**Author details**

**Figure 27.** Ultrasound-induced drug delivery. Microbubbles carrying drugs are destructed by ultrasound (A) and the

The indicated bioeffects can be utilized in ultrasound induced drug delivery. The general goal of encapsulated drug delivery and targeting is to improve the efficacy of drugs within the region of diseased tissue while reducing undesired side effects in the healthy tissues. As an example, with non-encapsulated conventional chemotherapy systemic toxicity limits the drug concentration that can be obtained within the tumor and hence the efficacy of the therapy. With focused ultrasound, it is possible to obtain release of encapsulated drugs and this release

Ultrasound energy deposition within a localized tissue region provides a potentially efficient way of releasing drugs encapsulated in thermally sensitive carriers [179-181] by inducing a temperature increase and in sonosensitive carriers [182-184] by inducing cavitation (figure 27). The thermal and especially the mechanical cavitation effects of ultrasound also pro‐ vide ways of perturbing cell membranes and thus increasing their permeability for im‐ proved drug delivery. With the introduction of microbubbles administered intraveneously that will serve as cavitation nuclei, the threshold for cavitation is significantly reduced hence facilitating this effect for endothelial cells that are close to the administered microbubbles. This effect of increased cell membrane permeability has been investigated extensively in the brain where the blood-brain barrier acts as an effective barrier for delivery of more than 95% of the drugs that potentially could be interesting for treatment of diseases in the central nervous system [185, 186]. For blood clot dissolution the combined use of ultrasound, microbubbles and thrombolytic agents have been demonstrated in several clinical trials to result in faster clot dissolution without release of large amounts of potentially hazardous clot

Ultrasound has been used for many years as a diagnostic and interventional imaging modality, and the use is increasing in a number of different clinical areas. It is often conceded that the image quality of ultrasound is inferior to that attainable with MR or CT, but the rapid devel‐ opment of new ultrasound technology (scanners, transducers, specialized probes, etc.) has

transported substances are released into the surrounding tissue (B).

68 Advancements and Breakthroughs in Ultrasound Imaging

can be controlled both temporally and spatially.

fragments [187, 188].

**9. Conclusions**

Frank Lindseth1,2,4, Thomas Langø1,4, Tormod Selbekk1,2,4, Rune Hansen1,2,4, Ingerid Reinertsen1,4, Christian Askeland1,4, Ole Solheim2,3,4, Geirmund Unsgård2,3,4, Ronald Mårvik2,3,4 and Toril A. Nagelhus Hernes1,2,4

