Table 1.

Outcome measures, clinically relevant biochemical correlates, reported ranges for healthy and OA-diseased cartilage in literature, and advantages and disadvantages per quantitative imaging technique^*

Technique	Clinically relevant biochemical correlate	Outcome measure	Reported outcome range†		References, reported outcome range	Advantage	Disadvantage
			Healthy cartilage	OA cartilage‡
dGEMRIC§	GAG	T1 relaxation time	600–800 ms	300–600 ms	52, 57, 59, 64, 169, 172	Currently best validated indirect GAG measurement	Use of contrast agent with associated risks Long examination time
T2 mapping	Collagen content and orientation	T2* relaxation time	30–45 ms	40–60 ms	92, 98, 99, 105, 173–175	Correlation with collagen content and orientation without need for exogenous contrast agent	May possibly detect degenerative cartilage changes at a later stage than GAG specific techniques Magic angle effect
T1rho mapping	PG/GAG	T1rho relaxation time	30–50 ms	40–80 ms	92, 98, 99, 174, 176	Advocated to be sensitive to PG depletion without need for exogenous contrast agent	Exact biochemical correlate still controversial High RF power required, thus limited by SAR
Ultrashort TE	Collagen content and orientation	T2* relaxation time	20–30 ms	NR	148, 177	Enables visualization of deep cartilage layers, osteochondral junction, and subchondral bone	Long scan times Several technical MRI challenges
gagCEST#	GAG	CEST asymmetry	4–15%	NR	152–154	Direct measure of GAG content without need for exogenous contrast agent	Technically complex Requires high magnetic field strength Sophisticated postprocessing tools required
Sodium MRI¶	GAG	Sodium (23NA) signal intensity	10–35	NR	152, 154, 162, 178	Strong correlation with GAG content without need for exogenous contrast agent	Demanding MRI hardware requirements: (ultra) high field scanners, special RF coils Limited spatial resolution Long examination time
CT arthrography	GAG	X-ray attenuation	NR	NR	NA	Enables quantitative cartilage imaging in subjects with MRI contra-indications Short examination time (seconds instead of minutes) Detailed information on subchondral bone	Use of intraarticular contrast with associated risks Use of ionizing radiation Limited information on other soft tissues

^*OA = osteoarthritis; dGEMRIC = delayed gadolinium-enhanced magnetic resonance imaging (MRI) of cartilage; GAG = glycosaminoglycan; PG = proteoglycan; RF = radio frequency; SAR = specific absorption rate; TE = time to echo; NR = range not reported for in vivo human knee cartilage in the published literature; gagCEST = GAG-specific chemical exchange saturation transfer; CT = computed tomography; NA = not applicable.

^†Ranges are reported for human in vivo (patellar, femoral, or tibial plateau) cartilage of the knee examined with 3.0T MRI equipment unless indicated otherwise.

^‡All stages of OA according to Kellgren and Lawrence grading (179) were included in the OA cartilage outcome range.

^§Reported dGEMRIC outcome range for double dose (0.2 mmole/kg) intravenous contrast agent administration.

^¶Reported outcome range acquired at 7.0T instead of 3.0T.