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Biomedical subjects

B Kiefer

Publications and source records attributed to B Kiefer.

At least 37 records · Page 2Linked to original sources
PubMed1996

[MR-Cholangiopancreatography as a single-shot projection: techniques and results of 200 examinations].

PURPOSE: Evaluation of utility and value of a selective projection technique for bile and pancreatic ducts in MRI. MATERIAL AND METHODS: 200 patient examinations of the pancreaticobiliary duct system using a turbo-SE pulse sequence in "single-shot" technique were evaluated in retrospect concerning anatomic display and diagnostic accuracy compared to surgery, ERCP, i.v. cholangiography, ultrasound and clinical course. RESULTS: Non-dilated ducts allowed visualisation of gallbladders in 78%, common bile ducts in 97%, cystic ducts in 80%, intrahepatic main ducts in 71% and pancreatic main ducts in 69%. When dilatation was present, all common bile, intrahepatic main and pancreatic ducts were visible. Display of cystic ducts and gallbladders with a detection rate of 69 and 85%, respectively, did not improve. Sensitivities for diagnosing papillary stenoses (n = 6), pancreatic ductal stenoses and dilatation (n = 13), compressions and dilatations of the biliary tree (n = 33) as well as for one choledochal cyst were 100%. Choledocholithiasis could correctly be predicted in 11/15 cases (73%), cholecystolithiasis in 71/120 cases (59%). CONCLUSION: "Single-shot" MR-cholangiopancreatography is a fast and non-invasive modality which can replace i.v. cholangiography and restrict the indication for ERCP to therapeutic indications and problem cases.

Adult↗
PubMed1996

Cholangiography before biliary surgery: single-shot MR cholangiography versus intravenous cholangiography.

PURPOSE: To compare depiction of the biliary tract with magnetic resonance (MR) and intravenous cholangiography before biliary surgery. MATERIALS AND METHODS: Intravenous cholangiograms and heavily T2-weighted single-shot MR images in 60 patients with biliary calculi were compared prospectively. Images obtained with each technique were independently assessed for depiction of anatomy and calculi. RESULTS: The gallbladder was adequately visualized with intravenous cholangiography in 77% of patients and with MR cholangiography in 88%. Rates for visualization of the common bile duct were 97% and 100%, respectively; for the cystic duct, 27% and 75%; and intrahepatic ducts, 28% and 77%. With either technique, calculi in the gallbladder were correctly predicted as solitary or multiple in approximately 80% of patients. Five cases of common bile duct calculi were correctly predicted with this technique, two cases with cystic duct calculi were depicted with only MR cholangiography. CONCLUSION: Single-shot MR cholangiography may replace intravenous cholangiography for visualization of the biliary tract. However, the delineation of tiny gallbladder calculi and shrunken gallbladders with thickened bile is limited.

Bile Duct Diseases↗
PubMed1996

Focal liver lesions: fast T2-weighted MR imaging with half-Fourier rapid acquisition with relaxation enhancement.

PURPOSE: To compare the clinical usefulness of the half-Fourier rapid acquisition with relaxation enhancement (RARE) technique at T2-weighted magnetic resonance (MR) imaging of focal liver lesions with that of multishot RARE MR imaging and contrast material-enhanced helical computed tomography (CT). MATERIALS AND METHODS: Half-Fourier RARE and multishot RARE imaging and helical CT were performed in 48 patients with 102 focal liver lesions and in three patients with diffuse metastatic liver disease. Images were compared qualitatively and quantitatively for image quality, lesion conspicuity, and ability to help differentiate solid lesions from hemangiomas. RESULTS: All half-Fourier RARE images were free of respiratory artifact. In the 48 patients with 102 focal lesions, CT, half-Fourier RARE, and multishot RARE images depicted 101, 99, and 90 lesions (99%, 97%, and 88%), respectively. CT failed to depict focal lesions in one patient with diffuse metastatic liver disease. All techniques had high accuracy for distinction of hemangiomas from solid masses (areas under the receiver operating characteristic curves were between 0.96 and 0.99). CONCLUSION: Half-Fourier RARE MR imaging is a rapid and accurate technique for detection and characterization of focal liver lesions.

Adult↗
PubMed1995

GRASE improves spatial resolution in single shot imaging.

In single shot echo train imaging all the data required for a two dimensional image is acquired from a series of echoes generated following a single RF excitation pulse. Spatial resolution is limited because all samples must be acquired before the signal decays. In this paper we show theoretically that more echoes and hence better spatial resolution can be obtained with single shot GRASE imaging than with either echo planar imaging or single shot RARE imaging. This conclusion holds for both conventional imaging hardware and specialized gradient hardware designed for EPI. High quality single shot GRASE images support the theoretical conclusions.

