Spiral-CT in diagnosis of vascular involvement in pancreatic cancer

BACKGROUND/AIMS: The purpose of this prospective study was to evaluate the efficacy of spiral-CT for the identification of portal venous, superior mesenteric artery and celiac trunk infiltration in the staging of pancreatic (n = 29) and periampullary (n = 6) cancers. MATERIALS AND METHODS: All patients were examined by contrast enhanced spiral-CT using a total volume of 240 ml contrast medium i.v. With a slice thickness of 5 mm and a table increment of 7 mm/sec a overlapping data set, representing a total volume of 21 cm, was covered. The images were reconstructed in 4 mm intervals. In 28 patients the spiral CT results were correlated with surgical findings. RESULTS: Regarding portal venous infiltration spiral-CT had a sensitivity of 91% (10/11), a specificity of 9.4% (16/17), a positive predictive value of 91% (10/11), a negative predictive value of 94% (16/17) and, an overall accuracy of 92.8% (26/28). Spiral CT correctly identified arterial involvement in 5 patients, and no false negative result compared to surgical findings was observed. CONCLUSIONS: These results indicate that spiral-CT reliably verifies occlusion, stenosis and encasement of the major peripancreactic vessels caused by pancreatic cancer

Correlation of strain, wing tilt, dislocation density, and photoluminescence in epitaxial lateral overgrown GaN on SiC substrate

Epitaxial lateral overgrown (ELOG) gallium nitride (GaN) on SiC is being studied as a possible substrate for blue laser diodes. A defect density below 2.2×107 cm–2 in the wings, compared to 2×109 cm–2 in the windows, was achieved. Interaction of the overgrown GaN with the SiO2 mask causes a few degree wing tilt and a transition region of high defect density between windows and wings. Diminished PL, strong tensile stress, and a defect correlated line at around 3.4 eV emerge in this up to two-micron-wide transition region. By changing the mask material from SiO2 to SiN we were able to reduce the wing tilt drastically to below 0.7°. This eliminates the defective transition region and extends the low strain and the low defect density area of the ELOG wings. The methods used to study strain, wing tilt, and threading dislocations in the ELOG samples are microphotoluminescence (µPL), transmission electron microscopy, x–ray diffraction, and scanning electron microscope. We also demonstrate the use of the first momentum of the µPL spectra as an effective means to measure strain distribution