Lateral geniculate nucleus volumetry at 3T and 7T: Four different optimized magnetic-resonance-imaging sequences evaluated against a 7T reference acquisition
Introduction
The LGN is the main thalamic node of the visual pathway between the retina and the visual cortex (Guillery et al., 2001; Leventhal et al., 1981; RW, 1988; Sherman and Guillery, 2002) and is involved in visual processing but also in control of visual spatial attention (Schneider and Kastner, 2009). Located superiorly to the hippocampus and medially to the optic radiation (Gray, 1918), each LGN consists of retinotopically organized (two) magnocellular and (six) parvocellular neuronal layers (Guillery, 1979; Hickey and Guillery, 1979) which process complementary information of visual stimuli. In healthy adults, it has been shown by functional magnetic resonance imaging (fMRI) that the LGN exhibited significant attentional enhancements during an attention task (Poltoratski et al., 2017). However, the LGN was defined functionally, and thus no segmentation of the LGN was performed which makes it difficult to attribute fMRI signal changes solely to the LGN in this study. The LGN volume is altered in ophthalmologic and neurodegenerative pathologies of afferent and efferent visual systems such as albinism, amblyopia, and glaucoma (Barnes et al., 2010; Lee et al., 2014; Mcketton et al., 2014).
To determine structural and volumetric variability or subtle anatomical alterations of the LGN, precise visualization of its morphology is needed. However, its small size and its deep brain localization make in vivo evaluation challenging (Andrews et al., 1997). To depict morphological LGN changes and to measure its volume in-vivo, proton density weighted (PDw) magnetic resonance imaging (MRI) 2-dimensional (2D) acquisitions have been applied (Bridge et al., 2008; Horton et al., 1990; Kitajima et al., 2015; Lee et al., 2014; Mcketton et al., 2014). Moreover, functional imaging at field strengths of 3 T (3T) and 7 T (7T) applying visual stimuli varying in space, time, luminance, or color revealed subdivisions of the functional maps in the LGN (Denison et al., 2014).
In other studies, MPRAGE sequences have depicted various intra-thalamic structures including the LGN (Dai et al., 2011; Fujita et al., 2001; Kitajima et al., 2015; Korsholm et al., 2007; Li et al., 2012; Wang et al., 2015). The different myelin concentrations of thalamic nuclei and the fact that myelin influences T1 contrast allowed improvements of MPRAGE contrast of the LGN by optimizing inversion times (TI) to null either with white matter (WMn) (Sudhyadhom et al., 2009; Vassal et al., 2012), grey matter (GMn) (Bender et al., 2011; Magnotta et al., 2000; Wyss et al., 2014, 2016) or both (Tourdias et al., 2014). For example, Tourdias et al. (2014) applied WMn and GMn, and found that WMn improved the contrast between the thalamus and the surrounding tissues, and also revealed best intrathalamic contrast. The above mentioned studies optimized their sequences for the maximal contrast between WM and GM. Yet, the accuracy of simulations reported in these studies is limited not only by the model assumptions, but also by the variability of the tissue properties, by the lack of estimation or measurements of the LGN's relaxation times, and by spin density (Deichmann et al., 2000).
Previous MRI studies, however, lack sufficient contrast for accurate LGN volume quantification or use intricate processing methods and thereby limit clinical and neuroscientific applicability of LGN imaging (Yu et al., 2015). Therefore, a fast, clinically as well as neuroscientifically implementable MRI method to investigate LGN morphology is needed. Here, we present a 3D isotropic high-resolution reference acquisition for LGN volume determination with optimized CNR at 7T. In addition, we recorded fast MRI sequences using an isotropic high-resolution MPRAGE with a TI that nulled either WM or GM signals (i.e. WMn and GMn, respectively). Next, WMn-GMn were tested on volume rating reliability and CNR (efficiency) against the clinical standard (PD 2D Turbo-Spin-Echo) and the reference acquisition.
Section snippets
Subjects
Prospectively, 31 healthy subjects (mean age 31 and standard deviation (STD) 7.0 years, range: 18–49 years, 18 women) gave informed written consent to attend this project accepted by the ethics committee, Canton Zurich, Switzerland. To be included, subjects had to be older than 18 years, with no history of neurologic, psychiatric or ophthalmologic diseases affecting the LGN. On 3T and 7T MRI Scanners (Philips Healthcare, Best, the Netherlands) with 2 channel transmit and 32-channels receive
Results
Sample characteristics evaluations showed that volume and CNR of the 31 subjects and of the subgroup of 20 subjects were normally distributed for all sequences on both scanner (Shapiro-Wilk tests: all p > 0.05). Only the CNR of the PD-TSE at 7T had a distribution over the subjects significantly different for normal distribution (p = 0.04 Shapiro-Wilk test corrected for multiple comparisons). Simulations of the signal and contrast of GM and WM for MPRAGE sequences are shown in Supplementary
Discussion
This study aimed at determining an MR sequence that assesses the LGN volume more accurately, when compared to the currently used 2D sequences and to a reference acquisition. We found that 3D MPRAGE imaging of the LGN resulted in a higher CNR and volume determination accuracy. Our results indicate that reliable LGN volume quantification can be achieved by short scanning on standard 3T scanners.
