CT pulmonary angiography in elderly patients: outcomes in patients aged >85 years.

AIM: To assess the quality, safety, and outcomes following computed tomography pulmonary angiography (CTPA) performed in elderly patients. MATERIALS AND METHODS: CTPA examinations were performed in 140 patients aged >85 years in three UK acute National Health Service (NHS) hospitals. Images were assessed for quality, pulmonary emboli, and other disease entities. Patients were assessed for contrast medium-induced nephropathy (CIN), and short-term and long-term survival. Statistics included Fisher's exact, Mann-Whitney U, and logrank tests. RESULTS: The mean age of patients was 92 years with baseline creatinine ranging 57-310 µmol/l. CTPA was of good quality in 79% (110/140) of cases and pulmonary emboli were demonstrated in 16% (23/140). Warfarin or inferior vena cava (IVC) filter insertion was instigated in 70% (16/23) of patients with pulmonary emboli. No patient had an immediate contrast medium reaction or required renal replacement therapy. CIN was seen following 6% (8/140) of examinations but was not predicted by baseline renal function (p = 0.62). There was a trend towards increased patient mortality in the presence of CIN, although this did not reach statistical significance (p > 0.10). Patients with pulmonary emboli had improved median survival, although this did not reach significance (28 months versus 12 months, p = 0.16). Patients with other significant diseases reported on CTPA had significantly worse median survival (4 months versus 17 months, p = 0.025). CONCLUSIONS: Patients aged >85 years undergoing CTPA have a low (6%) rate of CIN: this was not predicted by baseline renal function and did not impact on survival. CTPA in elderly patients is safe, facilitates active management of pulmonary emboli, and the discovery of additional disease entities informs survival.

Apodization technique for fiber grating fabrication with a halftone transmission amplitude mask.

Experimental results of fiber Bragg gratings fabricated with halftone amplitude transmission masks and 10-cm-long phase masks are presented for the first time to our knowledge. The performance of the devices is evaluated in terms of their spectral characteristics and deviation from linear group delay. Good out-of-band sidelobe suppression of -27 dB and group-delay ripple of ?9.5 ps is achieved for fully apodized grating devices.

Bragg gratings in defect-free germanium-doped optical fibers.

Bragg gratings have been written in germanium-doped optical fibers that have been treated to remove the UV absorption bands associated with oxygen-deficient defects. When one is using high-intensity 193-nm light from an ArF excimer laser to fabricate the gratings, the refractive index increases and the grating transmission spectra are similar to those obtained in standard (untreated) fiber.

Variable-spectral-=response optical waveguide Bragg grating filters for optical signal processing.

A simple method is described that permits the spectral response (spectral width, shape, and center resonant wavelength) of an optical waveguide Bragg grating to be controlled accurately in a prescribed manner. The control methodology consists of bonding the Bragg grating along the length of a mechanical support structure, which is then loaded with an appropriate force distribution. The function of the support structure is to transfer the strain induced by loading to the grating, thus modifying the grating's spectral response in accordance with the variation in effective optical pitch induced by the strain transfer. We design and demonstrate a support structure that provides independent control over the spectral width and center wavelength of a Bragg grating.

Photosensitivity in Ge-doped silica optical waveguides and fibers with 193-nm light from an ArF excimer laser.

Photosensitivity in optical fibers and waveguides has been associated with the bleaching of an absorption band located near 5.0 eV (or 242 nm). We present new results for Bragg grating formation and UV bleaching experiments carried out using 193-nm light from an ArF excimer laser instead of the usual laser sources operating near 242 or 248 nm.

Chirped in-fiber Bragg gratings for compensation of optical-fiber dispersion.

A linearly chirped in-fiber Bragg grating is reported that can compensate at 1549 nm for the dispersion [ approximately -19 ps/(nmkm)] of standard telecommunications optical fiber optimized for 1300-nm operation.

Photosensitization of optical fiber and silica-on-silicon/silica waveguides.

Localized heating with a flame is shown to be a simple and effective method for substantially augmenting the photosensitivity of high-silica optical waveguides to (UV) light. The method increases the photosensitivity of standard (Ge-doped core) telecommunications fiber by a factor greater than 10 (photoinduced Deltan(uv) > 10(-3)) and renders strongly photosensitive the cores of high-quality Ge:SiO(2)-on-Si and Ge:SiO(2)-on-SiO(2) planar waveguides that were negligibly photosensitive before treatment. We have written large-modulation-depth Bragg gratings, in both fiber and planar optical waveguides photosensitized by our method, using KrF (249-nm) radiation incident upon the waveguides through a zero-order-nulled phase mask. It is noteworthy that photosensitization by our method is achieved with a negligible increase in loss at the three principal optical communication windows.

