Pleural thickening: a comparison of oblique chest radiographs and high-resolution computed tomography in subjects exposed to low levels of asbestos pollution.

The present study was conducted to investigate the value of oblique chest radiographs, compared with high-resolution computed tomography (HRCT), in the assessment of pleural asbestosis in a group of subjects exposed to low levels of asbestos pollution. The study population consisted of 23 people derived from a previously reported cohort of subjects working in university buildings insulated with asbestos-containing material. Subjects were selected on a voluntary basis from among patients whose initial oblique chest X-rays showed pleural thickening. Sixteen patients were maintenance workers occupationally exposed to asbestos; the remaining seven were environmentally exposed to asbestos. For each subject, two standard chest radiographs [posteroanterior (PA) and right anterior oblique (RAO) views] were taken and HRCT was performed. Films were interpreted after agreement by three chest physicians and a radiologist. Pleural thickening was considered present in all 23 patients on RAO films and in six patients on PA films. HRCT revealed unequivocal pleural plaques in three maintenance workers and doubtful pleural abnormalities in three other maintenance workers. Considering HRCT as the "gold standard," the positive predictive value of RAO film was only 13%-26%. Most of the 17 false-positive diagnoses of pleural fibrosis were due to significant subpleural fat. These results suggest that the routine use of oblique radiographs as a screening test in cohorts of subjects exposed to low levels of pollution by asbestos should be reevaluated.

Measurement of loss and output numerical aperture of optical fiber splices.

An ensemble of optical fiber splices has been evaluated to determine how source launching conditions and length of fiber between the source, splice, and detector affect the splice loss and far field output NA. The loss of a splice is strongly dependent upon the energy distribution and NA of the beam at the input of the splice. For the range of NA's considered, the splice loss varied by 0.5 dB. The average NA at the output of the ensemble of splices was greater than its corresponding input NA by as much as 12%. The splice appears to act as a transformer converting the input energy distribution into one at the output that contains a greater amount of its energy in higher order modes. As a consequence of this, the loss of a fiber following the splice in a long transmission path is greater than the loss the fiber would exhibit if measured with steady state excitation conditions.

Delay distortion characteristics of optical fiber splices.

The delay distortion characteristics of optical fiber splices are evaluated. Two 1.35-km graded index fibers with different transmission characteristics were each bisected and spliced together to determine how longitudinal and transverse displacement of fibers in a splice affect the delay distortion characteristics of a transmission path. The transmission characteristics of both the optical source and the fibers used play an important role in determining how delay distortion is affected by splice misalignment. The first fiber exhibited a great deal of mode mixing and a very small increase in delay distortion as the fibers were offset in the splice. In contrast, the second fiber exhibited very little mode mixing, but increased markedly in delay distortion as the fibers in the splice were displaced.

Multigroove embossed-plastic splice connector for joining groups of optical fibers.

To install and maintain successfully an optical fiber communications system, techniques for splicing individual and groups of optical fibers under field conditions must be developed. In this paper a technique for splicing groups of optical fibers with a one piece multigroove embossed plastic connector is described. Using 132-microm multimode fibers with 94-microm core diameters, the average transmission loss of the splice joints measured was 0.12 dB with a standard deviation of 0.11 dB and a range of loss values from 0.0 dB to 0.53 dB.

Transmission characteristics of three corning multimode optical fibers.

The loss spectra, refractive-index profiles, numerical apertures, and pulse dispersion characteristics of three multimode optical fibers made by Corning Glass Works have been measured at Bell Laboratories. The lowest transmission loss, 4.3-6.8 dB/km, was observed at 1.06-microm wavelength; in the 0.8-0.9-microm spectral region the losses ranged from 6.6 dB/km to 11.6 dB/km. The numerical apertures of the fibers, designated as Nos. 1, 2, and 3, were calculated from the measured refractive-index differences to be 0.133, 0.157, and 0.121, respectively. Pulse dispersion due to multimode effects in fiber No. 1 (1 km long) was 8.4 nsec at 0.9-microm wavelength; the values were 6.0 nsec for fiber No. 2 (0.363 km long) and 2.6 nsec for fiber No. 3 (0.290Km).