RESUMO
Tannic acid (TA) can be used as an additive to improve the properties of hydrogels, but it acts as a radical scavenger, which hinders radical polymerization. In this study, we successfully and easily synthesized a TA-incorporated 2-acrylamido-2-methylpropanesulfonic acid (AMPS) hydrogel using an electron beam (E-beam) in a one-pot process at room temperature. TA successfully grafted onto AMPS polymer chains under E-beam irradiation, but higher TA content reduced grafting efficiency and prevented hydrogel formation. Peel strength of the AMPS hydrogel increased proportionally with TA, but cohesive failure and substrate residue occurred above 1.25 phm (parts per 100 g of AMPS) TA. Tensile strength peaked at 0.25 phm TA but decreased below the control value at 1.25 phm. Tensile elongation exceeded 2000% with TA addition. Peel strength varied significantly with substrate type. The wood substrate had the highest peel strength value of 150 N/m, while pork skin had a low value of 11.5 N/m. However, the addition of TA increased the peel strength by over 300%. The ionic conductivity of the AMPS/TA hydrogel increased from 0.9 S/m to 1.52 S/m with TA content, while the swelling ratio decreased by 50% upon TA addition and increased slightly thereafter.
RESUMO
PURPOSE: To prospectively evaluate accuracy of arterial phase multi-detector row helical computed tomography (CT) for detection and localization of acute massive gastrointestinal (GI) bleeding, with angiography as reference standard. MATERIALS AND METHODS: Institutional review board approved this study; written informed consent was obtained from each patient or patient's family after procedures, including radiation dose, were explained. Twenty-six consecutive patients (17 men, nine women; age range, 18-89 years) had acute massive GI bleeding (defined as requirement of transfusion of at least 4 units of blood during 24 hours in the hospital or as hypotension with systolic blood pressure <90 mm Hg) and underwent arterial phase multi-detector row CT before angiography. Scans were obtained during arterial phase to identify extravasation of contrast material with attenuation greater than 90 HU within bowel lumen; this finding was considered diagnostic for active GI bleeding. Presence of contrast medium extravasation in each anatomic location was recorded. Sensitivity, specificity, positive and negative predictive values, and accuracy of multi-detector row CT for detection of acute GI bleeding were assessed. Accuracy for localization of acute GI bleeding was assessed by comparing locations of active bleeding at both multi-detector row CT and angiography in each patient who had active bleeding. RESULTS: Arterial phase multi-detector row CT depicted extravasation of contrast material in 21 of 26 patients. Overall location-based sensitivity, specificity, accuracy, and positive and negative predictive values of multi-detector row CT for detection of GI bleeding were 90.9% (20 of 22), 99% (107 of 108), 97.6% (127 of 130), 95% (20 of 21), and 98% (107 of 109), respectively. Overall patient-based accuracy of multi-detector row CT for detection of acute GI bleeding was 88.5% (23 of 26). The location of contrast material extravasation on multi-detector row CT scans corresponded exactly to that of active bleeding on angiograms in all patients with contrast medium extravasation at both multi-detector row CT and angiography. CONCLUSION: Arterial phase multi-detector row CT is accurate for detection and localization of bleeding sites in patients with acute massive GI bleeding.
