Bio‐SCOPE: fast biexponential T 1 ρ mapping of the brain using signal‐compensated low‐rank plus sparse matrix decomposition

Purpose To develop and evaluate a fast imaging method based on signal‐compensated low‐rank plus sparse matrix decomposition to accelerate data acquisition for biexponential brain T 1 ρ mapping (Bio‐SCOPE). Methods Two novel strategies were proposed to improve reconstruction performance. A variable‐rate undersampling scheme was used with a varied acceleration factor for each k‐space along the spin‐lock time direction, and a modified nonlinear thresholding scheme combined with a feature descriptor was used for Bio‐SCOPE reconstruction. In vivo brain T 1 ρ mappings were acquired from 4 volunteers. The fully sampled k‐space data acquired from 3 volunteers were retrospectively undersampled by net acceleration rates (R) of 4.6 and 6.1. Reference values were obtained from the fully sampled data. The agreement between the accelerated T 1 ρ measurements and reference values was assessed with Bland‐Altman analyses. Prospectively undersampled data with R = 4.6 and R = 6.1 were acquired from 1 volunteer. Results T 1 ρ ‐weighted images were successfully reconstructed using Bio‐SCOPE for R = 4.6 and 6.1 with signal‐to‐noise ratio variations <1 dB and normalized root mean square errors <4%. Accelerated and reference T 1 ρ measurements were in good agreement for R = 4.6 (T 1 ρ s : 18.6651 ± 1.7786 ms; T 1 ρ l : 88.9603 ± 1.7331 ms) and R = 6.1 (T 1 ρ s : 17.8403 ± 3.3302 ms; T 1 ρ l : 88.0275 ± 4.9606 ms) in the Bland‐Altman analyses. T 1 ρ parameter maps from prospectively undersampled data also show reasonable image quality using the Bio‐SCOPE method. Conclusion Bio‐SCOPE achieves a high net acceleration rate for biexponential T 1 ρ mapping and improves reconstruction quality by using a variable‐rate undersampling data acquisition scheme and a modified soft‐thresholding algorithm in image reconstruction.