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J Kress

Publications and source records attributed to J Kress.

12 recordsLinked to original sources
PubMed2001

Site distribution in resin beads as determined by confocal Raman spectroscopy.

Scanning confocal Raman spectroscopy was used to study the distribution of reactive sites within a resin bead used for solid-phase synthesis. The distribution of NH2 groups in aminomethylated polystyrene resin (APS) was determined by doping with varying amounts of 4-cyanobenzoic acid. The extent of loading was determined by both elemental analysis and ninhydrin assays. The spatial distribution of the coupled 4-cyanobenzamide within the bead was determined to an in-plane resolution of 1 microm and depth resolution of about 4 microm, using the strong Raman CN stretching vibrational transition at 2230 cm(-1). Dry and swollen beads were studied and the distribution was found to be essentially uniform throughout the bead in all cases.

Journal Article↗
PubMed2000

Depsipeptide dendrimers.

The convergent synthesis of a new class of chiral dendrimers is described. Owing to their structural resemblance to depsipeptides they are called depsipeptide dendrimers. The ex-chiral pool synthesis starts from (R,R)-, (S,S)-, and meso-tartaric acid as branching units and dipeptides or tripeptides consisting of glycine, (L)-alanine, and (L)-leucine as chiral-spacer building blocks. The key intermediates for the convergent assembly of such depsipeptide dendrimers are the peptide-tartaric acid conjugates 13a,b, 19a,b, 25, and 27, which contain either an unprotected C terminus of the peptide chain (13 a,b, 25) or two unprotected hydroxy groups within the tartaric acid termini. Dendra up to the third-generation, by using different combinations of stereoisomeric building blocks, were synthesized and completely characterized. Since this construction principle of chiral depsipeptide dendrimers allows for a wide variation of the length, the primary structure of the peptide spacer, and the configuration of both the amino acid and the tartaric acid moieties, access to new combinatorial libraries is conceptually provided.

Combinatorial Chemistry Techniques↗
PubMed1999

Usability of semiautomatic segmentation algorithms for tumor volume determination.

RATIONALE AND OBJECTIVES: Tumor volume is an important parameter for clinical decision making. At present, semiautomatic image segmentation is not a standard for tumor volumetry. The aim of this work was to investigate the usability of semiautomatic algorithms for tumor volume determination. METHODS: Semiautomatic region- and volume-growing, isocontour, snakes, hierarchical, and histogram-based segmentation algorithms were tested for accuracy, contour variability, and time performance. The test were performed on a newly developed organic phantom for the simulation of a human liver and liver metastases. The real tumor volumes were measured by water displacement. These measured volumes were used as the gold standard for determining the accuracy of the algorithms. RESULTS: Variability of the segmented volumes ranging from 3.9 +/- 3.2% (isocontour algorithm) to 11.5 +/- 13.9% (hierarchical segmentation) was observed. The segmentation time per slice varied between 32 (volume-growing) and 72 seconds (snakes) on an IBM/RS6000 workstation. CONCLUSIONS: Only the region-growing and isocontour algorithms have the potential to be used for tumor volumetry. However, further improvements of these algorithms are necessary before they can be placed into clinical use.

Algorithms↗
PubMed1999

Patient position verification using CT images.

The use of ions in the radiotherapy of cancer patients requires an accurate patient positioning in order to exploit its potential benefits. Using CT images as the basis for the setup verification offers the advantage of a high in-plane resolution in combination with a geometrically accurate, volumetric information. Before each fraction a single CT slice is acquired at the isocenter level after the positioning procedure. This single slice is registered to the planning CT cube using automated image registration algorithms. Thus any erreonous translation or rotation can be detected and quantified. The registration process involves the interpolation of the volumetric data, the calculation of an energy function, and the minimization of this energy function. Several data interpolation functions as well as minimization algorithms were compared. CT studies with a head phantom were performed in which defined translations and rotations were simulated by moving a motor-driven treatment chair. Different slice thicknesses and anatomical sites were studied to investigate their potential influence on the registration accuracy. The accuracy of the registration was found to be a fraction of a voxel size for suitable combinations of algorithms (typically better than 0.16 mm/deg). A significant dependancy of the registration accuracy on the CT slice thickness and the anatomical site was found (the accuracy ranges from 0.05 mm/deg to 0.16 mm/deg depending on the site). The calculation time is dependant on the used algorithms and the magnitude of the setup error. For the standard combination of algorithms as proposed by the authors (Downhill Simplex minimization with Trilinear interpolation) the typical calculation time is about 20 s for a Sun UltraSPARC processor. Taking into account the mechanical accuracy of the setup device (motor-driven chair) the registration of CT images is thus a useful tool for detecting and quantifying any significant error in the patient position.

