3t connectome scanner

We also tested our method using the MGH HCP data set acquired on the Siemens 3T Connectome scanner with maximum gradient strength of 300 mT/m. The spatial resolution of this data set was 1.5 × 1.5 × 1.5 mm³. The experimental parameters were TR/TE = 8800/57 ms, δ = 12.9 ms and Δ = 21.8 ms. The data set consisted of four b-values with b = 1000, 3000, 5000 and 10000 s/mm². The number of gradient directions at each b-shell were 64, 64, 128 and 256, respectively. More detailed information about data acquisition and pre-processing steps can be found in (Setsompop et al., 2013 (link)).
The maximum q-value that can be reached in this data set is about 0.7559 rad/μm, which allows for probing short-range disturbances as well. In order to incorporate short-range disturbances, we extend the model (34) to the three-dimensional case as follows:
$$s(q,\mathit{u})={\mathit{u}}^T{M}_2\mathit{u}+q^2{\mathit{u}}^T{M}_4\mathit{u}+(1-{\mathit{u}}^T{M}_2\mathit{u}-q^2{\mathit{u}}^T{M}_4\mathit{u})e^{-q^2(\mathrm{\Delta }-\delta /3){\mathit{u}}^{T}D\mathit{u}},$$ where M₂ and D are both 3 × 3 positive semidefinite tensors as before. Similar to the previous experiment, we assume that Û₂, Û₄ and D₀ all have the same set of eigenvectors. From M₂ and M₄, we define Û₂ := M₂D and Û₄ = M₄D. The eigenvalues for the three tensors are denoted by {û_2,‖, û_2,⊥, û_2,⊥}, {û_4,‖, û_4,⊥, û_2,⊥} and {d_‖, d_⊥, d_⊥}, respectively.

Diffusion data for the HCP was acquired on a customized Siemens 3 T Connectome Scanner using a standard 32-channel Siemens receiver head coil and a “body” transmission coil designed by Siemens. The customized hardware includes gradient coils and gradient power amplifiers that increase the maximum gradient strength from 40 mT/m to 100 mT/m, which specifically provides benefits for the quality of the diffusion imaging [58 (link)]. The diffusion sequence consisted of a Spin-echo EPI (TR 5520 ms, TE 89,5 ms, flip angle 78 deg, refocusing flip angle 160 deg, FOV 210 × 180 (RO × PE), matrix 168 × 144 (RO × PE), slice thickness 1.255 mm, 111 slices, 1.25 mm isotropic voxels, multiband factor 3, echo spacing 0.78 ms, BW 1488 Hz/Px, phase partial fourier 6/8), with the full diffusion session including 6 runs (approximately 9 minutes and 50 seconds each) of three different gradient tables acquired in both right-left and left-right phase encoding directions. Each diffusion gradient table included 90 diffusion weighted directions with 6 interspersed b=0 acquisitions. The three diffusion gradients consisted of b=1000, 2000, and 3000s/mm² shells with approximately equal acquisitions for each run [57 (link)], [58 (link)].