Medical Information Technology (MedIT), Helmholtz-Institute for Biomedical Engineering, RWTH Aachen University, Pauwelsstr. 20, D-52074 Aachen, Germany.
Physiol Meas. 2021 Jun 29;42(6). doi: 10.1088/1361-6579/ac0402.
. Multi-channel bioimpedance spectroscopy (BIS) systems typically sample each channel's impedance sequentially using multiplexers and a single analog-to-digital converter. These systems may lose their real-time capability with an increasing number of channels, especially for low excitation frequencies. We propose a new method, called orthogonal baseband shifting (OBS), for high-speed parallel BIS data acquisition at multiple excitation frequencies with low hardware and computational effort.. Similar to orthogonal frequency-division multiplexing, used for digital data transmission, OBS systems use channel-specific orthogonal carrier frequencies to modulate the voltage response of the tissue. Given a suitable choice of carrier frequencies, the modulated signals of all channels sum up without loss of information and cross-talk. The fast Fourier transform (FFT) of the summed signal reveals a spectrum of non-overlapping, interleaved BIS data from which the corresponding BIS data of each channel can be calculated.. In simulations, the system design requires a minimum signal-to-noise ratio of 30 dB to achieve amplitude errors below 1% and phase errors below 0.8°. The hardware realization, called 'AixBIS', has been evaluated for impedance measurements between 0.1 and 10 Ω with multi-frequency excitations between 45 and 180 kHz. The impedance values acquired had an averaged precision of 3.67 mΩ, which is only 0.65‰ in relation to the measured impedance. The phase had a mean precision of 0.46°. Moreover,measurements achieved 140 full spectrum acquisitions per second. The impedance change measured in a silicone heart phantom showed a high correlation of 0.83 with the ventricles volume change (flow).. The proposed method enables very fast impedance acquisition of all channels. A complete measurement is performed in the time of a single FFT acquisition, which is equal to the resolution bandwidth of the FFT. In addition, portable and low-power multi-channel BIS devices profit from highly reduced hardware effort. The outstanding performance of OBS measurements with the AixBIS system have the potential forBIS measurements in real-time.
多通道生物阻抗谱（BIS）系统通常使用多路复用器和单个模数转换器顺序采样每个通道的阻抗。随着通道数量的增加，这些系统可能会失去实时能力，尤其是对于低激励频率。我们提出了一种新方法，称为正交基带移位（OBS），用于以低硬件和计算复杂度在多个激励频率下高速并行 BIS 数据采集。类似于用于数字数据传输的正交频分复用，OBS 系统使用特定于通道的正交载波频率来调制组织的电压响应。给定适当的载波频率选择，所有通道的调制信号相加不会丢失信息和串扰。总和信号的快速傅里叶变换（FFT）揭示了非重叠、交错的 BIS 数据谱，从中可以计算出每个通道的相应 BIS 数据。在模拟中，系统设计要求最小信噪比为 30dB，以实现幅度误差低于 1%和相位误差低于 0.8%。称为“AixBIS”的硬件实现已针对 0.1 至 10Ω 的阻抗测量和 45 至 180kHz 之间的多频激励进行了评估。获得的阻抗值的平均精度为 3.67mΩ，相对于测量的阻抗仅为 0.65‰。相位的平均精度为 0.46%。此外，每秒可实现 140 次全谱采集。在硅心脏模拟物中测量的阻抗变化与心室体积变化（流量）的相关性高达 0.83。所提出的方法能够非常快速地获取所有通道的阻抗。完整的测量在单个 FFT 采集的时间内完成，这等于 FFT 的分辨率带宽。此外，便携式和低功耗多通道 BIS 设备受益于高度降低的硬件工作量。AixBIS 系统的 OBS 测量的出色性能具有实时 BIS 测量的潜力。
