Experimental Study of Cerebral Hemorrhage Imaging Based on Frequency-Differential Electrical Capacitance Tomography

Currently, electrical capacitance tomography (ECT) is limited to time-differential imaging for monitoring dynamic alterations in cerebral hemorrhage. However, the inherent constraint of this approach renders it unsuitable for rapid hemorrhage detection, as it requires a reference measurement from a non-hemorrhaging brain. To address this limitation, this study proposes a novel approach of frequency-differential ECT (FDECT) for cerebral hemorrhage imaging in practice. The method entails identification of a frequency range wherein the permittivity variation of cerebral blood with frequency is much greater than the variation of other brain tissues. Within this identified range, two optimal frequencies are selected, and the permittivity difference at these two frequencies are used for imaging. With this method, cerebral hemorrhage is highlighted and other brain tissue is suppressed, thereby achieving the absolute distribution of cerebral hemorrhage and eliminating the need for non-hemorrhagic baseline data. Simulation results demonstrate that FDECT imaging quality correlates directly with the frequency-dependent permittivity difference between the target and background media, thereby validating FDECT's theoretical basis and highlighting the critical role of optimal frequency selection. Before conducting in vitro animal imaging, we analyzed the dielectric spectra of ex vivo sheep blood, pig fat, and pig brain tissue to identify the optimal frequency range for differentiating blood from these tissues. In vitro experiments confirmed that FDECT with the optimal frequencies effectively images blood within pig fat or brain tissue, contrasting with the suboptimal results from non-ideal frequencies. Although essential for FDECT success, optimal frequency pairing does not eliminate the higher noise levels in FDECT images, largely due to the background brain tissue's frequency-dependent dielectric characteristics. To mitigate this inherent limitation and improve imaging quality, we intend to implement a three-frequency FDECT approach, reducing background tissue interference.