The present invention relates to an ultrasonic system for measuring a micro-vascular flow distribution of a tissue portion of a mammal comprising an ultrasonic transducer (101) arranged for measuring a first indicator (MTT) for the blood flow through a capillary bed in the tissue portion, and arranged for measuring a second indicator of heterogeneity (CTTH, σ) of the blood flow in said capillary bed, and a processor (110) arranged for using the first (MTT) and the second (σ) indicator to estimate an extraction capacity (EC) of a substance from the blood in said capillary bed.
