On cortical folds and neuromagnetic fields

A folded cortical source of neuromagnetic fields, similar in configuration to the visual cortex, was simulated. Cortical activity was modelled by different distributions of independent current dipoles. The map of the summed fields of the dipoles of this cruciform model changed, depending upon the statistical distribution of the electrical activity of the dipoles and its geometry. Arrays of dipoles of random orientations and strengths produced field patterns that could be interpreted as due to moving neural currents, although the geometry of the neural tissue remained unchanged and the average activity remained approximately constant. The field topography at any instant was apparently unrelated to the depth or orientation of the underlying structure, thus raising questions about how to interpret topographic MEG and EEG displays. Furthermore, asynchronous activity (defined as independent directions and magnitudes of activity of the dipoles) did not result in less field power than when the dipoles were synchronized, i.e., when the direction of current flow was correlated across all of the dipoles within the cruciform structure. Therefore, in this model 'alpha blockage' cannot be mimicked by desynchronization. More generally, for the cruciform or any other symmetrically folded and active cortical sheet, 'blockage' cannot be attributed to desynchronization. The same is true for the EEG except that smooth unfolded sheets of radially oriented dipoles would result in enhancement of voltage due to synchronization. Such radial dipoles do not contribute to the MEG. Blockage was simulated by reducing the amount of activity within different portions of the synchronized cruciform model. This resulted in a dramatic increase in the net field because attenuation broke the symmetry of the synchronized cruciform structure. With asynchronous dipoles populating the structure, the attenuation of the same portion of the structure had no easily discerned effect on the net field. However, maps of average field power were consistently related to the position of the region of attenuated activity. The locations of regions of attenuated activity were determined by taking the difference between the mean square field pattern obtained when all portions of the cruciform structure were active and the pattern obtained when a portion of the structure was relatively inactive. When activity of the same portions were incremented rather than attenuated, the resulting plot of average power was essentially the same as that of the attenuated portion derived by taking these differences between power distributions. The major conclusions are that the concepts of synchronization and desynchronization have no explanatory power unless the physical conditions under which they occur are specified precisely.(ABSTRACT TRUNCATED AT 400 WORDS)

Quality control in antimicrobial disk susceptibility testing: a Belgian multicenter study

A Belgian multicenter trial was conducted to evaluate problems encountered with quality control results of antimicrobial disk susceptibility testing and to compare the performance of BBL disks and Rosco tablets. Over a period of four weeks 18 laboratories daily tested three reference strains against eight antibiotics. A standardised method was used by all participants. For all results together 10.4% and 7.3% of the measurements with BBL disks and Rosco tablets, respectively, were outside the recommended range. Major problems were observed for some specific strain-antibiotic combinations. Standard deviations were similar for both systems; their precision was comparable. The results suggest that cooperation between manufacturers and some reference laboratories could be improved in order to establish optimal quality control limits.

Impact of section doubling on lesion contrast

Misregistration between section position and a feature of interest, such as a lesion, can result in loss of contrast on magnetic resonance images. Because the section direction typically has the poorest resolution, reduction of section misregistration can improve lesion contrast. Lesions occur at random sites; hence, to reduce misregistration, it is necessary to repeat imaging with a small amount of offset. This is impractical. Therefore, a reconstruction algorithm that yields offset sections was implemented, in which sections were produced with a zero- and a half-section shift. This algorithm was tested in 14 patients with multiple sclerosis. As expected, because of randomness associated with section placement relative to lesions, the half-shifted sections provided greater contrast as often as the zero-shifted sections. The combined set improved contrast significantly in 39% of lesions; improvement was greatest in lesions with lesser contrast. Signal-to-noise ratios were not affected by this process, which appears to be useful in magnetic resonance image reconstruction.

