Sunnybrook Research Institute, Toronto, ON, Canada.
Ultrasound Med Biol. 2012 Oct;38(10):1799-810. doi: 10.1016/j.ultrasmedbio.2012.05.013. Epub 2012 Aug 21.
Perfluorocarbon (PFC) nanodroplets (NDs) have been proposed as phase-change contrast agents for ultrasound imaging. Since the ultrasound energy required to convert PFC droplets to microbubbles is inversely related to size, the conversion of PFC NDs at clinically-relevant pressures is challenging. We propose that if PFC NDs can accumulate in a close-packed configuration and grow in size in situ, phase-change conversion can occur at lower ultrasound pressures compared with isolated NDs. In this article, we show that PFC NDs can be designed to grow in size after loading in cells, from 0.26 ± 0.09 μm to 1.7 ± 0.6 μm after 2 h. This growth allowed for a substantial decrease in the ultrasound conversion threshold (to 1.4 MPa and 4.8 MPa at 1 MHz and 18 MHz, respectively), whereas non-coalesced NDs in cells and NDs alone were not converted up to the maximum applied pressure (2.1 MPa and 6.3 MPa at 1 MHz and 18 MHz, respectively). These results indicate that PFC NDs with conversion pressures too high for diagnostically feasible conversion can be used as phase-change agents if they can be induced to grow in size in situ.
全氟碳（PFC）纳米液滴（NDs）已被提议作为超声成像的相变型造影剂。由于将 PFC 液滴转换为微泡所需的超声能量与尺寸成反比，因此在临床相关压力下转换 PFC NDs 具有挑战性。我们提出，如果 PFC NDs 可以在紧密堆积的配置中积累并原位增大尺寸，那么与孤立的 NDs 相比，在较低的超声压力下就可以发生相变型转换。在本文中，我们表明 PFC NDs 可以在细胞内加载后增大尺寸，在 2 小时后从 0.26 ± 0.09 μm 增大到 1.7 ± 0.6 μm。这种生长允许超声转换阈值大幅降低（在 1 MHz 和 18 MHz 时分别为 1.4 MPa 和 4.8 MPa），而细胞内未聚结的 NDs 和单独的 NDs 即使在施加的最大压力下（在 1 MHz 和 18 MHz 时分别为 2.1 MPa 和 6.3 MPa）也没有转换。这些结果表明，如果可以诱导 PFC NDs 在原位增大尺寸，那么对于诊断上可行的转换压力过高的 PFC NDs 也可以用作相变型造影剂。
