CHARACTERISATION OF RADIOPHOTOLUMINESCENCE DOSIMETRY SYSTEM FOR INDIVIDUAL MONITORING

Performance evaluation is typically assessed as part of the approval procedure to verify that a dosimetry system fulfils specified national or international type-test requirements under representative exposure conditions that are expected to mimic workplace fields from the radiological activities being monitored. The International Atomic Energy Agency Radiation Safety Technical Services Laboratory has recently implemented an integrated radiophotoluminescence (RPL) personal dosimetry system developed by Chiyoda Technol Corporation. This paper reports on the successful verification of dosimetric performance properties of the RPL dosimetry system to IEC 62387:2020, in which the badges were exposed to a range of radiation energies and angles of incidence as well as other influence parameters. Characteristics under test included the coefficient of variation, non-linearity of response due to dose dependence as well as the energy and angular response to photon and beta radiation.

Regulatory Considerations for the Clinical and Research Use of Transcranial Direct Current Stimulation (tDCS): review and recommendations from an expert panel

The field of transcranial electrical stimulation (tES) has experienced significant growth in the past 15 years. One of the tES techniques leading this increased interest is transcranial direct current stimulation (tDCS). Significant research efforts have been devoted to determining the clinical potential of tDCS in humans. Despite the promising results obtained with tDCS in basic and clinical neuroscience, further progress has been impeded by a lack of clarity on international regulatory pathways. We therefore convened a group of research and clinician experts on tDCS to review the research and clinical use of tDCS. In this report, we review the regulatory status of tDCS, and we summarize the results according to research, off-label and compassionate use of tDCS in the following countries: Australia, Brazil, France, Germany, India, Iran, Italy, Portugal, South Korea, Taiwan and United States. Research use, off label treatment and compassionate use of tDCS are employed in most of the countries reviewed in this study. It is critical that a global or local effort is organized to pursue definite evidence to either approve and regulate or restrict the use of tDCS in clinical practice on the basis of adequate randomized controlled treatment trials.

Localization of auditory evoked potentials related to selective intermodal attention

A long-standing question in attention research is the extent to which selection involves gates in the sensory stream and the extent to which they involve added secondary processes. Intermodal attention paradigms are useful for examining this issue since different modalities involve readily distinguished cortical regions. Evoked potential studies have identified an attention-related frontal negativity labeled the Nd in auditory attention studies. It has been suggested that it arises from modulation of the auditory cortex (compatible with gating mechanisms) or of the frontal cortex (compatible with secondary processes such as short-term memory buffers). Efforts to localize the Nd have been impaired by the finding that the Nd comprises multiple components. Some novel procedures utilizing principal components analysis, in conjunction with high-density 64-channel recordings, were used to address this issue. Results suggest that the major source of the early Nd (the portion of most interest) resides in the frontal cortex, supporting the secondary process view for this particular mechanism.

Towards normalization of soybean somatic embryo maturation

Soybean (Glycine max L. Merrill) somatic embryos have been useful for assaying seed-specific traits prior to plant recovery. Such traits could be assessed more accurately if somatic embryos more closely mimicked seed development. Amino acid supplements, carbon source, and abscisic acid and basal salt formulations were tested in an effort to modify existing soybean embryogenesis histodifferentiation/maturation media to further normalize the development of soybean somatic embryos. The resultant liquid medium, referred to as soybean histodifferentiation and maturation medium (SHaM), consists of FNL basal salts, 3% sucrose, 3% sorbitol, filter-sterilized 30 mM glutamine and 1 mM methionine. SHaM-derived somatic embryos are more similar to seed in terms of protein and fatty acid/lipid composition, and conversion ability, than somatic embryos obtained from traditional soybean histodifferentiation and maturation media.

Localizing acute stroke-related EEG changes: assessing the effects of spatial undersampling

Because of its sensitivity to metabolic and ionic disturbances related to ischemia, the EEG can be a potentially useful tool for acute stroke detection and for monitoring affected tissue. However, the clinical use of the EEG in detecting stroke is determined in part by how accurately the spatial information is characterized. The purpose of the current study was to determine the effects of spatial undersampling on the distribution and interpretation of the stroke-related topographic EEG. Using a 128-channel sensor montage, EEG was recorded from six stroke patients acutely (between 8 and 36 hours) after symptom onset. The EEG was submitted to a spectral analysis and was compared with patient symptoms and MRI and computed tomographic findings. To determine loss of spatial and clinical information resulting from spatial undersampling, the average-referenced data from the original 128-channel recording montage were subsampled into 64-, 32-, and 19-channel arrays. Furthermore, the analytical findings were compared with a board-certified electroencephalographer's review of the raw EEG using a conventional clinical montage. As predicted, the results showed that accurate description of stroke-related topographic EEG changes is dependent on adequate spatial sampling density. Accurate description of the spatial distribution of the stroke-related EEG was achieved only with the 64- and 128-channel EEG. As the recording density decreases to 32 channels, the distribution of the scalp EEG spectra is distorted, potentially resulting in mislocalization of the affected region. Results of the clinical review by an expert electroencephalographer corroborated the quantitative analyses, and the results also demonstrated the shortcomings of the conventional 10-20 recording density for capturing focal EEG abnormalities in several cases. The EEG provides useful information about the localization of acute cerebral ischemia, but recording densities of 64 channels or higher are required for accurate spatial characterization of focal stroke-related EEG changes.

