“…Since April 1998, 34 studies [35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69] that consider different CEUS techniques have been published. Of these, 23 were on harmonic gray-scale CEUS [48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70], 12 were on Doppler CEUS modalities [36,37,38,39,40,41,42,43,44,45,46,47,48], one study compared both approaches [48] and another reported on carbon dioxide CEUS [35] Two studies have been excluded from our discussion due to the unavailability of papers [71,72].…”