Volumetric Tissue Organization Mapping Using Backscatter Tensor Imaging With a Row Column Addressing Transducer

Alterations in tissue organization are involved in numerous pathologies and may influence disease progression and therapeutic response. Backscatter Tensor Imaging (BTI), an emerging ultrasound (US) technique based on local spatial coherence, can be used to map tissue structure in a whole volume. However, previous volumetric implementations were limited by prolonged acquisition times or required high channel count systems. Row Column Addressing transducers (RCA) achieve volumetric acquisitions with a low channel count, making it potentially compatible with clinical settings, but have never been used for BTI. Here, we aimed to evaluate the feasibility of mapping tissue organization with an RCA probe.

This was done using a 6 MHz RCA probe driven by a 256-channel programmable US machine. A rotation motor was used to image the medium at 36 angular positions with respect to a reference position. The local spatial coherence of backscattered signals was calculated at each position, and the coherence values used to determine the medium orientation and fractional anisotropy. This methodology was validated in vitro in a metal needle immersed in water to test for its ability to identify a highly organized medium. We then tested the ability of our method to accurately map complex medium organization in an agar phantom consisting of fishing lines wrapped around a cylindrical structure, and an ex vivo phantom of orthogonally stacked chicken breasts.

The measured coherence was significantly higher in the organized needle structure than in water (+20.8%, p = 0.0167). In the cylindrical phantom, measured medium orientations at the location of the fishing lines followed the expected circumferential organization, yielding a regression slope of 0.836, a bias of 9.0°, and a regression coefficient R² of 0.979. In ex vivo tissue, the measured organization agreed visually with the fiber orientation observed on corresponding tissue sections. Acquisitions required approximately 5 min and covered a cylindrical imaging volume with a radius of 12.8 mm and a depth of 50 mm.

These results demonstrate the feasibility of volumetric BTI using an RCA transducer for the characterization of medium organization. Future work will focus on eliminating probe rotation to enable more practical clinical implementation.