Algorithms↗
PubMed1997

Single-and dual-energy CT with monochromatic synchrotron x-rays.

We explored the potential for clinical research of computed tomography (CT) with monochromatic x-rays using the preclinical multiple energy computed tomography (MECT) system at the National Synchrotron Light Source. MECT has a fixed, horizontal fan beam with a subject apparatus rotating about a vertical axis; it will be used for imaging the human head and neck. Two CdWO4-photodiode array detectors with different spatial resolutions were used. A 10.5 cm diameter acrylic phantom was imaged with MECT at 43 keV and with a conventional CT (CCT) at 80 kVp: spatial resolution approximately equal to 6.5 line pairs (lp)/cm for both; slice height, 2.6 mm for MECT against 3.0 mm for CCT; surface dose, 3.1 cGy for MECT against 2.0 cGy for CCT. The resultant image noise was 1.5 HU for MECT against 3 HU for CCT. Computer simulations of the same images with more precisely matched spatial resolution, slice height and dose indicated an image-noise ratio of 1.4:1.0 for CCT against MECT. A 13.5 cm diameter acrylic phantom imaged with MECT at approximately 0.1 keV above the iodine K edge and with CCT showed, for a 240 micrograms I ml-1 solution, an image contrast of 26 HU for MECT and 13 and 9 HU for the 80 and 100 kVp CCT, respectively. The corresponding numbers from computer simulation of the same images were 26, 12, and 9 HU, respectively. MECT's potential for use in clinical research is discussed.

Acrylates↗
PubMed1988

[Rotation angioplasty--initial clinical results of peripheral vascular occlusions].

After experimental investigations in postmortem human arteries, 19 patients with chronic peripheral artery occlusions were treated with a new technique between December 1986 and October 1987. In 17 patients the superficial femoral artery, and in two patients the popliteal artery, was completely occluded. The length of occlusions were between 5 and 25 cm (mean 10.9 cm); the duration (estimated according to patient's history) was 5-48 months (mean 17.2 months). In five patients, durations of up to 30 months had been documented by angiography. A flexible, blunt, motor-driven rotating catheter was introduced over an 8 or 9 F sheet and rotational angioplasty was performed at low speed, up to 200 rpm. In 11/14 patients in whom this new technique was used as the first attempt, the occlusions could be successfully reopened. In two patients after failure of the conventional technique the rotating catheter could not bypass the preexisting dissections in the same intervention. In 2/3 further patients after failure of the conventional technique the occlusions could be successfully reopened in a second intervention after several weeks. In none of our 19 patients did a perforation occur. It is concluded that by using the new technique, chronic peripheral artery occlusions can be reopened with a high success rate and without the danger of vessel wall perforation. The method can also be applied in patients in whom conventional techniques have failed.

Adult↗
PubMed1987

[Rotation angioplasty--a new procedure for reopening and dilating blood vessels. Experimental findings].

16 fresh postmortem specimens of human femoral and popliteal arteries with severe atherosclerosis were removed and angiography was performed. Eight vessels were completely occluded and eight showed stenoses of up to 60%. All occluded vessels were heavily calcified. The duration of occlusion, estimated according to the patient's history, ranged from 1 to 2 years. In one case, a duration of 18 months was documented by angiography. The lengths of the occlusions were between 5 and 12 cm. A rotating catheter was introduced through a 9F guiding catheter. All stenosed vessels were passed and seven out of eight occluded vessels, in which passage was not possible using conventional wires, were successfully reopened at low speed rotation of 200 rpm. Angiography, as well as histology, showed no perforation, and angioscopy revealed a smooth surface of the new channel. In three vessels this new channel was dilated with a balloon catheter and in one with an elastic element under rotation. It is concluded that with the new technique it is possible to reopen totally occluded human arteries which cannot be passed by conventional methods.

Angioplasty, Balloon↗