Brain↗
PubMed1995

Increased flexibility in GRASE imaging by k space-banded phase encoding.

GRASE (GRadient and spin Echo) is an echo train imaging technique that combines gradient and RF refocusing. Although overall signal decay is with T2 and field inhomogeneity phase errors do not accumulate, the small residual phase errors are periodic with echo number. The echo order described previously eliminates the phase error periodicity in k space but instead creates periodicity in the T2 modulation function that can also cause artifacts. In addition, with this order, the effective TE must be half the echo train time, and asymmetric Fourier sampling is difficult to implement. A new method is described that greatly reduces artifacts due to T2 decay, permits greater control of T2 contrast, and lends itself to asymmetric Fourier sampling. Different time segments of the echo train are encoded with different bands of spatial frequency in k space (hence "k banding"). Both computer simulations and experimental results demonstrate improvements in GRASE images acquired by this method.

Abdomen↗
PubMed1995

The potential of magnetic resonance imaging (MRI) for quantifying articular cartilage thickness -- a methodological study.

The thickness of patellar articular cartilage was assessed in a cadaveric human knee joint by magnetic resonance imaging. Imaging was conducted at 1.0 T, using three-dimensional gradient-echo sequences. From each of the sequences the total cartilage volume, the size of the articular surface, the mean cartilage thickness and the regional distribution of cartilage thickness were determined by image analysis. These values were then compared with those obtained from anatomical sections. The fat-suppressed FLASH sequence was found to allow the most accurate evaluation of the total volume and the regional distribution of the articular cartilage. Slight underestimation of the cartilage thickness by about 5% may be due to the fact that the calcified layer is not made visible by magnetic resonance imaging. There is, however, a very high degree of similarity between the distribution patterns obtained from the MR images and the anatomical sections. The contrast-to-noise ratios and reproducibility were also highest with the fat-suppressedFLASH sequence. This pulse sequence can therefore be recommended for experimental and clinical use.

Journal Article↗
PubMed1995

[Knee joint cartilage in magnetic resonance tomography. MR chondrovolumetry (MR-CVM) using fat-suppressed FLASH 3D sequence].

UNLABELLED: The objective of this study was to optimize the demonstration of articular cartilage with magnetic resonance tomography (MRT) and to assess its accuracy in determining the articular cartilage volume of the knee joint. METHODS: A fat-suppressed FLASH-3D sequence was optimized on healthy volunteers. A fresh cardaveric knee joint was removed from a 82-year-old man and immediately imaged without being frozen or fixed. MRT was carried out at 1.5 T and 25 mT/m (Vision, Siemens, Erlangen, Germany) with a conventional CP knee coil. Sagittal and transverse sections were acquired perpendicular to the articular surfaces, and then, parallel to these imaging planes, anatomical sections were obtained with a diamond band saw. The volumes of the patellar, tibial and femoral cartilages were determined from both the images and the sections, using an image analysing system. RESULTS: Signal intensities and contrast-to-noise ratios depend on the parameters used. The highest contrast between the cartilage and the periarticular tissues was obtained at a flip angle of 30 degrees (TR = 60 ms, TE = 11 ms). However, a flip angle of 60 degrees was judged to provide optimal subjective image quality. Using these parameters, the deviations between the radiological and the anatomical cartilage volumes were -4.7% in the patella, -3.1% in the tibial plateau and -4.2% in the femur. CONCLUSIONS: The volumes of the knee-joint cartilages may be accurately determined with MRT if an appropriate pulse sequence is chosen. From a clinical point of view the differences between MR images and anatomical sections can be considered negligible. These differences may be explained on the basis that MRT delineates uncalcified cartilage only and that the calcified layer is demonstrated as part of the subchondral bone plate. However, close correlation of the thicknesses of the uncalcified and the calcified layer has been reported in the literature, so the relative distribution of articular cartilage should be accurately reflected in MR images.

Aged↗
PubMed1994

Activation of cAMP-dependent protein kinase alters the chromatin structure of the urokinase-type plasminogen activator gene promoter.

In LLC-PK1 cells, the urokinase-type plasminogen activator (uPA) gene is induced by two of the major signal transduction pathways, the protein kinase C (PKC) and the cAMP-dependent protein kinase (PKA) pathways. We have analyzed the chromatin structure of 26 kb of the uPA gene locus and have shown that PKA activation but not PKC activation induce major chromatin structural alterations in the uPA gene promoter. In uninduced cells, several DNase I hypersensitive (HS) sites were detected in the 5' and 3' flanking regions but not in the transcribed region. Two of the sites correspond to previously characterized regulatory sites: a cAMP responsive site at nucleotide position -3500 with respect to the initiation site, and the PEA3/AP1 site at -2100 that mediates PKC activation. After the activation of PKA but not PKC, a strong HS site was induced at -2600. Functional analysis of this region revealed cAMP responsive activity. Chromatin structural alterations again brought about specifically by PKA but not by PKC were were also detected in the upstream of the promoter by topoisomerase I cleavage site analysis, with two prominent sites appearing at -2800 and -3300. These results suggest that the strong cAMP induction of the uPA gene requires structural alterations that permit cooperative interactions between the multiple cAMP responsive sites.