Regulating action: alternating activation of midline frontal and motor cortical networks

OBJECTIVES

Focal electrical fields recorded over the midline prefrontal cortex have been found to index rapid evaluative decisions, including the recognition of having made an error in a speeded response task. The nature of these electrical fields and how they are related to cortical areas involved in response execution remains to be clarified.

METHODS

As subjects performed a speeded response task the EEG was recorded with a 128-channel sensor array. By filtering out the large slow waves of the event-related potential, we found that the error-related negativity (Ne/ERN) arises from a midline frontal oscillation that alternates with oscillations over lateral sensorimotor cortex. Electrical source analyses were used to determine the brain sources involved in the generation of these oscillations.

RESULTS

The results show that the midline and lateral oscillations have a period of about 200 ms (theta), and they are present for both correct and error responses. When an error is made, the midline error oscillation is recruited strongly, and it becomes correlated with the motor oscillation. Source analyses localized the midline error oscillation to centromedial frontal cortex and the lateral oscillation to sensorimotor cortices.

CONCLUSIONS

Because of the similarity between the midline oscillation observed in the present study and frontal midline theta, the nature of the Ne/ERN may be clarified by the frontal midline theta literature. The correlation between the midline and sensorimotor oscillations suggests a possible mechanism for how midline frontal evaluative and monitoring networks contribute to action regulation.

Frontal evaluation and posterior representation in target detection

This study examined the topography of the event-related potential in visual-spatial compared to visual-object target detection. The initial index of target detection in the ERP was an inferior anterior P2a accompanied by a posterior N2b. Single unit studies in the monkey indicate that the detection of task-relevant stimuli requires interaction between prefrontal cortex and perceptual representation areas in the posterior brain. The posterior brain processes the physical features of stimuli while frontal cortex performs higher-order operations, such as evaluating the task-relevance of a stimulus. Target detection requires an interaction between feature representations and relevance representations. We hypothesize that the P2a and N2b ERP indices of target detection reflect this frontal/posterior interaction. Visual-spatial feature information is processed in the dorsal posterior brain (posterior parietal cortex) and visual-object information is processed in the ventral posterior brain (inferior occipito-temporal cortex). We observed that at the peak of the P2a the N2b was located over posterior dorsal leads in visual-spatial target detection and over posterior ventral leads in visual-object target detection. The P2a was largest over inferior prefrontal leads in both tasks. We suggest that this distribution is consistent with interaction between orbitofrontal cortical areas of salience representation and posterior cortical areas of stimulus feature representation.

Scalp electrode impedance, infection risk, and EEG data quality

OBJECTIVES

Breaking the skin when applying scalp electroencephalographic (EEG) electrodes creates the risk of infection from blood-born pathogens such as HIV, Hepatitis-C, and Creutzfeldt-Jacob Disease. Modern engineering principles suggest that excellent EEG signals can be collected with high scalp impedance ( approximately 40 kOmega) without scalp abrasion. The present study was designed to evaluate the effect of electrode-scalp impedance on EEG data quality.

METHODS

The first section of the paper reviews electrophysiological recording with modern high input-impedance differential amplifiers and subject isolation, and explains how scalp-electrode impedance influences EEG signal amplitude and power line noise. The second section of the paper presents an experimental study of EEG data quality as a function of scalp-electrode impedance for the standard frequency bands in EEG and event-related potential (ERP) recordings and for 60 Hz noise.

RESULTS

There was no significant amplitude change in any EEG frequency bands as scalp-electrode impedance increased from less than 10 kOmega (abraded skin) to 40 kOmega (intact skin). 60 Hz was nearly independent of impedance mismatch, suggesting that capacitively coupled noise appearing differentially across mismatched electrode impedances did not contribute substantially to the observed 60 Hz noise levels.

CONCLUSIONS

With modern high input-impedance amplifiers and accurate digital filters for power line noise, high-quality EEG can be recorded without skin abrasion.

Modification and benchmarking of MCNP for low-energy tungsten spectra

The MCNP Monte Carlo radiation transport code was modified for diagnostic medical physics applications. In particular, the modified code was thoroughly benchmarked for the production of polychromatic tungsten x-ray spectra in the 30-150 kV range. Validating the modified code for coupled electron-photon transport with benchmark spectra was supplemented with independent electron-only and photon-only transport benchmarks. Major revisions to the code included the proper treatment of characteristic K x-ray production and scoring, new impact ionization cross sections, and new bremsstrahlung cross sections. Minor revisions included updated photon cross sections, electron-electron bremsstrahlung production, and K x-ray yield. The modified MCNP code is benchmarked to electron backscatter factors, x-ray spectra production, and primary and scatter photon transport.

Regional head tissue conductivity estimation for improved EEG analysis

We develop a method for estimating regional head tissue conductivities in vivo, by injecting small (1-10 microA) electric currents into the scalp, and measuring the potentials at the remaining electrodes of a dense-array electroencephalography net. We first derive analytic expressions for the potentials generated by scalp current injection in a four-sphere model of the human head. We then use a multistart downhill simplex algorithm to find regional tissue conductivities which minimize the error between measured and computed scalp potentials. Two error functions are studied, with similar results. The results show that, despite the low skull conductivity and expected shunting by the scalp, all four regional conductivities can be determined to within a few percent error. The method is robust to the noise levels expected in practice. To obtain accurate results the cerebrospinal fluid must be included in the forward solution, but may be treated as a known parameter in the inverse solution.

