Wi Hun, Sohal Harsh, McEwan Alistair Lee, Woo Eung Je, Oh Tong In
IEEE Trans Biomed Circuits Syst. 2014 Feb;8(1):119-28. doi: 10.1109/TBCAS.2013.2256785.
Electrical Impedance Tomography (EIT) is a safe medical imaging technology, requiring no ionizing or heating radiation, as opposed to most other imaging modalities. This has led to a clinical interest in its use for long-term monitoring, possibly at the bedside, for ventilation monitoring, bleeding detection, gastric emptying and epilepsy foci diagnosis. These long-term applications demand auto-calibration and high stability over long time periods. To address this need we have developed a new multi-frequency EIT system called the KHU Mark2.5 with automatic self-calibration and cooperation with other devices via a timing signal for synchronization with other medical instruments. The impedance measurement module (IMM) for flexible configuration as a key component includes an independent constant current source, an independent differential voltmeter, and a current source calibrator, which allows automatic self-calibration of the current source within each IMM. We installed a resistor phantom inside the KHU Mark2.5 EIT system for intra-channel and inter-channel calibrations of all voltmeters in multiple IMMs. We show the deterioration of performance of an EIT system over time and the improvement due to automatic self-calibration. The system is able to maintain SNR of 80 dB for frequencies up to 250 kHz and below 0.5% reciprocity error over continuous operation for 24 hours. Automatic calibration at least every 3 days is shown to maintain SNR above 75 dB and reciprocity error below 0.7% over 7 days at 1 kHz. A clear degradation in performance results with increasing time between automatic calibrations allowing the tailoring of calibration to suit the performance requirements of each application.
电阻抗断层成像（EIT）是一种安全的医学成像技术，与大多数其他成像方式不同，它不需要电离辐射或热辐射。这使得临床上对其用于长期监测产生了兴趣，可能在床边进行，用于通气监测、出血检测、胃排空和癫痫病灶诊断。这些长期应用需要自动校准和长时间的高稳定性。为满足这一需求，我们开发了一种新的多频EIT系统，称为KHU Mark2.5，它具有自动自校准功能，并通过定时信号与其他设备协作，以便与其他医疗仪器同步。作为关键组件的用于灵活配置的阻抗测量模块（IMM）包括一个独立的恒流源、一个独立的差分电压表和一个电流源校准器，这允许在每个IMM内对电流源进行自动自校准。我们在KHU Mark2.5 EIT系统内部安装了一个电阻体模，用于对多个IMM中的所有电压表进行通道内和通道间校准。我们展示了EIT系统性能随时间的恶化以及自动自校准带来的改善。该系统在连续运行24小时的情况下，对于高达250 kHz的频率能够保持80 dB的信噪比，互易误差低于0.5%。结果表明，至少每3天进行一次自动校准，可在1 kHz频率下7天内保持信噪比高于75 dB，互易误差低于0.7%。随着自动校准之间时间间隔的增加，性能会明显下降，这使得可以根据每个应用的性能要求调整校准。
