Magnetization-prepared spoiled gradient-echo snapshot imaging for efficient measurement of R-2-R-1 rho in knee cartilage

Purpose: To validate the potential of quantifying R-2-R-1 rho using one pair of signals with T-1 rho preparation and T-2 preparation incorporated to magnetization-prepared angle-modulated partitioned k-space spoiled gradient-echo snapshots (MAPSS) acquisition and to find an optimal preparation time (T-prep) for in vivo knee MRI. Methods: Bloch equation simulations were first performed to assess the accuracy of quantifying R-2-R-1 rho using T-1 rho- and T-2-prepared signals with an equivalent T-prep. For validation of this technique in comparison to the conventional approach that calculates R-2-R-1 rho after estimating both T-2 and T-1 rho, phantom experiments and in vivo validation with five healthy subjects and five osteoarthritis patients were performed at a clinical 3T scanner. Results: Bloch equation simulations demonstrated that the accuracy of this efficient R-2-R-1 rho quantification method and the optimal T-prep can be affected by image signal-to-noise ratio (SNR) and tissue relaxation times, but quantification can be closest to the reference with an around 25 ms T-prep for knee cartilage. Phantom experiments demonstrated that the proposed method can depict R-2-R-1 rho changes with agarose gel concentration. With in vivo data, significant correlation was observed between cartilage R-2-R-1 rho measured from the conventional and the proposed methods, and a T-prep of 25.6 ms provided the most agreement by Bland-Altman analysis. R-2-R-1 rho was significantly lower in patients than in healthy subjects for most cartilage compartments. Conclusion: As a potential biomarker to indicate cartilage degeneration, R-2-R-1 rho can be efficiently measured using one pair of T-1 rho-prepared and T-2-prepared signals with an optimal T-prep considering cartilage relaxation times and image SNR.