T1rho relaxation quantification using spiral imaging: a preliminary study

Osteoarthritis (OA) is a disease of articular cartilage degeneration. Early detection of changes in cartilage would be essential for preventing the progression of disease and for monitoring therapy in OA. The T_1ρ relaxation parameter describes the spin-lattice relaxation in the rotating frame and has been considered as a promising tool to detect the loss of proteoglycan (PG), which is an early precursor of OA. The goal of this study was to develop a T_1ρ-weighted imaging method based on spiral imaging and to examine the feasibility of applying it to in vivo cartilage imaging. T_1ρ-weighted imaging with a pre-encoded spin-lock pulse cluster followed by a spiral acquisition sequence was implemented on GE 1.5 T scanners. tip maps were generated by a pixel-by-pixel fit of the T_1ρ-weighted data to an exponential decay. Homogeneous agarose phantoms and the patella cartilage of one healthy volunteer were imaged using the developed techniques. T_1ρ in agarose phantoms decreased as agarose concentration increased. No significant tip dispersion was seen within spin-lock frequencies ranging from 150 Hz to 1000 Hz in agarose phantoms. T_1ρ-weighted images of the healthy volunteer showed good contrast between cartilage and surrounding tissues. The fitted T_1ρ value of patella cartilage was within the range of 30-100 ms.