Table 1.

Pros and cons of quantitative MRI sequences and techniques.

Techinque	Sequences Used/Component Assessed	Pros	Cons
T2-mapping	T2*, UTE-T2*, T2w SE, FSE, Multi Echo SE, Turbo Gradient SE, DESS Cartilage hydratation, Cartilage, Water	High reproducibility. T2* and UTE sequences allow a better visualization of deep cartilage and osteochondral junction. Predictive for OA in areas with much compression loading. No contrast administration.	Susceptible of magic angle artifact and magnetic field inhomogeneity.
T1ρ	FSE, TSE, balanced GRE Tissue proteins and composition, GAGs	Quantitative and sequence-independent voxel values. Excellent reproducibility and sensitivity in detecting GAGs depletion. No contrast administration. No special hardware needed.	High SAR, long acquisition time, pulse sequence must be adapted.
dGEMRIC (delayed gadolinium-enhanced)	T1-mapping after gadolinium administration GAG content	Evaluation of cartilage repair following regenerative treatments. Suitable for visualization of osteo-chondral interface and zonal variation of GAG content.	Intravascular or intrarticular administration of contrast. No standard time for intracartilage diffusion (usually after 90 min). Values not directly correlated with GAG concentration.
Sodium MRI	UTE T1w Na+ concentration of cartilage ECM	Promising technique for non-invasive evaluation of articular cartilage and repair tissue. Direct correlation with Na+ cartilage content. No contrast administration.	Low Na SNR, need of 3T or higher. Partial volume effect for intra- and extra-cellular sodium signals. Need of specialized RF coils and customized UTE sequences.
DTI (Diffusion Tensor Imaging)	Pulse sequences with steady precession, double echo SSFO, RAISED Collagen, PG	High sensitivity and specificity detecting early cartilage degeneration and collagen structure alteration. No contrast administration.	Limited SNR, motion sensitive, long acquisition time. High-field MRI (3T).
UTE (Ultrashort time echo) MRI	T1, T2, T2*, T1ρ, magnetization transfer (MT), DESS, IR, quantitative susceptibility mapping Cartilage deep layers, osteochondral junction	Assessment of thin articular structures with short-T2 other than long-T2 structure. Lower susceptibility artifacts and magic angle effect than conventional quantitative MRI. Excellent interobserver agreement to cartilage endplate damage and intervertebral disc degeneration.	Not well validated. Inhomogeneous data on compositional quantification.
GAG-CEST (glycosaminoglycan chemical exchange saturation transfer imaging)	Magnetization transfer (MT)	Direct quantification of GAG content. Promising for identification of initial knee-joint cartilage damage. Comparable to dGEMRIC and T2 mapping. Good to excellent reproducibility at 7T MRI.	High-field MRI (3T or more). Not yet well validated.