Polymer Reaction Engineering VI Halifax,Canada May 21–26, 2006

Conference Reports: This section contains reports on topical conferences. Reports are usually written at the request of the editorial office, but unsolicited contributions are also welcome. Suggestions should be sent to the editorial office of the Macromolecular journals, preferably by E‐mail to macromol@wiley‐vch.de.     

Adiabatic refocusing pulses for volume selection in magnetic resonance spectroscopic imaging.

Because of their excellent slice profiles and high immunity to RF inhomogeneity, adiabatic full passage (AFP) pulses are ideal for use in spatial localization. The nonlinear, position-dependent phase of a single AFP pulse generated during refocusing of transverse magnetization traditionally is eliminated by using identical pairs of AFP pulses, at the expense of increased RF power deposition and increased echo time (TE). Here it is shown that one can achieve significant phase refocusing by executing single AFP pulses along non-equivalent spatial axes. When used for volume selection in MR spectroscopic imaging (MRSI) the remaining nonlinear phase becomes inconsequential when the phase across a spectroscopic volume is small. Selection of rectangular and octagonal volumes is demonstrated with half the number of AFP pulses used in the traditional approach. It is shown that octagonal volume selection in the human brain provides excellent suppression of extracranial lipids, and thus allows multislice (1)H MRSI at 4 Tesla to be performed within the guidelines for RF power deposition.     

Tamponade caused by cardiac lipomatous hypertrophy.

Cardiac lipomatous hypertrophy is an unusual disorder that typically affects the interatrial septum. We report a case in which large subpericardial deposits of fat were initially mistaken for a pericardial effusion and the subsequent clinical picture resembled tamponade. The patient improved following a pericardiectomy.     

Fast method for 1D non-cartesian parallel imaging using GRAPPA.

MRI with non-Cartesian sampling schemes can offer inherent advantages. Radial acquisitions are known to be very robust, even in the case of vast undersampling. This is also true for 1D non-Cartesian MRI, in which the center of k-space is oversampled or at least sampled at the Nyquist rate. There are two main reasons for the more relaxed foldover artifact behavior: First, due to the oversampling of the center, high-energy foldover artifacts originating from the center of k-space are avoided. Second, due to the non-equidistant sampling of k-space, the corresponding field of view (FOV) is no longer well defined. As a result, foldover artifacts are blurred over a broad range and appear less severe. The more relaxed foldover artifact behavior and the densely sampled central k-space make trajectories of this type an ideal complement to autocalibrated parallel MRI (pMRI) techniques, such as generalized autocalibrating partially parallel acquisitions (GRAPPA). Although pMRI can benefit from non-Cartesian trajectories, this combination has not yet entered routine clinical use. One of the main reasons for this is the need for long reconstruction times due to the complex calculations necessary for non-Cartesian pMRI. In this work it is shown that one can significantly reduce the complexity of the calculations by exploiting a few specific properties of k-space-based pMRI.     

Atypical forms of isolated partial atrioventricular septal defect increase the risk of initial valve replacement and reoperation.

OBJECTIVE: We consider the short- and long-term outcomes of the repair of the isolated partial atrioventricular (AV) septal defect to determine the role played by the atypical forms on the initial AV valve replacement and on the risk of reoperation. METHODS: Two hundred and eight patients underwent an operation for this malformation between 1974 and 2001. Clinical and echocardiographic examinations were performed on all patients, the AV valve regurgitation was graded from 1 to 4 and a residual interatrial shunt was sought. Median age at the intervention was 5.8 years (3 months to 67 years). RESULTS: Median follow-up time was 7.5 years (range 0-22.6 years). The cumulative 30-day, 5- and 20-year survival rates were 96.5, 95.4 and 94.6%, respectively. AV valve replacement was associated with a high mortality (P<0.001). A reoperation was performed on 12 patients (5.7%) including six patients within less than a 30-day period, especially to repair residual AV valve regurgitation. We performed four AV valve repairs by annuloplasty and six AV valve replacements. Two patients who had initially undergone an AV valve replacement underwent a reoperation for valve thrombosis. The cumulative 30-day, 5- and 20-year rates of freedom from reoperation were 96.5, 93.6 and 83%, respectively. An atypical form was present in 24 patients (11.5%) and was a risk factor for initial AV valve replacement (P<0.001) and for reoperation (P<0.001). A complete AV block occurred in 13 patients (6.2%), all of them within a 30-day period. The AV valve replacement was a high risk factor for a complete AV block (P<0.001). At the end of our study 180 patients (96%) were in NYHA I and 8 in NYHA II. CONCLUSIONS: The morbi-mortality of the isolated partial AV septal defect is primarily perioperative and is linked with the presence of an atypical form of the lesion. This atypical form was the main reason for reoperation for AV valve regurgitation. The AV valve replacement was associated with a high mortality and with the occurrence of complete AV block. Using a standardized technique, the AV septal defect can be repaired with excellent long-term clinical and echographic results.     