Animals↗
PubMed1994

Okadaic acid-dependent induction of the urokinase-type plasminogen activator gene associated with stabilization and autoregulation of c-Jun.

We have previously shown that the tumor promoter okadaic acid (OA), an inhibitor of protein phosphatases 1 and 2A, transcriptionally induces the urokinase-type plasminogen activator (uPA) gene in LLC-PK1 cells. This induction occurs independently of the protein kinase C- and cAMP-dependent signaling pathways. Here we show that a sequence located 2.0 kilobases upstream of the uPA gene, which resembles an AP-1-recognition sequence, mediates the action of OA. DNA-protein interaction studies, together with mRNA and protein analyses, indicate that c-Jun, but not c-Fos, is involved in OA-dependent uPA gene induction. The appearance of high levels of uPA mRNA and DNA binding activity of c-Jun to the AP-1-like site correspond to the appearance of c-Jun accumulation, suggesting that c-Jun accumulation is a critical event in OA-dependent uPA gene induction. c-Jun protein levels increase significantly between 100 and 160 min following OA treatment, whereas c-Jun translation increases only slightly in this time frame, suggesting that post-translation mechanisms are also involved in c-Jun accumulation. Pulse-chase analyses shows that OA specifically stabilizes c-Jun. We discuss our results with respect to the possibility that protein phosphatase 2A maintains c-Jun in its down-regulated state in LLC-PK1 cells.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1994

Dual contrast GRASE (gradient-spin echo) imaging using mixed bandwidth.

Equal time spacing of RF pulses in the CPMG sequence imposes a constraint of equal signal read periods in spin-echo train imaging. GRASE imaging differs by using multiple read gradients in each pi-pi time interval, which are not constrained to be equal in number or duration. This additional degree of freedom is developed in dual contrast imaging. Closely spaced read periods are used for the PDW image to reduce T2 decay effects, while fewer low-bandwidth read periods in each of several pi-pi intervals are used to raise the signal-to-noise ratio and avoid signal averaging in the T2-weighted image.

Electron Spin Resonance Spectroscopy↗
PubMed1994

[The use of new turbo spin-echo pulse sequences with and without fat suppression in the diagnosis and staging of prostatic carcinoma].

MR studies using turbo spin-echo pulse sequences (TSE) were performed on 27 patients with histologically confirmed prostate cancer. A prospective study was conducted in 15 patients who underwent radical prostatectomy. Turbo SE pulse sequences generate strongly T2-weighted images of excellent quality with reduction of measurement time by a factor of 4-6. A comparison with standard T2-weighted spin-echo pulse sequences indicated an objective improvement in the contrast of pathological structures (p < 0.001). With respect to differentiation of stages T2 and T3 (TNM) during pathohistological correlation, sensitivity of 80%, specificity of 40% and an accuracy rate of 67% were obtained. Sensitivity of 71% and specificity of 75% were obtained when decoding cases of infiltration into the seminal vesicles, with an accuracy rate of 73%.

Adipose Tissue↗
PubMed1993

Cytoskeletal reorganization and TPA differently modify AP-1 to induce the urokinase-type plasminogen activator gene in LLC-PK1 cells.

Urokinase-type plasminogen activator (uPA) is an extracellular protease and expressed in various cells that exhibit dynamic changes in cell morphology, suggesting a link between cytoskeletal reorganization (CSR) and uPA expression. CSR can be induced by pharmacological agents, such as by colchicine for microtubule cytoskeleton and by cytochalasin for microfilament cytoskeleton. Using these agents, we previously showed that CSR induced the uPA gene in LLC-PK1 cells independently of the protein kinase C and cAMP-dependent protein kinase. Here we show that the induction of the uPA gene by CSR is mediated by the activation of c-Jun which interacts with an AP-1-like site located 2 kb upstream of the uPA gene. 12-O-tetradecanoylphorbol 13-acetate (TPA) induces the uPA gene through the same elements, but additionally utilizes an adjacent PEA3 element and induces c-fos. Furthermore, CSR induces a greater accumulation and a more pronounced phosphorylation of c-Jun than TPA induction. AP-1 is a positive regulator of growth and oncogenesis, and CSR is an integral part of these processes. Our results provide a view how CSR and AP-1 could be coupled in these processes. We also show that TPA and CSR act synergistically, suggesting a model where an initial activation signal could be amplified by CSR.

