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Objective We assessed whether intraoperative squash cytology could provide surgeons with a qualitative diagnosis of brain lesions when frozen section diagnosis is equivocal. Methods The study included 51 lesions that were diagnosed intraoperatively as equivocal brain tumour on the basis of frozen section. We retrospectively classified the lesions into five groups according to the final histopathological diagnoses (I: malignant lymphomas; II: diffuse astrocytic and oligodendroglia tumours; III: pituitary adenomas, IV: metastatic carcinomas; V: others). We assessed the squash cytology features of Groups I-IV and of the specific lesion types, and compared features among the groups. Results The four groups differed in a range of salient cytomorphological features: lymphoglandular bodies in Group I (eight of nine cases), cytoplasmic fibrillary processes in Group II (six of eight cases), low-grade nuclear atypia in Group III (seven of seven cases), and large nuclei (approximately 80 μm2 ) and nuclear crush artefacts in Group IV (seven of nine cases). Conclusion Findings of lymphoglandular bodies on intraoperative squash cytology can be considered characteristic of malignant lymphomas, while cytoplasmic fibrillary processes indicate diffuse astrocytic and oligodendroglial tumours. We conclude that squash cytology could yield a qualitative intraoperative diagnosis in over 25% of cases for which frozen section yields a diagnosis of equivocal brain tumour.

Background: This study investigated hyperintense vessel signs (HVS) on fluid-attenuated inversion recovery imaging in the P1–2 portions of posterior cerebral arteries (PCAs) as a “hyperintense PCA sign” and HVS of cortical arteries. We retrospectively examined whether these signs would be useful in diagnosing reversible cerebral vasoconstriction syndrome (RCVS) in the acute phase. Methods: Eighty patients with RCVS who underwent initial magnetic resonance imaging (MRI) within 7 days of onset were included in this study. HVS and related clinical factors were examined. Results: On initial MRI of RCVS patients, hyperintense PCA sign and HVS of cortical arteries were seen in 21 cases (26%) and 38 cases (48%), respectively. In patients showing hyperintense PCA sign, vasoconstriction of the A2–3 portion was a significant clinical factor. Conversely, vasoconstriction of the M1 and P1 portions and the presence of white matter hyperintensity on initial and chronic-stage MRI were significantly associated with the presence of HVS in cortical arteries. Conclusion: Because rich collateral flow exists around PCAs, the frequency of hyperintense PCA sign is not high. However, hyperintense PCA sign findings in patients with suspected RCVS offer credible evidence of extreme flow decreases due to vasoconstriction in peripheral PCAs and other arteries associated with the collateral circulation of PCAs. Conversely, HVS in cortical arteries tend to reflect slow antegrade circulation due to vasoconstriction of peripheral vessel and major trunks. Both signs appear useful for auxiliary diagnosis of acute-phase RCVS.

It is known that the cerebrospinal fluid (CSF) pulsation flow sign in the lateral ventricles directly above the foramen of Monro (CPF-M) on axial fluid attenuated inversion recovery (FLAIR) is a normal physiological finding as an artifact of FLAIR. In this study, whether CPF-M can be used as a neuroradiological finding related to pathological conditions in patients with acute aneurysmal subarachnoid hemorrhage (aSAH) was investigated. CPF-M-related clinical features were retrospectively evaluated in 147 aSAH patients who underwent adequate serial MRI examinations without massive intraventricular hemorrhage (IVH) of the lateral ventricle within 48 h of ictus. The frequency of the CPF-M in the control group was 32% (57/178), 33% (40/123), and 38% (45/117) for the normal control, chronic cerebral infarction, and deep white matter lesion (WML) groups, respectively. In aSAH patients, the overall prevalence of the CPF-M was 57% (84/147), significantly higher than in the three control groups. Multivariate analysis showed that age

Introduction We previously reported centripetal propagation of vasoconstriction at the time of thunderclap headache remission in patients with reversible cerebral vasoconstriction syndrome. Here we examine the clinical significance of centripetal propagation of vasoconstriction. Methods Participants comprised 48 patients who underwent magnetic resonance angiography within 72 h of reversible cerebral vasoconstriction syndrome onset and within 48 h of thunderclap headache remission. Results In 24 of the 48 patients (50%), centripetal propagation of vasoconstriction occurred on magnetic resonance angiography at the time of thunderclap headache remission. The interval from first to last thunderclap headache in patients with centripetal propagation of vasoconstriction (14 ± 10 days) was significantly longer than that of patients without centripetal propagation of vasoconstriction (4 ± 2 days). In the patients with centripetal propagation of vasoconstriction at the time of thunderclap headache remission, the incidence of another cerebral lesion (38%, 9 of 24 cases) was significantly higher than in patients without centripetal propagation of vasoconstriction (0%). From findings of sequential magnetic resonance angiography before and after thunderclap headache remission, we observed tendencies in which centripetal propagation of vasoconstriction gradually progressed after the onset of reversible cerebral vasoconstriction syndrome and peaked at the time of thunderclap headache remission. The progress of centripetal propagation of vasoconstriction concluded with thunderclap headache remission. Conclusions Centripetal propagation of vasoconstriction has clinical significance as an indicator of the severity of reversible cerebral vasoconstriction syndrome. The presence of centripetal propagation of vasoconstriction is associated with an increased risk of brain lesions and a longer interval from first to last thunderclap headache. Moreover, repeat magnetic resonance angiography to assess centripetal propagation of vasoconstriction during the time from onset to thunderclap headache remission can help diagnose reversible cerebral vasoconstriction syndrome.