Siberian ginseng (Eleutheroccus senticosus) effects on CYP2D6 and CYP3A4 activity in normal volunteers.

Siberian ginseng ([SG]; Eleutherococcus senticosus) is a commonly used herbal preparation. The objective of this study was to assess in normal volunteers (n = 12) the influence of a standardized SG extract on the activity of cytochrome P450 CYP2D6 and 3A4. Probe substrates dextromethorphan (CYP2D6 activity) and alprazolam (CYP3A4 activity) were administered orally at baseline and again following treatment with SG (1 x 485 mg twice daily) for 14 days. Urinary concentrations of dextromethorphan and dextorphan were quantified, and dextromethorphan metabolic ratios (DMRs) were determined at baseline and after SG treatment. Likewise, plasma samples were collected (0-60 h) for alprazolam pharmacokinetics at baseline and after SG treatment to assess effects on CYP3A4 activity. Validated high performance liquid chromatography methods were used to quantify all compounds and relevant metabolites. There were no statistically significant differences between pre- and post-SG treatment DMRs indicating a lack of effect on CYP2D6 (P > 0.05). For alprazolam there also were no significant differences in the pharmacokinetic parameters determined by noncompartmental modeling (C(max), T(max), area under the curve, half-life of elimination) indicating that SG does not significantly induce or inhibit CYP3A4 (P > 0.05). Our results indicate that standardized extracts of SG at generally recommended doses for over-the-counter use are unlikely to alter the disposition of coadministered medications primarily dependent on the CYP2D6 or CYP3A4 pathways for elimination.     

Fluorescence and photobleaching dynamics of single light-harvesting complexes

Single light-harvesting complexes LH-2 from Rhodopseudomonas acidophila were immobilized on various charged surfaces under physiological conditions. Polarized light experiments showed that the complexes were situated on the surface as nearly upright cylinders. Their fluorescence lifetimes and photobleaching properties were obtained by using a confocal fluorescence microscope with picosecond time resolution. Initially all molecules fluoresced with a lifetime of 1 ± 0.2 ns, similar to the bulk value. The photobleaching of one bacteriochlorophyll molecule from the 18-member assembly caused the fluorescence to switch off completely, because of trapping of the mobile excitations by energy transfer. This process was linear in light intensity. On continued irradiation the fluorescence often reappeared, but all molecules did not show the same behavior. Some LH-2 complexes displayed a variation of their quantum yields that was attributed to photoinduced confinement of the excited states and thereby a diminution of the superradiance. Others showed much shorter lifetimes caused by excitation energy traps that are only ≈3% efficient. On repeated excitation some molecules entered a noisy state where the fluorescence switched on and off with a correlation time of ≈0.1 s. About 490 molecules were examined.     

Sarcoid Myelopathy

A 45-year-old woman with history of iritis, uveitis, and sarcoidosis of the skin presented with a subacute cervical myelopathy. Magnetic resonance imaging (MRI) ;howed patchy, multifocal, gadoliniumenhancing intramedullary lesions of the spinal cord, and extramedullary lesions of the basal cisterns and fourth ventricle. Symptoms and MRI abnormalities were improved within 1 month of corticosteroid therapy.