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Thomas Lange

Publications and source records attributed to Thomas Lange.

11 recordsLinked to original sources
PubMed2006

Prostate spectroscopy at 3 Tesla using two-dimensional S-PRESS.

Two-dimensional (2D) strong-coupling point-resolved spectroscopy (S-PRESS) is introduced as a novel approach to (1)H MR spectroscopy (MRS) in the prostate. The technique provides full spectral information and allows for an accurate characterization of the citrate (Cit) signal. The method is based on acquiring a series of PRESS spectra with constant total echo time (TE). The indirect dimension is encoded by varying the relative lengths of the first and second TEs (TE(1) + TE(2) = TE). In the resulting 2D spectra, only the signal of strongly coupled spin systems is spread into the second dimension, which leads to more clearly arranged spectra. Furthermore, the spectral parameters of Cit (coupling constant J and chemical shift difference delta of the AB spin system) can be determined with high accuracy in vivo. The sequence is analytically optimized for maximal "strong coupling peaks" of Cit at 3T. 2D S-PRESS spectra are compared with JPRESS spectra in vitro as well as in vivo.

Algorithms↗
PubMed2006

Improved two-dimensional J-resolved spectroscopy.

Localised two-dimensional J-resolved spectroscopy (JPRESS) is optimised for the in vivo detection of J-coupled metabolites using magnetic resonance spectroscopy at 3 T. The acquisition of echo signals starts as early as possible (i.e. maximum-echo sampling). This sampling scheme increases sensitivity and decreases overlap of peak tails, hence alleviating baseline problems. Reconstruction issues are discussed and the sensitivity is compared analytically with that of 1D PRESS. The qualitative behaviour of eddy currents in JPRESS is outlined and a 2D eddy current correction procedure based on the 1D phase deconvolution method is proposed.

Adult↗
PubMed2006

The imprecise science of evaluating scholarly performance: utilizing broad quality categories for an assessment of business and management journals.

In a growing number of countries, government-appointed assessment panels develop ranks on the basis of the quality of scholarly outputs to apportion budgets in recognition of evaluated performance and to justify public funds for future R&D activities. When business and management journals are being grouped in broad quality categories, a recent study has noted that this procedure was placing the same journals in essentially the same categories. Drawing on journal quality categorizations by several German- and English-speaking business departments and academic associations, the author performs nonparametric tests and correlations to analyze whether this claim can be substantiated. In particular, he examines the ability of broad quality categorizations to add value to governmental, administrative, and academic decision making by withstanding the criticism traditionally levied at research quality assessments.

Commerce↗
PubMed2004

Visualization of the variability of 3D statistical shape models by animation.

Models of the 3D shape of anatomical objects and the knowledge about their statistical variability are of great benefit in many computer assisted medical applications like images analysis, therapy or surgery planning. Statistical model of shapes have successfully been applied to automate the task of image segmentation. The generation of 3D statistical shape models requires the identification of corresponding points on two shapes. This remains a difficult problem, especially for shapes of complicated topology. In order to interpret and validate variations encoded in a statistical shape model, visual inspection is of great importance. This work describes the generation and interpretation of statistical shape models of the liver and the pelvic bone.

Humans↗
PubMed2003

Vessel-based non-rigid registration of MR/CT and 3D ultrasound for navigation in liver surgery.

OBJECTIVE: Computer assisted planning of liver surgery based on preoperative computed tomography (CT) or magnetic resonance imaging (MRI) data can be an important aid to operability decisions and visualization of individual patients' 3D anatomy. A navigation system based on intraoperative 3D ultrasound may help the surgeon to precisely localize vessels, vascular territories or tumors. The preoperative planning must be transferred to the intraoperative ultrasound data and thus to the patient on the operating table. Due to deformations of the liver between planning and surgery, a fast non-rigid registration method is needed. MATERIALS AND METHODS: A feature-based non-rigid registration approach based on the centerlines of the portal veins has been developed. The combination of an iterative closest point (ICP) approach and Multilevel B-Spline transformations offers a fast registration method. The vessels are segmented and their centerlines extracted from preoperative CT/MRI and intraoperative 3D Powerdoppler ultrasound data. Anatomical corresponding points on the centerlines of both modalities are determined in each iteration of the ICP algorithm. The search for corresponding points is restricted to a given search radius and the direction of the vessels is incorporated. RESULTS: The algorithm has been evaluated on two transcutaneous and one intraoperative clinical ultrasound data set from three different patients. Only a very few vessel segments were not assigned correctly compared to manual assignments. Using non-rigid transformations improved the root mean square target registration error of the vessels by approximately 3-5 mm. CONCLUSIONS: The proposed registration method is fast enough for clinical application in liver surgery. Initial accuracy results are promising and must be further evaluated, particularly in the operating room.

Algorithms↗
PubMed2003

Automatic segmentation of the liver for preoperative planning of resections.

This work presents first quantitative results of a method for automatic liver segmentation from CT data. It is based on a 3D deformable model approach using a-priori statistical information about the shape of the liver gained from a training set. The model is adapted to the data in an iterative process by analysis of the grey value profiles along its surface normals after nonlinear diffusion filtering. Leave-one-out experiments over 26 CT data sets reveal an accuracy of 2.4 mm with respect to the manual segmentation.

