How stable are 20th century calibration models? A high-resolution summer temperature reconstruction for the eastern Swiss Alps back to A.D. 1580 derived from proglacial varved sediments

We found a significant positive correlation between local summer air temperature (May-September) and the annual sediment mass accumulation rate (MAR) in Lake Silvaplana (46°N, 9°E, 1800 m a.s.l.) during the twentieth century (r = 0.69, p < 0.001 for decadal smoothed series). Sediment trap data (2001-2005) confirm this relation with exceptionally high particle yields during the hottest summer of the last 140 years in 2003. On this base we developed a decadal-scale summer temperature reconstruction back to AD 1580. Surprisingly, the comparison of our reconstruction with two other independent regional summer temperature reconstructions (based on tree-rings and documentary data) revealed a significant negative correlation for the pre-1900 data (ie, late ‘Little Ice Age’). This demonstrates that the correlation between MAR and summer temperature is not stable in time and the actualistic principle does not apply in this case. We suggest that different climatic regimes (modern/‘Little Ice Age’) lead to changing state conditions in the catchment and thus to considerably different sediment transport mechanisms. Therefore, we calibrated our MAR data with gridded early instrumental temperature series from AD 1760-1880 (r = -0.48, p < 0.01 for decadal smoothed series) to properly reconstruct the late LIA climatic conditions. We found exceptionally low temperatures between AD 1580 and 1610 (0.75°C below twentieth-century mean) and during the late Maunder Minimum from AD 1680 to 1710 (0.5°C below twentieth-century mean). In general, summer temperatures did not experience major negative departures from the twentieth-century mean during the late ‘Little Ice Age’. This compares well with the two existing independent regional reconstructions suggesting that the LIA in the Alps was mainly a phenomenon of the cold season.

High-resolution morphological and biochemical imaging of articular cartilage of the ankle joint at 3.0 T using a new dedicated phased array coil: in vivo reproducibility study

OBJECTIVE: The objective of this study was to evaluate the feasibility and reproducibility of high-resolution magnetic resonance imaging (MRI) and quantitative T2 mapping of the talocrural cartilage within a clinically applicable scan time using a new dedicated ankle coil and high-field MRI. MATERIALS AND METHODS: Ten healthy volunteers (mean age 32.4 years) underwent MRI of the ankle. As morphological sequences, proton density fat-suppressed turbo spin echo (PD-FS-TSE), as a reference, was compared with 3D true fast imaging with steady-state precession (TrueFISP). Furthermore, biochemical quantitative T2 imaging was prepared using a multi-echo spin-echo T2 approach. Data analysis was performed three times each by three different observers on sagittal slices, planned on the isotropic 3D-TrueFISP; as a morphological parameter, cartilage thickness was assessed and for T2 relaxation times, region-of-interest (ROI) evaluation was done. Reproducibility was determined as a coefficient of variation (CV) for each volunteer; averaged as root mean square (RMSA) given as a percentage; statistical evaluation was done using analysis of variance. RESULTS: Cartilage thickness of the talocrural joint showed significantly higher values for the 3D-TrueFISP (ranging from 1.07 to 1.14 mm) compared with the PD-FS-TSE (ranging from 0.74 to 0.99 mm); however, both morphological sequences showed comparable good results with RMSA of 7.1 to 8.5%. Regarding quantitative T2 mapping, measurements showed T2 relaxation times of about 54 ms with an excellent reproducibility (RMSA) ranging from 3.2 to 4.7%. CONCLUSION: In our study the assessment of cartilage thickness and T2 relaxation times could be performed with high reproducibility in a clinically realizable scan time, demonstrating new possibilities for further investigations into patient groups.