Objective: The aim of this study was to determine whether intraoperative cytological evaluation of squash preparations is of benefit for differentiating high-grade from low-grade astrocytomas. Methods: Squash preparations of 42 astrocytomas were classified histologically according to the World Health Organization (WHO) 2007 classification system as grade II (n = 12), grade III (n = 11), and grade IV (n = 19) and were divided into 2 groups, namely a low-grade group (grade II) and a high-grade group (grades III and IV). The focus was on morphological cell and vessel characteristics, namely nuclear atypia, chromatin pattern, nuclear enlargement, variation in nuclear size, the presence of nucleoli, mitosis, tumor necrosis, cell density, multibranched vessels, and vascular dilatation, and these characteristics were compared between the low- and high-grade groups. Results: Nuclear atypia, the presence of coarse chromatin, variations in nuclear size, and cell density ≥200 per high-power field were significantly more prevalent in high- than in low-grade astrocytomas (p = 0.0407, p < 0.01, p < 0.01, and p < 0.01, respectively). Vessels with > 3 branches and a mean vessel diameter ≥20 μm were more prevalent in high- than in low-grade astrocytomas (p < 0.01). Conclusion: Squash preparation cytology provides added benefit for the intraoperative identification of high-grade astrocytoma.

An 89-year-old male presented with cerebrospinal fluid (CSF) rhinorrhea associated with head trauma sustained as a pedestrian in a traffic accident. Computed tomography (CT) showed pneumocephalus and multiple cranial bone fractures, including the clivus. Although the CSF rhinorrhea was treated conservatively for a week, clinical symptoms did not improve and surgical repair was performed. Preoperative thin-sliced bone CT and steady-state magnetic resonance images revealed a bone defect at the middle clivus and a collection of CSF fluid from the clival fistula in the sphenoid sinus. Endoscopic endonasal reconstruction was performed, and the 3-mm diameter dural tear and bone defect at the middle clivus were well visualized. The fistula was repaired using a pedicled nasoseptal mucosal flap. The CSF rhinorrhea completely disappeared as a result of the endoscopic endonasal surgery. The present report describes a rare case of CSF rhinorrhea caused by a traumatic clival fracture and surgical management by endoscopic endonasal surgery.

BACKGROUND AND PURPOSE: In major SAH, the only method to diagnose a preceding minor leak is to ascertain the presence of a warning headache by interview; however, poor clinical condition and recall bias can cause inaccuracy. We devised a neuroradiologic method to diagnose previous minor leak in patients with SAH and attempted to determine whether warning (sentinel) headaches were associated with minor leaks before major SAH. MATERIALS AND METHODS: We retrospectively evaluated 127 patients who were admitted with SAH within 48 hours of ictus. Previous minor leak before major SAH was defined as T1WI-detected clearly bright hyperintense subarachnoid blood accompanied by SAH blood on FLAIR images that was distributed over a larger area than bright hyperintense subarachnoid blood on T1WI (T1-FLAIR mismatch). RESULTS: The incidence of warning headache before SAH was 11.0% (14 of 127 patients, determined by interview). The incidence of T1-FLAIR mismatch (neuroradiologic diagnosis of minor leak before major SAH) was 33.9% (43 of 127 patients). Of the 14 patients with warning headache, 13 had a minor leak diagnosed by T1-FLAIR mismatch at the time of admission. Variables identified by multivariate analysis as significantly associated with minor leak diagnosed by T1-FLAIR mismatch included 80 years of age or older, rebleeding after admission, intracerebral hemorrhage on CT, and mRS scores of 3–6. CONCLUSIONS: We conclude that warning headaches diagnosed by interview are not a product of recall bias but are the result of actual leaks from aneurysms.

Microvascular decompression (MVD) of hemifacial spasm (HFS) associated with the vertebral artery (VA) shows higher rates of incomplete cure and complications compared to non-VA-related HFS. Purely endoscopic MVD for VA-associated HFS via a retrosigmoid keyhole was performed. Neurovascular conflicts by a directly offending artery and VA around the root exit zone of the facial nerve were clearly demonstrated under 30° endoscopic view without significant cerebellar retraction. The VA and directly offending artery were safely transposed with preservation of perforators under excellent view. Endoscopic MVD offers reliable decompression for VA-associated HFS with minimal invasiveness.

