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At least 1,477 records · Page 82Linked to original sources
PubMed1991

Seeing through the skull: advanced EEGs use MRIs to accurately measure cortical activity from the scalp.

There is a vast amount of untapped spatial information in scalp-recorded EEGs. Measuring this information requires use of many electrodes and application of spatial signal enhancing procedures to reduce blur distortion due to transmission through the skull and other tissues. Recordings with 124 electrodes are now routinely made, and spatial signal enhancing techniques have been developed. The most advanced of these techniques uses information from a subject's MRI to correct blur distortion, in effect providing a measure of the actual cortical potential distribution. Examples of these procedures are presented, including a validation from subdural recordings in an epileptic patient. Examples of equivalent dipole modeling of the somatosensory evoked potential are also presented in which two adjacent fingers are clearly separated. These results demonstrate that EEGs can provide images of superficial cortical electrical activity with spatial detail approaching that of O15 PET scans. Additionally, equivalent dipole modeling with EEGs appears to have the same degree of spatial resolution as that reported for MEGs. Considering that EEG technology costs ten to fifty times less than other brain imaging modalities, that it is completely harmless, and that recordings can be made in naturalistic settings for extended periods of time, a greater investment in advancing EEG technology seems very desirable.

Brain↗
PubMed1990

Analysis of scalp voltage asymmetries using Hotelling's T2 methodology.

Topographic mapping procedures are becoming increasingly popular, and scalp voltage asymmetries are a measure of specific interest. Standard statistical techniques in the field to detect voltage asymmetries, "significance probability mapping (SPM)" and repeated-measures analysis of variance (ANOVA) have statistical assumptions which are not in accord with electrophysiological data, and which therefore may lead to serious statistical errors. These limitations and a superior method using multivariate analysis are discussed. This paper provides a sample data set, for illustration of specific computational steps, and to provide an empirical example and reference for the theoretical discussion.

Brain Mapping↗
PubMed1996

Some methods for dynamic analysis of the scalp recorded EEG.

This paper describes methods for quantifying the spatiotemporal dynamics of EEG. Development of these methods was motivated by watching computer-generated animations of EEG voltage records. These animations contain a wealth of information about the pattern of change across time in the voltages observed across the surface of the scalp. In an effort to quantify this pattern of changing voltages, we elected to extract a single quantifiable feature from each measurement epoch, the highest squared voltage among the various electrode sites. Nineteen channels of EEG were collected from subjects using an electrode cap with standard 10-20 system placements. Two minute records were obtained. Each record was sampled at a rate of 200 per second. Thirty seconds of artifact-free data were extracted from each 2 minute record. An algorithm then determined the location of the channel with the greatest amplitude for each 5 msec sampling epoch. We quantified these spatio-temporal dynamics as scalars, vectors and cluster analytic plots of EEG activity for finger tapping, cognitive effort (counting backwards) and relaxation to illustrate the utility of the techniques.

Algorithms↗
PubMed1995

Equivalent source estimation of scalp potential fields contaminated by heteroscedastic and correlated noise.

The customary ordinary least squares (OLS) approach to the estimation of equivalent sources of scalp potential fields relies on the assumption that noise in the potential measurements has an equal variance and is uncorrelated over leads. It is shown that this assumption is likely to be violated in practice, for instance by the use of a common reference lead. We describe tests to detect these violations and we propose several versions of an alternative estimation method called iterated generalised least squares (IGLS), which accounts for heteroscedastic or correlated noise by incorporating an estimate of the covariance matrix of the noise derived from single trial OLS residuals. Simulation results indicate that these alternatives give a considerable increase in the accuracy of both the parameter and the standard error and confidence interval estimates. The proposed tests and methods are finally integrated into a stepwise approach to equivalent source estimation, which incorporates in addition a test on the goodness of fit of the model, an assessment of the confidence intervals of the parameters and a powerful test of differences between experimental conditions. This stepwise approach is applied to the modelling of equivalent sources of early visual potentials elicited in a spatial attention task.

Brain↗
PubMed1995

Precision of dipole localization in a spherical volume conductor: a comparison of referential EEG, magnetoencephalography and scalp current density methods.

In this study, we determined the influence of dipole orientation, dipole location, and number of recording sites on the precision of dipole localization in a spherical volume conductor. We compared localization from referential EEG (R-EEG), scalp current density EEG (SCD-EEG) and magnetoencephalography (MEG). Dipole orientation had a small influence on the precision of dipole localization for R-EEG and SCD-EEG. Dipole location relative to the recording sites, dipole depth, and number of recording channels strongly influenced the precision of dipole localization. Assuming equal signal to noise conditions for each recording method, MEG and SCD-EEG had a similar precision for dipole localization of a single tangential dipole source and both methods were more precise than R-EEG. However, SCD-EEG was inferior to MEG for distinguishing a single tangential current source from a pair of deeper radial current sources. In summary, these results suggest that the MEG will be most useful for localization of multiple simultaneous dipole sources.