High-resolution computer simulation of electrophoretic mobilization in isoelectric focusing

Cationic and anionic electrophoretic mobilization for focusing of hemoglobins (Hb's) in the presence of 100 carrier ampholytes covering a pI range of 6.00-7.98 was studied by computer simulation at a constant current density of 300 A/m(2). Electropherograms that would be produced by whole column imaging and by single detectors placed at different locations along the focusing column are presented. Upon mobilization, peak heights of the Hb zones decrease, but the zones retain a relatively sharp constant profile and are migrating at a constant velocity. A further peak decrease occurs during readjustment at the locations of the original buffer/column interfaces, indicating that detection sensitivity is the lowest at these locations. An anionic carrier ampholyte mobility smaller than that of its cationic species produces a cathodic drift which is smaller than the transport rate used for electrophoretic mobilization. Compared to the case with equal mobilities of carrier ampholyte species, a small increase (decrease) is predicted for the cationic (anionic) mobilization rate within the focusing column. Simulation data suggest that electrophoretic mobilization after focusing and focusing with concurrent electrophoretic mobilization are comparable isotachophoretic processes that occur when there is an uninterrupted flux of an ion through the focusing column. Cathodic drift caused by unequal mobilities of the species of carrier ampholytes, electrophoretic mobilization, and decomposition occurring at the pH gradient edges are related electrophoretic processes.

High-resolution computer simulation of the dynamics of isoelectric focusing: in quest of more realistic input parameters for carrier ampholytes

The impact of the systematic variation of either DeltapK(a) or mobility of 140 biprotic carrier ampholytes on the conductivity profile of a pH 3-10 gradient was studied by dynamic computer simulation. A configuration with the greatest DeltapK(a) in the pH 6-7 range and uniform mobilities produced a conductivity profile consistent with that which is experimentally observed. A similar result was observed when the neutral (pI = 7) ampholyte is assigned the lowest mobility and mobilities of the other carriers are systematically increased as their pI's recede from 7. When equal DeltapK(a) values and mobilities are assigned to all ampholytes a conductivity plateau in the pH 5-9 region is produced which does not reflect what is seen experimentally. The variation in DeltapK(a) values is considered to most accurately reflect the electrochemical parameters of commercially available mixtures of carrier ampholytes. Simulations with unequal mobilities of the cationic and anionic species of the carrier ampholytes show either cathodic (greater mobility of the cationic species) or anodic (greater mobility of the anionic species) drifts of the pH gradient. The simulated cationic drifts compare well to those observed experimentally in a capillary in which the focusing of three dyes was followed by whole column optical imaging. The cathodic drift flattens the acidic portion of the gradient and steepens the basic part. This phenomenon is an additional argument against the notion that focused zones of carrier ampholytes have no electrophoretic flux.

Improved impurity fingerprinting of heparin by high resolution (1)H NMR spectroscopy

For improving the identification of potential heparin impurities such as oversulfated chondroitin sulfate (OSCS) the standard 2D (1)H-(1)H NMR NOESY was applied. Taking advantage of spin diffusion and adjusting the experimental parameters accordingly additional contaminant-specific signals of the corresponding sugar ring protons can easily be detected. These are usually hidden by the more intense heparin signals. Compared to the current 1D (1)H procedure proposed for screening commercial unfractionated heparin samples and focusing on the contaminants acetyl signals more informative and unique fingerprints may be obtained. Correspondingly measured (1)H fingerprints of a few potential impurities are given and their identification in two contaminated commercial heparin samples is demonstrated. The proposed 2D NOESY method is not intended to replace the current 1D method for detecting and quantifying heparin impurities but may be regarded as a valuable supplement for an improved and more reliable identification of these contaminants.

High-resolution computer simulations of EKC

The electrophoresis simulation software, GENTRANS, has been modified to include the interaction of analytes with an electrolyte additive to allow the simulation of liquid-phase EKC separations. The modifications account for interaction of weak and strong acid and base analytes with a single weak or strong acid or base background electrolyte additive and can be used to simulate a range of EKC separations with both charged and neutral additives. Simulations of separations of alkylphenyl ketones under real experimental conditions were performed using mobility and interaction constant data obtained from the literature and agreed well with experimental separations. Migration times in fused-silica capillaries and linear polyacrylamide-coated capillaries were within 7% of the experimental values, while peak widths were always narrower than the experimental values, but were still within 50% of those obtained by experiment. Simulations of sweeping were also performed; although migration time agreement was not as good as for simple EKC separations, peak widths were in good agreement, being within 1-50% of the experimental values. All simulations for comparison with experimental data were performed under real experimental conditions using a 47 cm capillary and a voltage of 20 kV and represent the first quantitative attempt at simulating EKC separations with and without sweeping.