Animals↗
PubMed1991

In vitro production of anti-neutrophilocyte-cytoplasm-antibodies (ANCA) by Epstein-Barr virus-transformed B-cell lines in Wegener's granulomatosis.

The frequent detection of anti-neutrophilocyte-cytoplasm-antibodies (ANCA) in patients with Wegener's granulomatosis (WG) led to the supposition that this disease might be of autoimmune nature. For some authors assume that Epstein-Barr virus (EBV) infection of human B-lymphocytes besides polyclonal activation could reveal the cryptic immune status against different autoantigens in patients with autoimmune diseases we investigated EBV-transformed B-lymphocytes from patients with Sjögren's syndrome, mixed connective tissue disease, WG and healthy blood donors. Two stable B-cell lines (Ho3, We1) could be established. Inhibition experiments showed that antibodies produced by transformed B-lymphocytes and serum ANCA (C-ANCA type) of 10 WG patients recognized the identical antigen. Stimulation of one clone (Ho3) with interleukin 6 (IL-6) led to a switch from IgM to IgG production. Antibodies produced by this clone also stained glomeruli of human frozen kidney sections. Western blot analysis using immunoaffinity purified antigen prepared from human granulocytes revealed a reaction with a protein of approx. 29 kD MW. Our data underscore some new aspects concerning the direct pathogenicity of C-ANCA confirming the hypothesis that the autoimmune B-cell repertoire in WG not only reflects a polyclonal B-cell activation but is shaped by antigen driven responses.

Aged↗
PubMed1990

Ca2+ potentiates cAMP-dependent expression of urokinase-type plasminogen activator gene through a calmodulin- and protein kinase C-independent mechanism.

In the porcine renal epithelial cell line, LLC-PK1, activation of the cAMP-dependent signal transduction pathway induces the urokinase-type plasminogen activator (uPA) gene. We show here that the cAMP response is enhanced when the intracellular calcium concentration is increased. When LLC-PK1 cells were treated with the calcium ionophore ionomycin alone, there was no uPA mRNA accumulation. However, in the presence of ionomycin the dose-response of 8-bromo-cAMP (Br-cAMP) with respect to uPA mRNA accumulation was shifted toward the lower concentrations of Br-cAMP. A Northern blot analysis after the inhibition of RNA synthesis and nuclear run-on assays showed that the synergistic effect of Ca2+ could be attributed to increases in uPA gene transcription and mRNA stability. In the presence of cycloheximide, a protein synthesis inhibitor, uPA mRNA was stabilized, but the effect of ionomycin on Br-cAMP-induced mRNA accumulation was still maintained. The result suggests that the Ca2+, at least on transcription, does not require new protein synthesis. Ionomycin treatment did not modify the activity of the cAMP-dependent protein kinase, suggesting that Ca2+ either affects a step in the pathway between the kinase and the uPA gene, or acts independently of the cAMP-dependent protein kinase pathway. The effect of ionomycin was not suppressed by protein kinase C down-regulation nor by inhibitors of calmodulin. Synergism was also observed when Br-cAMP was replaced with calcitonin, a peptide hormone which is coupled to adenylate cyclase, and when ionomycin was replaced with another ionophore A23187, suggesting that the synergism is due to an interaction between cAMP-dependent and Ca2(+)-dependent signal transduction pathways.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1987

Analysis of adenomatous structures in histopathology.

A new idea of structure analysis in histopathology based upon first-order and third-order structures is presented. Networks formed by single cells and by tubulopapillary formations in adenomatous tissue were analyzed. The algorithm applied is based on the neighborhood conditions defined by O'Callaghan, using graph theory procedures. Twenty cases each of healthy colon mucosa, tubulovillous adenomas and highly to moderately differentiated adenocarcinomas of colon plus ten cases of mesotheliomas and ten cases of adenocarcinomas metastatic to the pleura were analyzed. Statistically significant differences were found in the cyclomatic number of neighboring elements. Classification of specimens of colon mucosa using discriminant analysis yielded correct results in 85% of the 20 cases. All ten cases of metastatic adenocarcinoma and nine of the ten cases of mesothelioma were also correctly classified by the same procedure. A trial of prospective diagnostic assistance in routine histology based upon these cases gave correct classification of three mesotheliomas and of two adenocarcinomas. The procedures are now being used successfully in the routine diagnosis of pleural epithelial/biphasic mesothelioma and of pleuritis carcinomatosa.

Adenocarcinoma↗