Measurement and validation of benchmark-quality thick-target tungsten X-ray spectra below 150 kVp

Pulse-height distributions of two constant potential X-ray tubes with fixed anode tungsten targets were measured and unfolded. The measurements employed quantitative alignment of the beam, the use of two different semiconductor detectors (high-purity germanium and cadmium-zinc-telluride), two different ion chamber systems with beam-specific calibration factors, and various filter and tube potential combinations. Monte Carlo response matrices were generated for each detector for unfolding the pulse-height distributions into spectra incident on the detectors. These response matrices were validated for the low error bars assigned to the data. A significant aspect of the validation of spectra, and a detailed characterization of the X-ray tubes, involved measuring filtered and unfiltered beams at multiple tube potentials (30-150 kVp). Full corrections to ion chamber readings were employed to convert normalized fluence spectra into absolute fluence spectra. The characterization of fixed anode pitting and its dominance over exit window plating and/or detector dead layer was determined. An Appendix of tabulated benchmark spectra with assigned error ranges was developed for future reference.

Using measured 30-150 kVp polychromatic tungsten x-ray spectra to determine ion chamber calibration factors, Nx (Gy C(-1))

Two methods for determining ion chamber calibration factors (Nx) are presented for polychromatic tungsten x-ray beams whose spectra differ from beams with known Nx. Both methods take advantage of known x-ray fluence and kerma spectral distributions. In the first method, the x-ray tube potential is unchanged and spectra of differing filtration are measured. A primary standard ion chamber with known Nx for one beam is used to calculate the x-ray fluence spectrum of a second beam. Accurate air energy absorption coefficients are applied to the x-ray fluence spectra of the second beam to calculate actual air kerma and Nx. In the second method, two beams of differing tube potential and filtration with known Nx are used to bracket a beam of unknown Nx. A heuristically derived Nx interpolation scheme based on spectral characteristics of all three beams is described. Both methods are validated. Both methods improve accuracy over the current half value layer Nx estimating technique.

Statistical control of artifacts in dense array EEG/MEG studies

With the advent of dense sensor arrays (64-256 channels) in electroencephalography and magnetoencephalography studies, the probability increases that some recording channels are contaminated by artifact. If all channels are required to be artifact free, the number of acceptable trials may be unacceptably low. Precise artifact screening is necessary for accurate spatial mapping, for current density measures, for source analysis, and for accurate temporal analysis based on single-trial methods. Precise screening presents a number of problems given the large datasets. We propose a procedure for statistical correction of artifacts in dense array studies (SCADS), which (1) detects individual channel artifacts using the recording reference, (2) detects global artifacts using the average reference, (3) replaces artifact-contaminated sensors with spherical interpolation statistically weighted on the basis of all sensors, and (4) computes the variance of the signal across trials to document the stability of the averaged waveform. Examples from 128-channel recordings and from numerical simulations illustrate the importance of careful artifact review in the avoidance of analysis errors.

Differentiating the N3 and N4 electrophysiological semantic incongruity effects

An event-related potential termed the N4 has been widely studied due to its sensitivity to semantic incongruity. A recent report (Nobre & McCarthy, 1994) indicates there is also an N3 component that is sensitive to semantic incongruity. To differentiate these two components, an existing data set with 65 electrode sites, 78 subjects, and 120 sentences was examined. Instead of the usual procedure of averaging over the stimuli within distinct categories for each subject, a new approach--averaging over subjects--was employed. In this item average approach, 120 averages (one per sentence) were produced. Correlational analyses indicate that the N3 is equally sensitive to cloze probability and sentential constraint. The N4, by contrast, is more sensitive to sentential constraint and less to cloze probability; it is also correlated with familiarity. We interpret these results as evidence that the N3 is more responsive to semantic fit whereas the N4 is more responsive to semantic expectancy.

Medial frontal cortex in action monitoring

Effective behavior requires continuous action monitoring. Electrophysiological studies in both monkeys and humans have shown activity in the medial frontal cortex that reflects dynamic control and monitoring of behavioral acts. In humans, the centromedial frontal cortex shows an electrical response within 100 msec of an error, the error-related negativity (ERN). The ERN occurs only when subjects are aware of making an error, suggesting that a critical factor may be self-monitoring of the action process. In the present study, we examined late responses in a deadline reaction time task, in which the subject becomes increasingly aware of making an error as the response becomes increasingly late. We found evidence of response conflict before errors defined by late responses but not before errors defined by incorrect responses. The results also show a linear increase in the amplitude of the ERN with increasingly late responses. These data suggest that frontal networks provide dynamic representations that monitor and evaluate the unfolding action plan.

The polar average reference effect: a bias in estimating the head surface integral in EEG recording

A reference-independent measure of potential is helpful for studying the multichannel EEG. The potentials integrated over the surface of the body is a constant, i.e. inactive across time, regardless of the activity and distribution of brain electric sources. Therefore, the average reference, the mean of all recording channels at each time point, may be used to approximate an inactive reference. However, this approximation is valid only with accurate spatial sampling of the scalp fields. Accurate sampling requires a sufficient electrode density and full coverage of the head's surface. If electrodes are concentrated in one region of the surface, such as just on the scalp, then the average is biased toward that region. Differences from the average will then be smaller in the center of the region, e.g. the vertex, than at the periphery. In this paper, we illustrate how this polar average reference effect (PARE) may be created by both the inadequate density and the uneven distribution of EEG electrodes. The greater the coverage of the surface of the volume conductor, the more the average reference approaches the ideal inactive reference.

