PubMed Health⌕ Search

Biomedical subjects

G Harding

Publications and source records attributed to G Harding.

12 recordsLinked to original sources
PubMed1992

The topographic distribution of the magnetic P100M to full- and half-field stimulation.

Visual evoked magnetic responses were recorded to full-field and left and right half-field stimulation with three check sizes (70', 34' and 22') in five normal subjects. Recordings were made sequentially on a 20-position grid (4 x 5) based on the inion, by means of a single-channel direct current-Superconducting Quantum Interference Device second-order gradiometer. The topographic maps were consistent on the same subjects recorded 2 months apart. The half-field responses produced the strongest signals in the contralateral hemisphere and were consistent with the cruciform model of the calcarine fissure. Right half fields produced upper-left-quadrant outgoing fields and lower-left-quadrant ingoing fields, while the left half field produced the opposite response. The topographic maps also varied with check size, with the larger checks producing positive or negative maximum position more anteriorly than small checks. In addition, with large checks the full-field responses could be explained as the summation of the two half fields, whereas full-field responses to smaller checks were more unpredictable and may be due to sources located at the occipital pole or lateral surface. In addition, dipole sources were located as appropriate with the use of inverse problem solutions. Topographic data will be vital to the clinical use of the visual evoked field but, in addition, provides complementary information to visual evoked potentials, allowing detailed studies of the visual cortex.

Adult↗
PubMed1992

Single dose treatment failure in women with acute cystitis.

Single dose treatment regimens (SDT) are effective, inexpensive alternatives to longer courses of therapy for adult females with acute cystitis or asymptomatic bacteriuria. A number of SDT regimens consistently cure 85 to 100% of women with acute cystitis and 50 to 80% of women with asymptomatic bacteriuria. However, SDT is inherently less effective than longer regimens because many upper tract infections are not cured. Initial SDT studies suggested that most patients with significant renal invasive disease or underlying urological abnormalities fail therapy. As a result, SDT has been proposed as an efficient strategy to diagnose significant upper tract infections with accompanying pathology that merit additional investigation or treatment. Few studies have refuted or supported this hypothesis. Single-dose treatment studies show an association between the site of infection as determined by the antibody-coated bacteria (ACB) test and treatment outcome. Patients with ACB-negative tests have a cure rate of over 90% in almost all studies in which the organism is susceptible to the agent chosen. Patients with positive ACB tests tend to have treatment failure rates of 30 to 50%. However, imaging studies have not been carried out in parallel with these studies and the validity of using single-dose treatment failure to screen women for significant upper tract pathology has still not been established.

Acute Disease↗
PubMed1992

Bone composition measured by x-ray scattering.

Ten composite samples consisting of cortical bone and adipose tissue, in known proportions, were made. The intensity of monochromatic x-rays (energy 8 keV) scattered by these samples was determined as a function of the modulus of the scattering vector, K. The ratio of the heights of peaks at K values of around 134 and 22 nm-1 provided a measure of the ratio of adipose tissue to bone mineral in these samples. This method was then used to determine the ratio of adipose tissue to mineral in samples of trabecular bone from 16 vertebral bodies. The results were correlated with measurements of the bone composition determined by ashing (r = 0.66) and histomorphometry (r = 0.66). Furthermore, the ashing and histomorphometry results were correlated with each other (r = 0.68). The feasibility of using higher energy x-rays (35-80 keV) for obtaining the same information from bone within the body is briefly discussed.

Adipose Tissue↗
PubMed1992

Survey of Bacteroides fragilis group susceptibility patterns in Canada.

The in vitro activities of penicillin, clindamycin, chloramphenicol, metronidazole, piperacillin, piperacillin-tazobactam, ticarcillin, ticarcillin-clavulanate, ampicillin-sulbactam, cefoxitin, ceftizoxime, cefotetan, moxalactam, and imipenem against 348 Bacteroides fragilis group isolates collected from six Canadian cities during 1990 were determined by the National Committee for Clinical Laboratory Standards (NCCLS) agar dilution technique. All isolates were susceptible to chloramphenicol, metronidazole, piperacillin-tazobactam, and imipenem. For the other antibiotics tested, the following resistance rates were observed: penicillin, 97%; clindamycin, 9%; piperacillin, 19%; ticarcillin, 31%; ticarcillin-clavulanate, 0.28%; ampicillin-sulbactam, 0.85%; cefoxitin, 26%; ceftizoxime, 15%; cefotetan, 53%; and moxalactam, 17%. Susceptibility profiles to beta-lactam antibiotics varied among the different species tested: B. fragilis and Bacteroides vulgatus demonstrated lower resistance rates than Bacteroides distasonis and indole-positive Bacteroides thetaiotaomicron and Bacteroides ovatus. Ceftizoxime results should be interpreted cautiously, because the MICs obtained with the recommended NCCLS control strain were lower than expected.

