Visualization of intra-thalamic nuclei with optimized white-matter-nulled MPRAGE at 7T.
NeuroImage. 2014-01-01; 84: 534-545
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1. Neuroimage. 2014 Jan 1;84:534-45. doi: 10.1016/j.neuroimage.2013.08.069. Epub
2013 Sep 7.
Visualization of intra-thalamic nuclei with optimized white-matter-nulled MPRAGE
Tourdias T(1), Saranathan M, Levesque IR, Su J, Rutt BK.
(1)Richard M. Lucas Center for Imaging, Radiology Department, Stanford
University, 1201 Welch Road, Stanford, CA 94305-5488, USA. Electronic address:
Novel MR image acquisition strategies have been investigated to elicit contrast
within the thalamus, but direct visualization of individual thalamic nuclei
remains a challenge because of their small size and the low intrinsic contrast
between adjacent nuclei. We present a step-by-step specific optimization of the
3D MPRAGE pulse sequence at 7T to visualize the intra-thalamic nuclei. We first
measured T1 values within different sub-regions of the thalamus at 7T in 5
individuals. We used these to perform simulations and sequential experimental
measurements (n=17) to tune the parameters of the MPRAGE sequence. The optimal
set of parameters was used to collect high-quality data in 6 additional
volunteers. Delineation of thalamic nuclei was performed twice by one rater and
MR-defined nuclei were compared to the classic Morel histological atlas. T1
values within the thalamus ranged from 1400ms to 1800ms for adjacent nuclei.
Using these values for theoretical evaluations combined with in vivo
measurements, we showed that a short inversion time (TI) close to the white
matter null regime (TI=670ms) enhanced the contrast between the thalamus and the
surrounding tissues, and best revealed intra-thalamic contrast. At this
particular nulling regime, lengthening the time between successive inversion
pulses (TS=6000ms) increased the thalamic signal and contrast and lengthening the
α pulse train time (N*TR) further increased the thalamic signal. Finally, a low
flip angle during the gradient echo acquisition (α=4°) was observed to mitigate
the blur induced by the evolution of the magnetization along the α pulse train.
This optimized set of parameters enabled the 3D delineation of 15 substructures
in all 6 individuals; these substructures corresponded well with the known
anatomical structures of the thalamus based on the classic Morel atlas. The mean
Euclidean distance between the centers of mass of MR- and Morel atlas-defined
nuclei was 2.67mm (±1.02mm). The reproducibility of the MR-defined nuclei was
excellent with intraclass correlation coefficient measured at 0.997 and a mean
Euclidean distance between corresponding centers of mass found at first versus
second readings of 0.69mm (±0.38mm). This 7T strategy paves the way to better
identification of thalamic nuclei for neurosurgical planning and investigation of
regional changes in neurological disorders.
PMID: 24018302 [Indexed for MEDLINE]