Quantification of embolic showers using radio-frequency based TCD analysis.

During cardiac surgery and cardiology interventions, microemboli may be generated and disperse in the systemic circulation. The amount of microemboli that ends up in cerebral blood vessels is associated with postoperative neurologic complications. During cardiac surgery a large amount of cerebral microemboli can occur at once and create so-called "cerebral embolic showers." To correlate postoperative neurologic outcome to cerebral embolic load, a quantitative evaluation of these embolic showers is necessary. The standard monitoring technology to visualize cerebral microemboli is transcranial Doppler (TCD). Although the conventional TCD systems are equipped with software claiming to detect microembolic signals, none of the existing TCD systems is capable of an accurate estimation of the number of cerebral microemboli in embolic showers. In this study, an algorithm with a high temporal resolution, based on the radiofrequency (RF) signal of a TCD system, has been designed to quantify these showers. Evaluation by three independent observers of a training set demonstrates that the proposed method has a sensitivity of at least one order of magnitude better than the automatic detection algorithm on the existing Doppler device used. RF-based emboli detection can possibly become a standard addition to conventional Doppler methods, considering that accurate estimation of the embolic load supports quantification of neurologic risk during various surgical procedures.