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Biomedical subjects

G Adam

Publications and source records attributed to G Adam.

At least 163 records · Page 9Linked to original sources
PubMed1998

Device visualization for interventional MRI using local magnetic fields: basic theory and its application to catheter visualization.

This paper addresses one of the major problems in Interventional magnetic resonance imaging (MRI): the visualization of interventional devices. For visualization locally induced magnetic fields are used, which disturb the homogeneity of the main magnetic field of the MR scanner. This results in signal loss in the vicinity of the device due to intravoxel dephasing, and leads to a disturbance of the phase image. The local fields are established by a low current in a closed copper loop along the device. This method will be introduced as a means for catheter visualization. The basic theory behind this method is presented. Simulations are performed to determine the effect of intravoxel dephasing, without interfering effects like susceptibility or radio-frequency artifacts. Scanned and simulated data is used to verify the theoretical consideration. Different configurations of wire loops are discussed and two types of catheter visualization scans are proposed. Results from a pig study show that this methods holds promise for intravascular interventions under MRI guidance.

Animals↗
PubMed1998

Abdominal MR angiography performed using blood pool contrast agents: comparison of a new superparamagnetic iron oxide nanoparticle and a linear gadolinium polymer.

OBJECTIVE: We evaluated and compared two different experimental blood pool contrast agents for abdominal MR angiography in an animal model. MATERIALS AND METHODS: In seven pigs, coronal T1-weighted three-dimensional fast field-echo images were obtained on a conventional 1.5-T MR imaging system before and after i.v. injection of the ultrasmall superparamagnetic iron oxide agent FeO-BPA. In another seven pigs, MR angiograms were acquired using the gadolinium polymer WIN 22181. Enhanced images were obtained 5-210 min after injection of FeO-BPA and 1-120 min after injection of WIN 22181. RESULTS: Both blood pool agents yielded detailed angiograms of the abdominal vascular tree when imaging lasted 2 min. In-plane running vessels were imaged without saturation effects and with equivalent maximum signal-to-noise ratios. Half the maximum signal-to-noise ratio was reached 150 min after injection of FeO-BPA, whereas this interval was approximately 70 min for the gadolinium polymer. Because of these different imaging half-life periods, the effective diagnostic window provided by FeO-BPA was six to eight times longer than that of WIN 22181. In the liver, the vascular T1 shortening and the parenchymal T2* effect of FeO-BPA complemented each other, resulting in an optimal contrast-to-noise ratio significantly higher than that achieved with WIN 22181. This "double-contrast effect" in the liver was especially helpful when obtaining detailed MR portograms. CONCLUSION: The blood pool agents FeO-BPA and WIN 22181 can be used to produce high-quality abdominal MR angiograms on standard MR imaging equipment. The contrast-to-noise ratio of hepatic vessels is best on iron oxide-enhanced images because of a T1-T2* synergistic effect in the liver. The longer diagnostic window provided by FeO-BPA coupled with the option of in-plane imaging suggests the usefulness of FeO-BPA in future MR imaging-guided vascular interventions.

Abdomen↗
PubMed1998

Spontaneous retroperitoneal haemorrhage associated with renal disease.

Spontaneous retroperitoneal haemorrhage is an uncommon entity. It is even rarer when the underlying cause is associated with renal disease. In most cases the non-traumatic rupture of a kidney requires an emergency surgical intervention as the underlying disease only becomes clear intra-operatively. Most patients with a spontaneous kidney rupture have a renal tumour. Of these renal tumours, angiomyolipomas show a particular tendency to rupture. The cases are reported of five patients who presented with an acute onset of spontaneous retroperitoneal haemorrhage from different kidney disorders. The importance of considering the possibility of spontaneous kidney rupture in the evaluation of patients presenting with spontaneous retroperitoneal haemorrhage is stressed.

Adult↗
PubMed1998

[Fiber optic measurements with the Bilitec probe for quantifying bile reflux after aboral stomach resection].

