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Diagnostic Ultrasound
Published in Michael Ljungberg, Handbook of Nuclear Medicine and Molecular Imaging for Physicists, 2022
The mechanical index, MI, is intended to indicate the risk for cavitation (or more precisely inertial cavitation). Basically, the risk increases with the amount of under-pressure applied, that is the peak negative pressure excursion of the ultrasound pulse. Also, the time during which this under-pressure acts also plays a role: Lower frequencies have longer period times, and the chance of cavitation is thus larger than for a higher frequency. Empirically, the following relation between peak negative pressure p- (in MPa) and employed frequency f (in MHz), has been found to reflect the chance of cavitation, and thus serves as the definition of the mechanical index: MI=p−f
Ultrasound-triggered imaging and drug delivery using microbubble-self-aggregate complexes
Published in Journal of Biomaterials Science, Polymer Edition, 2022
In Jae Chung, Hyungwon Moon, Seong Ik Jeon, Hak Jong Lee, Cheol-Hee Ahn
The hydrophobic drugs also can be loaded in the shell of MBs or attached to MBs via physical or chemical interactions [19]. When loading drugs in the MB shells, however, it was difficult to contain a sufficient amount of the drug as the loading site was limited to thin shells of MBs [20]. To increase the drug loading amount, the introduction of oils that solubilize the hydrophobic drugs in MBs was also investigated, resulting in unnecessary stabilization of MBs. [21–23]. Their cavitation effect was decreased and only ultrasound with high intensity could break down the stabilized shells of MBs. For effective ultrasound-mediated drug delivery, inertial cavitation of the MBs should occur with moderate insonation, otherwise it will directly damage to tissues. FDA has limited the mechanical index of clinical ultrasound not to exceed 1.9 [24–26]. Therefore, the development of a new MB-based carrier that does not affect the echogenicity and cavitation effect of MBs is necessary for the hydrophobic drug delivery.