Fig. 1.

Flowchart of our registration method that cascades (a) a 3D B-scan registration algorithm with (b) a global A-line registration algorithm. The 3D B-scan registration algorithm registers multiple target volumes $T=(1,2,\dots )$ to a single reference volume $R$. A coarse-to-fine registration approach improves processing speed and accuracy (Sec. 3.1.2.3), accelerated by parallel computing (Sec. A in Supplementary Material). Global A-line registration registers individual A-lines in all volumes to a global coordinate system. The approach consists of three steps: (1) multiple-reference registration to separately register all target volumes to each of multiple reference volumes (Sec. 4.1.1), (2) global registration of individual B-scans (Sec. 4.1.2) to derive a single mapping of individual B-scans to the multiple-reference global coordinate system, and (3) global registration of individual A-lines (Sec. 4.1.3) to correct en face affine transformations among volumes and estimate 3D global coordinates for individual A-lines. Abbreviations: POC, phase-only correlation; NCC, normalized cross-correlation.