[Wavelet modulus maxima of multifractality based analysis of the pathological ECG signals].

In this paper, wavelet moudulus maxima based multifractal analysis was used to study the multifractal characteristics of the atrial premature beat (APB) signal, the premature ventricular contraction (PVC) signal and normal ECG signal. By analyzing the multifractal spectrum, it was obtained that three kinds of signals had different multifractal strengths. Normal ECG signals had the strongest singularity strength. The PVC beats had the second stronger singularity strength. And the APB beats had the weakest singularity strength. The T test indicated that above-mentioned analysis could disclose significant differences among these three signals. It has meaningful reference for clinical diagnosing and distinguishing with PVC and APB signals.

Noninvasive Treatment-Efficacy Evaluation for HIFU Therapy Based on Magneto-Acousto-Electrical Tomography.

OBJECTIVE: As a novel noninvasive modality of oncotherapy or stroke treatment, high-intensity focused ultrasound (HIFU) has drawn more and more attention in the past decades. Whereas, real-time temperature monitoring and treatment-efficacy evaluation are still the key issues for HIFU therapy. METHODS: Based on the temperature-conductivity relation of tissues with a sharp conductivity variation of irreversible thermocoagulation at 69 °C, a noninvasive method of treatment-efficacy evaluation for HIFU ablation using the magneto-acousto-electrical tomography (MAET) technology is theoretically studied. By applying the nonlinear Khokhlov-Zabolotskaya-Kuznetsov equation and Pennes equation, a cylindrical model is established to simulate the distributions of pressure, temperature, and conductivity with the consideration of harmonic components. RESULTS: The MAET signals are simulated to analyze the characteristics of the peak amplitude and the axial interval of the two clusters generated by the conductivity boundary of HIFU ablation. CONCLUSION: The axial interval can be used as the indictor to evaluate the size of HIFU ablation with the minimum axial width of one wavelength. SIGNIFICANCE: The favorable results demonstrate the feasibility of real-time treatment-efficacy evaluation for HIFU therapy using the MAET technology and suggest potential applications in clinical practice.

Conductivity Anisotropy Influence on Acoustic Sources for Magnetoacoustic Tomography With Magnetic Induction.

OBJECTIVE: As the multi-physics imaging approach, magnetoacoustic tomography with magnetic induction (MAT-MI) attracts more and more attentions, focusing on image reconstruction for conductivity isotropic tissues. METHODS: By introducing vector analyses to electromagnetic stimulation and magnetoacoustic excitation for a single-layer cylindrical conductivity anisotropic model, the acoustic source strength (ASS) of MAT-MI is derived in explicit formula and the influence of the anisotropic conductivity tensor is also analyzed. RESULTS: Theoretical and numerical studies demonstrate that the ASS generated at the tissue boundary is composed of an alternating current (AC) fluctuation and a direct current (DC) bias, where the distribution of the AC fluctuation with respect to the spatial angle exhibits a double-period cosine function, and the DC bias remains constant at each angle. The dependences of the AC fluctuation and the DC bias on the anisotropic component ratio (ACR) and the conductivity tensor are proved by numerical results, which are also verified by the special cases of the zero AC fluctuation for the conductivity isotropic medium and the negative DC bias of the low-conductivity medium. CONCLUSION: With the measurements of the ASS around the model, the anisotropic conductivity tensor can be reconstructed by the amplitudes of the AC fluctuation and the DC bias with the conductivity of the isotropic surrounding medium. SIGNIFICANCE: The favorable results provide a new method for anisotropic conductivity measurement, and suggest the application potential of MAT-MI in biomedical imaging and nondestructive testing for conductivity anisotropic tissues.