Near‐silent distortionless DWI using magnetization‐prepared RUFIS

Abstract

Purpose To develop a near‐silent and distortionless DWI (sd‐DWI) sequence using magnetization‐prepared rotating ultrafast imaging sequence. Methods A rotating ultrafast imaging sequence was modified with driven‐equilibrium diffusion preparation, including eddy‐current compensation methods. To compensate for the T1 recovery during readout, a phase‐cycling method was used. Both compensation methods were validated in phantoms. The optimized sequence was compared with an EPI diffusion sequence for image distortion, contrast, ADC, and acoustic noise level in phantoms. The sequence was evaluated in 1 brain volunteer, 5 prostate volunteers, and 10 pediatric patients with joint diseases. Results Combination of several eddy‐current compensation methods reduced the artifact to an acceptable level. Phase cycling reduced T1 recovery contamination during readout. In phantom scans, the optimized sequence generated similar image contrast to the EPI diffusion sequence, and ADC maps between the sequences were comparable; sd‐DWI had significantly lower acoustic noise (P < .05). In vivo brain scan showed reduced image distortion in sd‐DWI compared with the EPI diffusion, although residual motion artifact remains due to brain pulsation. The prostate scans showed that sd‐DWI can provide similar ADC compared with EPI diffusion, with no image distortion. Patient scans showed that the sequence can clearly depict joint lesions. Conclusion An sd‐DWI sequence was developed and optimized. Compared with conventional EPI diffusion, sd‐DWI provided similar diffusion contrast, accurate ADC measurement, improved image quality, and minimal ambient scanning noise. The sequence showed the ability to obtain in vivo diffusion contrast in relatively motion‐free body regions, such as prostate and joint.

Silent myelin-weighted magnetic resonance imaging

“…This restricts a naïve RUFIS implementation to Proton-Density (PD) weighting 31 . To circumvent this limitation, the sequence can be segmented, with preparation pulses played in between segments; this approach has previously been utilised for T2 32 and diffusion prepared RUFIS imaging 33 .…”

“…The RUFIS images were reconstructed using the manufacturer’s proprietary Orchestra toolbox (GE Healthcare). The reconstruction consisted of nearest-neighbour gridding on a twice-oversampled grid 41 , k -space center filling 42 , 43 , and Total Generalised Variation (TGV) regularization 33 , 44 . The TGV regularisation parameter was set to λ = 0.01 with a maximum of 64 iterations.…”

Near‐Silent and Distortion‐Free Diffusion MRI in Pediatric Musculoskeletal Disorders: Comparison With Echo Planar Imaging Diffusion

“…The purpose of this study was to evaluate a distortion‐free and near‐silent diffusion‐weighted (DW‐SD) sequence 25,26 and compare it with the standard 2D EPI diffusion‐weighted (DW‐EPI) sequence in the setting of pediatric extremity MRI. We hypothesized that the ADCs measured from each sequence would not be significantly different and that qualitatively DW‐SD will be equivalent or preferred over DW‐EPI.…”

Distortion‐free 3D diffusion imaging of the prostate using a multishot diffusion‐prepared phase‐cycled acquisition and dictionary matching

“…These eddy current-induced magnitude errors (EiMEs) are (1) spatially dependent, (2) constant throughout the multishot acquisition, and (3) proportional to the strength of the diffusion gradients. The eddy current problem has been previously accounted for by employing a pair of bipolar rather than monopolar gradients to compensate currents with opposite signs, [22][23][24][25] by performing phase cycling of the DP tip-up pulse, 17,25 or by adding magnitude stabilizers gradients. 20…”

“…The first challenge was addressed using bipolar gradients, [22][23][24] and a combination of oversampled k-space center averaging and phase cycling. Other studies have previously used phase cycling to account for motion and eddy currents in DP sequences, 17,25 at the cost of doubling the scan time. Here, each phase-cycled acquisition was undersampled by a factor of two, ie, the total acquisition time was not increased.…”