Background Skull base reconstruction is an essential technique for repairing cerebrospinal fluid (CSF) leakage. A reliable method for middle cranial fossa (MCF) reconstruction with minimal invasiveness has not been reported. An initial case of endoscopic MCF reconstruction with a subtemporal keyhole is described. Case Description A 57-year-old man developed severe meningitis and was diagnosed with spontaneous CSF leakage from bone defects on the tegmen tympani. Endoscopic MCF reconstruction with a subtemporal keyhole was carried out. Three skin incisions, including 1 subtemporal incision for a subtemporal keyhole and 2 temporal line incisions on the superior temporal line, were made, and a 0-degree endoscope was introduced into the subcutaneous space. The deep temporal fascia (DTF) was bluntly dissected and separated from the superficial temporal fascia and the temporal muscle, and the DTF was incised to shape a pedicled flap under endoscopic view. Blood supply to the pedicled DTF flap was confirmed with indocyanine green angiography. A subtemporal keyhole was then made, and a 30-degree endoscope was used to explore the extradural space of the MCF floor, visualizing the bone defects on the tegmen tympani. The vascularized DTF flap passed easily through the subtemporal keyhole and adequately overlaid the bone defects. The patient's postoperative course was uneventful, and the CSF leakage disappeared without mastication problems. Conclusions This purely endoscopic technique using a vascularized DTF flap provided reliable MCF reconstruction through a subtemporal keyhole. This technique is also expected to be applicable for MCF reconstruction after subtemporal keyhole surgery for skull base tumors.

OBJECTIVEThis study attempted to determine whether a previous minor leak correlated with the occurrence of symptomatic delayed cerebral ischemia (sDCI).METHODSThe authors retrospectively evaluated sDCI-related clinical features and findings from MRI, including T1-weighted imaging (T1WI)–FLAIR mismatch at the time of admission, in 151 patients admitted with subarachnoid hemorrhage (SAH) within 48 hours of ictus.RESULTSThe overall incidence of sDCI was 23% (35 of 151 patients). In all subjects, multivariate analysis revealed that World Federation of Neurosurgical Societies Grades II–V, age 70 years or older, presence of rebleeding after admission, a previous minor leak before the major SAH attack as diagnosed by T1WI-FLAIR mismatch, acute infarction on diffusion-weighted imaging, and CT SAH score were significantly associated with occurrence of sDCI. In patients with no previous minor leak before major SAH as diagnosed by T1WI-FLAIR mismatch, the incidence of sDCI was only 7% (7 of 97 patients).CONCLUSIONSA previous minor leak before major SAH as diagnosed by T1WI-FLAIR mismatch represents an important sDCI-related factor. When the analysis was restricted to patients with true acute SAH without a previous minor leak diagnosed by T1WI-FLAIR mismatch, the incidence of sDCI was extremely low.

The lateral limit of endoscopic endonasal surgery has yet to be defined. The aim of this study was to investigate the lateral limit of endoscopic endonasal surgery at the level of the sphenoid sinus. Access from the sphenoid sinus to the middle cranial fossa through the cavernous sinus triangles was evaluated by cadaver dissection. Anatomical analysis demonstrated that the medial temporal dura mater was exposed through the anterior area of the clinoidal triangle, anteromedial triangle, and superior area of the anterolateral triangle, indicating potential corridors to the middle cranial fossa. This study suggests that the cavernous sinus triangles are applicable in selected cases to manage middle cranial fossa lesions by endoscopic endonasal surgery.

Background Endoscopic microvascular decompression (MVD) offers reliable identification of neurovascular conflicts under superb illumination, and it provides minimally invasive surgery for trigeminal neuralgia and hemifacial spasm. Transposition techniques have been reported as a decompression method to prevent adhesion and granuloma formation around decompression sites, providing better surgical outcomes. The feasibility and effects of transposition under endoscopic MVD were evaluated. Material and Methods Fully endoscopic MVD was performed using 4-mm 0- and 30-degree endoscopes. The endoscope was fixed with a pneumatic holding system, and a bimanual technique using single-shaft instruments was performed. Transposition was performed with Teflon felt string and fibrin glue. Surgical results were evaluated using the scoring system proposed by Kondo et al. Results The endoscope was introduced via a retrosigmoid keyhole. The 0-degree endoscope was advanced through the lateral aspect of the cerebellar tentorial surface to the trigeminal nerve in cases of trigeminal neuralgia and through the petrosal surface of the cerebellum to the facial nerve in cases of hemifacial spasm. Neurovascular conflicts and perforators from the offending artery were clearly demonstrated under the 30-degree endoscopic view, and transposition of the offending artery was safely performed with preservation of perforators. Clinical symptoms improved without permanent complications. Conclusion Endoscopic MVD with the transposition technique is feasible. Superb endoscopic views demonstrate perforators arising from the offending artery behind the corner, allowing damage to perforators to be avoided during the transposition technique. Endoscopic MVD using the transposition technique is expected to offer excellent surgical results.

