Biomedical subjects

J P De Wilde

Publications and source records attributed to J P De Wilde.

7 recordsLinked to original sources

PubMed2001

Investigation of acoustic noise on 15 MRI scanners from 0.2 T to 3 T.

Acoustic noise levels for fast MRI pulse sequences were surveyed on 14 systems with field strengths ranging from 0.2 T to 3 T. A microphone insensitive to the magnetic environment was placed close to the magnet isocenter and connected via an extension cable to a sound level meter outside the scan room. Measured noise levels varied from 82.5 +/- 0.1 dB(A) for a 0.23 T system to 118.4 +/- 1.3 dB(A) for a 3 T system. Further measurements on four of the closed-bore systems surveyed showed that: 1) pulse sequence parameters (particularly FOV and TR) were more influential in determining noise level than field strength, 2) the noise level was found to vary along the z-direction with a maximum near the bore entrance, and 3) in one of two systems tested there was a significant increase in noise with a volunteer present instead of a test object. The results underline the importance of hearing protection for patients and for staff spending extended periods in the scan room.

Ear Protective Devices↗

PubMed1998

Surgical trauma does not decrease resistance to infection.

OBJECTIVE: To investigate the effect on survival of two operations done at various intervals before the induction of monobacterial or multibacterial peritonitis in rats. DESIGN: Laboratory study. SETTING: Teaching hospital, Belgium. MATERIAL: Inbred male white wistar R/A rats. INTERVENTIONS: Posterolateral laparotomy, hindleg amputation, or control (anaesthetic only) (n=90 animals in each group), followed by induction of Escherichia coli or Staphylococcus aureus peritonitis at 1, 7 or 14 days. Further groups of rats were similarly operated on (50 in each group), but peritonitis was induced by caecal ligation and puncture. MAIN OUTCOME MEASURE: Survival 7 days after induction of peritonitis. RESULTS: Of the rats in which E. coli was used to induce peritonitis 27/28 (96%), 29/29 (100%), and 21/30 (70%) had survived 7 days after induction of peritonitis in the group that underwent posterolateral laparotomy, compared with 18/30 (60%), 20/28 (71%), and 18/28 (64%) in the control group; p 0.001, 0.002, and 0.78, respectively. The figures for hindleg amputation were 21/27 (78%), 23/27 (85%), and 17/30 (57%). The corresponding figures for S. aureus peritonitis were for posterolateral laparotomy 28/30 (93%), 20/30 (67%), and 24/29 (83%) compared with controls 21/30 (70%), 9/30 (30%), and 20/29 (69%); p 0.04, 0.009, and 0.75, respectively. The figures for hindleg amputation were 21/30 (70%), 12/30 (40%), and 23/30 (77%). Similar results were obtained with peritonitis induced by caecal ligation and puncture. CONCLUSIONS: Although surgical trauma may depress various aspects of the immune response in rats, it does not decrease their resistance to intraperitoneal microbial infections. The previous opening of the peritoneal cavity seemed to improve survival in our model.

Animals↗

PubMed1998

Absence of direct relationship between intraperitoneal cellular influx and resistance to experimental peritonitis.

Intraperitoneal inflammation is an essential defence mechanism against microbial invasion of the abdominal cavity. We have recently demonstrated that a single contact with heat killed E. Coli or Staphylococcus aureus increased the intraabdominal leukocyte influx in rats later challenged by these microorganisms. The aim of the present study was to investigate some of the mechanisms of this phenomenon and to determine its effect on rats survival in an experimental model of peritonitis. The intraabdominal influx of leukocytes following intraperitoneal injection of E. coli, Pseudomonas aeruginosa or Staphylococcus was stimulated by previous intraperitoneal injection of heat killed microbes. The phenomenon was not specific, pretreatment with E. Coli enhanced the intraperitoneal inflammatory reaction against Pseudomonas and vice versa. On the contrary, pretreating the rats with heat killed microorganisms specifically improved their survival after induction of peritonitis with live bacteria, there was no cross-protection. Heat killed staphylococcus aureus which stimulated a subsequent inflammatory reaction against heat killed E. Coli had no effect on the mortality rates of E. Coli peritonitis. In conclusion, there is no direct relationship between resistance to peritonitis and the amount of leukocytes migrating into the abdominal cavity.

Animals↗

PubMed1997

Information in magnetic resonance images: evaluation of signal, noise and contrast.