Anti-Bacterial Agents↗
PubMed1978

Prospective comparison of cefoxitin and cefazolin in infections caused by aerobic bacteria.

Intravenous cefazolin and cefoxitin were compared in a prospective randomized trial in infections where the suspected pathogen was expected to be susceptible to both antibiotics. In the cefazolin group (12 patients) the diagnosis was pneumonia in 4, including 2 with pneumococcal bacteremia, soft tissue infection in 5, Staphylococcus aureus bacteremia in 1, acute pyelonephritis in 1, and disseminated gonococcal infection in 1. In the cefoxitin group (10 patients) the diagnosis was pneumonia in 4, including 2 with pneumococcal bacteremia, soft tissue infection in 4, acute pyelonephritis in 1, and disseminated gonococcal infection in 1. In the cefazolin group receiving an evaluable course of therapy, a good clinical response was seen in 10 of 11 patients, and a bacteriological response was seen in 5 of 7. Cefazolin failed to eradicate S. aureus bacteremia in 1 patient and S. aureus in a skin ulcer of another patient. All 10 cefoxitin patients had good clinical and bacteriological responses, but in 1 patient S. aureus colonization of a postoperative wound recurred after discontinuation of the drug. Side effects in both groups included skin rash, phlebitis, and elevation of the serum alkaline phosphatase. Both cefoxitin and cefazolin appeared effective in infections caused by susceptible aerobic pathogens with the possible exception of S. aureus, although all 11 strains of S. aureus isolated in this study were susceptible in vitro to both antibiotics. Cefoxitin appeared to be equivalent to cefazolin in efficacy and occurrence of side effects.

Adult↗
PubMed1977

Optimum spread functions in linear tomography.

Recent attempts to reduce artefacts in tomographic blurring, using a transfer function approach, have so far taken little explicit account of the lessening in the degree of blurring which accompanies transfer function correction. A simple comparative measure R of the blurring effect of a linear tomographic movement is proposed. The parameter R is related to the ratio of the area of the point spread function (PSF) to its peak height. It is shown that the PSF having the greatest value of R (maximum blurring), whilst having an entirely positive transform, is of triangular form. Conversely, any PSF for which the value of R exceeds Rtriangle is inevitably associated with phase reversals. The problem of finding the PSF with R greater than Rtriangle, which leads to the minimum degree of phase reversal, has been tackled by determining the transfer function which, for the given value of R, has the minimum area under its subsidiary maxima. Transfer functions optimized in this way, and their corresponding PSFS, are calculated for four values of R using the method described by Jacquinot and Roizen-Dossier. The results of this procedure are discussed and its possible extensions noted.

Technology, Radiologic↗
PubMed1976

Blurring quality in spiral tomography.

In view of the close relationship which exists between image aberrations and the form of the transfer function, the transfer functions of some different types of spiral tomographic movements have been calculated numerically. The results allow prediction of a type of spiral movement which yields blurring of favourable quality. The validity of this approach has been demonstrated experimentally, by comparing the blurring characteristics of tomographs with single and multiple circular movements. When the radii of the circles in the latter case are chosen with reference to the form of the transfer function, a marked improvement in blurring quality is apparent.

Mathematics↗
PubMedDate not supplied

Towards optimum blurring in spiral tomography.

Attempts to increase the degree of blurring of nonfocused layers in tomography are inevitably associated with a worsening in the amount of artefactual detail introduced. A mathematical optimization technique has been employed to indicate how these conflicting characteristics may best be reconciled. The technique uses plausible definitions, based on the transfer function, of the effectiveness and the fidelity of the blurring, and generates a sequence of spread functions in which these two aspects are optimally combined.

Mathematics↗