Brain↗
PubMed1991

Fibrosarcoma of the scalp following postoperative radiotherapy for medulloblastoma.

A rare case of fibrosarcoma of the scalp following postoperative radiotherapy for medulloblastoma is reported. A review of similar cases in the literature was undertaken in an attempt to find a correlation between the dose of radiation, the length of the latent period, and the nature of the neoplasm. A significantly shorter latent period was found for sarcomas. No relationship was observed between the radiation dose and the latent period. The present case is unique in that the post-irradiation neoplasm (PIN) occurred in a predominantly extracranial site after treatment for a desmoplastic medullobastoma and had a remarkably short latent period.

Cerebellar Neoplasms↗
PubMed1994

A simple technique for the excision of vascular malformations of the scalp.

A simple technique for the excision of vascular malformations of the scalp is described herein. Surgical excision is easily accomplished by placing hemostatic sutures all around the lesion outside the line of excision, whereby minimal blood loss is achieved. The resulting defect can be covered by a split skin graft or flap.

Arteriovenous Malformations↗
PubMed1981

Pseudotumor of the scalp caused by a chronic hygroma with a traumatic CSF fistula.

A 6 1/2-year-old child, who had suffered a depressed fracture of the skull at the age of 1 1/2, had an extensive tumor of the scalp. Microscopic evaluation showed the growth to be a pseudotumor. The spongy tissue proved to be a chronic subdural hygroma containing structures resembling pacchionian granulations. A CSF fistula was demonstrated surgically. The fistula was assumed to be responsible for the metaplastic proliferation of subcutaneous and galeal connective tissue. A growing fracture was not present.

Cerebrospinal Fluid↗
PubMed1992

Fascial layers of the scalp. A study of 48 cadaveric dissections.

The arrangement and structure of the fascial layers of the scalp were studied in 48 red neoprene latex-injected cadavers with the aid of an operating microscope. The galea aponeurotica was continuous with a superficial temporal fascia. Deep to the galea, the subaponeurotic connective tissue was bilaminar. There was an outer, vascular, areolar layer, and an inner, avascular, membranous layer. Underlying the temporalis muscle, the pericranium was thinner and more adherent than elsewhere with no subpericranial tissue.

Fascia↗
PubMed1990

Congenital scalp and skull defects with terminal transverse limb anomalies (Adams-Oliver syndrome): report of three additional cases.

Aplasia cutis congenita of the scalp combined with terminal transverse limb defects (Adams-Oliver syndrome) is a rare congenital disorder with autosomal dominant inheritance. Thirty-one patients with the complete syndrome have been published. We report three additional patients (one mother and her affected child, one sporadic case) and discuss the probable vascular disruptive pathogenesis, the clinical variability and the treatment of this condition in the light of a comprehensive review of the literature.

Family Health↗
PubMed1978

Evaluation of continuous fetal scalp pH during labor.

Continuous monitoring of fetal scalp tissue pH was technically acceptable in 79.4% of 35 patients sequentially studied. Overall, the correlation coefficient (r) between the continuous pH readings and the intermittent pH values was 0.75. The accuracy improved greatly in the latter 23 patients. This was probably due to improved skills of the operators but also to a revision of the calibration technique. The correlation coefficient in these 23 patients was 0.82, and 87% of the records were accurate. The mean monitoring time was 2.39 h and eight infants were monitored throughout delivery and post natal. Although good results were obtained in this study, the method still demands technical skill in order to achieve clinically useful results.

Adolescent↗
PubMed1991

A new scalp flap for baldness.

The technique and results of a new scalp flap that solves frontal baldness are described. As a bipediculate flap it offers a great amount of hair when advanced and has a low rate of complications. This kind of flap has been used by us for four years in 36 patients in the age group between 20 and 60 years. The results obtained with the flap have been very satisfactory.

Adult↗
PubMed2002

Linear and non-linear methods for automatic seizure detection in scalp electro-encephalogram recordings.

