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At least 667 records · Page 37Linked to original sources
PubMed1995

Noninvasive cerebral optical spectroscopy: depth-resolved measurements of cerebral haemodynamics using indocyanine green.

To investigate the feasibility of a newly developed, near-infrared optical spectroscopy device, we analysed measurements of the infrared tracer indocyanine green (ICG) using sensors with a single near infrared light source and multiple light detectors. Two ml of ICG dye, 1.0 mg ml-1 in concentration, were injected into the internal carotid artery during cerebral angiography in 14 adult patients. The resultant washout curves were measured bilaterally using sensors with 4 detectors spaced at 10, 20, 30 and 40 mm from the infrared light source on the right side, and 15, 25, 35 and 45 mm from the source for the left side, respectively. Washout curves were analysed to determine the relative amplitude of the ICG absorption signal and deduce each detector's penetration distance. When ICG was injected into the internal carotid artery, relative absorption increased with detector distance from the light source. No substantial difference in attenuation was observed in any of the detectors during external carotid injection of ICG. The resultant information related depth of penetration of the light with source-detector separation distances. The feasibility of the system for measuring cerebral oxygen saturation and haemodynamics noninvasively or monitoring at bedside is discussed.

Adult↗
PubMed1990

Initial results of phase I/II interstitial thermoradiotherapy for primary advanced and local recurrent tumors.

Since January 1986 in a phase I/II study, 45 lesions (30 head and neck, 11 pelvic, and 4 other lesions) in 44 patients (24 men, 20 women; age 18-81 years) received a combination of interstitial Ir-192 radiotherapy (IRT) and interstitial 915 MHz MW hyperthermia (IHT) supplemented by external radiation (ERT). In June 1989, evaluation was performed for lesions with minimum follow-up (FU) of 6 months and FU periods between 6 and 39 months (mean: 16 months, SD +/- 9). The tumors comprised 21 advanced primary (AP) lesions without prior ERT, 18 local recurrent (LR) and 6 local metastatic (LM) lesions with variable prior treatment modes; 24 lesions had received prior ERT between 40 and 70 Gy, 23 chemotherapy and 30 prior surgery. The mean dimensions of 42 lesions were 4.5 X 4.0 X 3.0 (cm3) with tumor volumes ranging from 12 to 135 cm3 (mean: 54 cm3, SD +/- 35); 3 lesions had extensive tumor volumes greater than 225 cm3. IHT was applied immediately prior to and/or after low-dose Ir-192 IRT (20-30 Gy) for 60 min at temperatures between 41 and 44 degrees C. ERT (40-50 Gy) was always given for AP and LM lesions, but variably applied for previously irradiated LR lesions, thereby avoiding the cumulative radiation dose exceeding 110 Gy per site. IRT doses ranged from 17-48 Gy (mean: 26.8 Gy, SD +/- 8) at a dose rate of 25-70 cGy/h (mean: 42 cGy/h, SD +/- 12). Thirty-three lesions received additional ERT of 30-56 Gy (mean: 46.5 Gy, SD +/- 9). Total radiation dose (IRT + ERT dose) ranged from 31 to 82 Gy (mean: 61 Gy, SD +/- 18). The hyperthermia systems of Lund/Buchler 4010 and Clini-Therm Mark VI/IX with thermistor or fiber-optic thermometry devices were employed. Initial response at 3 months FU showed 31 (69%) lesions complete response (CR), 10 (22%) partial response (PR), and 4 (9%) no change (NC). Long-term response of 30 lesions at 12 months FU revealed a total of 27 (90%) with local control (LC) and 3 (10%) in-field recurrences. Six patients died prior to 12 months FU, three with LC and three with progressive disease. So far 10 (22%) patients have developed distant metastases. Acute side-effects occurred in 15 lesions (33%) resulting in 12 (27%) long-term complications with 3 lesions (7%) requiring surgery.(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗
PubMed2004

Enhancement of stability following anterior cervical corpectomy: a biomechanical study.

