RESUMO Objetivo: Investigar o valor preditivo do ultrassom de Doppler transcraniano (TCD) para doença de pequenos vasos (SVD) em pacientes idosos. Métodos: ultrassonografia de TCD e ressonância magnética (RM) foram realizadas em 184 idosos portadores de SVD cerebral. As relações das características clínicas e os parâmetros ultrassonográficos do TCD com lesão grave de substância branca (WML) no desempenho da RM foram investigados por análise univariada e análise multivariada. Resultados: A análise univariada mostrou que, a idade, a velocidade média de fluxo (MFV) da artéria média cerebral (MCA) esquerda, a MFV da MCA direita e o índice de pulsatilidade (PI) médio estiveram significativamente relacionados à WML grave (P <0,05). A análise de regressão logística multivariada mostrou que apenas a idade (razão de chances: 1,21; IC95%: 1,10-1,36; P <0,01) e o PI da MCA (razão de dominância: 1,13; IC 95%: 1,06-1,80; P = 0,02) estiveram significativamente relacionados a WML grave. A análise dos parâmetros ultrassonográficos do TCD mostrou que, quando o ponto de corte do IP do MCA foi 1,04, ele pôde identificar à WML grave. A área sob a curva foi de 0,70 (IC 95%: 0,60-0,80). A sensibilidade e especificidade foram de 63,0% e 72,0%, respectivamente. Os valores preditivos positivos e negativos foram de 35,4% e 86,6%, respectivamente. Conclusão: O PI da MCA na ultrassonografia do TCD está significativamente relacionado à WML grave. A ultrassonografia TCD pode orientar a ressonância magnética seletiva para detecção da WML.

ABSTRACT Objective: To investigate the predictive value of transcranial Doppler (TCD) ultrasound for cerebral small vessel disease in elderly patients. Methods: Transcranial Doppler ultrasound and magnetic resonance imaging (MRI) were performed on 184 elderly patients with cerebral small vessel disease. The relationship of clinical characteristics and TCD ultrasound parameters with severe white matter lesions (WMLs) in MRI were investigated by univariate analysis and multivariate analysis. Results: The univariate analysis showed that age, left middle cerebral artery (MCA) mean flow velocity, right MCA mean flow velocity and mean MCA pulsatility index were significantly correlated with severe WMLs (p < 0.05). The multivariate logistic regression analysis showed that only age (odds ratio: 1.21; 95%CI: 1.10–1.36; p < 0.01) and MCA pulsatility index (dominance ratio: 1.13; 95%CI: 1.06–1.80; p = 0.02) were significantly correlated with severe WMLs. The analysis of TCD ultrasound parameters showed that when the cut-off for MCA pulsatility index was 1.04, it could identify severe WMLs. The area under the curve was 0.70 (95%CI: 0.60–0.80). The sensitivity and specificity were 63.0% and 72.0%, respectively. The positive and negative predictive values were 35.4% and 86.6%, respectively. Conclusion: The MCA pulsatility index in TCD ultrasound is significantly correlated with severe WMLs; and TCD ultrasound can guide selective MRI for the detection of WMLs.

Naked Co68.25Fe4.5Si12.25B15 metal fibers with diameter from 25 µm to 100 µm are produced by melt extraction method. Significant diameter dependence of magnetic properties is studied. Their microstructure and magnetic properties of hysteresis loops and giant magneto impedance (GMI) effect at frequencies from 0.1MHz to13MHz are investigated. The results show that the coercivity increases with the diameter of fibers and the GMI effect is best in fiber with a diameter of 35µm. It is found that the cooling rate of solidification decreases with the increase of fiber diameter. And fibers are amorphous with the diameter of 50µm and there are nanocrystallines in fibers with a diameter of 85µm. The grain boundary blocks the magnetization process which makes lower circular permeability, larger coercivity and lower field sensitivity of GMI effect. The original microstructure of Co-based fibers decides their magnetic properties. Therefore, material design is important to improve the GMI effect in magnetic field sensor making.

The giant magneto impedance, GMI, effect of Co-based metallic fibers prepared by melt-extracted technology is investigated under different bias direct electrical current Ib. The GMI curves have single peaks which are symmetric about zero field at and below 1MHz. However, the bimodal GMI curves which have asymmetric peaks are observed when Ib is over 2mA at 0.1MHz. And asymmetric GMI, AGMI, effect is also appeared at 1MHz when Ib just is 1mA and the field sensitivity of GMI effect is increased 5.6 times. The GMI effect and magnetization process is affected by the bias magnetic field profoundly induced by Ib, which is correlated with the outer shell domain structures with circumferentially magnetization easy axis existed in the outer shell of Co-rich magnetic wires with low and negative magnetostriction. Below 1 MHz, only if the bias current is over 1.5mA which induces a magnetic circumferential magnetic field is above the coercivity of 14.4A/m, the circumferential magnetization and GMI effect can experience the bias magnetic field effect. Above 1MHz, the skin effect gets stronger and significantly decreases the total participants of circular magnetization process in the fibers and consequently, the circular outer shell magnetization process gets much sensitive to circular bias magnetic field. AGMI effect with high field sensitivity is realized due to the bias current.