Mood and spatial memory: emotion and right hemisphere contribution to spatial cognition

Depressed persons show an impairment of spatial cognition that may reflect the influence of affective arousal on right hemisphere cognition. We examined normal university students to determine whether individual differences in mood and arousal levels would be related to performance on a spatial memory task. Right-hemisphere specialization for this spatial memory task was confirmed by a left field advantage for the targets and this field asymmetry was enhanced as task difficulty was increased. Event-related brain potentials (ERPs), assessed with a 64-channel sensor array, showed a processing negativity contralateral to the target in the P300 interval (300-500 ms after the target appeared). This effect increased as task difficulty was increased. A stronger posterior negativity for good (rather than bad) targets may suggest that attention was allocated toward the good locations. A suggestion of right hemisphere sensitivity to mood in this normal sample was a tendency for the subjects high in Negative Arousal not to show the normal right hemisphere (left field) superiority for the spatial memory task. Interestingly, a medial frontal lobe negativity was elicited in the ERPs by the bad targets, perhaps paralleling the error-related negativity observed in other paradigms. This medial frontal negativity was also seen in response to the feedback stimulus for the bad targets. Motivation may be important to this frontal effect: It was enhanced for subjects describing themselves as high in either positive or negative affective arousal during the task.

EEG coherency II: experimental comparisons of multiple measures

OBJECTIVE

A concentric spheres model was used in an earlier paper to estimate the effects of volume conduction, reference electrode and spatial filtering on different EEG coherence measures. EEG data are used here to verify theoretical predictions.

METHODS

Three EEG data sets were: (1) 64 channel, recorded during 7 alternating periods of resting and mental calculation. (2) 128 channel, for comparison of eyes open versus eyes closed coherence. (3) 128 channel, recorded during deep sleep (stages 3 and 4) and REM.

RESULTS

The directions of large scale (lobeal) coherency changes between brain states are relatively independent of coherence measure. However, coherence between specific electrode pairs is sensitive to method and frequency. Average reference and digitally linked mastoids provide reasonable semi-quantitative estimates of large-scale neocortical source coherence. Close bipolar, Laplacian, and dura image methods remove most reference electrode and volume conduction distortion, but may underestimate coherence by spatial filtering.

CONCLUSION

Each EEG coherence method has its own potential sources of error and provides coherence estimates for different neural population sizes located in different locations. Thus, studies of coherence and brain state should include several different kinds of estimates to take full advantage of information in recorded signals.

Bayesian estimates of error bounds for EEG source imaging

Given a set of electrical potential measurements at the surface of the head, localizing the sources of the electrical activity is an inherently ill-posed problem. Bayesian methods can be used to specify prior information to constrain the possible source solutions. We show that Bayesian analysis can also provide a means for characterizing system noise levels, estimating the "error bars" surrounding source localization results, and estimating the information about brain processes conveyed by dense sensor array electroencephalographic (EEG) recordings. This method is, in principal, applicable to any linear model of EEG or magnetoencephalographic (MEG) processes. A series of simulations demonstrated the internal consistency of our method, the robustness to noise levels, and the limitations of accurate source localization with large numbers of sources.

Dense sensor array topography of the event-related potential to task-relevant auditory stimuli

High spatial density recording and better topographic mapping algorithms have improved the spatial resolving power of the event-related potential (ERP), adding to its already excellent temporal resolution. This study used a 64 channel recording array and spherical spline interpolation to create topographic descriptions of the voltage and current density scalp distributions of the ERP in an auditory oddball paradigm. Frequent (standard) and infrequent (target) tones were presented at a rate of one every approximately 2500 ms to a group of 20 college undergraduates in passive listening and active (count the infrequent tones) task blocks. ANOVAs and topographic analyses were performed on the primary deflections in the 'late' portion of the ERP: the P1, N1, P2, N2 and P3. A target minus standard difference wave was also created for each task. The difference wave contained a mismatch negativity (MMN), an N2b and a P3d. The MMN did not differ between the passive and active tasks and had a topography similar to the N1; also the difference wave P3d was topographically similar to the target P3. The N2b, which occurred only to targets in the active condition, and was the first index of target detection, had a scalp distribution consistent with generation in frontal and superior temporal cortex, suggesting activity in cortical areas of selective attention and auditory stimulus representation.

Health effects of diesel emissions

We have reviewed the literature relating to the health effects of diesel emissions with particular reference to acute and chronic morbidity and to carcinogenicity. It is apparent that exposure to diesel fumes in sufficient concentrations may lead to eye and nasal irritation but there is no evidence of any permanent effect. A transient decline of ventilatory capacity has been noted following such exposures. There is also some evidence that the chronic inhalation of diesel fumes leads to the development of cough and sputum, that is chronic bronchitis, however, it is usually impossible to show a cause and effect relationship because of the concomitant and confounding exposures to mine dust and cigarette smoke. Although there have been a number of papers suggesting that diesel fumes may act as an carcinogen, the weight of the evidence is against this hypothesis. Finally, the role of small particles, less than 10 microns, which are frequently present in diesel emissions requires further study since there is some limited evidence that they may be partly responsible for some of the exacerbations of asthma.

