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

## TL;DR

This paper introduces a new MRI method that simultaneously measures Rex and T1 in a single scan, improving efficiency and image quality.

## Contribution

A novel acquisition and reconstruction method for joint CEST Rex and T1 estimation in a single scan.

## Key findings

- The method achieves strong agreement with conventional techniques and ground truth.
- Acquisition time is reduced by 20–30% with improved SNR in parameter maps.
- Validated in phantom and in vivo studies on a clinical 3T scanner.

## Abstract

This work proposes a method for the simultaneous estimation of the exchange‐dependent relaxation rate Rex and the longitudinal relaxation time T1 from a single acquisition.

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 Rex and T1. The proposed method was validated using a numerical phantom and benchmarked against conventional CEST and Look‐Locker T1 mapping in a phantom and in vivo on a clinical 3T scanner.

The joint estimation approach demonstrated strong agreement with ground truth and conventional methods across a wide range of T1 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.

The proposed technique enables robust and efficient simultaneous quantification of CEST Rex and T1 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.