Dynamic Transitions for Fast Joint Acquisition and Reconstruction of CEST- R e x $$ {R}_{ex} $$ and T 1 $$ {T}_1 $$

Abstract

Purpose: This work proposes a method for the simultaneous estimation of the exchange-dependent relaxation rate $R_{ex}$ and the longitudinal relaxation time $T_1$ from a single acquisition.

Methods: A novel acquisition scheme was developed that combines CEST saturation with an inversion pulse and a Look-Locker readout to capture the magnetization evolution starting from the inverse transient Z-spectrum. The corresponding signal model, derived from the Bloch-McConnell equations, describes both the transient Z-spectrum and the Look-Locker dynamics. A model-based reconstruction approach is employed to jointly estimate $R_{ex}$ and $T_1$ . The proposed method was validated using a numerical phantom and benchmarked against conventional CEST and Look-Locker $T_1$ mapping in a phantom and in vivo on a clinical 3T scanner.

Results: The joint estimation approach demonstrated strong agreement with ground truth and conventional methods across a wide range of $T_1$ and CEST parameters. The acquisition time was reduced by 20%-30% compared to standard CEST protocols, while providing a higher signal-to-noise ratio (SNR) in parameter maps.

Conclusion: The proposed technique enables robust and efficient simultaneous quantification of CEST $R_{ex}$ and $T_1$ in a single acquisition. It improves parameter map quality and reduces scan time, making it suitable for both phantom and in vivo imaging across a wide range of physiological conditions.

Keywords: APTw; AREX; CEST; Look‐Locker; QUASS; T1; TGV; model‐based reconstruction; rNOE; ssMT.