Mechanisms of Action
Tissue can be destroyed in two ways. The first is through heating. If tissue is heated enough, proteins in the tissue denature which leads to cell death. This effects cells tumours or healthy cells otherwise. Cells can also disrupt cells through purely mechanical effects without heating the tissue. On e effect is cavitation and occurs when bubbles of gas oscillate and then collapse in the ultrasonic field. It generates enough force to destroy tissue.
Focused ultrasound can heat tissue and denature the proteins in it.
Blood Brain Barrier Opening
The blood brain barrier (BBB) is a tightly knit group of cells. The brain is arguably the most important organ in the body and has evolved to stop potentially harmful foreign bodies entering the brain. This is problematic for treating diseased tissue in the brain however: drugs are too large to pass through this barrier.
Microbubbles (previously mentioned) and lipsomes can be functionalised to have drugs attached to them. Drugs can then be released using mechanical or thermal effects only where the ultrasound is focused.
Tissue can be mildly heated (42C) to induce hyperfusion.
Drugs usually act from the inside of cells. Cell membranes can prevent drugs from entering. Ultrasound can be used to non-thermally induce holes in the cells to assist drug delivery.
Ultrasound can be used to widen at a target area. This increases blood flow to the area, allowing more effective delivery of drugs to a region.
Gas bubbles can will oscillate and then eventually explode when they’re exposed to ultrasound. This can be used for destructive cavitation or sonoporation. There are a number of other effects that are out of the scope of this article
- Amplifications of cancer biomarkers
- Blood vessel occlusion and coagulation
- Clot lysis
- Sensitisation to chemotheraphy and radiotherapy
- Sonodynamic therapy
- Stem cell homing
You can read more about these other effects here.