Table 1. Summary of animal and clinical studies on venous clot aging using elastography techniques.

Authors	Elastography technique	Experimental setting	Thrombus model	Thrombus ages	Outcomes
Emelianov et al. (17)	Strain	In vivo	Rat IVC	2, 6, and 9 days	Older clots were consistently harder (higher Young’s modulus) and more homogenous than younger ones
Rubin et al. (18)	Strain	Clinical	Lower extremity DVT	25 days and 3 years	Chronic clot was more homogenous with strain 10× smaller than vessel wall; subacute clot had strain 3–4× greater than the vessel wall
Xie et al. (19)	Strain	In vivo	Rat IVC	3, 4, 5, 6, 7, and 10 days	Strain magnitude progressively decreases as clot ages; model developed that could estimate clot age accurate within 0.8 days
Aglyamov et al. (20)	Strain	In vivo and ex vivo	Rat IVC explanted in gelatin	2 and 9 days	Elasticity reconstruction may prove to be a practical adjunct to triplex scanning to detect, diagnose, and stage DVT
Xie et al. (21)	Strain	In vivo and ex vivo	Rat IVC	3, 6, 10, 12, and 14 days	Strong agreement between mechanical measurement of Young’s modulus and that measured by ultrasound
Geier et al. (22)	Strain	Ex vivo	Explanted porcine iliac vein	1, 3, 6, 9, 12, and 15 days	The most pronounced changes in clot elasticity occurred between the 6th and 12th days, P<0.01
Rubin et al. (23)	Strain	Clinical	Lower extremity DVT	Acute (mean =5.7 days) and chronic (>8 months)	Median normalized strain magnitude for the acute cases was 2.75, with an interquartile range of 2.40 to 3.71, whereas the median normalized strain magnitude for the chronic cases was 0.94, with interquartile range of 0.48 to 1.36
Yi et al. (24)	Strain	Clinical	Lower extremity DVT	Various	The strain ratio of the chronic thrombosis group and the subacute thrombosis group were higher than that of the acute thrombosis group (P<0.001, <0.05)
Mfoumou et al. (25)	Shear wave	In vivo and ex vivo	Rabbit IJ	Every 10 minutes for 2 hours and up to 2 weeks	Stagnant blood in the region of interest underwent clotting and progressive hardening with thrombus aging; transition points observed around day 7
Liu et al. (26)	Shear wave	In vivo and ex vivo	Rabbit IVC	Every 10 minutes for 2 hours and up to 2 weeks	Strain elastography measurements consistent with histological analysis; days 4 and 7 after thrombus induction may represent the transition points for acute, sub-acute and chronic thrombi in rabbit models

IVC, inferior vena cava; DVT, deep venous thrombosis; IJ, internal jugular.