Anh T. Van

In vivo investigation of restricted diffusion in the human brain with optimized oscillating diffusion gradient encoding

Previous studies in phantoms and animals using animal MR systems have shown promising results in using oscillating gradient spin echo (OGSE) diffusion acquisition to depict microstructure information. The OGSE approach has also been shown to be a sensitive biomarker of tumor treatment response and white matter‐related diseases. Translating these studies to a human MR scanner faces multiple challenges due to the much weaker gradient system. The goals of this study are to optimize the OGSE acquisition for a human MR system and investigate its applicability in the in vivo human brain.

Comparison of Readout-Segmented Echo-Planar Imaging (EPI) and Single-Shot EPI in Clinical Application of Diffusion-Weighted Imaging of the Pediatric Brain

OBJECTIVEnReadout-segmented echo-planar imaging (EPI) has been suggested as an alternative to single-shot EPI for diffusion-weighted imaging (DWI) with reduced distortion. However, clinical comparisons of readout-segmented EPI and EPI DWI are limited by unmatched imaging parameters and reconstruction procedures. Our goal was to compare the clinical utility of generalized autocalibrating partial parallel acquisition (GRAPPA)-accelerated readout-segmented EPI DWI with GRAPPA-accelerated EPI DWI for visualization of the pediatric brain in regions prone to distortion, such as the orbit, skull base, and posterior fossa.nnnSUBJECTS AND METHODSnThirty consecutive patients (mean age, 7.8 years) presenting with orbital, skull base, and posterior fossa neuropathologic abnormalities were scanned at 3 T. Images were obtained using GRAPPA-accelerated readout-segmented EPI and GRAPPA-accelerated EPI with an identical scanning time, acceleration factor, target resolution, and image postprocessing procedure. The two datasets were independently reviewed by two blinded neuroradiologists. Imaging studies were evaluated for resolution, signal-to-noise ratio (SNR), contrast, distortion, lesion conspicuity, and diagnostic confidence and graded using a 7-point Likert scale (1, nondiagnostic; 7, outstanding).nnnRESULTSnThere was good reader agreement in the scores (κ = 0.66; 95% CI, 0.54-0.78). The mean scores for EPI and readout-segmented EPI, respectively, were as follows: resolution, 5.0 and 6.0; SNR, 5.5 and 3.0; contrast, 3.7 and 3.2; distortion, 4.8 and 6.0; lesion conspicuity, 4.6 and 5.1; and diagnostic confidence, 4.7 and 5.4. Readout-segmented EPI was superior in resolution, distortion reduction, lesion conspicuity, and diagnostic confidence, whereas EPI scored better in SNR and contrast. Readout-segmented EPI was considered the better sequence overall in 85% of the cases.nnnCONCLUSIONnThis study shows the benefits of improved resolution and reduced distortion of readout-segmented EPI in evaluating the orbit, skull base, and posterior fossa, sites of common neuropathologic abnormalities in children.

Diffusion tensor imaging (DTI) with retrospective motion correction for large-scale pediatric imaging

To develop and implement a clinical DTI technique suitable for the pediatric setting that retrospectively corrects for large motion without the need for rescanning and/or reacquisition strategies, and to deliver high‐quality DTI images (both in the presence and absence of large motion) using procedures that reduce image noise and artifacts.

3D isotropic high-resolution diffusion-weighted MRI of the whole brain with a motion-corrected steady-state free precession sequence.

The main obstacle to high‐resolution (<1.5 mm isotropic) 3D diffusion‐weighted MRI is the differential motion‐induced phase error from shot‐to‐shot. In this work, the phase error is addressed with a hybrid 3D navigator approach that corrects motion‐induced phase in two ways. In the first, rigid‐body motion is corrected for every shot. In the second, repeatable nonrigid‐body pulsation is corrected for each portion of the cardiac cycle. These phase error corrections were implemented with a 3D diffusion‐weighted steady‐ state free precession pulse sequence and were shown to mitigate signal dropouts caused by shot‐to‐shot phase inconsistencies compared to a standard gridding reconstruction in healthy volunteers. The proposed approach resulted in diffusion contrast more similar to the contrast observed in the reference echo‐planer imaging scans than reconstruction of the same data without correction. Fractional anisotropy and Color fractional anisotropy maps generated with phase‐corrected data were also shown to be more similar to echo‐planer imaging reference scans than those generated without phase correction. Magn Reson Med 70:466–478, 2013.

Slab profile encoding (PEN) for minimizing slab boundary artifact in three-dimensional diffusion-weighted multislab acquisition

To propose a method for mitigating slab boundary artifacts in three‐dimensional (3D) multislab diffusion imaging with no or minimal increases in scan time.

An introduction to model-independent diffusion magnetic resonance imaging.

Abstract q-Space–based techniques such as diffusion spectrum imaging, q-ball imaging, and their variations have been used extensively in research for their desired capability to delineate complex neuronal architectures such as multiple fiber crossings in each of the image voxels. The purpose of this article was to provide an introduction to the q-space formalism and the principles of basic q-space techniques together with the discussion on the advantages as well as challenges in translating these techniques into the clinical environment. A review of the currently used q-space–based protocols in clinical research is also provided.

Effect of number of acquisitions in diffusion tensor imaging of the pediatric brain: optimizing scan time and diagnostic experience.

Diffusion tensor imaging (DTI) is useful for multiple clinical applications, but its routine implementation for children may be difficult due to long scan times. This study evaluates the impact of decreasing the number of DTI acquisitions (NEX) on interpretability of pediatric brain DTI.

Real-time correction of rigid body motion-induced phase errors for diffusion-weighted steady-state free precession imaging.

Diffusion contrast in diffusion‐weighted steady‐state free precession magnetic resonance imaging (MRI) is generated through the constructive addition of signal from many coherence pathways. Motion‐induced phase causes destructive interference which results in loss of signal magnitude and diffusion contrast. In this work, a three‐dimensional (3D) navigator‐based real‐time correction of the rigid body motion‐induced phase errors is developed for diffusion‐weighted steady‐state free precession MRI.

Slab profile encoding (PEN) for minimizing slab boundary artifact in three-dimensional diffusion-weighted multislab acquisition: Slab Profile Encoding

To propose a method for mitigating slab boundary artifacts in three‐dimensional (3D) multislab diffusion imaging with no or minimal increases in scan time.

Effect of Number of Acquisitions in Diffusion Tensor Imaging of the Pediatric Brain

Diffusion tensor imaging (DTI) is useful for multiple clinical applications, but its routine implementation for children may be difficult due to long scan times. This study evaluates the impact of decreasing the number of DTI acquisitions (NEX) on interpretability of pediatric brain DTI.