Non-invasive Imaging the Relative Changes in Cerebral Blood Volume during Total Aortic-arch Replacement Using Electrical Impedance Tomography: a First Study

Total aortic-arch replacement (TAR) is one of the major cardiovascular surgeries, which is by far the most effective emergency treatment of Acute Aortic Dissection type-A (AADA). In TAR, cardiopulmonary bypass is established and the aortic arch is replaced and reconstructed. Though hypothermic circulatory arrest (HCA) and unilateral antegrade cerebral perfusion (uACP) are often used for brain protection, parts of the brain may still encounter insufficient blood supply. With prolonged HCA time, this insufficiency causes brain injuries. Currently, there lacks an effective, real-time cerebral imaging technique that can be used in cardiac surgeries. Electrical impedance tomography (EIT) is a low-cost, non-invasive imaging method, which is sensitive to the bio-electrical impedance of tissues. In this study, we are the first using electrical impedance tomography (EIT) intraoperatively to image and monitor the relative changes in cerebral blood volume (rc-CBV). A subject with AADA is monitored using EIT in TAR surgeries and EIT images during the HCA + uACP period are reconstructed and analyzed. A blood factorization model was proposed to estimate the relative changes in blood proportion using EIT images. We found that (1) EIT images are sensitive to the changes in the rate of cerebral perfusion. (2) During uACP, the right hemisphere is perfused directly via cannulation into the right subclavian artery and the circulation to the left cerebral is mainly compensated through the circle of Willis. EIT and rc-CBV images show relatively high impedance and low blood ratios in the left hemisphere, which indicates that the patient may have insufficient collateral circulation. (3) EIT has moderate spatial resolutions, which provides additional information regarding the pathological changes in different regions deep in the brain. We conclude that cerebral EIT is a promising imaging method and it may provide early warning signs regarding insufficient cerebral blood supply in TAR surgeries.