A method for measuring B₀ field inhomogeneity using quantitative double‐echo in steady‐state

Abstract

To develop and validate a method for B 0 mapping for knee imaging using the quantitative Double-Echo in Steady-State (qDESS) exploiting the phase difference (Δ𝜃) between the two echoes acquired. Contrary to a two-gradient-echo (2-GRE) method, Δ𝜃 depends only on the first echo time.Methods: Bloch simulations were applied to investigate robustness to noise of the proposed methodology and all imaging studies were validated with phantoms and in vivo simultaneous bilateral knee acquisitions. Two phantoms and five healthy subjects were scanned using qDESS, water saturation shift referencing (WASSR), and multi-GRE sequences. ΔB 0 maps were calculated with the qDESS and the 2-GRE methods and compared against those obtained with WASSR. The comparison was quantitatively assessed exploiting pixel-wise difference maps, Bland-Altman (BA) analysis, and Lin's concordance coefficient (𝜌 c ). For in vivo subjects, the comparison was assessed in cartilage using average values in six subregions. Results:The proposed method for measuring ΔB 0 inhomogeneities from a qDESS acquisition provided ΔB 0 maps that were in good agreement with those obtained using WASSR. ΔB 0 𝜌 c values were ≥ 0.98 and 0.90 in phantoms and in vivo, respectively. The agreement between qDESS and WASSR was comparable to that of a 2-GRE method. Conclusion:The proposed method may allow B0 correction for qDESS T 2 mapping using an inherently co-registered ΔB 0 map without requiring an additional B0 measurement sequence. More generally, the method may help shorten knee imaging protocols that require an auxiliary ΔB 0 map by exploiting a qDESS acquisition that also provides T 2 measurements and high-quality morphological imaging.

Rapid whole brain 3D T2 mapping respiratory‐resolved Double‐Echo Steady State (DESS) sequence with improved repeatability

“…Recent works have shown that the DESS sequence can be used for B 0 mapping 10 . Reconstructing one B 0 map and one T 2 map per respiratory phase could potentially improve the accuracy of the T 2 estimates.…”

“…4,8 Recent works have shown that the DESS sequence can be used for B 0 mapping. 10 Reconstructing one B 0 map and one T 2 map per respiratory phase could potentially improve the accuracy of the T 2 estimates. Indeed, the gold standard spin-echo sequence provides longer T 2 values in GM and WM regions than the current protocol, [45][46][47] which is not the case for phantom experiments (details in Table S1 F I G U R E 7…”

“…The ratio of both images is highly sensitive to the T 2 relaxation time 1 and can hence be used to procure T 2 maps. The possibility to estimate other quantitative parameters, such as diffusion, 9 B 0 10 and white matter (WM) myelin water content, 11 has also been investigated with DESS‐type sequences. Being a steady‐state sequence, it employs short TRs that are especially practical for rapid 3D imaging.…”

Updates on Compositional MRI Mapping of the Cartilage: Emerging Techniques and Applications

“…New extensions of DESS sequences have appeared in the study by Zijlstra et al, 77 with the proposal of a new sequence called multiple‐echo steady‐state (MESS) to jointly produce T 2 mapping and water–fat separation with chemical‐shift correction. It was shown that quantitative DESS (qDESS) could be used to measure B 0 field inhomogeneity 78 . The diagnostic quality of a 5‐minute (min) sequence based on qDESS was evaluated to detect knee joint pathology, showing high interreader agreement between the new 5‐minute sequence and a conventional 20‐minute MRI 60 .…”

“…It was shown that quantitative DESS (qDESS) could be used to measure B 0 field inhomogeneity. 78 The diagnostic quality of a 5-minute (min) sequence based on qDESS was evaluated to detect knee joint pathology, showing high interreader agreement between the new 5-minute sequence and a conventional 20-minute MRI. 60 Figure 7 illustrates some of the images obtained in the study.…”