Topographic distribution of the tibial somatosensory evoked potential using coherence

The objective of the present study was to determine the adequate cortical regions based on the signal-to-noise ratio (SNR) for somatosensory evoked potential (SEP) recording. This investigation was carried out using magnitude-squared coherence (MSC), a frequency domain objective response detection technique. Electroencephalographic signals were collected (International 10-20 System) from 38 volunteers, without history of neurological pathology, during somatosensory stimulation. Stimuli were applied to the right posterior tibial nerve at the rate of 5 Hz and intensity slightly above the motor threshold. Response detection was based on rejecting the null hypothesis of response absence (significance level α= 0.05 and M = 500 epochs). The best detection rates (maximum percentage of volunteers for whom the response was detected for the frequencies between 4.8 and 72 Hz) were obtained for the parietal and central leads mid-sagittal and ipsilateral to the stimulated leg: C4 (87 percent), P4 (82 percent), Cz (89 percent), and Pz (89 percent). The P37-N45 time-components of the SEP can also be observed in these leads. The other leads, including the central and parietal contralateral and the frontal and fronto-polar leads, presented low detection capacity. If only contralateral leads were considered, the centro-parietal region (C3 and P3) was among the best regions for response detection, presenting a correspondent well-defined N37; however, this was not observed in some volunteers. The results of the present study showed that the central and parietal regions, especially sagittal and ipsilateral to the stimuli, presented the best SNR in the gamma range. Furthermore, these findings suggest that the MSC can be a useful tool for monitoring purposes.

Use of magnitude-squared coherence to identify the maximum driving response band of the somatosensory evoked potential

The present study proposes to apply magnitude-squared coherence (MSC) to the somatosensory evoked potential for identifying the maximum driving response band. EEG signals, leads [Fpz'-Cz'] and [C3'-C4'], were collected from two groups of normal volunteers, stimulated at the rate of 4.91 (G1: 26 volunteers) and 5.13 Hz (G2: 18 volunteers). About 1400 stimuli were applied to the right tibial nerve at the motor threshold level. After applying the anti-aliasing filter, the signals were digitized and then further low-pass filtered (200 Hz, 6th order Butterworth and zero-phase). Based on the rejection of the null hypothesis of response absence (MSC(f) > 0.0060 with 500 epochs and the level of significance set at a = 0.05), the beta and gamma bands, 15-66 Hz, were identified as the maximum driving response band. Taking both leads together ("logical-OR detector", with a false-alarm rate of a = 0.05, and hence a = 0.0253 for each derivation), the detection exceeded 70 percent for all multiples of the stimulation frequency within this range. Similar performance was achieved for MSC of both leads but at 15, 25, 35, and 40 Hz. Moreover, the response was detected in [C3'-C4'] at 35.9 Hz and in [Fpz'-Cz'] at 46.2 Hz for all members of G2. Using the "logical-OR detector" procedure, the response was detected at the 7th multiple of the stimulation frequency for the series as a whole (considering both groups). Based on these findings, the MSC technique may be used for monitoring purposes.

Statistical analysis of event-related potential elicited by verb-complement merge in Brazilian Portuguese

An interesting fact about language cognition is that stimulation involving incongruence in the merge operation between verb and complement has often been related to a negative event-related potential (ERP) of augmented amplitude and latency of ca. 400 ms - the N400. Using an automatic ERP latency and amplitude estimator to facilitate the recognition of waves with a low signal-to-noise ratio, the objective of the present study was to study the N400 statistically in 24 volunteers. Stimulation consisted of 80 experimental sentences (40 congruous and 40 incongruous), generated in Brazilian Portuguese, involving two distinct local verb-argument combinations (nominal object and pronominal object series). For each volunteer, the EEG was simultaneously acquired at 20 derivations, topographically localized according to the 10-20 International System. A computerized routine for automatic N400-peak marking (based on the ascendant zero-cross of the first waveform derivative) was applied to the estimated individual ERP waveform for congruous and incongruous sentences in both series for all ERP topographic derivations. Peak-to-peak N400 amplitude was significantly augmented (P < 0.05; one-sided Wilcoxon signed-rank test) due to incongruence in derivations F3, T3, C3, Cz, T5, P3, Pz, and P4 for nominal object series and in P3, Pz and P4 for pronominal object series. The results also indicated high inter-individual variability in ERP waveforms, suggesting that the usual procedure of grand averaging might not be considered a generally adequate approach. Hence, signal processing statistical techniques should be applied in neurolinguistic ERP studies allowing waveform analysis with low signal-to-noise ratio.