Automation↗
PubMed2002

Synthesis and oxidation behavior of 2,4,5,7,8-pentamethyl-4H-1,3-benzodioxin-6-ol, a multifunctional oxatocopherol-type antioxidant.

2,4,5,7,8-Pentamethyl-4H-1,3-benzodioxin-6-ol (PBD, 1) is a novel 3-oxa-tocopherol-type stabilizer, which is obtained as a mixture of two diastereomers by condensation of trimethylhydroquinone with acetaldehyde in an acid-catalyzed reaction. The oxidation behavior of 1 is governed by the amount of water available. In aqueous media, 1 is oxidized by one oxidation equivalent to 2,5-dihydroxy-3,4,6-trimethylacetophenone (3) via 2-(1-hydroxyethyl)-3,5,6-trimethylbenzo-1,4-quinone (2). The acid-catalyzed conversion of 2 into 3 proceeds in solution with first-order kinetics with regard to 2 but works also in solid phase. Oxidation in the presence of just 1 equiv of water produces acetophenone 3 as well, but according to a different mechanism involving o-quinone methide 5 and styrene derivative 6, from which finally acetaldehyde is released. A [1,5]-sigmatropic proton shift from the C-4a methyl group to the exocyclic methylene group in 5 causes formation of 6, as demonstrated by labeling experiments. In addition, the presence of both intermediates was proven by hetero-Diels-Alder trapping reactions. In the absence of water, oxidation of 1 produces chromenone 10 via the intermediates 5 and 6 and chromanone 9, and oxidation of 9 to 10 is preferred to oxidation of starting material 1. When the formation of an exocyclic methylene group at C-4 is impossible as a result of structural prerequisites, as in the diphenyl derivative 12, the initially generated o-quinone methide 5 cannot form 6 but undergoes dimerization to spiro-compounds. The transformation of p-quinone 2 into acetophenone 3 might contribute to the chemistry of tocopherols oxidized at C-4, i.e., 4-hydroxy-alpha-tocopherol and 4-oxo-alpha-tocopherol, which have been proposed as precursors of natural vitamin E metabolites.

Antioxidants↗
PubMed2002

Synthesis of oxidized methyl 4-O-methyl-beta-D-glucopyranoside and methyl beta-D-glucopyranosyl-(1-->4)-beta-D-glucopyranoside derivatives as substrates for fluorescence labeling reactions.

The synthetic cellulose model compounds methyl 4-O-methyl-beta-D-glucopyranoside and methyl 4-O-methyl-beta-D-glucopyranosyl-(1-->4)-beta-D-glucopyranoside and related 6-O-protected intermediates were oxidized in good to fair yields using Swern-conditions or bromine/bis(tributyltin) oxide, respectively, to afford compounds containing 6-aldehyde, 3-keto, and 2,3-diketo groups. Cellobiose and oxidized monosaccharides were then labeled with the carbonyl-selective fluorescence marker 9-(7-amino-1,4,7-trioxaheptyl)-9H-carbazolecarboxamide (CCOA). The labeled derivatives serve as model compounds for the determination of minute amounts of carbonyl groups in cellulosic polysaccharides.

Aldehydes↗
PubMedDate not supplied

A novel method for the determination of carbonyl groups in cellulosics by fluorescence labeling. 1. Method development.

A novel method to accurately determine the carbonyl content in cellulosic materials by fluorescence labeling with carbazole-9-carboxylic acid [2-(2-aminooxyethoxy)ethoxy]amide has been developed. The procedure can readily be incorporated into a gel permeation chromatography (GPC) system with refractive index and multiple-angle laser light scattering detection. Both a homogeneous procedure, working in DMAc/LiCl (2.5%, w/v), and a heterogeneous derivatization approach, using aqueous buffer pH 4.0, for determination of carbonyls in pulps have been optimized with regard to reaction conditions, presence of catalysts, reproducibility, and completeness of conversion. The homogeneous labeling requires prolonged reaction times and removal of excess marker prior to GPC analysis by a time-consuming precipitation-washing-redissolution sequence, which is not needed in the heterogeneous approach. The heterogeneous procedure offers the additional advantages of higher efficiency, shortened analysis times, increased simplicity, and widest applicability.

Aldehydes↗
PubMedDate not supplied

A novel method for the determination of carbonyl groups in cellulosics by fluorescence labeling. 2. Validation and applications.

Fluorescence labeling with the marker carbazole-9-carboxylic acid [2-(2-aminooxyethoxy)ethoxy]amide was shown to be a promising approach toward the accurate determination of carbonyls in cellulosic materials. Combined with gel permeation chromatography in DMAc/LiCl with fluorescence/multiple-angle laser light scattering/refractive index detection, the method yields carbonyl profiles relative to the molecular weight of the cellulosic material. The derivatization procedure can be carried out either homogeneously in DMAc/LiCl or advantageously as heterogeneous derivatization in aqueous buffer. The heterogeneous carbonyl group determination, offering shorter reaction times and increased simplicity as compared to the homogeneous approach, was comprehensively validated. The carbonyl content in numerous dissolving pulps of different provenience has been determined, including pulps with carbonyl contents additionally increased by oxidative treatment. The method was also applied to follow bleaching sequences and oxidative treatments of pulps.

Aldehydes↗