High-resolution animal imaging is an integral part of preclinical drug development and the investigation of diseases' pathophysiology. Quantitative mapping of T 2 relaxation times (qT 2 ) is a valuable tool for both preclinical and research applications, providing high sensitivity to subtle tissue pathologies. High-resolution T 2 mapping, however, suffers from severe underestimation of T 2 values due to molecular diffusion. This affects both single-echo and multi-echo spin echo (SSE and MESE), on top of the well-known contamination of MESE signals by stimulated echoes, and especially on high-field and preclinical scanners in which high imaging gradients are used in comparison to clinical scanners. Methods: Diffusion bias due to imaging gradients was analyzed by quantifying the effective b-value for each coherence pathway in SSE and MESE protocols, and incorporating this information in a joint T 2 -diffusion reconstruction algorithm. Validation was done on phantoms and in vivo mouse brain using a 9.4T and a 7T MRI scanner.Results: Underestimation of T 2 values due to strong imaging gradients can reach up to 70%, depending on scan parameters and on the sample's diffusion coefficient. The algorithm presented here produced T 2 values that agreed with reference spectroscopic measurements, were reproducible across scan settings, and reduced the average bias of T 2 values from −33.5 ± 20.5% to −0.1 ± 3.6%. Conclusions:A new joint T 2 -diffusion reconstruction algorithm is able to negate imaging gradient-related underestimation of T 2 values, leading to reliable mapping of T 2 values at high resolutions.