He explains that in traditional hand-held ultrasound systems, 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 2000 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 3D 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 nanosecond) 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 transmitted pulses come from an array of very small ultrasonic transducers of sub-millimeter dimensions. A parallel array of transducers on the other side receives the pulses after they travel through the imaged tissue.
A sophisticated coding/decoding signal scheme recognizes a small "sweet spot" of the signal coming from the opposite transducer, and only that transducer, and ignores all other pulses transmitted by neighboring transducers.
The transducer is able to distinguish the right signal from the right transducer by using coding that is almost identical to that used by a cell phone to detect signals sent to its number -- and its num
Source:University of Southern California