Gated acquisition of MR images of the thorax: advantages for the study of the hila and mediastinum.

Gated and nongated magnetic resonance (MR) scans of the chest were compared in five normal volunteers and 20 patients with chest disease to determine possible advantages of gated MR for delineation of noncardiac mediastinal anatomy. In order to compare gated and nongated images of the chest using similar imaging parameters, five spin-echo sequences were obtained in each of five normal volunteers: TR: 1000 msec, TE: 30 msec; gated to every heart beat (TR approximately 1000 msec, TE: 30 msec); TR: 2000 msec, TE: 30 msec; gated to every other heart beat (TR approximately 2000 msec), TE: 30 msec; TR: 500 msec, TE: 30 msec. In the 20 patients, the gated images were gated to every heart beat and the nongated images were obtained using a TR of 2000 msec, both with a TE of 30 msec. The noise in the periphery and in the center of the gated and nongated images at the level of the carina was compared in the five normal volunteers, using the signal intensity of the posterior chest wall as a control. There was 92% +/- 44% greater noise in the central region and 63% +/- 60% greater noise in the peripheral region on the nongated studies (TR: 1000 msec), than on the studies gated to every heart beat. In three of the five volunteers, the measured noise was greater on the nongated long TR (2000 msec) images than on the images gated to every other heart beat. However, the mediastinal structures below the level of the aortic arch were much better defined on the gated images in all five subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Nano-biocomposite films with modified cellulose nanocrystals and synthesized silver nanoparticles.

Ternary nano-biocomposite films based on poly(lactic acid) (PLA) with modified cellulose nanocrystals (s-CNC) and synthesized silver nanoparticles (Ag) have been prepared and characterized. The functionalization of the CNC surface with an acid phosphate ester of ethoxylated nonylphenol favoured its dispersion in the PLA matrix. The positive effects of the addition of cellulose and silver on the PLA barrier properties were confirmed by reductions in the water permeability (WVP) and oxygen transmission rate (OTR) of the films tested. The migration level of all nano-biocomposites in contact with food simulants were below the permitted limits in both non-polar and polar simulants. PLA nano-biocomposites showed a significant antibacterial activity influenced by the Ag content, while composting tests showed that the materials were visibly disintegrated after 15 days with the ternary systems showing the highest rate of disintegration under composting conditions.

Effects of modified cellulose nanocrystals on the barrier and migration properties of PLA nano-biocomposites.

The aim of this paper is to report the impact of the addition of cellulose nanocrystals on the barrier properties and on the migration behaviour of poly(lactic acid), PLA, based nano-biocomposites prepared by the solvent casting method. Their microstructure, crystallinity, barrier and overall migration properties were investigated. Pristine (CNC) and surfactant-modified cellulose nanocrystals (s-CNC) were used, and the effect of the cellulose modification and content in the nano-biocomposites was investigated. The presence of surfactant on the nanocrystal surface favours the dispersion of CNC in the PLA matrix. Electron microscopy analysis shows the good dispersion of s-CNC in the nanoscale with well-defined single crystals indicating that the surfactant allowed a better interaction between the cellulose structures and the PLA matrix. Reductions of 34% in water permeability were obtained for the cast films containing 1 wt.% of s-CNC while good oxygen barrier properties were detected for nano-biocomposites with both 1 wt.% and 5 wt.% of modified and un-modified cellulose nanocrystals, underlining the improvement provided by cellulose on the PLA films. Moreover, the migration level of the studied nano-biocomposites was below the overall migration limits required by the current normative for food packaging materials in both non-polar and polar simulants.

Migration study of carvacrol as a natural antioxidant in high-density polyethylene for active packaging.