High resolution fast T1 mapping technique for dGEMRIC

PURPOSE: To determine the feasibility of using a high resolution isotropic three-dimensional (3D) fast T1 mapping sequence for delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) to assess osteoarthritis in the hip. MATERIALS AND METHODS: T1 maps of the hip were acquired using both low and high resolution techniques following the administration of 0.2 mmol/kg Gd-DTPA(2-) in 35 patients. Both T1 maps were generated from two separate spoiled GRE images. The high resolution T1 map was reconstructed in the anatomically equivalent plane as the low resolution map. T1 values from the equivalent anatomic regions containing femoral and acetabular cartilages were measured on the low and high resolution maps and compared using regression analysis. RESULTS: In vivo T1 measurements showed a statistically significant correlation between the low and high resolution acquisitions at 1.5 Tesla (R(2) = 0.958, P < 0.001). These results demonstrate the feasibility of using a fast two-angle T1 mapping (F2T1) sequence with isotropic spatial resolution (0.8 x 0.8 x 0.8 mm) for quantitative assessment of biochemical status in articular cartilage of the hip. CONCLUSION: The high resolution 3D F2T1 sequence provides accurate T1 measurements in femoral and acetabular cartilages of the hip, which enables the biochemical assessment of articular cartilage in any plane through the joint. It is a powerful tool for researchers and clinicians to acquire high resolution data in a reasonable scan time (< 30 min).

Initial results of in vivo high-resolution morphological and biochemical cartilage imaging of patients after matrix-associated autologous chondrocyte transplantation (MACT) of the ankle

OBJECTIVE: The aim of this study was to use morphological as well as biochemical (T2 and T2* relaxation times and diffusion-weighted imaging (DWI)) magnetic resonance imaging (MRI) for the evaluation of healthy cartilage and cartilage repair tissue after matrix-associated autologous chondrocyte transplantation (MACT) of the ankle joint. MATERIALS AND METHODS: Ten healthy volunteers (mean age, 32.4 years) and 12 patients who underwent MACT of the ankle joint (mean age, 32.8 years) were included. In order to evaluate possible maturation effects, patients were separated into short-term (6-13 months) and long-term (20-54 months) follow-up cohorts. MRI was performed on a 3.0-T magnetic resonance (MR) scanner using a new dedicated eight-channel foot-and-ankle coil. Using high-resolution morphological MRI, the magnetic resonance observation of cartilage repair tissue (MOCART) score was assessed. For biochemical MRI, T2 mapping, T2* mapping, and DWI were obtained. Region-of-interest analysis was performed within native cartilage of the volunteers and control cartilage as well as cartilage repair tissue in the patients subsequent to MACT. RESULTS: The overall MOCART score in patients after MACT was 73.8. T2 relaxation times (approximately 50 ms), T2* relaxation times (approximately 16 ms), and the diffusion constant for DWI (approximately 1.3) were comparable for the healthy volunteers and the control cartilage in the patients after MACT. The cartilage repair tissue showed no significant difference in T2 and T2* relaxation times (p > or = 0.05) compared to the control cartilage; however, a significantly higher diffusivity (approximately 1.5; p < 0.05) was noted in the cartilage repair tissue. CONCLUSION: The obtained results suggest that besides morphological MRI and biochemical MR techniques, such as T2 and T2* mapping, DWI may also deliver additional information about the ultrastructure of cartilage and cartilage repair tissue in the ankle joint using high-field MRI, a dedicated multichannel coil, and sophisticated sequences.