EEG coherency. I: Statistics, reference electrode, volume conduction, Laplacians, cortical imaging, and interpretation at multiple scales

Several methodological issues which impact experimental design and physiological interpretations in EEG coherence studies are considered, including reference electrode and volume conduction contributions to erroneous coherence estimates. A new measure, 'reduced coherency', is introduced as the difference between measured coherency and the coherency expected from uncorrelated neocortical sources, based on simulations and analytic-statistical studies with a volume conductor model. The concept of reduced coherency is shown to be in semi-quantitative agreement with experimental EEG data. The impact of volume conduction on statistical confidence intervals for coherence estimates is discussed. Conventional reference, average reference, bipolar, Laplacian, and cortical image coherencies are shown to be partly independent measures of neocortical dynamic function at different spatial scales, due to each method's unique spatial filtering of intracranial source activity.

A digital imaging and communications in medicine (DICOM) print service for chest imaging

Large-scale picture archiving and communication systems (PACS) have not been widely implemented in this or other countries. In almost all radiology departments film remains the medium for diagnostic interpretation and image archive. Chest imaging is the dominant screening examination performed within most imaging departments and as such, is an extremely high-volume, low-margin examination. Digital technologies are being applied to chest imaging to overcome limitations of screen-film receptors (limited latitude) and current film management systems (single-image copy). Efficient management of images and information is essential to the success of a chest imaging program. In this article we report on a digital imaging and communications in medicine (DICOM)-based centralized printing network for chest imaging. The system components and their operational characteristics are described. Our experience integrating DICOM-compliant equipment supplied by several vendors is described. We conclude that the print model supported by DICOM is adequate for cross-sectional (eg, computed tomography and magnetic resonance) imaging but is too simplistic to be generally applied to projection radiography.

The relationship between pixel value and beam quality in photostimulable phosphor imaging

Direct digital capture systems are relatively new in diagnostic imaging. Full utilization of these devices requires a thorough understanding of the image formation process. The conversion of x-ray photon energy to a digital pixel value in a commercially available photostimulable phosphor (PSP) imaging system is investigated in this paper. Pixel values measured at 16 different combinations of 4 x-ray beam peak voltages (60, 80, 100, and 120 kVp) and 4 beam qualities are reported. At 60 and 80 kVp exposures were made at 2.58 x 10(-7) C/kg (1 mR); at 100 and 120 kVp exposures were made at 5.16 x 10(-7) C/kg (2 mR). Analysis of variance was used to determine the statistical significance of the relationship between pixel value and beam quality for a given kVp and exposure. A computer model accounting for x-ray spectral effects that accurately predicts pixel value is presented. Calculated pixel value agree within 5.0% of measured values over the range of beam energies, exposures, and qualities.

Tourette syndrome

This survey of recent literature addressing Tourette syndrome reflects clinical and laboratory findings of investigations of behavioral, neuropsychological, imaging, genetic, neurobiological and treatment considerations. Tourette syndrome is a prototypic neuropsychiatric disorder manifesting a full range of objectively describable phenomena from different scientific vantage points and serves as a model for study and integrative understanding of brain and behavior.

Canal wall planning by engine-driven nickel-titanium instruments, compared with stainless-steel hand instrumentation

Twenty-two mesial roots of extracted human mandibular molars were divided into two groups based on root curvature and length. The mesiolingual canals were instrumented using either Flexofiles in a step-back anticurvature filing method, or they were instrumented with engine-driven 0.02 taper nickel-titanium files. Ground sections were prepared at 1-, 2.5-, and 5-mm levels from the working length. The mesiobuccal canal was used as an uninstrumented control for predentin character. Digitizing software was used to calculate the instrumented portion as a percentage of the total canal perimeter. The results indicated no significant difference in overall canal wall planning between the two groups and no significant difference at each of the three levels.

A putative poststreptococcal case of OCD with chronic tic disorder, not otherwise specified

A 12-year-old girl presented with an atypical, recurrent, increasingly treatment-resistant case of obsessive-compulsive disorder and chronic tic disorder associated with profound separation anxiety, learning difficulty, and intermittent upper respiratory symptoms. In addition to detailed reviews of history and findings from many clinical caretakers from the prior 7 years, current pediatric, psychiatric, neuropsychological, neuroimaging, and clinical laboratory data were also available. Treatment options were considered from multiple perspectives: psychoanalytically oriented psychotherapy, conventional pharmacotherapy, family interventions, cognitive-behavioral therapy, and learning-supportive strategies. Psychological, neuropsychiatric, and neuroimmunological formulations of etiology were considered. Subsequent treatments included supportive psychotherapy, neuroleptic augmentation of selective serotonin reuptake inhibitors, prophylactic penicillin, and a course of six sessions of plasmapheresis over a 2-week period. The case raises questions for ongoing consideration that juxtapose dynamic, neuropsychiatric, and neuroimmunological perspectives.

Spatial sampling and filtering of EEG with spline laplacians to estimate cortical potentials

The electroencephalogram (EEG) is recorded by sensors physically separated from the cortex by resistive skull tissue that smooths the potential field recorded at the scalp. This smoothing acts as a low-pass spatial filter that determines the spatial bandwidth, and thus the required spatial sampling density, of the scalp EEG. Although it is better appreciated in the time domain, the Nyquist frequency for adequate discrete sampling is evident in the spatial domain as well. A mathematical model of the low-pass spatial filtering of scalp potentials is developed, using a four concentric spheres (brain, CSF, skull, and scalp) model of the head and plausible estimates of the conductivity of each tissue layer. The surface Laplacian estimate of radial skull current density or cortical surface potential counteracts the low-pass filtering of scalp potentials by shifting the spatial spectrum of the EEG, producing a band-passed spatial signal that emphasizes local current sources. Simulations with the four spheres model and dense sensor arrays demonstrate that progressively more detail about cortical potential distribution is obtained as sampling is increased beyond 128 channels.

