High-Resolution DTI of Distal Peripheral Nerves Using Flow-Compensated Diffusion-Prepared 3D TSE

Barbara Cervantes^{1}, Qinwei Zhang^{2}, Kim van de Ven^{3}, Hendrik Kooijman^{4}, Ernst Rummeny^{1}, Axel Haase^{5}, Gustav J Strijkers^{2}, Jan S Kirschke^{6}, Aart J Nederveen^{2}, and Dimitrios C Karampinos^{1}

Flow-compensated diffusion-prepared sequence: A sequence combining a flow-compensated diffusion-preparation with a 3D TSE readout was developed by adding dephasing and rephasing gradients during the preparation and in the TSE readout to reduce sensitivity to phase errors [9,10,11] (Fig.1).

SNR efficiency optimization: Refocusing angle schemes and
corresponding signal of nerve (T1=1000,T2=75ms) were simulated using extended
phase graphs (EPG) for 3D TSE for variable echo train length and TR. T1 and T2
relaxation effects were included during the refocusing pulse train and T1
relaxation was considered between shots. SNR and SNR efficiency values were
computed as: $$$\text{SNR}=s_{0}\,\Delta\text{x}\Delta\text{y}\Delta\text{z}\sqrt{\Delta
t\,N_{x}N_{y}N_{z}}$$$ and $$$\text{SNR}_{\text{eff}}=\text{SNR}\sqrt{\text{t}_\text{scan}}$$$,
where s_{0} is the signal at k=0, $$$\Delta\text{x}$$$, $$$\Delta\text{y}$$$
and $$$\Delta\text{z}$$$ are the acquisition voxel sizes, N_{x}, N_{y} and
N_{z} are the matrix dimensions, $$$\Delta\text{t}$$$ is the sampling interval and
t_{scan} is the scan time [12].

*In vivo* measurements: DTI of the knee of two healthy
volunteers was conducted using a 16-channel knee coil on a 3T Philips system with
the developed sequence. 1) A sagittal acquisition was performed on one subject
and 2) an axial acquisition on the second subject. Readout parameters: 1) FOV=160×127×100$$$\text{mm}^{3}$$$,
acquisition voxel=1.7×1.7×1.7$$$\text{mm}^{3}$$$, reconstruction voxel=0.5×0.5×0.85$$$\text{mm}^{3}$$$,
TR/TE=1700/19ms, TSEfactor=60, averages=2, duration=15m33s. 2) FOV=140×140×52$$$\text{mm}^{3}$$$,
acquisition voxel=0.7×0.7×8 $$$\text{mm}^{3}$$$, reconstruction voxel=0.49×0.49×0.4
$$$\text{mm}^{3}$$$, TR/TE=1650/21ms, TSEfactor=40, averages=2, duration=5m28s.
DTI: b=0 and b=600 in six directions were acquired with TEprep=60ms. An axial T2-weighted
mDIXON TSE scan with an acquisition voxel=0.3×0.38×4$$$\text{mm}^{3}$$$ was
acquired as an anatomical reference.

Post-processing: A coronal reformat was obtained from the sagittal dataset. Iso-diffusion-weighted images (iso-DWIs) were generated. Diffusion tensors were computed using linear fitting and DTI parameters were obtained from the derived eigenvalues. Mean values of mean diffusivity (MD) and fractional anisotropy (FA) were measured. Projections of the primary eigenvectors were generated for visualization purposes.

[1] Mathys, Muscle Nerve 48:889, 2013

[2] Bendszus, Nat Clin Pract Neurol 1:45, 2005

[3] Alexander, Magn Reson Med 44:283, 2000

[4] Mori, Neuron 51:527, 2006

[5] Kakuda Neurorad 53:955, 2011

[6] Karampinos, NMR Biomed 26:630, 2013

[7] Xie, J Cardiovasc Magn Reson 16:67, 2014

[8] Cervantes, Proc. ISMRM 2015, p. 101

[9] Alsop, Magn Reson Med 38:527, 1997

[10] Sinha, J Magn Reson Imaging 6:657, 1996

[11] Jeong, Magn Reson Med 56:1173, 2006

[12] Simon, J Magn Reson Imaging doi:10.1002/jmri.25056, 2015

Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)

4530