Pictures of the Future    Spring 2007

Detecting Cancer with Ultrasound

Along with PET and SPECT, ultrasound is also becoming established as a molecular imaging modality. Here too, research is focused on the development of new contrast media that can help to detect diseased structures at an early stage. Cadence CPS technology in particular is mostly used here, as it significantly improves the quality of the images recorded when contrast media are used. A patented Siemens technology, Cadence CPS can be found in the ACUSON Sequoia ultrasound device (top), among others. Microbubbles filled with air or gas are generally used as the contrast medium for ultrasound images, as they stand out very clearly. Special microbubbles outfitted with designer molecules on their surfaces will be used in the future for molecular imaging. These molecules will dock to the structures in the body—such as the fine blood vessels of a tumor—that need to be examined, for example, making them visible as red areas in an ultrasound image (bottom). At the moment, Siemens is working with Oregon Health and Science University on the development of microbubbles that attach to target cells on the walls of the coronary vessels and finer coronary blood vessels. In the event of a heart attack or circulatory problems, certain types of protein structures, such as the antigen P-selectin, form on these cells. Over the last two years, the Oregon researchers have succeeded in creating microbubbles with P-selectin antibodies. When these microbubbles dock to cells in the walls of coronary vessels, and in the even finer blood vessels in the heart, they make the damaged areas visible. This method makes it possible for the first time to determine at an early stage whether a patient complaining of chest pains actually has heart trouble. The affected vessel segment appears in the ultrasound image as a luminous structure. The new contrast medium is now being tested on mice and monkeys at Oregon Health and Science University.

The same principle can be applied to detecting tumors, as fast-growing tumors greatly stimulate the growth of new blood vessels (angiogenesis), upon whose surface the antigen ???3 can be found. In animal testing, tumors have already been detected with the help of microbubbles containing ???3 antibodies. "The advantage of ultrasound is that patients generally do not respond negatively to the contrast media used with it, and the media also don’t emit any radiation, which is not the case with PET and SPECT," says Jens Fehre, head of Urology Product Life Cycle Management at Siemens Medical Solutions in Erlangen. "In addition, ultrasound examinations can be performed right at the hospital bed." Ultrasound also offers another benefit: The microbubbles can be used to transport medication. This can be accomplished by using a powerful ultrasound pulse to burst them once they’ve docked to the target tissue, releasing angiogenesis inhibitors directly in the tumor, for example. This medication transport procedure is being tested with animals. Another procedure in which microbubbles dissolve dangerous thromboses will enter the clinical testing phase in just a few weeks. Here, bubbles collect at a clot and are then made to oscillate by means of short ultrasound pulses; the oscillation destroys the clot. An initial application of this technique will be the destruction of clots that form in the catheters used with dialysis patients. In the future, the method will also be used to help treat the effects of strokes. A group of researchers headed by Prof. Ferdinand Frauscher at the Medical University Innsbruck, Austria recently proved that conventional contrast media can also be used to detect cancer. Researchers employed a conventional contrast medium and the ACUSON Sequoia to visualize a prostate carcinoma that could barely be seen in a normal ultrasound image taken without a contrast medium. Frauscher showed that this technique can greatly increase the accuracy of biopsies, as normal prostate biopsies often fail to detect a tumor, which in many cases means that the procedure must be repeated.