Emotional expectancy: brain electrical activity associated with an emotional bias in interpreting life events

University students in either an optimistic or pessimistic mood state read brief stories of daily life events as event-related brain potentials were collected during the final word of each story. For subjects in a pessimistic mood, a bias to expect negative outcomes was seen as an N400/P300 effect over posterior scalp regions. For subjects in an optimistic mood, a differentiation between good and bad outcomes was also observed, but it was specific to medial frontal areas. Analysis of single-trial P300 latencies suggested that semantically incongruent and mood-incongruent outcome words resulted in increased median latency of the late positive complex (LPC) and resulted in increased variability of LPC latency across trials.

Social and emotional self-regulation

In humans, frontal lesions result in deficits of social and emotional behavior that are often surprising in the presence of intact language and other cognitive skills. The connections between the motivation and memory functions of limbic cortex and the motor planning functions of frontal neocortex must be fundamental to meeting the daily challenges of self-regulation. The connectional architecture of limbic and neocortical networks suggests a model of function. The densely interconnected paralimbic cortices may serve to maintain a global motivational context within which specific actions are articulated and sequenced within frontal neocortical networks. The paralimbic networks represent the visceral and kinesthetic information that is integral to the representation of the bodily self. In a general sense, the implicit self-representation within paralimbic networks may shape the significance of perceptions and the motivational context for developing actions. The network architecture of the frontal lobe reflects the dual limbic origins of frontal cortex, in the dorsal archicortical and ventral paleocortical structures. In this paper, we speculated that these two limbic-cortical pathways apply different motivational biases to direct the frontal lobe representation of working memory. The dorsal limbic mechanisms projecting through the cingulate gyrus may be influenced by hedonic evaluations, social attachments, and they may initiate a mode of motor control that is holistic and impulsive. In contrast, the ventral limbic pathway from the amygdala to orbital frontal cortex may implement a tight, restricted mode of motor control that reflects adaptive constraints of self-preservation. In the human brain, hemispheric specialization appears to have led to asymmetric elaborations of the dorsal and ventral pathways. Understanding the inherent asymmetries of corticolimbic architecture may be important in interpreting the increasing evidence that the left and right frontal lobes contribute differently to normal and pathological forms of self-regulation.

Quality assurance and quality control of an intensive care unit picture archiving and communication system

Most radiology departments have established quality assurance (QA) and quality control (QC) programs for conventional film-based image management systems. At many institutions, digital image management systems, or picture archiving and communication systems (PACS), are replacing part or all of the film management system. In these situations, it is important to control the quality of the digital images that are produced. The observed frequency of eight types of image-related errors occurring on an image viewing station located in a medical intensive care unit is reported. Images on the viewing station were checked for 12 consecutive weeks. Film images available in the radiology reading room and digital images on the viewing station were compared with a list of completed examinations produced by the radiological information system. Overall, 1,082 patient examinations were encountered. Seventy-six images (7.02% of all images) were observed with errors. In addition, four previously unencountered types of errors were observed in 11 images (1.01% of all images). The majority of the errors are attributed to interfaces either between information systems or between the PACS and the user. It is concluded that QA-QC procedures are necessary for PACS, and that good interfaces, both between information systems and between humans and computer systems, are essential for successful PACS implementations.

Picture archiving communication systems in the intensive care unit

The authors review the potential of picture archiving and communication systems (PACS) in the critical care environment. Presented and analyzed is a university hospital intensive care unit (ICU) PACS project. The objective of the project is to provide reliable, timely viewing of bedside radiographs in selected ICUs within the hospital. Key features include redundancy of critical hardware components and viewing stations that are simple to operate. The system was implemented in phases with incremental evaluation of performance and goals. PACS subsystems are discussed. On the basis of this experience, ICU PACS specifications and general considerations are presented. Also presented is a comparison of 10-year cost projections for conventional screen-film radiography and an ICU PACS that incorporates computed radiography. The costs of the two alternatives are comparable. PACS is a viable alternative to conventional screen-film imaging in the ICU setting and offers improved and more efficient patient care.

Digital chest radiography: comparison of unprocessed and processed images in the detection of solitary pulmonary nodules

PURPOSE

To compare the accuracy with which simulated solitary pulmonary nodules can be identified on digital images of the chest that are unprocessed, processed with adaptive spatial filtering, or processed with global filtering.

MATERIALS AND METHODS

Six experienced chest radiologists evaluated 408 test radiographs (136 from each of the three types, half with simulated nodules) and judged whether a nodule was present. Data from the 2,448 observations were evaluated by means of a receiver operating characteristic curve with location methods.

RESULTS

Accuracy was significantly better with the adaptive filter technique than with the global technique (P < .05), and it was better with adaptive filtering than with no processing in the detection of pulmonary nodules in the mediastinal-subdiaphragmatic areas (P < .05). No significant difference was found between no processing and global filtering.

CONCLUSION

Adaptive filtration is superior to global filtration in the identification of solitary pulmonary nodules and is superior to no processing in nodules projected over the radiopaque areas of the thorax on digital images.

