  Ultrasound localization microscopy (ULM) refers to a promising medical
imaging modality that systematically leverages the advantages of
contrast-enhanced ultrasound (CEUS) to surpass the diffraction barrier and
delineate the microvascular map. Localization and tracking of microbubbles
(MBs), two significant steps of ULM, facilitate generating the vascular map and
the velocity distribution, respectively. Herein, we propose a novel MB tracking
technique considering temporal pairing as a bubble-set registration problem.
Iterative registration is performed between the bubble sets in two consecutive
time instants by analytically optimizing a cost function that takes position
and point-spread function (PSF) similarities as well as physically plausible
levels of bubbles' movement into account. Furthermore, we infer MBs' parity in
a fuzzy manner instead of binary. The proposed technique performs well in
validation experiments with two synthetic and two in vivo datasets provided by
the Ultrasound Localisation and TRacking Algorithms for Super Resolution
(ULTRA-SR) Challenge.
