Optical phase contrast measurement of ultrasonic fields.

This report describes an optical phase contrast imaging technique for the measurement of wide bandwidth ultrasound fields in water. In this method, a collimated optical wavefront (lambda(l) = 810 nm) impinges on a wide bandwidth ultrasound pulse. The method requires that refractive index perturbations induced by the ultrasound field be sufficiently small. Specifically, on exit from the acoustic field, the phase of the optical wavefront must be proportional to the ray sum of local density taken in the direction of propagation of the incident optical wave. A similar restriction is placed on the dimensions of the ultrasound pulse. Repeated measurement of this phase as the ultrasound field is rotated through 180 degrees about an axis normal to the direction of propagation of the incident optical wave generates the Radon transform of the ultrasonically induced refractive index perturbation. Standard tomographic reconstruction techniques are used to reconstruct the full three-dimensional refractive index perturbation. A simple two-lens imaging system and an optical signal processing element from phase contrast microscopy provide a method of directly measuring an affine function of the desired optical phase for small optical phase shifts. The piezo- and elasto-optic coefficients (the first partial derivatives of refractive index with respect to density and pressure) relate refractive index to density and pressure via a linear model. The optical measurement method described in this paper provides a direct, quantitative measurement of the piezo- and elasto-optic coefficients (from the density or pressure fields).

Elecsys CEA, PSA and AFP. Clinical results of a multicentre evaluation.

Three tumormarker assays, Elecsys CEA, PSA and AFP, have been evaluated in an international multicentre study to characterize their clinical performance and to verify the comparability with the corresponding tests of the Enzymun-Test product line and other methods. For each of the markers results were obtained from four laboratories. On the basis of 314 and 199 specimens respectively, (preliminary) reference ranges could be established for CEA and PSA. For the prostate marker, the age dependence of the antigen level could be clearly confirmed. Mean concentrations range between 0.51 ng/ml (< 40 years) and 3.57 ng/ml (> 70 years). Referring to CEA, 95th percentiles of 4.31 ng/ml and 2.69 ng/ml were elaborated for smokers and nonsmokers. In general, good to excellent correlations (r > 0.98) were found between the Elecsys and Enzymun-Tests. Regarding the systematic comparability of both systems, most of the slopes derived from the individual method comparison studies are within the +/- 10% range of the respective standardization results. The specific distribution pattern of the individual tumormarker values elaborated with sample material of known clinical background, reflects the well established categorization of different benign and malignant diseases according to their characteristic marker levels. Of utmost importance, however, is the excellent comparability of the Elecsys assays with the corresponding Enzymun-Tests and the FDA approved AIA 1200 tests from TOSOH in follow-up studies. Almost superimposable concentration curves guarantee that identical diagnostic information is derived from all three methods. Especially for PSA, a series of measurements on sera of prostatectomized patients proved the usability and clinical value of the test also for this particular indication. For either one of the Elecsys tests, the feasibility of using plasma as sample material was verified.

Multicenter evaluation of a homogeneous assay for HDL-cholesterol without sample pretreatment.

We evaluated a new homogeneous assay for the measurement of HDL-cholesterol (HDL-C) in six European laboratories. The assay includes two reagents and is applicable to most autoanalyzers, which allows full automation. The total CVs of the new method ranged between 1.3% and 6.7%. Thereby determined HDL-C values were in good agreement with those obtained by precipitation with phosphotungstic acid/MgCl2 or by a combination of ultracentrifugation and precipitation (0.956 < r < 0.994). The assay was linear up to at least 1500 mg/L HDL-C. Hemoglobin did not interfere, whereas icteric samples with bilirubin > 100 mg/L showed discrepancies between the homogeneous and the precipitation assay. Lipemia up to total triglyceride concentrations of 8000 mg/L did not interfere with the homogeneous HDL-C assay. The homogeneous HDL-C assay was easy to handle and produced similar results in all laboratories participating in this study. This method will significantly facilitate the screening of individuals at increased risk for cardiovascular disease.