Correcting for imaging gradients–related bias of T2 relaxation times at high-resolution MRI
Natalie Bnaiahu, Noam Omer, Ella Wilczynski, Shir Levy, Tamar Blumenfeld-Katzir, Noam Ben-Eliezer
Abstract
Purpose
High-resolution animal imaging is an integral part of preclinical drug development and the investigation of diseases’ pathophysiology. Quantitative mapping of T2 relaxation times (qT2) is a valuable tool for both preclinical and research applications, providing high sensitivity to subtle tissue pathologies. High-resolution T2 mapping, however, suffers from severe underestimation of T2 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 T2-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 T2 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 T2 values that agreed with reference spectroscopic measurements, were reproducible across scan settings, and reduced the average bias of T2 values from −33.5 ± 20.5% to −0.1 ± 3.6%.
Conclusions
A new joint T2-diffusion reconstruction algorithm is able to negate imaging gradient–related underestimation of T2 values, leading to reliable mapping of T2 values at high resolutions.