The assessment of diagnostic image quality for MRI is considered. The assessment of three key image quality determinants is addressed: signal, noise and contrast. There is a distinction between random noise evaluation, for the calculation of the SNR, and structured noise evaluation for the assessment of image artefacts. Specific methods used are correlation techniques and the Wiener spectrum. Contrast is assessed by comparison of experimental data and theoretical predictions. For each assessment, the theory and method of the evaluation strategy are discussed. The discussion is illustrated with analysis results from commercial MR systems. The choice of analysis method and the subsequent derivation of quality indices are shown to be critical in respect of robustness and accuracy.

Artifacts↗

PubMed1996

Direct activation of human peritoneal mesothelial cells by heat-killed microorganisms.

OBJECTIVE: The aim of the study was to determine if human peritoneal mesothelial cells (HPMCs) can be activated directly by bacterial products contained in preparations of heat-killed Escherichia coli and staphylococci. SUMMARY BACKGROUND DATA: It has been shown recently that cytokine-activated HPMCs produce the inflammatory mediators, interleukin-1, interleukin-6, interleukin-8, and macrophage chemotactic protein-1. Studies concerning the effects of bacterial products on HPMCs are scarce and have not yielded conclusive results. METHODS: Growth-arrested HPMC monolayers were prepared from cell suspensions obtained by enzymatic disaggregation of small pieces of omentum. They were incubated for 24 hours with heat-killed E. coli (ATCC 25922), heat-killed staphylococci (ATCC 25933), or E. coli lipopolysaccharide, and the release of various cytokines in the culture media was measured by radioimmunoassays or enzyme-linked immunosorbent assays. Results were expressed as mean +/- standard error of the mean in picograms per milliliter of supernatant and analyzed with the Wilcoxon test; p values of less than 0.05 were considered significant. RESULTS: Baseline production of interleukin-6, interleukin-8, the chemokine "regulated upon activation, normal T cell expressed and secreted" (RANTES), and macrophage chemotactic protein-1 varied widely from one omental preparation to the other. E. coli increased the release of these mediators: from 1206 +/- 316 pg/mL to 8480 +/- 2189 pg/mL for interleukin-6, from 285 +/- 58 pg/mL to 3164 +/- 1053 pg/mL for interleukin-8, from 7 +/- 5 pg/mL to 684 +/- 264 pg/mL for RANTES, and from 2212 +/- 346 pg/mL to 7726 +/- 1473 pg/mL for macrophage chemotactic protein-1. Heat-killed staphylococci did not alter significantly the production of RANTES or macrophage chemotactic protein-1 but increased the production of the two other cytokines from 1325 +/- 389 pg/mL to 2206 +/- 523 pg/mL for interleukin-6 and from 318 +/- 70 pg/mL to 819 +/- 265 pg/mL for interleukin-8. CONCLUSIONS: The authors' results show that HPMCs are able to react to a direct stimulation with heat-killed microbes. They suggest that HPMCs, as well as resident macrophages, participate actively in the initiation and possibly in the modulation of intraperitonen inflammatory reactions.

Chemokine CCL2↗

PubMedDate not supplied

Arteriomegaly.

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Aged↗

PubMedDate not supplied

A review of the current use of magnetic resonance imaging in pregnancy and safety implications for the fetus.

This paper presents an overview of the application of and risks of exposure to Magnetic Resonance Imaging (MRI) in pregnancy. It reviews the risks to the fetus by considering the hazards in terms of the three main components of an MRI system. These are the static magnetic field, the time-varying magnetic gradient fields and the pulsed radio frequency fields. The hazards discussed are biological effects, miscarriage, heating effects and acoustic noise exposure. This paper also presents a survey of MRI sites within the United Kingdom to ascertain the extent of MRI usage in pregnancy. To validate the situation of MRI in pregnancy a survey was sent to 352 MR units throughout the United Kingdom. The questions were grouped to assess (a) maternal MRI diagnosis (b) fetal MRI and (c) work practices for pregnant MRI staff. The results showed that 91% of sites were imaging pregnant women in need of diagnosis in the second and third trimester. This paper highlights that MRI can add information for fetal central nervous system abnormalities identified by ultrasound screening, however within the UK direct fetal imaging was only performed in 8% of sites. This paper indicates the need for research to be undertaken for specific MRI clinical conditions. It also advises that risk assessment for pregnant staff working in MRI is performed, and that there is a clear need for further research into the effects of MRI in pregnancy as there is a need for clear authoritive advice.

Central Nervous System↗