The electro-encephalogram is a time-varying signal that measures electrical activity in the brain. A conceptually intuitive non-linear technique, multi-dimensional probability evolution (MDPE), is introduced. It is based on the time evolution of the probability density function within a multi-dimensional state space. A synthetic recording is employed to illustrate why MDPE is capable of detecting changes in the underlying dynamics that are invisible to linear statistics. If a non-linear statistic cannot outperform a simple linear statistic such as variance, then there is no reason to advocate its use. Both variance and MDPE were able to detect the seizure in each of the ten scalp EEG recordings investigated. Although MDPE produced fewer false positives, there is no firm evidence to suggest that MDPE, or any other non-linear statistic considered, outperforms variance-based methods at identifying seizures.

Electroencephalography↗
PubMed2004

Excess of counterclockwise scalp hair-whorl rotation in homosexual men.

While most men prefer women as their sexual partners, some are bisexual and others are homosexuals. It has been debated for a long time whether a person's sexual preference is innate, learned, or due to a combination of both causes. It was recently discovered that the human right-versus-left-hand use preference and the direction of scalp hair-whorl rotation develop from a common genetic mechanism. Such a mechanism controls functional specialization of brain hemispheres. Whether the same mechanism specifying mental makeup influences sexual preference was determined here by comparing hair-whorl rotation in groups enriched with homosexual men with that in males at large. Only a minority of 8.2% (n = 207) unselected 'control' group of males had counterclockwise rotation. In contrast, all three samples enriched with homosexual men exhibited highly significant (P < 0.0001), 3.6-fold excess (29.8%, n = 272) counterclockwise rotation. These results suggest that sexual preference may be influenced in a significant proportion of homosexual men by a biological/genetic factor that also controls direction of hair-whorl rotation.

Hair↗
PubMed1998

Determination of reference ranges for elements in human scalp hair.

Expected values, reference ranges, or reference limits are necessary to enable clinicians to apply analytical chemical data in the delivery of health care. Determination of references ranges is not straightforward in terms of either selecting a reference population or performing statistical analysis. In light of logistical, scientific, and economic obstacles, it is understandable that clinical laboratories often combine approaches in developing health associated reference values. A laboratory may choose to: 1. Validate either reference ranges of other laboratories or published data from clinical research or both, through comparison of patients test data. 2. Base the laboratory's reference values on statistical analysis of results from specimens assayed by the clinical reference laboratory itself. 3. Adopt standards or recommendations of regulatory agencies and governmental bodies. 4. Initiate population studies to validate transferred reference ranges or to determine them anew. Effects of external contamination and anecdotal information from clinicians may be considered. The clinical utility of hair analysis is well accepted for some elements. For others, it remains in the realm of clinical investigation. This article elucidates an approach for establishment of reference ranges for elements in human scalp hair. Observed levels of analytes from hair specimens from both our laboratory's total patient population and from a physician-defined healthy American population have been evaluated. Examination of levels of elements often associated with toxicity serves to exemplify the process of determining reference ranges in hair. In addition the approach serves as a model for setting reference ranges for analytes in a variety of matrices.

Adolescent↗
PubMed1998

Trace elements in human scalp hair and soil in Irian Jaya.

Pb, Cd, and Ni contents were determined in the scalp hair of the Asmat of Irian Jaya (Indonesian New Guinea) on 35 adult subjects. These data are presented together with those of Al, Ca, Ti, Fe, Cu, Zn and Sr, which were determined in previous research on the same group. Hair samples were analyzed by EDXRS and ICP. Trace elements were also determined in 12 soil samples from the same area by EDXRS (Al, Si, K, Ca, Fe) and ICP (Cu, Sr, Ti), and by AAS (Cd, Ni, Pb). When hair element levels are compared and discussed with those of other New Guinea populations, acculturated and nonacculturated tropical groups, populations from Western countries and from polluted areas, and "recommended levels" in the literature, they greatly exceed Western levels and generally fit those of other New Guinea populations, stressing the importance of common environment, subsistence, and behavior. The results of soil analyses are consistent with the presence of those elements in hair, and their quantitative distribution follows a common trend. Metal mobility in soil, patterns of absorption, and transfer from soil to plants and to humans are considered here.

Adolescent↗
PubMed1998

Structural and trace element changes in scalp hair of radiographers.

Scalp hair samples were collected from medical radiographers and nonradiographers of matching age groups. Structural morphology of hair was studied by scanning electron microscopy, and the trace element profiles in hair were measured using neutron activation analysis. The structural damage to the hair follicles of the radiographers was quite obvious, and this may be a good qualitative indicator of radiation damage at low doses. The concentrations of aluminum (Al), potassium (K), and vanadium (V) in hair of the radiographers were significantly higher, whereas those of antimony (Sb) and magnesium (Mg) were significantly lower than those of nonradiographers. Some of our findings were quite consistent with those of others in determining the changes in trace element concentrations in irradiated tissue.

Adult↗