We report results of experiments examining cross-phase modulation effect on fiber grating coupler (FGC). All-optical switching are observed in both cases of high pump pulses emitted from high-power Nd:YAG laser and mode-locked EDF laser. Based on coherent detection using a lock-in amplifier, the red-shift of the Bragg wavelength for a FGC was estimated to be 0.04–0.06 nm/1.5–1.7 kW peak power of EDF pump light at 1.55 μm. To avoid mixture of pump pulse and signal light at 1.55 μm, we have also performed the experiment using high power Nd:YAG laser as a pump power. For a Nd:YAG laser, the red-shift of Bragg wavelength is estimated to be 0.06 nm at maximum pump power of 2.1 kW. A simple model for the proposed detection scheme is given and the resultant red-shift is analyzed numerically.

ObjectInhibition of remyelination is part of the complex problem of persistent dysfunction after spinal cord injury (SCI), and residual myelin debris may be a factor that inhibits remyelination. Phagocytosis by microglial cells and by macrophages that migrate from blood vessels plays a major role in the clearance of myelin debris. The object of this study was to investigate the mechanisms underlying the failure of significant remyelination after SCI.MethodsThe authors investigated macrophage recruitment and related factors in rats by comparing a contusion model (representing contusive SCI with residual myelin debris and failure of remyelination) with a model consisting of chemical demyelination by lysophosphatidylcholine (representing multiple sclerosis with early clearance of myelin debris and remyelination).The origin of infiltrating macrophages was investigated using mice transplanted with bone marrow cells from green fluorescent protein–transfected mice. The changes in levels of residual myelin debris and the infiltration of activated macrophages in demyelinated lesions were investigated by immunostaining at 2, 4, and 7 days postinjury. To investigate various factors that might be involved, the authors also investigated gene expression of macrophage chemotactic factors and adhesion factors.ResultsActivated macrophages coexpressing green fluorescent protein constituted the major cell population in the lesions, indicating that the macrophages in both models were mainly derived from the bone marrow, and that very few were derived from the intrinsic microglia. Immunostaining showed that in the contusion model, myelin debris persisted for a long period, and the infiltration of macrophages was significantly delayed. Among the chemotactic factors, the levels of monocyte chemoattractant protein–1 and granulocyte–macrophage colony-stimulating factor were lower in the contusion model at 2 and 4 days postinjury.ConclusionsThe results suggest that the delayed infiltration of activated macrophages is related to persistence of myelin debris after contusive SCI, resulting in the inhibition of remyelination.

Object In February 2006, the magnetic resonance/x-ray/operating room (MRXO) suite opened at the authors' institution. This is the first hybrid neurosurgical procedure suite to combine magnetic resonance (MR) imaging, computed tomography (CT), and angiography within a neurosurgical operating room (OR). In the present paper the authors describe the concept of the MRXO as well as their first 10 months of experience using this suite, and discuss its advantages and limitations. Methods In the MRXO suite, the combined OR and angiography (OR–angiography) station is located in the middle of the suite, and the MR imaging and CT scanning stations are each installed in an adjoining bay connected to the OR–angiography station by shielded sliding doors. The surgical, MR imaging, angiography, and CT tables are positioned in order of use. The patient lies on a fully MR imaging– and radiography-compatible mobile patient tabletop that is used to move the patient quickly and safely among the tables in the imaging and operating components of the MRXO suite. Results The authors performed all interventional procedures safely. The specially designed operating tabletop of the MRXO suite reduced the limitations on neurosurgeons during standard neurosurgical procedures. This hybrid suite helps to provide high-quality intraoperative imaging, greatly reducing the risk of unexpected events during the procedure. Conclusions The MRXO suite, which combines OR and imaging equipment, represents a significant milestone in the improvement of neurosurgical diagnosis and treatment and other interventional procedures. Another advantage of the MRXO suite is its cost-effectiveness, which is partly due to its streamlined imaging procedure.

Supercontinuum (SC) spectrum generation in a biconical tapered fiber is theoretically studied by taking into account the varying dispersion characteristics. Our numerical model is based on the extended nonlinear Schrodinger equation including higher-order dispersive terms, self-steepening, and Raman nonlinearity terms. We demonstrate how the group velocity dispersion and effective core area vary in the input taper region, which is significant for the broadening of the SC spectrum in the subsequent waist region. The evolutions of the unwrapped spectral phase and the spectral intensity along the transition and waist regions of the tapered fiber are also investigated in detail. It is found that the output taper has a considerable effect on the nonlinear variation of the spectral phase, e.g., 6.5 rad/THz in the infrared range of 280–300 THz (i.e., 1071–1000 nm in wavelength) and 21 rad/THz in the visible range of 600–620 THz (i.e., 500–484 nm).

