1. Method for determining, in real time, the probability that target biological tissue is opposite an ultrasonic transducer, said method comprising: transmitting via an ultrasonic transducer, at least one ultrasonic signal into biological tissue; receiving, via said ultrasonic transducer, said at least one transmitted ultrasonic signal which has been backscattered by said biological tissue; calculating at least two instantaneous parameters of said at least one backscattered ultrasonic signal; calculating a predictive value of the presence of an acoustic signature of target biological tissue, said predictive value being calculated via a statistical law using said at least two calculated instantaneous parameters; estimating the probability that said target biological tissue is opposite said ultrasonic transducer, said estimation depending on said calculated predictive value and/or on at least one strength condition based on at least one of said two calculated instantaneous parameters.