Normalized average glandular dose in molybdenum target-rhodium filter and rhodium target-rhodium filter mammography

PURPOSE

To determine the normalized glandular dose (DgN) for molybdenum target-rhodium filter (Mo-Rh) and rhodium target-rhodium filter (Rh-Rh) mammography and compare the average glandular doses (Dg) that resulted with a conventional molybdenum target-molybdenum filter (Mo-Mo) source assembly.

MATERIALS AND METHODS

X-ray spectra models for Mo-Rh and Rh-Rh were developed and used to calculate DgN values for these target-filter combinations as a function of x-ray tube potential, half-value layer, and breast thickness for three breast compositions. For the average glandular dose comparisons, 50/50 phantoms were imaged for the three target-filter source assemblies at three tube potentials.

RESULTS

For the same parameters, DgN values for Mo-Rh and Rh-Rh were higher than for Mo-Mo. At the same voltage, the exposures required to image breast phantoms are substantially lower, and as a result, Dgs are also less with Mo-Rh and Rh-Rh than with Mo-Mo.

CONCLUSION

DgN values presented permit practical evaluations of average glandular doses for Mo-Rh and Rh-Rh mammography. At a given potential, dose savings are realized with Mo-Rh and Rh-Rh source assemblies.

Computed radiography: user-programmable features and capabilities

Digital or computed radiography (CR) using photostimulable storage phosphor plate technology is becoming increasingly popular in certain clinical applications, such as bedside radiography, where it possesses clear advantages over conventional screen-film imaging. The majority of CR systems in clinical use have been manufactured by Fuji Medical Systems USA, Inc (Stamford, CT) and provide a surprising degree of flexibility. Fuji CR units are delivered with preset menus, hardcopy format, and image-processing parameters for each examination. Of practical importance is that users may change the exam menu and printed film format as well as the image-processing parameters for each examination. There is, however, a lack of documentation describing these features and how they are programmed. This paper addresses these issues. Examples are given on how to change: 1) the printed film format, 2) the contrast and gray-scale processing, 3) spatial frequency enhancement, and 4) the appearance of the operator interface menus.

Spatial sampling of head electrical fields: the geodesic sensor net

In studying brain electrical activity from scalp sensors (electrodes), the optimal measurement would sample the potential field over the entire surface of the braincase, with a sufficient density to avoid spatial aliasing of the surface electrical fields. The geodesic sensor net organizes an array of sensors, each enclosed in a saline sponge, in a geodesic tension structure comprised of elastic threads. By fixing a sensor pedestal at each geodesic vertex, the geometry of the tension structure insures insures that the sensor array is distributed evenly across the accessible head surface. Furthermore, the tension of the network is translated into compression that is divided equally among the sensor pedestals and directed along head-radial vectors. Various geodesic partitioning frequencies may be selected to provide an even surface distribution of the dense sensor arrays (e.g., 64, 128, or 256) that appear to be necessary to provide adequate spatial sampling of brain electrical events.

Scatter in computed radiography

The effects of scatter radiation on images obtained with storage phosphor computed radiography (CR) were evaluated. The scatter degradation factor was extended to account separately for forward scatter and backscatter. Values for the ratios of forward scatter to primary radiation (sf/p) and backscatter to primary radiation (sb/p) were measured for various x-ray tube potentials, phantom thicknesses, and field sizes for CR imaging plates (IPs). Similar measurements were made for a common screen-film system. The sb/p values for the IPs were 0.05-3.80. Standard CR cassettes do not have lead foil behind the IP to control backscatter; the results of this study indicate that such control is needed. The sf/p values were 40%-70% higher in IPs (50%-120% higher when backscatter was included) than those in the conventional screen-film system. This difference is attributed to the differences in the K-absorption edges of barium and gadolinium and the fact that scatter has lower effective energy than the primary beam as they exit the patient.

Topography of the N400: brain electrical activity reflecting semantic expectancy

When subjects read an semantically unexpected word, the brain electrical activity shows a negative deflection at about 400 msec in comparison with the response to an expected word. In order to study the brain systems related to this effect we mapped it with a dense (64-channel) electrode array and two reference-independent measures, one estimating the average potential gradients and the other radial current density. With these measures, the event-related brain potential (ERP) begins at about 70 msec with the P1, reflecting bilateral current sources over occipitoparietal areas. A strongly left-lateralized N1 then follows, peaking at about 180 msec, accompanied by an anterior positivity, the P2. A separate posterior positive pattern then emerges that seems to repeat the topography of the P1. Next, at about 350 msec, the ERP for the congruous word develops a P300 or LPC, characterized by a diffuse positivity over the superior surface of the head and several negativities over inferior regions. This superior source/inferior sink pattern of the LPC is greater over the left hemisphere. In contrast, the ERP for the incongruous word in this interval displays the N400 as a period in which topographic features are absent. At about 400 msec the ERP for the incongruous word begins to develop an LPC, which then remains relatively symmetric over the two hemispheres.

Neural mechanisms of emotion

When viewed from an evolutionary perspective, the neural mechanisms of emotion can be seen to be distributed across the brainstem, limbic, paralimbic, and neocortical regions. Descending and ascending connections among these levels are discussed in relation to three types of emotional processes: peripheral effects on patterned bodily responses, central effects on cognitive processing, and subjective emotional experience. Descending influences from the higher to the lower levels allow for an increasing coordination and flexibility of emotional responses, culminating in patterned activity across the peripheral endocrine, autonomic, and motor systems. Ascending influences from lower to higher levels provide preparatory modulation of cortical pathways, thus enabling perceptual and cognitive processing that is adaptive given the current emotional state. The bodily feelings of emotion are a function of cortical interoceptive sensory fields, activated by centrally generated signals or peripheral inputs from the body.