A novel and efficient approach is proposed to calculate transmission and reflection spectra of propagating core mode and higher-order cladding modes when the fiber Bragg gratings (FBGs) are modulated by acoustically induced microbending. Based on a matrix form of first-order differential equations and its eigen-values/vectors using similarity transformation method, coupled-mode equations modeling acoustically induced microbending in FBG with a thin cladding can be transformed into a simple mathematical formulation. This method would be straightforward and thus beneficial to solve directly multimode coupled equations in comparison with a previous used fundamental matrix method and a Runge–Kutta algorithm. This simple model provides us a good view of co-directional and contra-directional couplings caused by acoustically induced microbending through FBGs.

BACKGROUND AND PURPOSE: Reversible cerebral vasoconstriction syndrome is characterized by thunderclap headache and diffuse segmental vasoconstriction that resolves spontaneously within 3 months. Previous reports have proposed that vasoconstriction first involves small distal arteries and then progresses toward major vessels at the time of thunderclap headache remission. The purpose of this study was to confirm centripetal propagation of vasoconstriction on MRA at the time of thunderclap headache remission compared with MRA at the time of reversible cerebral vasoconstriction syndrome onset. MATERIALS AND METHODS: Of the 39 patients diagnosed with reversible cerebral vasoconstriction syndrome at our hospital during the study period, participants comprised the 16 patients who underwent MR imaging, including MRA, within 72 hours of reversible cerebral vasoconstriction syndrome onset (initial MRA) and within 48 hours of thunderclap headache remission. RESULTS: In 14 of the 16 patients (87.5%), centripetal propagation of vasoconstriction occurred from the initial MRA to remission of thunderclap headache, with typical segmental vasoconstriction of major vessels. These mainly involved the M1 portion of the MCA (10 cases), P1 portion of the posterior cerebral artery (10 cases), and A1 portion of the anterior cerebral artery (5 cases). CONCLUSIONS: This study found evidence of centripetal propagation of vasoconstriction on MRA obtained at the time of thunderclap headache remission, compared with MRA obtained at the time of reversible cerebral vasoconstriction syndrome onset. If clinicians remain unsure of the diagnosis during early-stage reversible cerebral vasoconstriction syndrome, this time point represents the best opportunity to diagnose reversible cerebral vasoconstriction syndrome with confidence.

A new and simple mathematical formulation that is employed to analyze numerically coupled-mode equations modeling uniform and non-uniform gratings in optical fiber is investigated. This method would be straightforward and thus beneficial to solve multimode coupled equations in comparison with a previously used fundamental matrix method, and the Runge--Kutta algorithm. The new formulation proposed in this study is applied to calculate transmission and reflection spectra of core mode and higher-order cladding modes of acoustically induced superstructure modulation caused by microbending through fiber Bragg gratings (FBGs). Co-directional and contra-directional couplings based on acoustically induced modulation in FBGs have been discussed for a variety of induced coupling coefficients.

If the phase match condition is satisfied in a 1.55-µm dispersion-shifted fiber (DSF), four-wave mixing (FWM) between the signals is generated at a lower optical power level than other nonlinear phenomena. In this paper, the polarization dependence of the FWM generating efficiency is discussed. From the maximum mixing efficiency, the nonlinear refractive index and the zero-dispersion wavelength are simultaneously measured. Both DSFs of 20 and 4 km are used for studies of the polarization dependence of FWM light with respect to linear polarization from the wavelength variable DFB-LD. For a 20-km DSF, a nonlinear refractive index of n2 = 2.50 × 10−20 m2/W and a zero-dispersion wavelength of λ0 = 1553.0 nm are obtained. For a 4-km DSF, n2 = 2.42 × 10−20 m2/W and λ0 = 1557.9 nm. For the 4-km DSF, it is confirmed by the CW-SPM method that n2 = 2.40 × 10−20 m2/W. The measured results for the two methods are found to be in good agreement. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 87(3): 45–54, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.10146

It was found by numerical analysis that a 320 nm wide and flat spectrum at 20 dB less than the central maximum intensity is generated from cross-phase modulated soliton pulses with 3.5 ps pulse width and 2.3 W peak power, which are propagated through a 2.4km length of dispersion-flattened/decreasing fiber (DFDF). The cross-phase modulation (XPM) at a central wavelength of 1.55 μm is achieved by exciting two orthogonally polarized modes into the principal axes. The wave-vector mismatch between the orthogonal pulses can be neglected because of soliton trapping when the modal birefringence of the DFDF is less than |nox - n0y| = 10−6. The effect of modal birefringence on supercontinuum generation is discussed in temporal and spectral regimes by numerical analysis.

The fundamental mode can be launched in the multimode(MM) fibers with high accuracy by suppressing modal speckle by using broad-bandwidth excitation sources such as ultra-short pluses. As temporal coherence length of broad-bandwidth sources is very short, temporal interference between the modes and thus the presence of speckle is prevented. In this paper, single-mode(SM) excitation of step-index and graded-index multimode fibers with light sources with short temporal coherence lengths is demonstrated using a Ti:Sapphire laser with wavelengths of 790 ran and 836 nm and pulse widths of 60-90 fs. As a result, the stability of the spatial beam profile was verified by coupling the output of a MM fiber into SM fiber and SM excitation in the presence of mode-coupling for the MM fibers was confirmed by experiment.