STUDY DESIGN: An in vitro biomechanical study of various reconstructive techniques following decompression of the spondylotic cervical spine. OBJECTIVE.: To evaluate the biomechanical stability of anterior cervical plate fixation following three strategies of decompression for multilevel cervical spondylosis (three levels) of the cervical spine: three level discectomy, single corpectomy and discectomy, and a two-level corpectomy. SUMMARY OF BACKGROUND DATA: The main goals of surgical treatment for cervical myelopathy include adequate decompression and stabilization while maintaining or restoring cervical lordosis. Cervical decompression is often performed through a corpectomy followed by strut-graft reconstruction. An anterior cervical plate with end-fixation (two points of fixation) is then used to span the construct. The authors propose an alternative to multilevel corpectomy and long-segment end construct plate fixation. Often times, the cervical stenosis is confined to the area of the degenerative discs. As a result, the authors feel that either multilevel discectomy or a corpectomy combined with discectomy followed by segmental plate fixation may provide adequate decompression with increased biomechanical rigidity as compared to cervical plate-constructs with end-fixation only. METHODS: Seven human cadaveric fresh-frozen cervical spines from C1-T1 were utilized. Three-dimensional motion analysis with an optical tracking device was used to determine motion following various reconstruction methods. All seven cervical spines underwent testing in a randomized order. The end construct model consisted of a corpectomy at C4 and C5 with a polymethyl methacrylate strut graft and an anterior cervical PEAK (DePuy-AcroMed) plate. The two segmental constructs also utilized the PEAK plate with one construct undergoing discectomies at C3-C4, C4-C5, and C5-C6 with polymethyl methacrylate interbody grafts and the other segmental construct undergoing a discectomy at C3-C4 and a corpectomy of C5. All specimens underwent a pure moment application of 2 Nm with regards to flexion-extension, lateral bending, and axial rotation. RESULTS.: The three-level discectomy and combined one-level discectomy and corpectomy with segmental fixation was significantly more rigid in flexion-extension and lateral bending than the two-level corpectomy with end-construct plate fixation (P < 0.05). There was no increase in stability during extension between the end construct (two-level corpectomy) reconstruction model and the un-instrumented corpectomy and grafted specimen. No difference was noted between the segmental constructs and the end-construct with regards to axial rotation. CONCLUSIONS: Cervical myelopathy is traditionally treated with a multilevel corpectomy and an end-construct plate fixation spanning the strut graft. A large moment arm is generated at the ends of the construct, potentially leading to plate migration or dislodgment. Often times, adequate decompression can be achieved with either a multilevel discectomy or a combined discectomy and corpectomy with segmental plate fixation. This study clearly demonstrates that segmental plate fixation affords a more biomechanically rigid method of reconstruction with regards to flexion-extension and lateral bending than end-construct plate fixation. The increased rigidity afforded by segmental fixation may significantly decrease the likelihood of plate dislodgement in the setting of anterior instrumentation alone following anterior alone, long segment reconstruction procedures.

Biomechanical Phenomena↗
PubMedDate not supplied

Effects of hemoglobin glutamer-250 (bovine) (HBOC-201, Hemopure) on coagulation testing.

Polymerized bovine hemoglobin is currently under investigation as an alternative to blood-banked human red blood cells. Because of the dark red hemolyzed appearance of hemoglobin-based oxygen carrier (HBOC)-201, we sought to describe the effects of HBOC-201 on coagulation analyzers that perform prothrombin times, activated partial thromboplastin times, fibrinogen, and antithrombin. Pooled normal plasma was combined with HBOC-201 to achieve plasma hemoglobin levels of 1.4, 2.6, 3.8, 4.8, and 6.2 g/dL. Results for each test using HBOC-201-prepared plasma were compared with results using saline-matched controls. Two consecutive absolute result differences of >10% between saline controls and HBOC-201 samples were used for determining interference in test accuracy by the concentration of HBOC-201. Mechanical detection methods (fibrometer, STA, CS-190) and the MDA-180 method were less affected by increasing levels of HBOC-201 than optical detection devices for all test parameters.