Magnetic resonance imaging characteristics of multiple sclerosis plaques imaged with two-dimensional and three-dimensional Fourier transform techniques at low and mid field strengths

A total of 58 multiple sclerosis lesions from 16 patients were used to characterize the performance of a low field system for the detection of edematous (e.g., water-elevating) brain lesions. Contrast, signal-to-noise, and their product (signal difference to noise) were measured for two-dimensional and three-dimensional Fourier transform techniques at low field strength (640 G) and compared to two-dimensional sequences at mid field strength (3,500 G). The results showed numerically that low-field strength magnetic resonance imaging can reliably detect multiple sclerosis lesions, and, by extension, other water-elevating lesions, although with lower confidence levels.

Pharmacodynamic parameters and toxicity of netilmicin (6 milligrams/kilogram/day) given once daily or in three divided doses to cancer patients with urinary tract infection

The pharmacologic parameters and toxicity of netilmicin (6 mg/kg/day) given once daily (qd) or thrice daily (tid) for the treatment of urinary tract infections were studied in a randomized prospective study of 60 cancer patients. The overall efficacy was 96%. Nephrotoxicity, assessed by the measure of urinary excretion of phospholipids, was lower for the patients receiving the qd regimen than for those receiving the tid regimen. Elevation of serum creatinine (20% over baseline) occurred in one patient receiving the qd regimen and in three receiving the tid regimen. Cochleotoxicity, assessed by pure-tone audiometry (250 to 18,000 Hz) occurred in one patient receiving the qd regimen and none receiving the tid regimen. Concentrations in sera were measured on days 1 and 5. No significant accumulation was observed in either group. Median serum bactericidal titers, expressed as reciprocal values (percentage of the sera with a titer greater than or equal to 8), were measured against 25 test organisms in samples collected 6 h after the administration of netilmicin and were, for the qd group, 16 (82%) against members of the family Enterobacteriaceae and less than 2 (8%) against Pseudomonas aeruginosa, and for the tid group, 4 (57%) against members of the Enterobacteriaceae and less than 2 (0%) against P. aeruginosa. The rate of killing in serum was rapid (2 to 3 log in 2 h against P. aeruginosa; 3 to 5 log in 2 h against members of the Enterobacteriaceae) and correlated with the sampling time and hence the concentration in serum of netilmicin. The duration of the postantibiotic effect in serum depended also on the strain and the sampling time of the serum.

Advantages and limitations of magnetic source imaging

The term "magnetic source image" (MSI) describes the distribution of neuronal activity in the brain that can be deduced from measurements of the field pattern it produces across the scalp. The signals which provide the basis for an MSI are obtained from the magnetoencephalogram (MEG) which is conventionally recorded with superconducting detectors. Advances in MSI techniques during the past decade have revealed numerous aspects of the functional organization of human sensory systems that were previously unknown. In addition, studies of spontaneous signals, such as those in the alpha bandwidth, have identified specific cortical areas that support rhythmic activity. Extensions of this approach to cognitive research are able to determine the active cortical areas where spontaneous activity is suppressed when a person is engaged in a task such as mental imagery and auditory memory recall. Because only the component of the intracellular current tangential to the overlying skull contributes to the extracranial field, a confined source--modeled as a current dipole--has a characteristic field pattern that simplifies the pattern recognition problem of identifying the underlying sources. This advantage is illustrated by the identification of simultaneously active sources in auditory primary and association cortex. Their separate localization makes it possible to characterize their functional differences. Because the source strength in an MSI may be inferred without knowledge of the electrical conductivities of intervening tissue, it is also possible to estimate the extent of cortical involvement. From the tangential source strength in an MSI, it is possible in most cases to determine the total source strength by taking account of the orientation of the cortical surface. This provides an objective, quantitative measure of the strength of neuronal activity. At present, the major limitation in more extensive use of MSI is the cost of instrumentation. While it requires no contact with the head, and measurements can commence within a few minutes of the arrival of the subject or patient, the present cost of a large array of sensors is two to three million dollars.

