Ultrasound System Finds Tumor Blood Vessels

Acoustic angiography may aid monitoring of cancers near or on the skin.

The microvasculature around tumors is built rapidly and messily, and it's full of loops and twists. An “acoustic angiography” ultrasound imaging system developed by researchers at the University of North Carolina (UNC) in Chapel Hill can detect such differences in the blood vessels surrounding tumors compared to normal tissue in rats.

Researchers have previously shown that these blood-vessel changes can be found with magnetic resonance angiography. Paul Dayton, PhD, associate professor of biomedical engineering at UNC, sought to image the blood vessels with ultrasound, which is quick and inexpensive. Looking for changes in the tumor vasculature, rather than waiting to see whether the tumor has shrunk on a CT or MRI scan, eventually might be a simple way to monitor therapeutic response in tumors close to or on the skin, says Dayton.

The microvessel imaging system differs from conventional ultrasound in 3 ways.

First, it requires the use of a contrast agent to help the vasculature stand out from the surrounding tissue. Dayton's group used lipid-encapsulated microbubbles injected into the bloodstream. (Similar agents are approved for cardiac imaging.)

Second, the researchers developed an ultrasound probe modified to transmit and receive at 2 different frequencies.

Third, the investigators worked with Kitware of Carborro, NC, to create an algorithm to separate imaging of normal vessels from tortuous ones.

In a paper published in Radiology, the researchers showed that the acoustic angiography system can highlight the microvasculature around rat fibrosarcoma tumors. It took about 5 minutes to acquire the images. “We can distinguish between tumors and healthy tissue just by looking at the blood vessels,” says Dayton. The resolution of ultrasound decreases with depth, so this method will not be suitable for imaging the vasculature of deep tumors in humans.

The UNC group is now investigating whether this imaging method can detect changes in tumor vasculature following therapy. The investigators are also testing whether it can pick up the presence of tumors too small to show up on imaging scans by detecting characteristic changes in the vasculature that surrounds them.