The performance of a coherent optical continuous-phase frequency shift keying (CPFSK) system is evaluated theoretically including the combined effect of fiber chromatic dispersion, non-zero laser line width and receiver noises. The system limitations imposed by chromatic dispersion and laser phase noise are depicted. The system performance can be improved by shifting the zero-dispersion wavelength to the operating wavelength of the system and this shifting can be achieved efficiently by using a suitable combination of different types of optical fibers. Dispersion shifting characteristics are demonstrated using four kinds of fibers, namely: standard single-mode fiber (SMF), dispersion shifted fiber (DSF), dispersion compensated fiber (DCF) and large core fiber (LCF). The effect of dispersion shifting on the system performance is evaluated in terms of transmission distance and bit rate.

Identification of the internal carotid artery (ICA) is essential for successful endoscopic endonasal cavernous sinus tumor surgery. This study aimed to develop a method for identifying the ICA in cavernous sinus tumors at the superior part of the cavernous sinus. Ten fresh cadavers were studied with a 4-mm 0° and 30° endoscope to identify surgical landmarks of the ICA in the cavernous sinus. Clinical cases of cavernous sinus tumors were surgically treated using an endoscopic transpterygoid approach. Anatomical study indicated the ICA at the superior part of the cavernous sinus can be identified using three steps: 1) exposure of the optic nerve sheath by drilling the optic canal; 2) identification of the proximal orifice of the optic nerve sheath at the transition of the optic nerve sheath and dura mater of the tuberculum sellae; and 3) identification of the clinoid segment of the ICA at the distal dural ring just below the proximal orifice of the optic nerve sheath. Although the ICA was encased and transposed by tumors in preliminary surgical cases, the clinoid segment of the ICA was safely exposed at the superior part of the cavernous sinus using this method. Dural structures around the cavernous sinus are key to identifying the ICA at the superior part of the cavernous sinus. This method is expected to reduce the risk of ICA injury during endoscopic endonasal surgery for cavernous sinus tumors.

Nonlinear coupling characteristics taking account of evanescent field overlap were evaluated numerically by assuming a Gaussian field distribution for the mode field in nonlinear directional couplers (NLDC). The nonlinear coefficients Q3 to Q5 were found to be Q3 = 3.7 × 10−12 cm−1, Q4 = Q5 = 0 for the plane wave approximation used in Jensen's paper [1], with a core radius of 4 μm, a core spacing of 5 μm, a core refractive index of 1.455, and a nonlinear refractive index of 1.1 × 10−12 esu; and the wavelength of the incident light was 1.06 μm. On the other hand, in the case of the Gaussian field approximation, Q3 = 2.5 × 10−12 cm−1, Q4 = 2.2 × 10−14 cm−1, and Q5 = 7.3 × 10−14 cm−1 were obtained, indicating that these values cannot be ignored. The full coupling period is increased by increasing the core spacing, and the full coupling period is decreased by using a longer wavelength. Further, from the dependence of nonlinear coupling characteristics on optical wavelength, it is confirmed that wavelength selective characteristics with a sharp bandpass filtering can be realized in NLDC.

This paper reports a modification of an interferometric technique [ H. Tsuchida , “ A Novel Technique for Measuring the Frequency Deviation of Semiconductor Lasers under Direct Modulation,” Jpn. J. Appl. Phys.22, L19– L21 ( 1983)] for measuring the frequency deviation and phase difference between the AM and FM modulation of semiconductor laser diodes. The frequency deviation can be determined by the fringe visibility of interference patterns provided the phase difference, AM index, and time delay in an unbalanced Michelson interferometer are given. It covers a wide range of modulation frequencies, i.e., 10 Hz to 10 MHz. This method has such advantages that a high speed photodetector is not necessary and the accuracy of the measurement is not reduced by the spectral linewidth of the lasers.

Laser light, which is doubly phase modulated by an ultrasonic wave, can be utilized for speckle reduction. The double phase modulation is found to be more effective for speckle reduction than single phase modulation, since the doubly modulated laser beam for illumination is much degraded in spatial coherence with the same ultrasonic conditions. Average contrast is discussed analytically and experimentally as a measure of image-speckle reduction. Agreement between the measured and calculated results are recognized to the extent that the ultrasonic wave can be regarded as a pure phase grating. The average contrasts for two kinds of diffuser decrease similarly down to a minimum of ~0.4 by increasing the ultrasonic power.

