Dynamic Transitions for Fast Joint Acquisition and Reconstruction of CEST‐Rex R₄ₗ and T1 T₁

ABSTRACT Purpose This work proposes a method for the simultaneous estimation of the exchange‐dependent relaxation rate and the longitudinal relaxation time 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 and . The proposed method was validated using a numerical phantom and benchmarked against conventional CEST and Look‐Locker 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 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 and 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.