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

Purpose To validate the potential of quantifying R 2 ‐R 1ρ using one pair of signals with T 1ρ 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 1ρ using T 1ρ ‐ 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 1ρ after estimating both T 2 and T 1ρ , 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 1ρ 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 1ρ changes with agarose gel concentration. With in vivo data, significant correlation was observed between cartilage R 2 ‐R 1ρ 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 1ρ 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 1ρ can be efficiently measured using one pair of T 1ρ ‐prepared and T 2 ‐prepared signals with an optimal T prep considering cartilage relaxation times and image SNR.