Topographic aspects of photic driving in the electroencephalogram of children and adolescents

The electroencephalogram amplitude spectra at 11 fixed frequencies of intermittent photic stimulation of 3 to 24 Hz were combined into driving "profiles" for 14 scalp points in 8 male and 7 female normal subjects aged 9 to 17 years. The driving response varied over frequency and was detected in 70 to 100 percent of cases in the occipital areas (maximum) and in 27 to 77 percent of cases in the frontal areas (minimum) using as a criterion peak amplitude 20 percent higher than those of the neighbors. Each subject responded, on average, to 9.7 ñ 1.15 intermittent photic stimulation frequencies in the right occipital area and to 6.8 ñ 1.97 frequencies in the right frontal area. Most of the driving responses (in relation to the previous background) were significant according to the spectral F-test (a = 0.05), which also detected changes in some cases of low amplitude responses not revealed by the peak criterion. The profiles had two maxima in the alpha and theta bands in all leads. The latter was not present in the background spectra in the posterior areas and was less pronounced in the anterior ones. The weight of the profile theta maximum increased towards the frontal areas where the two maxima were similar, while the profile amplitudes decreased. The profiles repeated the shape of the background spectra, except for the theta band. The interhemispheric correlation between profiles was high. The theta driving detected in all areas recorded suggests a generalized influence of the theta generators in prepubertal and pubertal subjects.

Detecção da resposta auditiva no EEG de crianças utilizando técnicas no domínio da freqüência / Detection of EEG auditory response in children, using frequency domain techniques

A triagem auditiva, especialmente de recém nascidos (RN) que apresentem fatores de risco, tem sido recomendada por diversas entidades internacionais. O exame de potencial evocado auditivo de tronco cerebral (BERA - Brainstem Evoked Responses Audiometry) é atualmente considerado como referência para detecção do limiar auditivo em RNs, embora seja um procedimento demorado e de interpretação subjetiva. Para detecção objetiva da resposta auditiva em crianças foram aplicadas duas técnicas que utilizam a Transformada de Fourier: o CSM (Component Synchrony Meadure) e o MSC (Magnitude Squared Coherence). Sinais EEG de 32 crianças foram adquiridos durante BERA com estimulação por clicks a 20 Hz. Colheram-se ao todo 73 sinais EEG, cada um abrangendo 1024 estímulos de 85 dBHL. Destes 73 sinais, a interpretação clínica dos potenciais evocados indicou haver resposta (audição intacta) em 55. Um critério heurístico de detecção de resposta baseado em um conjunto de harmônicos da freqüência de estimulação (20 a 900 Hz) resultou em sensibilidade de 93 por cento e especificidade de 78 por cento para o MSC, e 98 por cento e 72 por cento para o CSM, respectivamente. Como o desempenho na detecção da surdez (resultado negativo) é o desejado, MSC seria mais adequado à detecção de resposta auditiva no EEG de crianças e recém-nascidos.

