Insights of cartilage imaging in cartilage regeneration

Table 2 Advanced magnetic resonance imaging compositional metrics for cartilage assessment

Compositional technique	Quantitative parameter	Underlying biophysical principle	Advantages	Current technical challenges	Potential clinical utility
T2 mapping	T2 relaxation time	Reflects water content and collagen fiber orientation within the matrix	Sensitive to early changes; quantitative; non-invasive	Susceptibility to motion artifacts; magnetic field inhomogeneities	Early detection of collagen disruption; monitoring therapeutic response
T2 mapping*	T2* relaxation time	Uses gradient-echo sequences with shorter echo times to capture rapid decay signals	Enables rapid, high-resolution 3D imaging	Sensitive to field inhomogeneities; requires high-field systems	Detailed microstructural assessment with improved spatial resolution
dGEMRIC	T1 relaxation time (post-contrast)	Inverse correlation between GAG concentration and gadolinium uptake	Direct evaluation of GAG content; effective for early degeneration detection	Prolonged imaging protocol; reliance on contrast agents; potential nephrotoxicity	Assessment of cartilage biochemical integrity; predicting osteoarthritis progression
Sodium MRI	Sodium ion concentration	Measures sodium ions linked to proteoglycan density in the extracellular matrix	Contrast-agent free; direct assessment of proteoglycan content	Low signal-to-noise ratio; specialized hardware requirements	Early biomarker for proteoglycan loss; research tool for regenerative interventions
T1ρ imaging	T1ρ relaxation time	Sensitive to interactions between water molecules and macromolecules (proteoglycans)	Early detection of proteoglycan depletion; non-invasive	Limited availability; extended scan times; technical complexity	Early identification of biochemical changes in cartilage; monitoring early degeneration
gagCEST	Chemical exchange saturation transfer effect	Utilizes the exchange of protons between water and GAGs to generate contrast	High specificity to GAG; no contrast agents required	Requires very high field strengths; long scan durations	Promising tool for early osteoarthritis detection and precise regenerative monitoring

dGEMRIC: Delayed gadolinium-enhanced magnetic resonance imaging of cartilage; 3D: Three-dimensional; GAG: Glycosaminoglycan; MRI: Magnetic resonance imaging; gagCEST: Glycosaminoglycan chemical exchange saturation transfer.