Low-field 3-DFT MRI: conceptual, analytical, and experimental aspects

Three-dimensional Fourier transform (3-DFT) magnetic resonance imaging (MRI) offers advantages in terms of signal-to-noise (S/N) per unit of time for the case where a large number of slices is desired. This advantage is enhanced when the relaxation time, T(1 ), is short. Because time limitations in 3-DFT imaging force the use of short time intervals, TR, between excitations of a slice, lesion contrast is often undesirable at mid-and high-field strength even when the S/N is good. At low fields, where T(1) values are short, high S/N and contrast can both be achieved with 3-DFT MR images. The conceptual and analytical aspects of low-field 3-DFT MRI are presented and demonstrated at 640 G.

MR imaging of excessively obese patients: the use of an open permanent magnet

Excessive obesity can pose a limitation to both clinical and radiographic evaluation. Although CT and MR have revolutionized head and body imaging, patients with weights above 300 lb present a restriction of these imaging modalities. Magnetic resonance imaging (MRI) is well suited for imaging excessively obese patients, because the RF used does not have difficulty in penetrating large amounts of adipose tissue as ionizing radiation or sound waves does. The limitations of conventional MR imaging in these obese patients are the gantry size and the table weight limit. The recent development of a new low field MR imager with a larger gantry size and greater weight capacity, has the potential for imaging obese patients that cannot be evaluated by standard CT or MR. In this paper, we report our experience in imaging nine excessively obese patients with weights between 350 and 490 lb using a permanent magnet operating at 0.064 T.

Nasal and retrobulbar mass in a cat caused by Pythium insidiosum

Nasal and retrobulbar infection caused by the Oomycete Pythium insidiosum is described in a cat. The diagnosis was established on three criteria. The staining of broad, sparsely septate hyphal elements in biopsy tissue using a fluorescein-labelled antiglobulin specific for P. insidiosum, detection of antibodies to P. insidiosum by an immunodiffusion test, and isolation of the aetiological agent in pure culture from the biopsy tissue. Treatment with ketoconazole for 6 weeks resulted in clinical improvement, but proptosis of the left eye slowly appeared after the discontinuation of treatment. This case represents a new host for P. insidiosum, namely, a domestic, shorthaired cat, from North Carolina, U.S.A.

Applications of voxel shifting in magnetic resonance imaging

Due to the nature of three-dimensional Fourier transform (3-DFT) data acquisition in magnetic resonance imaging (MRI), the spatial relation between a resolved volume element (a voxel) and the object can be manipulated easily. Those manipulations have practical consequences in terms of registering slice positions with respect to features of interest in producing oblique reformatted images where volume resolution is preserved, and in generating reformatted images that project the viewing plane onto a surface through the object that has an arbitrary shape.

Comparison of cell growth in different parts of breast cancers

This study was performed to answer the question: which parts of breast cancers are active in terms of proliferation as measured by the Ki-67 antibody and in terms of cell division as measured by the mitotic index. Forty-six breast samples were studied, including 34 breast cancers and 12 benign conditions. The intraductal component of infiltrating breast cancers showed a significantly lower proliferation index than the infiltrating component. The cells at the periphery of infiltrating tumour strands showed a higher proliferation activity than the cells in the core. These findings suggest that infiltration advances through preferential active growth of the cells at the invasion front.

CT-scan study of the incidence of sinus involvement and nasal anatomic variations in 196 children

CT-scan was used to examine rhinosinusitis in the developing sinuses; 196 children aged from 3 to 14 years were selected on the base of their chronic rhinorrhea, nasal congestion and cough. The patients were subdivided into six age groups (3-4, 5-6, 7-8, 9-10, 11-12 and 13-14 years). In the youngest age group, the authors noted maxillary involvement in 63%, ethmoidal involvement in 58%, and even sphenoidal sinus involvement in 29% of the children. Involvement decreased gradually with age, with 10% of ethmoidal and 0% of sphenoidal involvement in the 13-14 years age group. Maxillary sinusitis, however, persisted very frequently in the oldest age group (65%). Frontal involvement seems to become significant at the age of 7-8 years (7%) but it never exceeds 15% (11-12 age group). Septal deviations occurred in 16% of the youngest up to 72% in the oldest age group. The prevalence of bullous conchae increased with age too, although less prominently.

