Measuring Arterial Stiffness In Vivo: From Global Indices to Full-Field, Patient-Specific Arterial Mechanics

Arterial stiffness is a marker of vascular ageing, cardiovascular risk, and local mechanical vulnerability in aneurysmal disease, yet patient-specific stiffness remains difficult to quantify in vivo because wall deformation is small, rapid, heterogeneous, and superimposed on rigid-body motion. This review evaluates representative methodologies and asks which approaches can move beyond regional indices to spatially resolved, patient-specific arterial mechanics. For this critical narrative review, targeted searches of ScienceDirect, PubMed, Scopus, Web of Science, and Google Scholar identified literature up to July 2026. Representative studies were selected for methodological relevance and validation evidence, then compared by measurement principle, spatial and temporal resolution, validation status, vessel applicability, and limitations. Carotid-femoral pulse wave velocity and applanation tonometry provide mature regional measures but cannot resolve local heterogeneity. Ultrasound diameter tracking, speckle tracking, and pulse wave imaging improve specificity in accessible vessels but remain constrained by acoustic access, operator dependence, and penetration. Phase-contrast and 4D flow MRI overcome depth limitations and support intracranial assessment but infer stiffness from flow-derived metrics; cine MRI measures boundary motion but is constrained by spatial and temporal resolution. Deformable image registration provides full-field displacement and strain maps, but CT-based implementations have been validated only in large vessels. The major unresolved gap is the translation of registration-based wall strain analysis to smaller and intracranial arteries using radiation-free 4D PC-MRI. This requires adaptation to MRI data followed by staged verification and validation using synthetic images, physical phantoms, cross-modality comparisons, test-retest studies, and multi-site evaluation.