When the transducer captures the signal, it is processed with advanced signal processing algorithms, specially developed by Marmarelis' group, to form the multi-band images. Different kinds of tissue allow slightly more, or slightly less of the pulse through -- the loss is called "attenuation," and varies according to the type of tissue, and the frequency of the pulse.
"Typically the resulting images represent minute variations in relative attenuation over various frequency bands and they define the different sections of the tissue in the image," said Marmarelis.
The two arrays, transmitter and receiver, are mounted on opposite sides of a drum that spins as it rises around the object (which is suspended in water), creating a stack of tomographic image slices which visualization algorithms turn into 3D images.
In the first set of experiments using the HUTT system, the Marmarelis team easily located a set of small metal balls smaller than a millimeter in diameter embedded in agar medium.
Many critical refinements occurred during the five-year process of development, as the team gained proficiency in imaging animal tissue, notably sheep kidneys and bovine liver.
The most critical feature of the HUTT imaging technology is its potential to reliably differentiate types of tissue based on their multi-band signatures caused by their varying attenuation patterns. 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 attenuation 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 3D.
The technology could also be used to isolate
Source:University of Southern California