Alves da Mota, P

Brownlee, WJ

Cardoso, MJ

Golay, X

Miller, DH

Ourselin, S

Prados Carrasco, F

Riemer, F

Solanky, BS

Wheeler-Kingshott, CAM

UCL Discovery

Regional variation of total sodium concentration in the healthy human brainFerran Prados , Bhavana S Solanky , Patricia Alves Da Mota , Manuel Jorge Cardoso , Wallace J Brownlee , Frank Riemer ,David H Miller , Xavier Golay , Sebastien Ourselin , and Claudia Angela Michela Gandini Wheeler-KingshottTranslational Imaging Group, Medical Physics and Biomedical Engineering, University College London, London, United Kingdom,NMR Research Unit, Queen Square MS Centre, Department of Neuroinflammation, UCL Institute of Neurology, University CollegeLondon, London, United Kingdom, Department of Radiology, University of Cambridge, Cambridge, United Kingdom, Brain Repair& Rehabilitation, UCL Institute of Neurology, University College London, London, United Kingdom, Brain Connectivity Center, C.Mondino National Neurological Institute, Pavia, ItalySynopsisNon-invasive measurement of in vivo total sodium concentration (TSC) has been possible due to advances in sodium MRI at clinical field strengths. Changes inwhite and grey matter concentrations have been reported in a number of different diseases like Multiple Sclerosis. However, the presence of regional differencesin normal healthy brain TSC has not been yet investigated. Here we use Geodesic Information Flow technique for computing per subject brain parcellations toallow differentiation of these areas and subsequently characterization of  regional TSC in healthy controls. IntroductionNon-invasive measurement of in vivo total sodium concentration (TSC) has been possible due to advances in sodium MRI at clinical field strengths. Changes inwhite matter (WM) and grey matter (GM) concentrations have been reported in a number of different diseases like, Multiple Sclerosis (MS). However, thepresence of regional differences in normal healthy brain TSC has not been yet investigated. Here we use Geodesic Information Flow  (GIF) technique forcomputing per subject brain parcellations to allow differentiation of these areas and subsequently characterization of regional TSC in healthy controls.MethodsSodium Protocol: 10 healthy controls were scanned on a 3T Philips Achieva and underwent two protocols in the same session using: a 32-channel head coil and afixed tuned sodium volume coil (Rapid Biomedical). The first protocol was composed of PD/T2 (1x1x3 mm ) and 3DT1-weighted (1x1x1 mm ) MRI. The second23Na-MRI protocol was a 3D-Cones UTE sequence  (3x3x3 mm ) (see Figure 1) and a 1H PD/T2w (1x1x3 mm ) sequence. Two agar phantoms with 40 and 80 mMNaCl were placed either side of the head for quantification.Processing: Probabilistic brain tissue segmentation was performed on the 3DT1 images using GIF (see Figure 2). The segmentation masks were registered to theTSC maps. To preserve mask integrity, masks were resampled to sodium space using a point-spread function  with a linear interpolation. The resample step wasperformed using the concatenation of three affine transformations from the registrations of: 3DT1 to the pseudo-T1 images (PDw-T2w images ), the T2w to the1H PD/T2w images, and finally 1H PD-T2w image to the TSC map.Partial volume correction: With the aim to remove the CSF sodium contribution in the brain tissues, we applied a voxel-by-voxel modified partition-based subject-specific correction . The average TSC for the voxels with 100% probability of being CSF were computed. Then the final tissue sodium concentration wasexpressed as  where C represents TSC and VF is the volume fraction provided by GIF. As in Paling et al., only voxels with at least 20%tissue VF were included to produce a mask threshold to 0.2 for each area. In order to reject unrealistically high TSC values, a threshold was set to 2 standarddeviations above the mean of the TSC in voxels with at least 95% of tissue probability (TSC ). This was used as an additional threshold so that only voxelswithin the 0.2 threshold mask, which also had TSC values within two standard deviations of the TSC , were included.Selected brain areas: We selected and compared the following brain areas from both the left and right hemispheres: Frontal Lobe, Occiptal Lobe, SensorimotorCortex, Hippocampus, Limbic System, Thalamus, Cerebral White Matter, Brainstem, Cerebellum White Matter, Cerebellum Grey Matter and Cerebellar Vermis. Followingthis the Sensorimotor Cortex area was split into two groups depending on whether the subjects were left or right handed.Results and DiscussionTable 1 shows the sodium concentration per brain tissue type, and Table 2 per brain area. Most of the brain regions have similar concentrations in bothhemispheres and differences are not significant. Only the Occipital Lobe (visual areas) has significant differences between hemispheres. The Sensorimotor Cortexfor left handed subjects has significant differences from the TSC of right-handed subjects, but this could be due to the lower sample size. All left handed subjectshave less sodium concentration in the right hemisphere and vice versa with right handed subjects.ConclusionsWe have presented the first regional sodium concentration study in human healthy brain. Future work will analyse a larger cohort and will explore thecorrelation with clinical scales for different diseases.AcknowledgementsNIHR BRC UCLH/UCL High Impact Initiative, EPSRC (EP/H046410/1,EP/J020990/1,EP/K005278), MRC (MR/J01107X/1), UK MS Society and Brain Research Trust.References1) Cardoso, IEEE-TMI, 2015;     2) Riemer, MAGMA, 2014;     3) Cardoso, MICCAI 2015;     4) Hickman, MS Journal, 2002;     5) Paling, Brain, 2014 1,2 2 2 1 2 32 4 1 2,5123 4513 32 3 3345$UJTTVF	 + 07 $WPYFM $$4' '$4'7'UJTTVFmean_95%mean_95%Abstract ID: 213FiguresFigure 1: raw sodium image example Figure 2: 3D T1 image and the colouredparcellation obtained from GIF, computed athttp://cmictig.cs.ucl.ac.uk/niftywebTable 1: Sodium concentration per brain tissueTable 2: Sodium concentration per brain areaand hemisphere side. Mean and standarddeviation are provided. Sensorimotor Cortex hasbeen split in left and right hand side subjects (3subjects LH, 7 subjects RH). Last column showspaired t-test between hemispheres.

Regional variation of total sodium concentration in the healthy human brain

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Regional variation of total sodium concentration in the healthy human brain

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