Immunodiffusion test for serodiagnosing subcutaneous zygomycosis

Culture filtrate antigens of Basidiobolus ranarum and Conidiobolus coronatus were analyzed by immunodiffusion (ID) with homologous rabbit antisera. B. ranarum and C. coronatus were each found to have five specific antigens. Results of tests with heterologous antisera indicated that all of the species shared at least one antigen. ID tests incorporating the specific precipitin bands as references were developed for detection of basidiobolomycosis and conidiobolomycosis. These tests were performed with sera from humans and horses with proven basidiobolomycosis and conidiobolomycosis as well as with control sera from humans and animals with and without heterologous mycotic and oomycotic infections. Only sera from cases of basidiobolomycosis and conidiobolomycosis produced lines of identity with the reference precipitates of B. ranarum and C. coronatus, respectively. The ID tests were found to be completely sensitive and specific for determining the etiology of zygomycosis caused by these two species. In addition they appeared useful for monitoring resolution of the infections.

Exfoliative colonic cytology. A simplified method of collection and initial results

Exfoliative colonic cytology for the diagnosis of colorectal cancer has been largely abandoned due to (1) the widespread use of colonoscopy, (2) the cumbersome methods of cell collection and (3) the occasional difficulty of interpreting the cytologic findings in the presence of inflammatory bowel disease or adenomas. This paper describes a newly formulated bowel preparation for routine colonoscopy, based on imbibing 2 L to 4 L of a balanced electrolyte solution, in which the recovered precolonoscopic effluent (using a convenient disposable collecting kit) yielded cells for cytologic evaluation from 70% of a group of 80 patients at high risk for large bowel neoplasia. Cytology demonstrated neoplastic cells in most cases of endoscopically proven cancer. These results suggest that colonic exfoliative cytology may be useful as a supplemental test to routine colonoscopy. This could be enhanced by further methodologic modifications to the collecting and cytologic methods; large long-term studies are needed to evaluate the potential usefulness of colonic exfoliative cytology.

Fibrinopeptide A levels indicative of pulmonary vascular thrombosis in patients with primary pulmonary hypertension

Although the mechanisms involved in the pathophysiology of primary pulmonary hypertension have not yet been delineated, thrombosis has been implicated. This study was designed to determine whether thrombin activity as reflected by plasma concentrations of fibrinopeptide A (FPA), a marker of the action of thrombin on fibrinogen, is increased in patients with primary pulmonary hypertension. To evaluate fibrinolytic activity, we measured plasma concentrations of tissue-type plasminogen activator, plasminogen activator inhibitor-1, and cross-linked fibrin degradation products. We studied 31 patients with primary pulmonary hypertension. Plasma FPA concentrations measured by radioimmunoassay, were elevated to 87.4 +/- 36.9 ng/ml (mean +/- SEM). Fifteen minutes after administration of heparin (5,000 U), FPA concentrations decreased to 6.8 +/- 1.4 ng/ml (p less than 0.001 compared with preheparin levels). In 21 of 30 patients (70%), FPA concentrations after heparin administration were less than half the preheparin levels, a response consistent with inhibition of thrombin by heparin and the short half-life of FPA. Despite evidence for marked thrombin activity, plasma concentrations of cross-linked fibrin degradation products were normal in all but four patients. Plasminogen activator inhibitor-1 activity was elevated in 19 of the 27 patients in whom it was measured, potentially limiting the fibrinolytic response. The elevations of FPA indicate that thrombin activity is increased in vivo in patients with primary pulmonary hypertension. Thus, sequential assays of plasma markers of thrombosis and fibrinolysis in vivo may help identify those patients who may benefit from treatment with anticoagulants.