The optimum condition for coupling energy into an optical fiber waveguide is theoretically computed for an incident beam with a Gaussian intensity distribution and a curved wavefront. The dependence of the modal excitation efficiencies on the tilt angle of the incident beam and on the refractive index difference of core and cladding is discussed. Numerical results show that maximum efficiency for the HE(11) mode can be achieved when the beam radius is chosen to be approximately 0.65 times the core radius. Excitation efficiencies of low-order modes, HE(1m) (m/= 2) approach 80% at their cutoff when the beam size is suitably larger than the core diameter.

Optical phase modulation induced in piezoelectric copolymer, vinylidene fluoride (73 mol.%)/trifluoroethylene (27 mol.%), coated single-mode fibers has been examined and analyzed from both experimental and theoretical aspects. High-sensitive phase modulation, which is more than four times as large as those of vinylidene fluoride/tetrafluoroethylene copolymer, is obtained over a flat response range from 10 kHz to 3 MHz. At frequencies below 7 kHz and higher than 6 MHz the optical responses are dominated by axial and radial resonances, respectively, of the fiber-jacket composite. The theoretical prediction on induced phase shifts at high frequencies is carried out based on radial vibration analysis and followed by the experimental results. >

A fiber-optic interferometer consisting of a multimode fiber-optical power divider was constructed in the Michelson arrangement and applied to measure a micrometer-order displacement of the vibrating object based on an optical homodyne technique. Improvement in the sensitivity of the apparatus is discussed from the viewpoint of increasing the minimum detectable beat signal.

An efficient numerical method to solve multimode-coupled equations with two point boundary conditions is improved. Our method [Abrishamian et al., Opt. Fiber Technol.13, 32-38 (2007)] based on theoretical matrix integration of coupled differential equations and then solving the system of equations by use of initial or final conditions would be straightforward and thus beneficial in comparison with previously used fundamental matrix methods that depend strongly on the initial guess. However, we found that the new analysis depends on how accurately the integrals of the matrix element are calculated. For accuracy in the matrix integration it is required to divide the system of equations into a large number of subsections. Then, the reflectivity calculated is found to be comparable to experimental data reported so far. The present method is highly applicable for simulation of any type of fiber Bragg gratings modulated by long period gratings.

The optical Kerr effect in coiled high-birefringent fibers was measured based on a double-beam polarimetric method. A Q-switched Nd:YAG laser, operating at 1.064 μm (FWHM of 80 ns at 1 kHz), was used as the pump beam and a cw 0.633-μm He–Ne laser was used as the probe beam with its polarization fixed at 45° with respect to the birefringent axis whereas orientation of the linearly polarized pump light varied. The phase shifts induced by an intense pump beam in a short bow-tie high-birefringent fiber were determined for different fiber lengths coiled into 15- and 30-cm-diameter drums. It was found that the induced phase shift changes drastically with the state of polarization of the pump light. A strong dependence of the phase shift on orientations of linear pump polarization is attributed to differential losses of eigenmodes peculiar to birefringent axes. Therefore, optical Kerr coefficients remain unchanged regardless of the dependence of the nonlinear response of the coiled high-birefringent fibers on pump polarization.

The location of corpus callosum injury was investigated using magnetic resonance imaging in 92 patients. The anatomical relationships in the region around the corpus callosum were also evaluated to clarify involvement in the mechanism of corpus callosum injury in 20 normal volunteers. Lesions in the posterior half of the corpus callosum accounted for 80% of corpus callosum injuries. The falx was increasingly elongated toward the posterior portion of the corpus callosum and the corpus callosum was thinnest at the body-splenium junction in the normal volunteers. The mechanism of corpus callosum injury apparently involves the following factors. The posterior half of the falx is closer to the corpus callosum than the anterior half. Therefore, the anterior part of the corpus callosum easily moves with lateral movement of the cerebral hemispheres, and the strain is likely to be concentrated in the posterior half of the corpus callosum, because the falx greatly limits lateral movement of the hemisphere in the posterior region. The corpus callosum is easily distorted at the thinnest part of the body-splenium junction. Therefore, corpus callosum injury predominantly occurs in the posterior half of the corpus callosum.

We propose a new technique for measuring displacement of an object based on dynamic, optical-heterodyne interferometry using a frequency-modulated laser diode. Vibration amplitudes ranging from 0.26 nm to 5.2 nm at 1 kHz of oscillation frequency are determined with high accuracy. Theoretical treatments explain the principles, and the experiments verify the feasibility of this technique. The available performance of the newly developed system is also discussed in some detail.

Based on coherent detection using a lock-in amplifier, the red-shift of the Bragg wavelength for a fiber grating coupler (FGC) was estimated to be 0.04-0.06nm .6nm /1.5-1.7kW peak power of pump light at 1.55, ?m, which was induced by Kerr nonlinearities due to cross-phase modulation in a FGC.