Single-excimer-pulse writing of fiber gratings by use of a zero-order nulled phase mask: grating spectral response and visualization of index perturbations.

Optical fiber Bragg reflectors have been written by irradiating the fiber from the side through a phase mask with a single pulse of high-power 249-nm excimer-laser light. Efficient tapping of light to the radiation modes has been achieved for light at wavelengths shorter than the Bragg wavelength. The photoinduced periodic refractive-index perturbations have been observed directly with an optical microscope and are shown to have the same period as the phase mask and to be highly localized on one side, the irradiated side of the fiber core-cladding boundary.

Long-length, long-period rocking filters fabricated from conventional monomode telecommunications optical fiber.

Using fiber photosensitivity, we have made efficient, application-specific rocking filters from conventional monomode telecommunications optical fiber. Filters with a length of 10.89 m, a bandwidth of 58 nm, and a transmission of 99% at the resonant wavelength of switching 200-fs solitons.

Refractive-index changes in fused silica produced by heavy-ion implantation followed by photobleaching.

The changes in refractive index, optical absorption, and volume of synthetic fused silica resulting from the implantation of germanium and silicon ions at energies of 3 and 5 MeV are reported. Implantation changes the density and generates ultraviolet color centers in the silica, which increases the refractive index at visible wavelengths by ~1%. Irradiation of the implanted samples with 249-nm light from a KrF excimer laser photobleaches the color centers and reduces the index by more than 0.1%. Photobleaching is used to write a 4.3-microm pitch diffraction grating in the implanted silica.

Ultraviolet light photosensitivity in Ge-doped silica fibers: wavelength dependence of the light-induced index change.

A novel technique is reported for detecting permanent and transient light-induced refractive-index changes (photosensitivity) in optical fibers. The index change is detected by irradiating one arm of an unbalanced Mach-Zehnder fiber interferometer with UV light, thereby changing its optical path length. From a measurement of the change in the spectral response of the Mach-Zehnder interferometer, the change in the fiber core index as a function of wavelength can be determined. The equilibrium change in the core index is found to have an almost constant value of approximately 2.3 x 10(-5) over the measured wavelength range of 700 to 1400 nm.

Ultraviolet-light photosensitivity in Er(3+)-Ge-doped optical fiber.

Light-induced refractive-index change in Er(3+)-Ge-doped optical fiber is reported for the first time to the authors' knowledge. Evidence of the change is observed when UV light (lambda = 249 nm) irradiates one arm of an unbalanced Mach-Zehnder interferometer made from Er(3+)-Ge-doped fiber. From a measurement of the change in the spectral response of the interferometer with UV exposure, the change in fiber core index as a function of wavelength is determined. The equilibrium change in core index is found to vary between 2.3 x 10(-5) and 3.7 x 10(-5) over the measured wavelength region of 800 to 1700 nm. Also for the first time to our knowledge, fused couplers made of Er(3+)-doped fiber are reported. These identical fiber couplers are used in a novel all-fiber unbalanced Mach-Zehnder interferometer.

Light-induced erasure of self-organized chi((2)) gratings in optical fibers.

Self-organized chi((2)) gratings in optical fiber, prepared by irradiating the fiber with 1.06-microm light from a Q-switched mode-locked Nd:YAG laser simultaneously with its second harmonic, can be erased optically. This is accomplished by irradiating the prepared fiber with the 532-nm mode-locked Q-switched light alone, without the 1.06-microm light, or with intense green or blue light from an argon laser. The erasure is reversible, and the fiber can be reprepared as before for second-harmonic conversion. The nonexponential time dependence of the erasure process can be explained by a model involving charge separation during seeding and recombination during erasure.

Optical fibers with negative group-velocity dispersion in the visible.

Dispersion measurements have been performed in optical fibers having a photoinduced refractive-index grating in the core. The results show that negative group-velocity dispersion can be obtained in these fibers over a frequency region of 500 MHz for wavelengths shorter than 550 nm.

Compact, low-loss, fused biconical taper couplers: overcoupled operation and antisymmetric supermode cutoff.

The automated manufacture and characterization of compact four-port highly overcoupled fused couplers is reported. During the pulling stage of the manufacturing process, the light power in such devices is observed to cycle back and forth up to 1000 times between the two output ports for elongations smaller than 20 mm. For sufficiently long pulls, antisymmetric supermode cutoff has been observed for the first time to our knowledge, manifested by a sudden cessation of the coupling process. The measured wavelength dependence of the coupling ratio together with the device dimensions are consistent with the observation of cutoff as observed in pull-signature characteristics.