Nonphysiological alkaline reflux after partial gastrectomy may produce a range of gastrointestinal disorders. The Bilitec probe is a fibroptic sensor that, for the first time, makes in vivo measurement of this reflux possible, by assay of spectrophotometric absorption of bilirubin. We studied 20 patients who had undergone partial gastrectomy for benign peptic ulcer disease. Ten patients had Billroth II reconstruction and ten had Roux-en-Y reconstruction. In the Roux-en-Y Group we found almost complete control of symptoms and no objective evidence of alkaline reflux as measured by the Bilitec probe. In the Billroth II group we detected by the fiberoptic sensor significant bile reflux into the stomach remnant. Based on these results we recommend Roux-en-Y gastrojejunostomy as the method of choice for reconstruction after distal gastric resection.

Adult↗
PubMed1998

FDG PET for detection and therapy control of metastatic germ cell tumor.

UNLABELLED: We investigated the use of PET and 2[18F]fluoro-2-deoxy-D-glucose (FDG) for detection and therapy control of metastatic germ cell cancer in comparison to CT. METHODS: Fifty-four PET studies were performed in addition to CT in 33 patients with histopathologically proven germ cell tumors (14 seminomas, 18 nonseminomas, 1 not classified). The scans were done either after initial diagnosis (Group 1; n = 12), within 2 wk after completion of chemotherapy (Group 2; n = 13) or 14-375 days after chemotherapy (Group 3; n = 29). PET and CT were validated either by histology (n = 19) or clinical follow-up for 182-1704 days (n = 35). Focal pathological uptake with PET was quantified using standardized uptake values (SUVs). RESULTS: PET was significantly more accurate than CT (0.86 versus 0.59; p < 0.025) for detection of residual viable tumor in Group 3. While sensitivities of PET and CT did not differ markedly, PET was significantly more specific than CT. No significant differences between PET and CT were found in Groups 1 and 2. PET scans after therapy resulted in false-negative findings in five of nine cases of Group 2 but only in two of nine cases of Group 3. False-positive PET findings occurred in three inflammatory processes. SUV of seminomas was significantly higher than in nonseminomas (p < 0.01). CONCLUSION: PET using FDG is superior to CT for assessment of residual tumor after chemotherapy of germ cell cancer and may thus have an increased effect on patient management in the future. PET must be performed at least 2 wk after completion of therapy. Further data are necessary to determine the role of FDG PET for initial staging of germ cell cancer.

Adult↗
PubMed1998

Early events of tomato spotted wilt transcription and replication in protoplasts.

A protoplast transfection system for tomato spotted wilt tospovirus (TSWV) was established by PEG-mediated infection of tobacco protoplasts. Analysis of viral RNA synthesis revealed an asymmetric production of viral (v) and viral-complementary (vc) strands of all three genomic RNA segments and a separation in time of subgenomic transcription during the first 72 hr post infection (p.i.). Synthesis of vc-RNA was detectable 8-10 hrs prior to v-RNA production. During the first 72 h of infection the accumulation of S-RNAs exceeded M- and L-RNAs and the amount of vc-RNAs was larger than that of genomic v-RNAs. The subgenomic N-mRNA was first detected 5 hr p.i., followed by vc-S RNA and the mRNA for the nonstructural protein (NSs) 15 hr later. The two subgenomic mRNA species of the S RNA appeared to be regulated independently from each other and from other viral mRNA species. Defective interfering (DI) elements from L RNA associated with the virus inoculum, were not preferentially replicated at the expense of full-sized L-RNA.

Immunohistochemistry↗
PubMed1997

7-alkylidenecephalosporin esters as inhibitors of human leukocyte elastase.

A series of 7-alkylidenecephalosporins and 7-vinylidenecephalosporins, as their benzhydryl esters, have been tested as inhibitors of both porcine pancreatic elastase and human leukocyte elastase. Selected 7-alkylidenecephalosporin esters are found to be potent inhibitors of HLE. One category of new inhibitors is the 7-(haloalkylidene)cephalosporins. In contrast to previously reported cephalosporin-based elastase inhibitors, these haloalkylidene cephems show optimum inhibitory activity as sulfides, rather than as sulfones. They are efficient and irreversible inhibitors. A second class of active compounds is represented by the benzhydryl ester 7-(cyanomethylidene)cephalosporin sulfone. In contrast to the activity of these new inhibitors, the benzhydryl ester of the mechanism-based beta-lactamase inhibitor, 7-[(2'-pyridyl)methylidene]-cephalosporin sulfone showed little inhibitory activity as an elastase inhibitor. 7-Vinylidenecephalosporins were also relatively poor inhibitors, although the terminally unsubstituted allene sulfide showed activity as an inhibitor of PPE. A modeling analysis suggests the 7-alkylidene substituents can be readily accommodated in the S1 pocket. A potential mechanism of inhibition is proposed.

