A method includes directing toward a portion of a subject's body a first pulse of electromagnetic energy. While the portion is in a functional state due to the first pulse, a second pulse is directed toward the portion. At a second-pulse time, reflected energy due to the second pulse is detected. While the portion is in a functional state due to the first and second pulses, a third pulse is directed toward the portion. At a third-pulse time, energy of the third pulse, reflected from the portion, is detected. In response to detecting the pulses at the second-pulse time and the third-pulse time, a characteristic of the portion is quantified resulting from (a) the functional state due to the first pulse and (b) the functional state due to the first and second pulses. A clinical state of the subject is identified. Other embodiments are described.