Mitigating slice cross-talk in multi-slice multi-echo spin echo T2 mapping
Ekaterina A. Brui, Zilya Badrieva, Charles-Alexis de Mayenne, Stanislas Rapacchi, Thomas Troalen, David Bendahan
Abstract
Purpose
To investigate whether a T2 inter-slice variation could occur when a multi-slice multi-echo spin echo (MESE) sequence is used for image acquisition and to propose an enhanced method for reconstructing T2 maps that can effectively address and correct these variations.
Methods
Bloch simulations were performed accounting for the direct saturation effect to evaluate magnetization changes in multi-slice 2D MESE sequence. Experimental phantom scans were performed to validate these simulations. An improved version of the dictionary-based reconstruction approach was proposed, enabling the creation of a multi-slice dictionary of echo modulation curves (EMC). The corresponding method has been assayed considering inter-slice T2 variation with phantoms and in lower leg.
Results
Experimental and numerical study illustrate that direct saturation leads to a bias of EMCs. This bias during the T2 maps reconstructions using original single-slice EMC-dictionary method led to inter-slice T2 variation of 2.03% in average coefficient of variation (CV) in agarose phantoms, and up to 2.8% in vivo (for TR = 2 s, slice gap = 0%). A reduction of CV was observed when increasing the gap up to 100% (0.36% in phantoms, and up to 1.5% in vivo) or increasing TR up to 4 s (0.76% in phantoms, and up to 1.9% in vivo). Matching the multi-slice experimental data with multi-slice dictionaries provided a reduced CV of 0.54% in phantoms and up to 2.3% in vivo.
Conclusion
T2 values quantified from multi-slice MESE images using single-slice dictionaries are biased. A dedicated multi-slice EMC method providing the appropriate dictionaries can reduce the inter-slice T2 variation.