most sparingly removed without additional sensorimotor deficit. In two cases improvement of a pre-operative paresis was observed immediately after surgery. Thanks to light-weight freehand pointing instruments and a ranging accuracy of +/- 1 mm, damage to functionally important brain areas and vessels was avoided by using uncommonly oblique, e.g., transsulcal ways of access which would hardly have been possible even with guidance by conventional stereotaxy. The demanding systematic cortical stimulation of the precentral gyrus applied in three cases was only sensitive in infiltrating tumours-e.g., low grade astrocytomas-where for want of adjuvant therapy it was essential to proceed to the extreme limits of resection. In general, precise anatomical localisation by computer aided surgery (CAS) is sufficient in small central lesions which guarantees minimally invasive surgery. The potential of this new, soon commercially available optical navigation system in (neuro) surgery, quality control and teaching is discussed.

Adult↗
PubMedDate not supplied

In vivo optical coherence tomography of the nasal mucosa.

BACKGROUND: Optical coherence tomography (OCT) is an emerging imaging modality that uses light to produce in vivo high-resolution cross-sectional images (7 microm) of tissues to depths of up to 3 mm. OCT is analogous to ultrasound, but relies on interferometry and low-coherence optical sources to produce images of tissue structure at the histological level. METHODS: In this study, OCT was used to image the mucosa overlying structures in the nasal cavity to obtain information regarding normative in vivo tissue microstructure. An OCT system using a Michaelson interferometer and a 1.3-microm broadband light source was incorporated into a fiber-optic imaging device that was inserted into the nasal cavity. Cross-sectional tomographic images of the anterior and posterior nasal septum, turbinates, and vestibule were acquired in 44 patients in either the office or the operating room during surgical endoscopy. RESULTS: OCT images of the nasal mucosa identified the distinct boundaries between the epithelium, lamina propria, and underlying bone/cartilaginous tissue. Within the lamina propria, features consistent with glands, ducts, and blood vessels were clearly identified. In patients who underwent decongestant therapy, before and after images showed distinct morphological changes in the mucosa. The thickness of the epithelium was tabulated, as well. CONCLUSION: This study establishes the potential of using OCT to produce high-resolution images of the nasal mucosa. As an in vivo tissue microstructural imaging modality, OCT may be valuable in studying the impact of allergic and infectious disease on the nasal mucosa and monitoring its response to pharmacologic therapy.

Adolescent↗
PubMed2006

Intercalated smectic a phases in banana-shaped liquid crystals with carbonate end groups.

Novel, symmetrical, bent-core mesogens, namely substituted 1,3-phenylenebis{4'-[(ethoxycarbonyl)oxy]-1,1'-biphenyl}-4-carboxylates, are prepared with carbonate groups at both ends of the molecules. The mesophase properties are investigated for different electron-donating and -withdrawing substituents connected to the central ring at different positions. These compounds exhibit nematic and/or smectic A intercalated (SmA(int)) mesophases. Electro-optical studies show a very significant electric-field-induced biaxiality that is fast (<1 ms) and large (0.03) associated with a high birefringence (0.33 at 500 nm, 10 V mum(-1) field) for the unsubstituted analogue. For one substance this effect is observable from above 100 degrees C down to room temperature. Such electric-field-induced biaxiality may find practical applications in fast electro-optic modulation devices.

Journal Article↗
PubMed1998

Clinical evaluation of the Codman microsensor intracranial pressure monitoring system.

INTRODUCTION: The use of the Camino fibre-optic subdural device for measuring Intracranial Pressure (ICP) in patients, has been shown to correlate well with recordings from the "gold standard" intraventricular fluid filled catheter [1]. Following this work, its use has become standard in the clinical monitoring of patients. More recently, laboratory studies have demonstrated accuracy, acceptable drift and high fidelity for the new Codman Microsensor ICP Transducer, a miniature strain gauge mounted on a flexible nylon catheter [3]. Its performance in patients, however, has yet to be fully assessed, in comparative studies. METHODS: Eight patients (5 head injured, 3 with an Intracerebral haematoma) had a Codman Microsensor inserted. A Camino Transducer was fitted immediately adjacent to it. A computerised system was used to continuously record both ICP readings. RESULTS: In total 140,323 recordings were made over a wide range of ICP values. Study periods ranged from 0.5 to 116 hours. In one patient the Codman transducer tracing failed after several days, probably due to fracture of electrical cable close to the interface box. The readings from the two ICP transducers were compared on Time Series, logistic regression and Altman-Bland plots. Drift of the ICP recorded by the Codman microsensor, was noted in 2 patients, 1 in positive direction (maximum 30 mmHg), 1 negative (max. 20 mmHg). In both cases the Camino ICP recording was relatively stable. In 24% of the recordings the Codman microsensor recorded ICP as 5 or more mmHg greater than the Camino, this difference was 10 mmHg or greater in 9% of recordings. Conversely the Camino recording was 5 mmHg or more, than the Codman, in 5% of all recordings, and 10 mmHg or more in 3%. CONCLUSION: These differences could in the majority of cases (excepting the negative drift) be explained by a constant offset of the Codman transducer, as described previously [6]. Further examination of this device is required.

Brain Injuries↗
PubMed1991

Biomagnetically localizable multipurpose catheter and method for MCG guided intracardiac electrophysiology, biopsy and ablation of cardiac arrhythmias.

A multipurpose catheter, specially designed to be biomagnetically localizable and the method for magnetocardiographic (MCG) guided intracardiac electrophysiological recordings, endomyocardial biopsy and ablation of cardiac arrhythmias are described. The catheter features two non-polarizable non-ferrous magnetic electrodes, arranged in such a way that, connected to an external current generator, an electromagnetic field of dipolar configuration can be generated in the heart. The connection is done with twisted pairs of non-ferrous magnetic conductors, to avoid the occurrence of spurious magnetic fields along the catheter during current injection to the electrodes. With this assembly the tip of the catheter can be localized (and driven close to an arrhythmogenic area) by MCG mapping. The same electrodes are feasible for monophasic action potential (MAP) recordings. One or more lumen allow fluid infusion, blood sampling, pressure measurements and introduction of steerable wires, pacing or ablation electrodes, bioptic devices, or optic fibers. On the basis of preoperative MCG three-dimensional localization of the arrhythmogenic substrate, the biomagnetically localizable catheter is driven, under fluoroscopic control, as close as possible to the suspected arrhythmogenic zone. MCG mapping is then performed under pacing, with adjustments of the catheter's tip, until the electrically induced magnetic field and catheter's localization parameters fit those generated by the spontaneous arrhythmia. MAP is recorded. The catheter position is accepted for ablation when electrophysiological abnormalities are identified in the MCG localized area.

Action Potentials↗