System Offers 3-D Images of Soft Tissue
A demonstration by the USC Viterbi School of Engineering shows that the images are superior to any produced by ultrasound or X-ray. The new system appears to be more comfortable for patients than alternatives.
Vasilis Marmarelis, professor of biomedical engineering in the USC Viterbi School, presented HUTT images of animal organ tissue at the 28th International Acoustical Imaging Symposium recently held in San Diego.
According to Marmarelis, HUTT offers nearly order-of-magnitude improvement in resolution of structures in soft tissue (i.e., 0.4 mm, compared to 2 mm for the best alternatives).
Several other features promise to make the technology a scientific and clinical tool of great power:
• Robust algorithmic tools enable HUTT to differentiate separate types of tissue based on their distinctive “frequency-dependent attenuation” profiles that should allow clinicians to distinguish malignant lesions from benign growths in a non-invasive and highly reliable manner.
• In addition to improved resolution, the system can locate tissue features with extreme precision in an objective, fixed-coordinate 3-D grid, crucial for guiding surgical procedures.
• Scans can be performed in a matter of a few minutes and because they are ultrasonic, they do not use potentially harmful ionizing radiation.
• The system requires a minimum of special pre-scan procedures and appears likely, in clinical use, to be more comfortable for patients than alternatives.
“The HUTT imaging system is a novel and potentially very useful approach to diagnostic ultrasound,” said Dr. Phillip W. Ralls, professor and vice chair in the Keck School of Medicine of USC department of radiology. “The potential clinical benefits of the superb images obtained by this completely safe, non-invasive technique are very exciting.”
In traditional hand-held ultrasound systems, he said, sound waves are broadcast into the tissue, and the echoes produce an image of the reflecting interfaces – that is, the sound transmitter and the receiver are both on the same side of the sample.
However, only a tiny fraction of the transmitted sound comes back as echo on soft tissues, while a much larger fraction (about 2,000 times bigger) is transmitted through the soft tissue.
Using the sound transmitted through tissue allows the formation of better images with greater clarity and resolution.
A hand-held apparatus cannot objectively locate objects in 3-D space (in a fixed-coordinate system), but only allows the user to subjectively observe where an object is in relation to other observable structures. Therefore, it is operator-dependent.
The HUTT system transmits an extremely short ultrasonic pulse (about 250 nanoseconds) of 4-12 megahertz frequency (far above human hearing) and picks up the pulse on the other side after it has traveled through the imaged object.
The most critical feature of the HUTT imaging technology is its potential to reliably differentiate types of tissue based on their multi-band signatures. This promises to allow non-invasive detection of lesions in clinical diagnosis, which represents the “holy grail” of medical imaging.
The team found it possible to identify various anatomical structures within the kidney based on their distinctive characteristics, so that computerized algorithms could display in color-coded fashion one tissue in red, another in green and so forth – thus assisting visualization in 3-D.
The technology could also be used to isolate one type of tissue, allowing, for example, all the blood vessel structures to be displayed alone and studied.
“Preliminary results on a sheep kidney show exquisite anatomic and tissue detail,” said radiologist Ralls.
Working with Marmarelis on the project are postdoctoral researchers. Dae C. Shin, Jeong-Won Jeong, Changzheng Huang and Syn-Ho Do.
Marmarelis is codirector of the Biomedical Simulations Resource, an NIH-funded center for the advancement of research in biomedical modeling. He also holds an appointment in the Viterbi School's department of electrical engineering.
Marmarelis’ work was funded by the Alfred E. Mann Institute for Biomedical Engineering at USC.