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Mechanical forces are closely associated with plaque progression and rupture. Precise quantifications of biomechanical conditions using  in vivo  image-based computational models depend heavily on the accurate estimation of patient-specific plaque mechanical properties. Currently, mechanical experiments are commonly performed on  ex vivo  cardiovascular tissues to determine plaque material properties. Patient-specific  in vivo  coronary material properties are scarce in the existing literature.   Methods:   In vivo  Cine intravascular ultrasound and virtual histology intravascular ultrasound (IVUS) slices were acquired at 20 plaque sites from 13 patients. A three-dimensional thin-slice structure-only model was constructed for each slice to obtain patient-specific  in vivo  material parameter values following an iterative scheme. Effective Young's modulus (YM) was calculated to indicate plaque stiffness for easy comparison purposes. IVUS-based 3D thin-slice models using  in vivo  and  ex vivo  material properties were constructed to investigate their impacts on plaque wall stress/strain (PWS/PWSn) calculations.   Results:  The average YM values in the axial and circumferential directions for the 20 plaque slices were 599.5 and 1,042.8 kPa, respectively, 36.1% lower than those from published  ex vivo  data. The YM values in the circumferential direction of the softest and stiffest plaques were 103.4 and 2,317.3 kPa, respectively. The relative difference of mean PWSn on lumen using the  in vivo  and  ex vivo  material properties could be as high as 431%, while the relative difference of mean PWS was much lower, about 3.07% on average.   Conclusion:  There is a large inter-patient and intra-patient variability in the  in vivo  plaque material properties.  In vivo  material properties have a great impact on plaque stress/strain calculations.  In vivo  plaque material properties have a greater impact on strain calculations. Large-scale-patient studies are needed to further verify our findings.

Quantifying Patient-Specific in vivo Coronary Plaque Material Properties for Accurate Stress/Strain Calculations: An IVUS-Based Multi-Patient Study