Som en konsekvens af det komplekse forhold mellem koncentrationen af mikrosfærer og ultralydsignalet, databehandling inde i ultralydsudstyret og den kendsgerning, at hvert individ responderer forskelligt grundet foranderlighed i hjerte - og lungefunktion, kan et nøjagtigt dosis/ respons- forhold ikke defineres.
As a consequence of the complex relationship between the concentration of the microspheres and the ultrasound signal, data processing within the ultrasound equipment and the fact that each individual responds differently due to variability in cardiac and pulmonary function, a strict dose/ response relationship cannot be defined.