Right hemisphere sensitivity to arousal and depression

Several lines of evidence show impaired right hemisphere function in depression. Lateralized simple reaction time tasks show impaired left visual field responses both in normals experiencing a depressed mood and in patients with mild unipolar depression. One interpretation for these findings is that depression impairs right hemisphere function by interfering with right hemisphere arousal and vigilance mechanisms. In order to test this hypothesis, subjects receiving either depression or relaxation mood suggestions performed an uncued reaction time task that has been shown to be sensitive to right posterior brain damage. Level of alertness was varied by contrasting uncued blocks with blocks in which targets were preceded by a warning tone. The results showed the predicted slowing of left visual field responses in the depressed mood, but only in women. The effect was significant only for the uncued blocks. The left visual field impairment was significantly larger during depression than in the relaxation state, but a smaller left visual field slowing was present in women in the relaxed state as well. These results may be consistent with the notion that depression interferes with right hemisphere function in part by influencing right hemisphere arousal mechanisms.

Neural mechanisms of emotion

When viewed from an evolutionary perspective, the neural mechanisms of emotion can be seen to be distributed across the brainstem, limbic, paralimbic, and neocortical regions. Descending and ascending connections among these levels are discussed in relation to three types of emotional processes: peripheral effects on patterned bodily responses, central effects on cognitive processing, and subjective emotional experience. Descending influences from the higher to the lower levels allow for an increasing coordination and flexibility of emotional responses, culminating in patterned activity across the peripheral endocrine, autonomic, and motor systems. Ascending influences from lower to higher levels provide preparatory modulation of cortical pathways, thus enabling perceptual and cognitive processing that is adaptive given the current emotional state. The bodily feelings of emotion are a function of cortical interoceptive sensory fields, activated by centrally generated signals or peripheral inputs from the body.

Molybdenum target x-ray spectra: a semiempirical model

A semiempirical model for generating molybdenum target x-ray spectra is presented. The model is an extension of a previous model developed by the authors for tungsten and takes into account the depth of production for both bremsstrahlung and characteristic x-ray photons. As in the previous work, the optimal model parameters were determined using nonlinear least-squares fits to experimental data. Good agreement between the two was obtained. By varying target angle, off-axis angle, and filtration in the model in accordance with the x-ray tube and geometry of interest, results consistent with tabulated spectra for different conditions have been obtained.

Spectral dependence of glandular tissue dose in screen-film mammography

The average glandular tissue dose in mammography is generally determined from published tables with knowledge of the breast entrance skin exposure, x-ray tube target material, beam quality (half-value layer [HVL]), breast thickness, and breast composition. Using a carefully designed and experimentally validated Monte Carlo simulation, the authors found that average glandular dose also depends on x-ray tube voltage and, to a lesser extent, on x-ray tube voltage waveform. For currently employed molybdenum target-molybdenum filter source assemblies, a difference in dose of 10% or more is possible in estimating the average glandular dose obtained with different x-ray tube voltages but with the same HVL. Presented are normalized average glandular tissue doses in units of radiation absorbed dose per unit entrance skin exposure for different tube voltages and tube voltage waveforms as well as for different breast thicknesses and compositions and beam filtrations.

Semiempirical model for generating tungsten target x-ray spectra

A semiempirical model for generating tungsten target x-ray spectra is presented. This model extends earlier work in two significant areas. First, both bremsstrahlung and characteristic x-ray production are assumed to occur at varying depths within the target. Second, optimal parameters for the model were determined from experimental spectra utilizing nonlinear least-squares techniques. As a result, good agreement is obtained between calculated and measured x-ray tube spectra and output for different target angles and a wide range of x-ray tube potentials. Such is not the case with previously published models.

A patient monitoring system designed as a platform for application development

This paper presents a patient data monitoring system for use in critical care areas. The system incorporates design criteria from the Institute of Electrical and Electronic Engineers' (IEEE) proposed standards body (P1073), the Medical Information Bus (MIB) and from our design team. Existing hardware and software technology is utilized wherever possible to maintain cost effectiveness. A major design objective is providing a consistent environment in which to develop applications for critical patient care delivery. The system allows applications to be developed without specific knowledge of the configuration of the bedside environment. Therefore, investments in 'user' application development are shielded from changes in patient care delivery technology. The system has been in limited operation in a surgical intensive care unit for several months with prototype applications.

Nutrition status and brain function in aging

Biochemical indices of nutrition status assessed in 28 healthy persons aged greater than 60 y were related to cognitive performance and electroencephalographic (EEG) indices of neuropsychological function. Performance data were most frequently related to indices of nutrition status when tasks were demanding. Numerous correlations were also found between EEG indices and indices of thiamin, riboflavin, and iron nutriture. Certain observations, such as a decrement in alpha-wave activity in the EEG of subjects with low thiamin status, suggest that subtle neuropsychological impairment can occur in association with mild deficits in nutrition status. Other findings indicate that EEG frequency responses of older subjects with high iron status are similar to those of younger persons; however, these data are more difficult to interpret. The results suggest that further research on nutrition and neuropsychological function will lead to a better understanding of the role of nutrition in maintaining the functional integrity of the aging brain.