A theoretical and experimental study of femtosecond supercontinuum generation in short tapered fibers with micrometer diameter waist has been carried out. In our numerical model, an extended nonlinear Schroedinger equation that involves the parameters of dispersion coefficient and effective core area varying along the length of tapered fiber is used to describe the evolution of intense femtosecond pulses centred at 850 nm. As a result, the supercontinuum is generated due to enhanced nonlinear effects in a narrow waist; the octave spanning spectra are found in an optimum structure with only short waist length of 8.0 mm and diameter of 2 μm for an input average power of 100mW. Experimental verification using a femtosecond pulse from a Ti: sapphire laser is then made and compared with the numerical simulations.

Mechanism of supercontinuum(SC) spectrum generation due to cross-phase modulation(XPM) in a dispersionflattened/decreasing fiber(DFDF) with low birefringence has been investigated theoretically and experimentally. By using a XPM, the measured SC spectum width becomes 33.6 % broader than that obtained by using only self-phase modulation (SPM). This fact implys that effectiveness and validity of the sc generation using XPM method. Furthermore, dependence of generated sc spectrum broadening on incident power, polarization angle of the input pulses, and modal birefringence are investigated. consequently, it was velifid that when a polarization angle of the input pulses is 45 degrees with regard to the principal axes of the fiber and incident average power is less than 0.147 mW, soliton trapping takes place due to a balance between soliton pulse powers and modal birefringence value. In addition, it was shown experimentally that for a polarization angle of the input pulses of 22.5 degrees, the sc spectrum is enlarged by the same amount as in the case of 45 degrees.

In this paper, a nondestructive measurement technique, which uses a four wavelength bidirectional optical time domain reflectometer (OTDR) to measure the chromatic dispersion distribution along an optical fiber transmission system, has been presented. A new formulation has been developed to enhance the correction factor, which leads to an improvement in the measurement results of a pre-existing method and the obtained experimental results are in good agreement with those obtained by the interferometric technique.

Intervertebral disc (IVD) degeneration, a common cause of low back pain in humans, is a relentlessly progressive phenomenon with no currently available effective treatment. In an attempt to solve this dilemma, we transplanted autologous mesenchymal stem cells (MSCs) from bone marrow into a rabbit model of disc degeneration to determine if stem cells could repair degenerated IVDs. LacZ expressing MSCs were transplanted to rabbit L2-L3, L3-L4 and L4-L5 IVDs 2 weeks after induction of degeneration. Changes in disc height by plain radiograph, T2-weighted signal intensity in magnetic resonance imaging (MRI), histology, immunohistochemistry and matrix associated gene expressions were evaluated between normal controls (NC) without operations, sham operated with only disc degeneration being induced, and MSC-transplanted animals for a 24-week period. Results showed that after 24 weeks post-MSC transplantation, degenerated discs of MSC-transplanted group animals regained a disc height value of about 91%, MRI signal intensity of about 81%, compared to NC group discs. On the other hand, sham-operated group discs demonstrated the disc height value of about 67% and MRI signal intensity of about 60%. Macroscopic and histological evaluations confirmed relatively preserved nucleus with circular annulus structure in MSC-transplanted discs compared to indistinct structure seen in sham. Restoration of proteoglycan accumulation in MSC-transplanted discs was suggested from immunohistochemistry and gene expression analysis. These data indicate that transplantation of MSCs effectively led to regeneration of IVDs in a rabbit model of disc degeneration as suggested in our previous pilot study. MSCs may serve as a valuable resource in cell transplantation therapy for degenerative disc disease.

The radiated power of scattered light caused by refractive-index inhomogeneities and waveguide wall irregularities in an asymmetric slab waveguide is investigated by using the stationary phase method on the basis of a first-order perturbation theory. The correlation between both imperfections of the refractive index and the waveguide wall is taken into consideration. It is found that the correlation between both imperfections hardly affects the radiated power caused by air radiation modes while it modifies the radiated power caused by substrate radiation modes.

The measurement and evaluation of power spectrum of a semiconductor laser by delayed self-heterodyne interferometer is demonstrated with the use of a short delay fiber. The measured spectrum is analyzed numerically including the effect of a delay time much less than the laser coherence time. The theoretical formulation developed here is found to be found to be accurate since it exhibits a peak with finite width at the center frequency of the measured lineshape. The white and 1/f components of the laser FM noise are then separated successfully by fitting numerical analysis to the experimental results.

An optical heterodyne interferometer with a frequency-ramped laser diode (LD) has been constructed for amplitude measurements of a sinusoidally oscillating object. In order to eliminate the effect of intensity modulation without complexity in optical setup, an optical interferometry operating under a small index of intensity modulation has been proposed and its effect on the amplitude measurements of an oscillating object has been analyzed based on spectral analysis of interference beat signal. From the simplified analysis for some ratios of beat frequency to modulation (ramped) frequency and for some intensity modulation indices, it is confirmed that the theoretical analysis and the experimental results are in relatively good agreement.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A flat and broad-band supercontinuum spectrum of soliton pulses in an optical fiber with dispersion flattened and dispersion decreasing characteristic along the axis was numerically analyzed using a split-step Fourier method and confirmed experimentally.