Clinical applications of advanced magnetic resonance imaging techniques for arthritis evaluation

Table 1 Fat suppression techniques in musculoskeletal system

	In phase-out of phase	Fat saturation (CHESS)	Water excitation	DIXON	STIR	SPIR	SPAIR
Physical basis	Change of TE	Selective RF pulse that suppresses fat	Selective RF pulse that excites water	Different TEs, mathematic post-processing	Selective inversion of short T1 tissues	Spectrally selective RF pulse that suppresses fat	Spectrally adiabatic selective RF pulse that suppresses fat
Advantages	Fast High SNR	High SNR Contrast enhanced studies	Fast 3D acquisition	Four images in one acquisition Quantification Less prone to B0 and B1	Less prone to B0 and B1	Pre- and post-contrast studies	Insensitive to B1
Drawbacks	Sensitivity to B0	Sensitivity to B0 and B1 at large FOV	Sensitivity to B0	Acquisition time	Suppress all short T1 structures	Sensitivity to B0	Sensitivity to B0
Clinical applications	Detection of bone infiltration	Bone edema evaluation in joints MR-arthrography	Cartilage evaluation	All in one technique High SNR Less metal induced artifacts	Large FOV (spine) Multiple interfaces (fingers, toes, metal)	Postcontrast imaging of inflammatory or neoplastic conditions	Large FOV and high SNR needed: thigh or MR- neurography

CHESS: Chemical Shift Selective; STIR: Short inversion time recovery; SPIR: Spectral presaturation with inversion recovery; SPAIR: Spectral adiabatic inversion recovery; TE: Time of echo; RF: Radiofrequency; SNR: Signal noise ratio; FOV: Field of view.

Table 2 Main parameters derived from dynamic contrast enhanced-magnetic resonance imaging studies

Parameter	Biological meaning
Area under the curve	The integral in a plot of concentration of contrast agent in blood plasma against time
Maximum (relative) enhancement	The maximum signal difference between the signal intensity at its maximum and baseline
Time to peak	Time elapsed between the arterial peak and the end of the steepest portion of enhancement
Wash in rate	The maximum slope between the time of onset of contrast inflow and the time of peak enhancement on the time intensity curve
Wash out rate	The clearance rate of contrast agent
Ktrans	Volume transfer constant between blood plasma and EES
Kep	Rate constant between EES and blood plasma
Ve	Volume of EES per unit of volume of tissue

EES: Extravascular extracellular space.