1. Method for determining, in real time, a probability that target biological tissue is opposite an ultrasonic transducer, said method comprising: transmitting, via an ultrasonic transducer, at least one ultrasonic signal into a biological tissue; receiving, via said ultrasonic transducer, at least one 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 a target biological tissue, said predictive value being calculated via a statistical law using said at least two calculated instantaneous parameters; and estimating a probability that said target biological tissue is opposite said ultrasonic transducer, said estimation depending on said calculated predictive value and on at least one strength condition based on at least one of said two calculated instantaneous parameters; and triggering, based on the estimated probability, a quantitative measurement of said target biological tissue when said ultrasonic transducer is opposite said target biological tissue.