High‐resolution diffusion tensor imaging of the human pons with a reduced field‐of‐view, multishot, variable‐density, spiral acquisition at 3 T

Abstract

Diffusion tensor imaging of localized anatomic regions, such as brainstem, cervical spinal cord, and optic nerve, is challenging because of the existence of significant susceptibility differences, severe physiologic motion in the surrounding tissues, and the need for high spatial resolution to resolve the underlying complex neuroarchitecture. The aim of the methodology presented here is to achieve high-resolution diffusion tensor imaging in localized regions of the central nervous system that is motion insensitive and immune to susceptibility while acquiring a set of two-dimensional images with more than six diffusion encoding directions within a reasonable total scan time. We accomplish this aim by implementing self-navigated, multishot, variable-density, spiral encoding with outer volume suppression. We establish scan protocols for achieving equal signal-to-noise ratio at 1.2 mm and 0.8 mm in-plane resolution for reduced field-of-view diffusion tensor imaging of the brainstem. In vivo application of the technique on the human pons of three subjects shows a clear delineation of the multiple local neural tracts. By comparing scans acquired with varying in-plane resolution but with constant signal-to-noise ratio, we demonstrate that increasing the resolution and reducing the partial volume effect result in higher fractional anisotropy values for the corticospinal tracts.

Assessment of reduced field of view in diffusion tensor imaging of the lumbar nerve roots at 3 T

“…Thus the effects of T2* decay are less important, resulting in a smaller loss of signal. As the readout time along the phase-encode dimension is also shorter, sensitivity to chemical shift and blurring artefacts is lessened [9,11]. However, one must keep in mind that the single-shot EPI base gives a lower limit for TE as the whole k-space has to be read by a single echo.…”

“…However, the relevance of such comparisons can be discussed [18], and this does not seem essential for DTI imaging of the lumbar nerves. The fact that this technique can be implemented at both fields is enough to perform clinical studies in any imaging centre [9,12].…”

“…An approach known as reduced field of view (rFOV) has been introduced in DTI with interesting results [8][9][10][11][12][13]. Only the signal coming from a pre-defined area of interest is conserved.…”

High-Resolution MR Imaging of the Human Brainstem In vivo at 7 Tesla

“…Higher spatial resolution is thus needed to delineate transverse pontine fibers unambiguously, which requires sophisticated modifications of the diffusion MRI sequence such as combining zoomed imaging and parallel imaging (Heidemann et al, 2012; Eichner et al, 2013). Karampinos et al (2009) were recently able to resolve transverse pontine fibers in direction-encoded fractional anisotropy maps with a resolution of 0.8 mm × 0.8 mm × 3 mm at 3T by applying a dedicated acquisition scheme (self-navigated, multi-shot, variable-density, spiral-imaging with outer volume suppression).…”

Optimal Imaging Parameters for Readout-segmented EPI of the Temporal Bone

“…However, bulk motion between shots may produce phase changes, which often produce artifacts. 5,6 To counter these issues, Porter and colleagues designed a method for segmenting the kspace in the readout direction and reading the signals in each segment 7 ( Fig. 1).…”