Color Doppler ultrasound twinkling in pathological biomineralizations

Abstract

The color Doppler ultrasound twinkling artifact has been observed on some kidney stones as well as various sites in the body where pathological biomineralization can occur. On kidney stones, twinkling was recently attributed to stabilized crevice microbubbles, which suggests that microbubbles may also be present on other minerals. However, it is unknown how crystal structure, composition, and the surrounding environment influences the presence and location of microbubbles and twinkling. Here, crystals found in pathological biomineralization (i.e., uric acid, cholesterol, calcium phosphate, and calcium oxalate), were grown in vitro, embedded in a tissue-mimicking phantom, and imaged with a research ultrasound system at 5 and 18.5 MHz. Doppler power was quantified and compared between crystal composition (n = 5 per type). We found twinkling was strongest in cholesterol crystals and weakest in calcium phosphate crystals. Micro-computed tomography (µCT) of an ex vivo calcium oxalate kidney stone (i.e., a heterogeneous crystal) submerged in water revealed the presence of gas within internal microcracks, which was confirmed by reducing the hydrostatic pressure in a subsequent µCT scan. Future work includes exposing pure in vitro crystals to µCT and ultrasound with changes in hydrostatic pressure to evaluate for internal gas pockets that may contribute to twinkling.