Gradient pre-emphasis to counteract first-order concomitant fields on asymmetric MRI gradient systems

Abstract

PURPOSE To develop a gradient pre-emphasis scheme that prospectively counteracts the effects of the first-order concomitant fields for any arbitrary gradient waveform played on asymmetric gradient systems, and to demonstrate the effectiveness of this approach using a real-time implementation on a compact gradient system. METHODS After reviewing the first-order concomitant fields that are present on asymmetric gradients, a generalized gradient pre-emphasis model assuming arbitrary gradient waveforms is developed to counteract their effects. A numerically straightforward, simple to implement approximate solution to this pre-emphasis problem is derived, which is compatible with the current hardware infrastructure used on conventional MRI scanners for eddy current compensation. The proposed method was implemented on the gradient driver sub-system, and its real-time use was tested using a series of phantom and in vivo data acquired from 2D Cartesian phase-difference, echo-planar imaging (EPI) and spiral acquisitions. RESULTS The phantom and in vivo results demonstrate that unless accounted for, first-order concomitant fields introduce considerable phase estimation error into the measured data and result in images exhibiting spatially dependent blurring/distortion. The resulting artifacts are effectively prevented using the proposed gradient pre-emphasis. CONCLUSION An efficient and effective gradient pre-emphasis framework is developed to counteract the effects of first-order concomitant fields of asymmetric gradient systems.

The effect of spiral trajectory correction on pseudo‐continuous arterial spin labeling with high‐performance gradients on a compact 3T scanner

“…All MR studies were conducted on a technology demonstrator C3T built by GE Global Research (Niskayuna, NY) . The C3T included an integrated T/R RF coil for transmission, and an 8‐channel brain coil (Invivo, Gainesville, FL) was used for reception.…”

“…The C3T included an integrated T/R RF coil for transmission, and an 8‐channel brain coil (Invivo, Gainesville, FL) was used for reception. B0 frequency tracking and linear concomitant field pre‐emphasis corrections were applied because of the asymmetric gradient design …”

“…A lightweight, low‐cryogen, compact 3T MRI system (C3T) has been developed and reported in the literature . It is equipped with high‐performance gradients, which can operate at 700 T/m/s simultaneously with an 80‐mT/m maximum gradient amplitude on each gradient axis . Typical whole‐body MR scanners offer up to a 200‐T/m/s gradient slew rate, and their performance may be further limited because of concerns about peripheral nerve stimulation (PNS) .…”

Improving apparent diffusion coefficient accuracy on a compact 3T MRI scanner using gradient nonlinearity correction

“…3D “gradwarp” correction for only spatial encoding distortion in the source images was enabled for the C3T and MR750w, while the software version on the Signa HDxt was limited to 2D “gradwarp” correction. The acquisitions on the C3T employed both real‐time gradient preemphasis and frequency shifting to compensate for additional concomitant field terms due to the asymmetric gradient design …”

Reduced acoustic noise in diffusion tensor imaging on a compact MRI system

“…All acquisitions on the C3T employed real-time gradient pre-emphasis [44] and B 0 compensation [45] to account for additional concomitant field terms due to the asymmetric gradient design of the transverse (physical X- and Y-) gradients on the C3T. For DTI processing, an independently-validated tenth- and even-ordered spherical harmonics-derived gradient field map [45] was used to correct for gradient nonlinearity of both spatial distortion and diffusivity-encoding [46–47].…”