Abstract
PurposeTo propose a T2-prepared 3D turbo spin echo (T2prep 3D TSE) sequence for B1-insensitive skeletal muscle T2 mapping and compare its performance with 2D and 3D multi-echo spin echo (MESE) for T2 mapping in thigh muscles of healthy subjects.MethodsThe performance of 2D MESE, 3D MESE and the proposed T2prep 3D TSE in the presence of transmit B1 and B0 inhomogeneities was first simulated. The thigh muscles of ten young and healthy subjects were then scanned on a 3 T system and T2 mapping was performed using the three sequences. Transmit B1-maps and proton density fat fraction (PDFF) maps were also acquired. The subjects were scanned three times to assess reproducibility. T2 values were compared among sequences and their sensitivity to B1 inhomogeneities was compared to simulation results. Correlations were also determined between T2 values, PDFF and B1.ResultsThe left rectus femoris muscle showed the largest B1 deviations from the nominal value (from 54.2% to 92.9%). Significant negative correlations between T2 values and B1 values were found in the left rectus femoris muscle for 3D MESE (r = -0.72, p<0.001) and 2D MESE (r = -0.71, p<0.001), but not for T2prep 3D TSE (r = -0.32, p = 0.09). Reproducibility of T2 expressed by root mean square coefficients of variation (RMSCVs) were equal to 3.5% in T2prep 3D TSE, 2.6% in 3D MESE and 2.4% in 2D MESE. Significant differences between T2 values of 3D sequences (T2prep 3D TSE and 3D MESE) and 2D MESE were found in all muscles with the highest values for 2D MESE (p<0.05). No significant correlations were found between PDFF and T2 values.ConclusionA strong influence of an inhomogeneous B1 field on the T2 values of 3D MESE and 2D MESE was shown, whereas the proposed T2prep 3D TSE gives B1-insensitive and reproducible thigh muscle T2 mapping.
Highlights
Acute inflammatory edematous alterations of skeletal muscles, reflecting disease activity, as well as fatty infiltration of chronically affected muscles are two main characteristics of neuromuscular diseases [1,2,3]
Significant negative correlations between T2 values and B1 values were found in the left rectus femoris muscle for 3D multi-echo spin echo (MESE) (r = -0.72, p
Reproducibility of T2 expressed by root mean square coefficients of variation (RMSCVs) were equal to 3.5% in T2prep 3D TSE, 2.6% in 3D MESE and 2.4% in 2D MESE
Summary
Acute inflammatory edematous alterations of skeletal muscles, reflecting disease activity, as well as fatty infiltration of chronically affected muscles are two main characteristics of neuromuscular diseases [1,2,3]. Conventional diagnostic magnetic resonance imaging (MRI), based on T1-weighted, T2-weighted and Short Tau Inversion Recovery (STIR) sequences, is only able to detect qualitative pathological changes in the muscle tissue. Semi-quantitative scales exist for judging the extent of fatty infiltration or edematous muscular alterations based on conventional MR images [4,5,6]. There is an emerging need for objective evaluation of fatty infiltration and inflammatory skeletal muscle alterations based on quantitative imaging. Chemical shift encoding-based water-fat MRI enables the assessment and quantification of the fatty infiltration in muscle tissue using the proton density fat fraction (PDFF) [7, 8]. T2 mapping is a quantitative MRI technique that enables the quantification of inflammatory changes [1,2,3]. Fat suppression has been proposed as a way to at least partially reduce the effect of fat content on the extracted T2 values [9, 10], with known limitations on totally removing the effect of the fat content from the extracted T2 values [11]
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