Animals↗
PubMed1997

Catheter visualization using locally induced, actively controlled field inhomogeneities.

A new technique for visualization of interventional devices using MR is presented. A prototype catheter was equipped with a thin copper wire loop, leading from the proximal end to the tip and back. A small current (10-150 mA) through these two parts of a wire induces a local magnetic field along the catheter. Introduction of this catheter into the main magnetic field of the MR imager locally disturbs the homogeneity of the magnetic field. Image locations within the locally induced fields appear dark due to signal loss, and the extent of this effect can be varied during the procedure by simply adjusting the current. Different dedicated wire configurations allow visualization of the catheter in its whole length or in parts, i.e., with markers for balloons. Fast gradient echo sequences that provide a bright signal from inflowing blood are used for rapid imaging.

Animals↗
PubMed1997

Fluorine-18 fluorodeoxyglucose positron emission tomography in the differential diagnosis of pancreatic carcinoma: a report of 106 cases.

The aim of this study was to evaluate fluorine-18 fluorodeoxyglucose positron emission tomography ([18F]FDG PET) as a tool for the differential diagnosis of pancreatic carcinoma while taking into account serum glucose level. A group of 106 patients with unclear pancreatic masses were recruited for the study. PET was performed following intravenous administration of an average of 190 MBq [18F]FDG. Focally increased glucose utilisation was used as the criterion of malignancy. In addition, the "standardised uptake value" (SUV) was determined 45 min after injection. Carcinoma of the pancreas was demonstrated histologically in 74 cases, and chronic pancreatitis in 32 cases. Employing visual evaluation, 63 of the 74 (85%) pancreatic carcinomas were identified by PET. In 27 of the 32 cases (84%) of chronic pancreatitis it was possible to exclude malignancy. False-negative results (n=11) were obtained mostly in patients with raised serum glucose levels (10 out of 11), and false-positives (n=5) in patients with inflammatory processes of the pancreas. Thus PET showed an overall sensitivity of 85%, a specificity of 84%, a negative predictive value of 71%, and a positive predictive value of 93%. In a subgroup of patients with normal serum glucose levels (n=72), the results were 98%, 84%, 96% and 93%, respectively. Quantitative assessment yielded a mean SUV of 6.4+/-3.6 for pancreatic carcinoma as against a value of 3.6+/-1.7 for chronic pancreatitis (P<0.001), without increasing the diagnostic accuracy. This shows PET to be of value in assessing unclear pancreatic masses. The diagnostic accuracy of PET examinations is very dependent on serum glucose levels.

Adenocarcinoma↗
PubMed1997

Characterization of more than 85% of cystic fibrosis alleles in the Greek population, including five novel mutations.

To completely characterize the spectrum of mutations in the cystic fibrosis transmembrane conductance regulator gene in Greek cystic fibrosis (CF) patients, we screened 500 CF chromosomes by denaturing gradient gel electrophoresis followed by direct sequencing. We identified 48 mutations, accounting for 85.6% of CF chromosomes. They included eight novel mutations, three of which we have described before and five (E822X, Y247X, 2752-26A-->G, 3152delT, and 2751 + T-->A), which are described in this report. The detection of such a high proportion of Greek CF mutations is important for improving prenatal and genetic diagnosis of CF in Greece.

Adult↗
PubMed1997

Brassinosteroids from seeds of Arabidopsis thaliana.

Extracts of seeds of Arabidopsis thaliana (ecotype 24) were analysed for the presence of free and conjugated brassinosteroids. 24-epi-Brassinolide (ca 220 ng kg-1) and castasterone (ca 360 ng kg-1) could be isolated and unambiguously identified as native brassinosteroids by GC/MS.

Arabidopsis↗
PubMed1997

Synthesis of new delta 5-7-oxygenated and delta 5,7-unsaturated brassinosteroid analogs.

