Search

Background: Serum CA19-9 concentration may be useful in triaging patients with pancreatic cancer for more intensive staging investigations. Our aim was to identify the CA19-9 cut-point with the greatest accuracy for detecting unresectable features not identified by CT scan, and to examine the performance of this and other cut-points in predicting the outcome of staging laparoscopy (SL). Methods: Patients with pancreatic cancer were drawn from two state-wide cancer registries between 2009 and 2011. We used classification and regression tree (CART) analysis to identify the CA19-9 cut-point which best predicted the presence of imaging-occult unresectable features, and compared its performance with that of a number of alternative cut-points. We then used logistic regression to test the association between CA19-9 concentration and detection of unresectable features in patients who underwent SL. Results: From the CART analysis, the optimal CA19-9 cut-point was 440 U/mL. CA19-9 ≥ 150 U/mL had a similar Youden Index, but greater sensitivity (69% versus 47%). This remained true for those who had obstructive jaundice at the time of CA19-9 sampling. CA19-9 concentration greater than or equal to 110 U/mL, 150 U/mL and 200 U/mL was associated with significantly greater odds of unresectable features being detected during SL. Conclusion: Elevated serum CA19-9 concentration is a valid marker for CT-occult unresectable features; the most clinically appropriate cut-point appears to be ≥ 150 U/mL irrespective of the presence of jaundice. Clinical trials which evaluate the value of CA19-9 in the staging algorithm for pancreatic cancer are needed before it is routinely used in clinical practice.

Optical and thermal properties of amorphous hydrogenated carbon (a-C:H) films deposited by plasma enhanced chemical vapor deposition (PECVD) and magnetron sputtering are reported. The deposition parameters were varied to produce a-C:H films with effective optical bandgaps from 0.3 eV to 2.3 eV. The optical properties of the a-C:H films deposited on glass substrates were determined from analysis of variable angle of incidence spectroscopic ellipsometry (VASE$\sp\circler)$ and transmittance data. An empirical parameterization for the a-C:H optical constants as a function of effective bandgap was developed based on the measured spectra, and this single parameter model was used to determine the optical constants and thickness of films deposited on silicon substrates. Forouhi and Bloomer optical parameters calculated from the measured optical constant spectra are tabulated. This model was modified to allow non-parabolic bands, and the resulting model was fit to the measured spectra to determine the energy dependence of the joint density of states function for each film. The thermal conductivities of fourteen a-C:H films on 5 mm thick silicon substrates were measured by photothermal deflection (PTD) experiments. The measurements were performed using mechanical chopping or photoacoustic modulation of the heating beam, with the sample in air or immersed in de-ionized water. An exact model for prediction of temperature distributions and PTD signals for multilayers heated by axially symmetric sources is presented, and FORTRAN programs to perform nonlinear multiple regression fits and simulated annealing fits to experimental PTD data using this model are described. Thermal conductivities of a-C:H films with bandgaps ranging from 1.2 to 2.3 eV were determined, and an exponential decrease of thermal conductivity with increasing bandgap is observed. The thermal conductivity for a given bandgap was also seen to decrease with decreasing film thickness.

Thin Co/Pt multilayers were prepared on Si and glass substrates by sputtering with Ar pressures ranging from 2.5 to 15 mTorr. The bilayer structure of the samples was Co(3 Å)/Pt(15 Å)×17, and all samples had the easy axis of magnetization perpendicular to the sample surface as determined with a SQUID magnetometer. All samples retained the layered structure, as revealed by low-angle x-ray diffraction. In addition, diffraction peaks due to the formation of Co-Pt compounds (presumably at the interfaces between Co and Pt) were identified. The coercivity of samples changed from about 400 Oe for films deposited at low Ar sputtering pressure (2.5 mTorr) to as high as 2300 Oe for films deposited at high Ar pressure (15 mTorr). Ellipsometry and atomic force microscopy were used to study surface roughness and microstructure of samples prepared at different sputtering pressures.

Amorphous Tb/Co compositionally modulated films were deposited on Si substrates with different modulation layer thicknesses ranging from about 2.5 to 15 Å. The nominal Tb to Co layer thickness ratios were systematically varied and the complex refractive index (n and k) and polar magneto-optical Kerr effects (rotation and ellipticity) were measured in the 3000–8000-Å spectral range as well. The samples were divided into two groups. In one group, the thickness of the Co layers was fixed, the Tb layer thickness varied. In the second group, the thickness of the Tb layer was fixed, and that of the Co layer thickness varied. The Kerr rotation and the coercivities of the samples showed very consistent and interesting changes. X-ray diffraction and x-ray fluorescence were also performed on the samples, which revealed layered structures, or compositional modulation, and provided information on the Tb to Co atomic ratios in the samples. Journal of Applied Physics is copyrighted by The American Institute of Physics.

A general expression for the magneto-optical polar Kerr effect is given for a bilayered configuration in which the optical constants of the two media differ. The equation shows that a giant enhancement of the Kerr effect in magneto-optical/metallic bilayers can be expected if the dielectric constants of the two materials are low or are matched well to the other. An explicit equation is also given to calculate the spectral enhancement due to a dielectric overcoating on magnetic substrates. An example is given for SiO-coated Dy/Co compositionally modulated alloys, yielding a good comparison to the experimental results in both the transparent and absorbing spectral regions of SiO. Journal of Applied Physics is copyrighted by The American Institute of Physics.