Monitorização do plano anestésico por técnicas estatísticas no domínio da freqüência / Monitoring depth of anaesthesia by frequency-domain statistical techniques

O potencial evocado auditivo de média latência (MLAEP) tem sido empregado na avaliação do nível anestésico, sendo usual a análise morfológica (AEPidx - Indice de Potencial Evocado Auditivo, e DT - Distância Taxonômica). Neste trabalho, técnicas de detecção objetiva de respostas no domínio da freqüência (MSC - Magnitude Quadrada da Coerência, e CSM - Medida de Sincronismo de Componentes) foram avaliadas a partir de EEG sob estimulação auditiva. Dez voluntários foram estimulados com cliques repetitivos (7,645 Hz, nível de pressão sonora de 75 dB SPL), sendo EEG adquirido na derivação Vértex - Lobo Auricular durante 10 min sem administração de anestésico e dois períodos consecutivos de infusão contínua de propofol (3 mg/Kg/h, sedação, e 9 mg/Kg/h, anestesia) de 45 min cada. O instante de perda de consciência foi estimado com base no pressionamento de uma maniqueta em resposta a estímulos luminosos a cada 15 s. MSC e CSM permitem a inferência estatística de ausência de resposta auditiva (valor crítico, para e.g. alfa = 1 por cento) ao longo do processo anestésico. Além disso, MSC(Ÿ) e CSM(Ÿ) se reduzem durante a infusão (mais expressivamente na anestesia), tendo maior concordância (diagramas de Bland-Altman) com os resultados da maniqueta que AEPidx e DT, e maior equivalência (Wilcoxon Signed-Rank Test, alfa = 5 por cento) que DT.

Análise espectral e de coerência de padröes do siclo sono-vígilia do EEG neonatal / Spectral analysis of pastterns coherence of sllep-awake cicle of neonatal ECG

O espectro de potência e a coerência inter-hemisférica foram estimados para segmentos dos padrões do ciclo sono-vigélia Low Voltage Irregular, Misto e High Voltage Slow. Diferenças significativas entre estes padrões foram encontradas, através da ANOVA, em uma larga faixa de frequência, principalmente para o espectro de potência até 15 Hz.

Modelagem AR de sinais EEG multicanal usando o TMS320C30 / AR modelling of multicanal EEG signals using the TMS320C30

Uma placa processadora digital de sinais (DSP), com o TMS320C30, em conjunto com um PC foi empregada na modelagem autoregressiva (AR) de sinais EEG. O sistema PC-DSP mostrou-se capaz de realizar a análise espectral destes sinais com tempo de processamento compatível com monitoração em tempo real do espectro de 16 canais EEG.

Radiologia diagnóstica e programa de garantia de qualidade: avaliaçäo crítica / Diagnostic Radiology and quality assurance program: critical evaluation

O Programa de Garantia de Qualidade, implementado no Serviço de Radiologia do Hospital da Polícia Militar - RJ, propiciou a reduçäo de 70 por cento na taxa de rejeiçäo de filmes e de 75 por cento nos custos. Entretanto, a descontinuidade do Programa tem conduzido ao retorno a situaçäo anterior a implementaçäo.

A Quality Assurance Program, implemented at the Radiology Service of the Hospital of the Military Police in Rio de Janeiro, brought about a reduction of 70% in the number of rejected films and 75% in the costs. The discontinuation of the program has however lead to a return to the former conditions.

Avaliando serviços de radiologia diagnóstica / Evaluate service of the diagnostic radiology

Radiação ionizante tem sido, cada vez mais, utilizada no diagnóstico e tratamento de doenças, sem a adequada adoção de métodos que garantem a qualidade do exame como um todo. Um Sistema de Garantia de Qualidade que vise reverter este cenário, depende das características de cada unidade, na qual Programas de Qualidade serão implementados. A avaliação preliminar de Serviços de Radiologia Diagnóstica, no que concerne a complexidade, oferta e qualidade dos serviços e disponibilidade de pssoal, constataram a utilização de técnicas de baixa voltagem, a não realização de testes de aceitação de aprelhos e acessórios e a não existência de profissional responsável pela proteção radiológica, entre outras limitações e deficiências.

The use of ionizing radiation is steadily increasing in diagnosis and treatment of diseases, in many cases however without the adoption of suitable methods that would garantee the quality of the exam as a whole. Improvements in this respect must be based on the present characteristics of the units in which Quality Control is to be introduced. Preliminary evaluation of Diagnostic Radiology Services showed, among other problems, the preferential use of low-voltage X-rays, the absence of acceptance triais of equipment and acessories and the lack of professionals responsible for radiological protection.