Say the word “ultrasound” and most people picture a doctor examining a pregnant woman’s fetus. Many people overlook the use of ultrasound technology to diagnose life-threatening conditions as well. Now doctors believe ultrasound technology will also be used to treat patients who require site-specific drug delivery.
Microbubbles are tiny gas bubbles that are smaller than red blood cells, and thus able to pass through veins without blocking them. They effectively scatter ultrasound, and in the last decade scientists have worked on exploiting this property in order to use microbubbles to diagnose medical conditions.
Doctors use ultrasound contrast imaging by inserting a contrast agent, composed of microbubbles, into a patient’s peripheral vein. The agent passes through the patient’s venous system to the monitored area. Ultrasound soundwaves interact with these microbubbles and produce a signal the ultrasound system captures for the physician. The bubbles dissolve innocuously in the body within a few minutes.
A new screening test for coronary heart disease, myocardial contrast echocardiography (MCE), uses protein-encapsulated microbubbles injected into the vein; the bubbles move with the blood flow into the arteries and feed the heart. The ultrasound image shows darker areas where artery blockage prevents blood from flowing properly. This non-invasive test replaces the more rigorous, expensive stress test physicians use to diagnose heart disease.
Researchers are also developing a way to use these microbubbles to deliver treatment for certain diseases and tumors. Scientists fill the bubbles with a drug and inject them into a patient’s vein, where the blood carries the bubbles to a target area. Then, using ultrasound technology, doctors burst the bubbles and release the medication inside to treat the specific area.
The microbubble technique represents a new development for drug delivery. By targeting the ultrasound into a tumor, for example, the concentration of the drug attacking the tumor increases. One of the drawbacks of anticancer drugs is their insolubility in water, which means that when they are administered intravenously, they must be immersed in toxic chemicals. Due to their toxicity, the administration of these drugs is often lengthy and taxing. Doctors hope to apply the microbubble technique to reduce the medication’s toxicity and increase its efficacy.
Theoretically, doctors will use this microbubble technique to treat or diagnose in any organ or tissue disease that is accessible by ultrasound. Chemotherapy would be the ideal application of this technology because of its potential to deliver the medicine directly to the tumor without systemic side effects. Researchers have already proven that they can deliver genes to the insulin-producing islet cells in the pancreas, which means that microbubbles potentially may be used to treat diabetes as well.