Effects of mechanical index on contrast-enhanced imaging of ultrasound-responsive polymeric nanodroplets / 中华超声影像学杂志

ABSTRACT

Objective:To prepare ultrasound-responsive nanodroplets with block polymer PEG-PCL as shell and perfluoropentane (PFP) as core, and study the effects of mechanical index (MI) on contrast-enhanced imaging properties of nanodroplet.Methods:PEG-PCL micelles were first prepared by dialysis, and then the micelles were mixed with PFP for emulsification to obtain nanodroplets. The particle size and zeta potential of nanodroplets were measured, and the morphology of nanodroplets were observed using transmission electron microscope (TEM). The stability of nanodroplets after storage at 25 ℃ and 37 ℃ was investigated. The phase transition and contrast-enhanced imaging of nanodroplets in vitro under a series of mechanical index (MI) were studied using an ultrasound diagnostic instrument.Results:The particle size of the nanodroplets was (356.6±5.6)nm, and the zeta potential was -(7.30±0.14)mV. The nanodroplets were close to spherical under TEM and had a clear core-shell structure. The particle size and dispersion of the nanodroplets increased after storage at 37 ℃ and 25 ℃. For imaging in vitro, no acoustic signal were observed at 25 ℃ when the MI varied from 0.08 to 1.0. At 37 ℃, acoustic signals were observed when MI≥0.4, and the intensity was stronger for higher MIs.Conclusions:The contrast-enhanced imaging of nanodroplets are closely related to the MI, and a higher MI could induce the phase transition of more nanodroplets and produce stronger contrast enhancement. This study could provide basis for the application of polymeric nanodroplets in ultrasound diagnosis and targeted therapy.