Antithrombins↗
PubMed1999

Nonlinearity of Pancharatnam's geometric phase in polarizing interferometers.

Earlier investigations show a time-variable nonlinear shift of the fringe pattern in a polarizing interferometer while rotating a polarizer at the exit. This effect was identified as Pancharatnam's geometrical phase and proposed for applications in interferometry and fast optical switching devices. A heterodyne analysis attributes moving fringes to a frequency difference between the interfering beams; thus changing fringe velocities point to a dynamic frequency development within the period of the uniformly rotating analyzer. This explanation offends the intuition and we undertake an experimental and theoretical investigation of the effect to solve the paradox. We determine, e.g., the complete frequency and mode spectrum of an arbitrary state of polarization P0 behind a rotating linear analyzer and behind a rotating arbitrary linear birefringent plate. We find that, in spite of a fast changing phase in the interferometer, no other (higher) frequency components appear in the spectral distribution of the intensity at the exit than the double of the rotary frequency of the analyzer: phase nonlinearities are compensated for by intensity changes. Only a phase-sensitive detector like an array of photodetectors is able to observe the nonlinearity of Pancharatnam's geometrical phase. A single detector only finds a sinusoidal intensity variation. Our insight into these relations leads us to two new applications of Pancharatnam's phase: supersensitivity of a polarizing double beam interferometer with a video camera acting as a phase detector and external tuning of a Fizeau interferometer.

Journal Article↗
PubMed2002

Quantum chaos in optical systems: the annular billiard.

We study the dielectric annular billiard as a quantum chaotic model of a micro-optical resonator. It differs from conventional billiards with hard-wall boundary conditions in that it is partially open and composed of two dielectric media with different refractive indices. The interplay of reflection and transmission at the different interfaces gives rise to rich dynamics of classical light rays and to a variety of wave phenomena. We study the ray propagation in terms of Poincaré surfaces of section and complement it with full numerical solutions of the corresponding wave equations. We introduce and develop an S-matrix approach to open optical cavities which proves very suitable for the identification of resonances of intermediate width that will be most important in future applications like optical communication devices. We show that the Husimi representation is a useful tool in characterizing resonances and establish the ray-wave correspondence in real and phase space. While the simple ray picture provides a good qualitative description of certain system classes, only the wave description reveals the quantitative details.

Journal Article↗
PubMed2004

Glass forming banana-shaped compounds: vitrified liquid crystal states.

The synthesis and physical properties, in particular electro-optic switching behavior, of 3-chloro-biphenyl-3',4-bis[4-[4-(3,7-dimethyloctyloxy)-phenyliminomethyl]] benzoate are reported. The compound exhibits an antiferroelectric tilted smectic liquid crystalline phase (Sm-CP) in a broad temperature range. Below 20 degrees C the sample goes over to a glassy state and no crystallization appears down to -50 degrees C. It is observed that below the glass transition temperature both achiral and chiral structures of the Sm-CP phase can be frozen. Each of them can have three polarization states (two ferroelectric and one antiferroelectric), thus giving six different vitrified textures. This enables atomic force microscopy studies of the different liquid crystalline states and suggests possibilities for electro-optical storage devices.

Journal Article↗
PubMed2001

Near-field scanner for moving molecules.

We have fabricated using electron beam nanolithography a fixed slit near-field optical scanning device which uses near-field fluorimetry to achieve 200 nm spatial resolution of objects moving over the slits. We explore the basic physics of operating narrow slits in the waveguide cutoff mode and present data from the passage of extended double-stranded DNA molecules passing over the slits as a first example of how this device can be used to do ultrahigh spatial resolution mapping of long polymers.

Algorithms↗
PubMed2001

Chaos synchronization and spontaneous symmetry-breaking in symmetrically delay-coupled semiconductor lasers.

