The effects of concomitant gradients on chemical shift encoded MRI

Abstract

Purpose To characterize the effects of concomitant gradients (CGs) on chemical shift encoded (CSE)-based estimation of B0 field map, proton density fat fraction (PDFF), and R2*. Theory A theoretical framework was used to determine the effects of CG-induced phase errors on CSE-MRI data. Methods Simulations, phantom experiments, and in vivo experiments were conducted at 3T to assess the effects of CGs on quantitative CSE-MRI techniques. Correction of phase errors attributable to CGs was also investigated to determine if these effects could be removed. Results Phase errors due to CGs introduce errors in the estimation of B0 field map, PDFF, and R2*. Phantom and in vivo experiments demonstrated that CGs can introduce estimation errors greater than 30 Hz in the B0 field map, 10% in PDFF, and 16 s−1 in R2*, 16 cm off isocenter. However, CG phase correction before parameter estimation was able to reduce estimation errors to less than 10 Hz in the B0 field map, 1% in PDFF, and 2 s−1 in R2*. Conclusion CG effects can impact CSE-MRI, leading to inaccurate estimation of B0 field map, PDFF, and R2*. However, correction for phase errors caused by CGs improve the accuracy of quantitative parameters estimated from CSE-MRI acquisitions.

Quantitative MRI and spectroscopy of bone marrow

“…Complex‐based techniques have been shown to possess superior noise performance compared to their magnitude‐based counterparts and lower sensitivity to fat signal modeling errors . However, complex‐based techniques are also prone to phase errors, induced by concomitant gradients, eddy currents, gradient delays, and other hardware sources . Such phase errors can introduce significant PDFF bias spatial patterns that depend on the spatial pattern of the underlying phase errors .…”

“…33,34 However, complex-based techniques are also prone to phase errors, induced by concomitant gradients, eddy currents, gradient delays, and other hardware sources. 35,36 Such phase errors can introduce significant PDFF bias spatial patterns that depend on the spatial pattern of the underlying phase errors. 36 For a given phase error, the relative phase errorinduced PDFF bias may be in general smaller in bone marrow regions with moderate fat fractions (e.g.…”

Characterizing a short T2* signal component in the liver using ultrashort TE chemical shift‐encoded MRI at 1.5T and 3.0T

“…The CSE‐MRI methods enable rapid 3D fat fraction mapping of the whole liver within a single breath hold, and thus enable a quantitative evaluation of the distribution of liver fat. Advanced CSE‐MRI methods correct for multiple confounding factors in the quantification of PDFF, including T 1 bias, noise bias, spectral complexity of fat, T 2 * decay, noise‐related bias, and phase errors resulting from eddy currents and concomitant gradients …”

Technical Note: Interleaved bipolar acquisition and low‐rank reconstruction for water–fat separation in MRI

“…Many studies have been performed to address the challenges of bipolar acquisition . To achieve water–fat separation without an artifact in a short imaging time, a recent work by Soliman et al .…”

“…Many studies have been performed to address the challenges of bipolar acquisition. 9,10,[13][14][15] To achieve water-fat separation without an artifact in a short imaging time, a recent work by Soliman et al 16 proposed an interleaved bipolar acquisition approach, using two sequences with reversedpolarity bipolar gradients. Accordingly, the echo signals from both gradient polarities are acquired at every echo time, meaning that the imaging time is doubled.…”