Noninvasive detection of lipids in atherosclerotic plaque using ultrasound thermal strain imaging: in vivo animal study.

OBJECTIVES: This study sought to examine the feasibility of in vivo detection of lipids in atherosclerotic plaque (AP) by ultrasound (US) thermal (or temporal) strain imaging (TSI).
BACKGROUND: Intraplaque lipid content is thought to contribute to plaque stability. Lipid exhibits a distinctive physical characteristic of temperature-dependent US speed compared with water-bearing tissues. As tissue temperature changes, US radiofrequency (RF) echoes shift in time of flight, which produces an apparent strain (thermal or temporal strain [TS]).
METHODS: US heating-imaging pulse sequences and transducers were designed and integrated into commercial US scanners for US-TSI of arterial segments. US-RF data were collected while gradually increasing tissue temperature. Phase-sensitive speckle tracking was applied to reconstruct TS maps coregistered to B-scans. Segments from injured atherosclerotic and uninjured nonatherosclerotic common femoral arteries (CFA) in cholesterol-fed New Zealand rabbits, and segments from control normal diet-fed rabbits (N =14) were scanned in vivo at different time points up to 12 weeks.
RESULTS: Lipid-rich atherosclerotic lesions exhibited distinct positive TS (+0.19 ± 0.08%) compared with that in nonatherosclerotic (-0.10 ± 0.13%) and control (-0.09 ± 0.09%) segments (p < 0.001). US-TSI enabled serial monitoring of lipids during atherosclerosis development. The coregistered set of morphological and compositional information of US-TSI showed good agreement with histology.
CONCLUSIONS: US-TSI successfully detected and longitudinally monitored lipid progression in atherosclerotic CFA. US-TSI of relatively superficial arteries may be a modality that could be integrated into a commercial US system for noninvasive lipid detection in AP.