We present experimental and numerical investigations of the dynamics of two device-identical, optically coupled semiconductor lasers exhibiting a delay in the coupling. Our results give evidence for subnanosecond coupling-induced synchronized chaotic dynamics in conjunction with a spontaneous symmetry-breaking: we find a well-defined time lag between the dynamics of the two lasers, and an asymmetric physical role of the subsystems. We demonstrate that the leading laser synchronizes its lagging counterpart, whereas the synchronized lagging laser drives the coupling-induced instabilities.

Journal Article↗
PubMed2003

Many-body and correlation effects on parametric polariton amplification in semiconductor microcavities.

The complexity induced by the Coulomb interaction between electrons determines the noninstantaneous character of exciton-exciton collisions. We show that the exciton-photon coupling in semiconductor microcavities is able to alter the exciton dynamics during collisions strongly affecting the effective scattering rates. Our analysis clarifies the origin of the great enhancement of parametric gain observed when increasing the polariton splitting. It also demonstrates that exciton-exciton collisions in semiconductors can be controlled and engineered to produce almost decoherence-free collisions for the realization of all-optical microscopic devices.

Journal Article↗
PubMed2003

Phase control of collective quantum dynamics.

The manipulation of the steady-state behavior of a collection of dipole-interacting three-level atoms in a V or Lambda configuration is investigated as a function of the relative phase of two strong coherent driving fields. For larger samples, the phase is shown to be a convenient parameter to rapidly populate or depopulate completely a trapping state of the ensemble. As applications, we present the appropriately prepared atomic sample as an optical switching device and show its virtues in controlling the collective steady-state resonance fluorescence intensity.

Journal Article↗
PubMed1983

Ethylene-induced lateral expansion in etiolated pea stems : kinetics, cell wall synthesis, and osmotic potential.

Treatment of etiolated pea (Pisum sativum L.) internode tissue with ethylene gas inhibits elongation and induces lateral expansion. Precise kinetics of the induction of this altered mode of growth of excised internode segments were recorded using a double laser optical monitoring device. Inhibition of elongation and promotion of lateral expansion began after about 1 hour of treatment and achieved a maximum by 3 hours. Similar induction kinetics were observed after treating internodes with colchicine and 2,6-dichlorobenzonitrile, an inhibitor of cellulose synthesis. In sealed flask experiments, ethylene had no detectable effect on incorporation of label from [(14)C]glucose into any of the classical pectin, hemicellulose, or cellulose wall fractions. Ethylene inhibited fresh weight increase (total cell expansion) of both excised internode segments (in sealed flasks) and intact seedlings. Ethylene treatment resulted in an increase in cell sap osmolality in those tissues (intact and excised) which are inhibited by the gas. A model for ethylene-induced inhibition of elongation and induction of lateral expansion is presented.

Journal Article↗
PubMed1998

Autoimmunity to myelin oligodendrocyte glycoprotein in rats mimics the spectrum of multiple sclerosis pathology.

Multiple sclerosis is a chronic inflammatory disease characterized by perivenous inflammation and focal destruction of myelin. Many attempts have been undertaken previously to create animal models of chronic inflammatory demyelinating diseases through autoimmunity or virus infection. Recently, however, a new model of myelin oligodendrocyte glycoprotein (MOG) induced autoimmune encephalomyelitis became available, which, in a very standardized and predictable way, leads to chronic (relapsing or progressive) disease and widespread CNS demyelination. In the present study we actively induced MOG-experimental autoimmune encephalomyelitis (EAE) in different inbred rat strains using different immunization protocols. The pathology found in our models closely reflects the spectrum of multiple sclerosis (MS) pathology: Classical MS as well as variants such as optic neuritis, Devic's disease and Marburg's type of acute MS are mimicked in rats immunized with MOG antigen. Furthermore we demonstrate, that by using the proper strain/sensitization regime, subforms of MS such as for instance neuromyelitis optica can be reproducibly induced. Our study further supports the notion, that incidence and expression of the disease in this model, alike the situation in multiple sclerosis, is determined by genetic and environmental factors.

Animals↗