Investigation of Cavitation Detector for Sonothrombolysis

Most deaths from acute myocardial infarction occur outside the hospital environment. A recent proposal called cardiac sonothrombolysis with microbubbles has the potential to promote significant improvements in patient care. However, it is essential that the main phenomenon – cavitation of microbubbles – be controlled to avoid harm to the patient. The objective of our work was to investigate the detection of cavitation in sonothrombolysis in order to allow control of pressure intensities, aiming at creating safer equipment for the patient. Sources of stable and inertial cavitation were simulated, and their waves were propagated through a medium. The signals were received by an 8x8 matrix of ultrasound transducers which were designed for emission and reception. The acoustic source was estimated by coherent summation using a delay-and-sum approach. Signal-to-noise ratio (SNR) in the frequency domain of the source signal were analyzed in characteristic bands. Mean effective SNRs in each band, after discounting effects from nearby bands, were used for cavitation detection. Using narrowband receivers, the area (AUC) under the receiver operating characteristic (ROC) curve for threshold SNR was as high as 0.94 for stable cavitation detection and 0.91 for inertial cavitation; using broadband receivers instead, these figures increased respectively to 0.95 and 0.99. The obtained sensitivity and specificity were in the range of 0.77 to 0.96. We conclude that it is possible to discriminate cavitation types with a single transducer set, or alternatively with broadband receivers.