We report on the synthesis of the brassinosteroid analogs (22R,23R)-3 beta, 7 beta, 22,23-tetrahydroxy-stigmast-5-ene (13), (22R,23R)-3 beta, 7 alpha, 22,23-tetrahydroxy-stigmast-5-ene (15), and (22R,23R)-3 beta, 22,23-trihydroxy-stigmast-5,7-diene (18) by means of the osmium-catalyzed asymmetric dihydroxylation of intermediate 1, available from stigmasterol. This reaction sequence produced the expected (22S,23S)- and (22R,23R)-triols 6 and 7 as well as the 22,23-diketo derivatives 2 and 3. The phytohormone activity of the new brassinosteroid analogs is discussed.

Plant Growth Regulators↗
PubMed1997

Retrofitting YACs for direct DNA transfer into plant cells.

The utility of plant YAC libraries prepared in conventional YAC vectors would be dramatically increased if these YACs could be used directly for plant transformation. A pair of vectors that allow clones from YAC libraries to be modified (retrofitted) for plant transformation by direct DNA transfer methods, such as particle bombardment or electroporation, has been developed. Modification of the YAC is achieved in two sequential yeast transformation steps by taking advantage of the homologous recombination system in yeast. Using this approach, two plant-selectable marker genes and DNA sequence elements required for copy number amplification in yeast can be introduced into YACs present in yeast strain AB1380. The utility of these vectors is demonstrated by retrofitting YACs that contain inserts ranging in size from 80 to 700 kb. The 6- to 12-fold increase in copy number of these modified YACs facilitates the isolation of YAC DNA for direct DNA transformation methods. Retrofitted YACs were used for particle bombardment to examine the efficiency with which their large DNA inserts are transferred into plant cells. The availability of these retrofitting vectors should facilitate the transfer of YAC DNA inserts into plant cells and thus help bridge the gap between existing mapping techniques and plant transformation procedures.

Chromosomes, Artificial, Yeast↗
PubMed1997

[Osteoporotic stress fractures of the sacrum: MR-tomography findings].

PURPOSE: Evaluation of the morphologic appearance of sacral osteoporotic insufficiency fractures in MRI. PATIENTS AND METHOD: 6 patients (5 female and one male, 54-80 years) with osteoporotic insufficiency fractures of the sacrum were examined with CT and MRI. Plain and contrast-enhanced T1- and T2-weighted spin-echo images were acquired, three patients were studied with T1-weighted gradient-echo-sequences with fat suppression. RESULTS: Fracture-lines and sclerotic areas of the massae laterales were visible in 5 of 6 CT examinations, one patient showed no abnormalities of the sacrum on the initially performed CT scans. All patients had a diffuse bone marrow oedema of the fractured massae laterales with a decreased signal on the T1-weighted spin-echo images and an increased signal on the T1-weighted gradient-echo images with fat suppression and in the T2-weighted SE-sequences. Gadopentate dimeglumine enhanced MRI images showed a remarkable diffuse configurated high signal of the whole sacrum in bilateral fractures (H-pattern). An additional soft tissue mass could be excluded in each case. CONCLUSION: Gadopentate dimeglumine enhanced MRI of sacral insufficiency fractures allows early diagnosis and helps to exclude intraosseous tumour formation.

Aged↗
PubMed1997

[Catheter visualization in MR-tomography: initial experimental results with field-inhomogeneity catheters].

PURPOSE: To assess the feasibility of a new developed field inhomogeneity catheter for interventional MR imaging in vivo. MATERIALS AND METHODS: Three different prototypes of a field inhomogeneity catheter were investigated in 6 pigs. The catheters were introduced in Seldinger technique via the femoral vessels over a guide wire on an interventional MR system (Philips Gyroscan NT combined with a C-arm fluoroscopy unit [Philips BV 212]). Catheters were placed in veins and arteries. The catheter position was controlled by a fast gradient echo sequence (Turbo Field Echo [TEE]). RESULTS: Catheters were introduced over a guide wire without complications in all cases. Using the field inhomogeneity concept, catheters were easily visualised in the inferior vena cava and the aorta by the fast gradient echo technique on MR in all cases. Although aortic branches were successfully cannulated, the catheters were not displayed by the TFE technique due to the complex and tortuous anatomy. All animals survived the experiments without complications. CONCLUSION: MR guided visualization of a field inhomogeneity catheter is a simple concept which can be realised on each MR scanner and may allow intravascular MR guided interventions in future.

Animals↗