Frequently Asked Questions
What is Ultrasound Imaging?
Ultrasound Imaging is a non-invasive technique that uses sound energy to visualize tissue and organs in the body. Some of the benefits of this technique compared to other non-invasive imaging modalities such as Magnetic Resonance Imaging (MRI), X-ray, or nuclear imaging techniques include good spatial resolution, the lack of radiation exposure to the patient, and the portability of ultrasound imaging systems, which permits imaging in a diverse range of physical settings. Ultrasound imaging technology currently has widespread use in the clinical setting for numerous applications ranging from body imaging, echocardiography (cardiac imaging), vascular imaging, to the intravascular imaging of the blood vessel wall. Ultrasound imaging often uses contrast agents (gas-filled micron-sized microspheres, or microbubbles), to illuminate tissues and vessels which may be of particular interest to the physician. The goal our Center is to develop new devices and methods to detect and treat cardiovascular disease using unique manipulations of ultrasound technology.
What are Ultrasound Contrast Agents?
Ultrasound contrast agents are tiny bubbles comprised of a gas that is surrounded by a shell made of a biocompatible material such as a lipid or biodegradable polymer. Once the contrast agents are injected into the body (intravenously), they circulate freely in the blood and can be visualized as opacification of the blood pool during ultrasound imaging. This contrast enhancement of the blood makes certain tissues and organs easier to see. Ultrasound contrast agents are currently used in the routine clinical practice of echocardiography to better visualize the heart in patients with technically difficult studies (e.g. due to lung disease, obesity, recent chest surgery, etc.). The Center is developing new ultrasound contrast agent applications beyond that of solely visualizing the blood during routine imaging. We are making “designer microbubbles” to address challenges in clinical imaging and therapeutics which are uniquely addressed by the interaction of microbubbles with ultrasound. In an appropriately applied ultrasound field, microbubbles oscillate (expand and contract) and become ultrasound emitters themselves. Both the ultrasound emissions as well as the mechanical consequences of oscillation on surrounding tissue are properties of ultrasound contrast agents that confer their unique diagnostic and therapeutic value.
What is Molecular Imaging?
Molecular imaging, for clinical purposes, utilizes medical imaging technologies, such as magnetic resonance imaging (MRI), ultrasound, positron emission tomography (PET), and nuclear scintigraphy, in conjunction with specialized probes, to identify molecules that are uniquely present within or on the surface of cells during specific physiologic states or disease states. Identification of these markers with non-invasive imaging may allow of early disease, or characterization of cellular physiology associated with known disease. By utilizing clinical imaging technologies, molecular imaging may provide a non-invasive method of identifying the onset of many diseases, including cancer and cardiovascular disease, in patients before clinical symptoms present. This approach may also assist in monitoring responses to therapy. Furthermore, by interrogating tissue on a molecular level, we can gain new physiologic insights into disease processes that can inform the development of new treatment strategies. Ultrasound molecular imaging is a potentially powerful diagnostic and therapeutic tool which takes advantage of currently used clinical ultrasound technologies. Ultrasound contrast agents for molecular imaging are microbubbles whose outer shells have been modified to hold a molecule on the surface that binds specifically to a cell maker of interest. This causes the microbubble to attach specifically to cells that express the marker. Since the acoustically active microbubbles recognize only the diseased tissue, these areas produce a strong video intensity signal in an ultrasound image, well above that of the healthy surrounding tissue. Because their target is specific, microbubbles may also be used as a vehicle for the delivery of treatments or drugs.
How can microbubbles be used to deliver treatment?
Microbubbles may also serve as carriers for drugs or genes. We are currently developing methods for packaging therapeutic genes inside the microbubble and, subsequent to delivering these microbubbles to the tissue location of interest, use ultrasound to non-toxically disrupt the microbubble and secondarily promote the local uptake of the gene therapy by the tissue. Microbubbles may also be useful in delivering cell therapies (e.g. stem cells) and dissolving blood clots (sonothrombolysis) that cause stroke.
What medical conditions might benefit from ultrasound molecular imaging and therapeutics?
Molecular imaging with ultrasound contrast agents may provide a method for safely and non-invasively addressing pre-clinical shortcomings in diagnosis, where less specific, more invasive, or fewer alternatives exist. For example, we have made microbubbles that bind specifically to leukocyte adhesion molecules (P and E selectin) that are expressed by the surface of endothelial cells after transient myocardial ischemia. These microbubbles can be used to identify whether acute or recent chest pain is a result of a cardiac (myocardial ischemia) or non-cardiac condition, thus facilitating a quick diagnosis of chest pain in the emergency room setting. Molecular imaging with targeted microbubbles can detect acute heart transplant rejection and new tumor microvessels (tumor angiogenesis). Ultrasound molecular imaging may be useful in characterizing atherosclerotic plaques in the coronary arteries and helping to predict the risk for heart attack. Microbubbles may be used for tracking the fate of stem cells that are delivered therapeutically to patients; stem cells that are labeled with microbubbles prior to delivery can subsequently be detected and tracked non invasively with ultrasound. In terms of treatment applications, ultrasound contrast agents have potential for treatment of blood clots (myocardial infarction, stroke, deep venous thrombosis, retinal vein thrombosis), gene and/or drug delivery (cancer, heart disease, diabetes.)
Is this clinically available?
The applications of ultrasound to molecular imaging and therapeutics are not yet clinically available. It is the mission of the Center to advance these technologies and bring them closer to clinical application.
