Three-Dimensional Sheaf of Ultrasound Planes Reconstruction (SOUPR) of Ablated Volumes

Abstract

This paper presents an algorithm for three dimensional reconstruction of tumor ablations using ultrasound shear wave imaging with electrode vibration elastography. Radiofrequency ultrasound data frames are acquired over imaging planes that form a subset of a sheaf of planes sharing a common axis of intersection. Shear wave velocity is estimated separately on each imaging plane using a piecewise linear function fitting technique with a fast optimization routine. An interpolation algorithm then computes velocity maps on a fine grid over a set of C-planes that are perpendicular to the axis of the sheaf. A full three dimensional rendering of the ablation can then be created from this stack of C-planes; hence the name “Sheaf Of Ultrasound Planes Reconstruction” or SOUPR. The algorithm is evaluated through numerical simulations and also using data acquired from a tissue mimicking phantom. Reconstruction quality is gauged using contrast and contrast-to-noise ratio measurements and changes in quality from using increasing number of planes in the sheaf are quantified. The highest contrast of 5 dB is seen between the stiffest and softest regions of the phantom. Under certain idealizing assumptions on the true shape of the ablation, good reconstruction quality while maintaining fast processing rate can be obtained with as few as 6 imaging planes suggesting that the method is suited for parsimonious data acquisitions with very few sparsely chosen imaging planes.

Comparison of three dimensional strain volume reconstructions using SOUPR and wobbler based acquisitions: A phantom study

“…The 3D reconstruction for SOUPR is modeled as an optimization problem with an objective function consisting of data consistency and smoothness constraints. 31 The data smoothness constraints utilized may result in the 3D volume reconstructed with SOUPR having lower data variance when compared to wobbler based data acquisition where the reconstruction is accomplished with a 3D cubical interpolation. The standard deviation of the SNRe metric for each displacement tracking kernel size is larger for SOUPR when compared with wobbler based reconstructions as illustrated in Figs.…”

“…Data consistency is aimed at keeping the reconstructed 3D strain or binary mask to be within a small variation from the known data measured at those 2D planes, and the data smoothness constraint was based on the assumption that the inclusion possessed a smooth ellipsoidal shape, which is common for thermal lesion. 31 The solution to this optimization problem and tuning of the regularization parameter η was described in detail in the paper by Ingle and Varghese. 31 A reconstructed 3D binary mask was used for inclusion volume estimation which is discussed in Sec.…”

“…31 The solution to this optimization problem and tuning of the regularization parameter η was described in detail in the paper by Ingle and Varghese. 31 A reconstructed 3D binary mask was used for inclusion volume estimation which is discussed in Sec. 2.D.…”

“…In order to overcome the mismatch of the imaging planes and the ellipsoid target shape, we introduced a rotational acquisition method for 3D US elastography in a previous study, referred to as sheaf of ultrasound planes reconstruction (SOUPR). 31 Instead of linearly translating the US transducer along the target surface, the acquisition planes are positioned rotationally with a specified angular increment. The sheaf of imaging planes is rotated along the central axis of the spherical or ellipsoidal target.…”

Three dimensional shear wave elastographic reconstruction of ablations

“…Each image plane is manually aligned by using angle markers on the phantom container and the needle as a guide. Misalignment variations are averaged out by acquiring five independent datasets [8]. …”