The migration behaviour of low molecular weight compounds from food packaging materials is one of the key issues in assessing the possibility of use in such applications. The aim of this work was to study the migration of carvacrol (1% and 2% w/w) when added to high-density polyethylene. All materials were exposed to the food simulants olive oil and distilled water separately at 40 degrees C and 25 degrees C. Three significant variables influencing the migration process were considered: incubation temperatures, the initial concentration of antioxidant, and the type of simulant (oil and aqueous). The amount of carvacrol migrating to olive oil was significantly higher than in water because of the higher solubility of this antioxidant in oil. Experimental results agreed reasonably well with those obtained by the application of a simple model derived from Fick's Second Law. Carvacrol could therefore be used in active packaging formulations as its release from the polymer matrix can be controlled.

Role of parallel transjugular intrahepatic portosystemic shunts in patients with persistent portal hypertension.

Transjugular intrahepatic portosystemic shunts (TIPS) were placed in 93 patients between June 1990 and January 1992 for treatment of variceal hemorrhage. In each case, a Wallstent (Schneider USA, Minneapolis) was used to support the hepatic parenchymal tract between the hepatic and portal veins. Currently, these stents have a maximal diameter of 10 mm. In eight of 93 patients, major portal hypertension persisted after placement of a 10-mm-diameter shunt, manifested by continued rapid variceal filling and elevated portosystemic gradients. A second TIPS was placed parallel to the first in these patients to allow further portal decompression. In two other patients, a second TIPS was placed because the initial shunt functioned suboptimally. The mean postprocedural portosystemic gradient in the patients who received one TIPS was 10.2 mm Hg +/- 3.7. In patients who received two TIPS, the mean postprocedural gradient was 19.1 mm Hg +/- 3.8 after placement of the first TIPS and 12.5 mm Hg +/- 3.5 after placement of the second. Two patients developed their first episode of encephalopathy after placement of two TIPS. The methods and indications for placing two TIPS in this select population are discussed.

Transjugular intrahepatic portosystemic shunts in patients with portal vein occlusion.

The feasibility and efficacy of transjugular intrahepatic portosystemic shunts (TIPS) were evaluated in 10 patients with preexisting portal vein occlusions. A standard transjugular approach was used in six of the 10 patients for both portal vein recanalization and TIPS placement. The protal veins were successfully recanalized and TIPS were established in three of the six patients. TIPS placement was unsuccessful in the other three patients because the catheters could not be advanced through the occluded segments. A transhepatic approach was used in four of the 10 patients for portal vein recanalization before transjugular catheterization and TIPS placement were attempted. Both portal vein recanalization and TIPS placement were technically successful in all four patients. Bleeding stopped in all patients after successful shunt placement. TIPS can be used to control variceal bleeding in some patients, despite preexisting portal vein occlusion. Preliminary recanalization of the occluded portal segment by means of the transhepatic approach may facilitate TIPS placement.

Transjugular intrahepatic portosystemic shunts: preliminary results in 25 patients.

A retrospective study of transjugular intrahepatic shunts performed between June 1990 and June 1991 is reported. Twelve patients were actively bleeding at the time of the procedure; 12 other patients had had one to five bleeding episodes within the previous 2 weeks, and one patient had massive ascites from Budd-Chiari syndrome. Most patients had severe liver disease: 21 Child's class C, three Child's class B, and one Child's class A. Transjugular intrahepatic shunting was technically successful in all cases. Portal vein pressures were reduced on average from 36 +/- 7 cm H2O to 22 +/- 6 cm H2O. Variceal bleeding ceased after transjugular intrahepatic shunting in all patients who were actively bleeding. Five patients died (30-day mortality, 20%), and eight patients subsequently underwent elective liver transplantation. The transjugular intrahepatic shunts in the 12 other patients have remained patent an average of 5.5 months. Shunt occlusion occurred in three patients at 21, 24, and 102 days, respectively. All three occlusions were successfully reopened with percutaneous techniques, yielding a primary shunt patency of 88% and secondary shunt patency of 100%. Complications included new onset encephalopathy in one patient, which cleared with medical therapy and transient renal failure in one patient. These preliminary data suggest that transjugular intrahepatic shunting is a safe and effective therapy for the short-term treatment of patients with variceal hemorrhage, particularly in patients with severe liver disease awaiting transplantation. The long-term benefit of transjugular intrahepatic shunting awaits further follow-up.