Table 1.

Techniques for imaging cartilage composition and their pros/cons

Technique	Outcome measure	Biochemical correlate	Advantages	Disadvantages
dGEMRIC	T1 relaxation time	GAG content	Well validated	Long exam time Requires use of contrast agent
T2 relaxation time  mapping	T2 relaxation time	Collagen content/  orientation	Assessment of collagen content  without contrast Widely available	Magic angle effect May not capture initial biochemical  changes to cartilage
T1ρ relaxation time  mapping	T1ρ relaxation time	GAG content	Assessment of GAG content  without contrast	SAR limits due to high RF power
Sodium MRI	23Na signal intensity/  concentration	GAG content	High specificity to GAG content  without contrast	Requires specialized MRI hardware Long scan time Low SNR Better results at 7 T
UTE	T1, T2, T2*, and T1ρ  relaxation times	Variable	Assessment of deep regions of  cartilage	Long scan time Requires specialized MRI sequences
gagCEST	CEST asymmetry	GAG content	High specificity to GAG content  without contrast	Difficult to perform at 3 T and below Requires advanced post-processing  tools
DWI	ADC	Collagen content/  orientation	Assessment of collagen content  without contrast Widely available	Low SNR Limited evaluation of deep cartilage  regions
CTa	X-ray attenuation	GAG content	Useful for patients who cannot  undergo MRI Short scan times	Ionizing radiation Requires use of contrast agent