MPRAGE improved imaging of the LGN (Yu et al., 2015) and revealed detailed intra-thalamic structures (
Conclusion
We obtained LGN images with high contrast by optimizing T1-contrast of MPRAGE scans and by correcting for motion. Based on this procedure, we provided reliable LGN volume quantification. Measuring LGN volume with 0.75 mm isotropic protocols with the short duration of about 15 min (using GMn – WMn) might thus be clinically and neuroscientifically relevant for diseases affecting the visual pathway or for further insight into the structural and functional connectivity of the LGN. The
Acknowledgment
We would like to acknowledge the King Abdulaziz University and The Saudi Arabian Cultural Office in Paris, France, for funding part of this Project.
References (55)
- et al.
Optimization of 3-D MP-RAGE sequences for structural brain imaging
Neuroimage
(2000) - et al.
Functional mapping of the magnocellular and parvocellular subdivisions of human LGN
Neuroimage
(2014) - et al.
Altered intraoperative cerebrovascular reactivity in brain areas of high-grade glioma recurrence
Magn. Reson. Imag.
(2016) A speculative essay on geniculate lamination and its development
Prog. Brain Res.
(1979)- et al.
Techniques for blood volume fMRI with VASO: from low-resolution mapping towards sub-millimeter layer-dependent applications
Neuroimage
(2018) - et al.
Visualization of subthalamic nuclei with cortex attenuated inversion recovery MR imaging
Neuroimage
(2000) - et al.
Stereologic analysis of the lateral geniculate nucleus of the thalamus in normal and schizophrenic subjects
Psychiatr. Res.
(2007) - et al.
A high resolution and high contrast MRI for differentiation of subcortical structures for DBS targeting: the Fast Gray Matter Acquisition T1 Inversion Recovery (FGATIR)
Neuroimage
(2009) - et al.
Visualization of intra-thalamic nuclei with optimized white-matter-nulled MPRAGE at 7T
Neuroimage
(2014) - et al.
Direct stereotactic targeting of the ventrointermediate nucleus of the thalamus based on anatomic 1.5-T MRI mapping with a white matter attenuated inversion recovery (WAIR) sequence
Brain Stimul.
(2012)
Automatic segmentation of the lateral geniculate nucleus: application to control and glaucoma patients
J. Neurosci. Methods
Advanced MR imaging of the visual pathway
Neuroimaging Clin.
Perceptual learning of contrast detection in the human lateral geniculate nucleus
Curr. Biol.
Correlated size variations in human visual cortex, lateral geniculate nucleus, and optic tract
J. Neurosci.
Decreased gray matter concentration in the lateral geniculate nuclei in human amblyopes
Invest. Ophthalmol. Visual Sci.
Optimized 3D magnetization-prepared rapid acquisition of gradient echo: identification of thalamus substructures at 3T
AJNR Am. J. Neuroradiol.
Changes in connectivity after visual cortical brain damage underlie altered visual function
Brain
Retinotopic mapping of lateral geniculate nucleus in humans using functional magnetic resonance imaging
Proc. Natl. Acad. Sci. Unit. States Am.
Guidelines, criteria, and rules of thumb for evaluating normed and standardized assessment instruments in psychology
Psychol. Assess.
Assessment of lateral geniculate nucleus atrophy with 3T MR imaging and correlation with clinical stage of glaucoma
Am. J. Neuroradiol.
Quantitative contrast ratio comparison between T1 (TSE at 1.5 T, FLAIR at 3T), magnetization prepared rapid gradient echo and subtraction imaging at 1.5 T and 3T
Quant. Imag. Med. Surg.
Radiofrequency ablation, MR thermometry, and high-spatial-resolution MR parametric imaging with a single, minimally invasive device
Radiology
Single-shot spiral imaging at 7 T
Magn. Reson. Med.
Lateral geniculate nucleus: anatomic and functional identification by use of MR imaging
Am. J. Neuroradiol.
Anatomy of the human body
Connections of higher order visual relays in the thalamus: a study of corticothalamic pathways in cats
J. Comp. Neurol.
Variability of laminar patterns in the human lateral geniculate nucleus
J. Comp. Neurol.
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