Haenelt, D.

Nasr, S.

Polimeni, J.

Sereno, M.

Tootell, R.

Trampel, R.

Weiskopf, N.

MPG.PuRe

Mapping colour-selective columns in V2 across cortical depth using GE- and SE-EPIDaniel Haenelt1, Robert Trampel1, Shahin Nasr2,3, Jonathan Polimeni2,3, Roger Tootell2,3, Martin Sereno4, Nikolaus Weiskopf11Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany, 2Athinoula A. Martinos Center for BiomedicalImaging, Massachusetts General Hospital, Charlestown, USA, 3Department of Radiology, Harvard Medical School, Boston, USA, 4Department of Psychologyand Neuroimaging Center, San Diego State University, San Diego, USAhaenelt@cbs.mpg.deNeuroCom•At ultra-high magnetic fields (≥ 7 T), fMRI enables the delin-eation of mesoscale human functional structures.•Recently, selective stripes were visualised in human visual ar-eas V2-V3 based on colour and disparity selectivity [1] anddifferences in temporal frequency sensitivity [2], respectively.•Although the spatial extent of those stripe-like structures maydepend on cortical depth to some degree, they approximatelyfollow a columnar arrangement penetrating uniformly the cor-tex [3].•However, when using a gradient-echo (GE) echo-planar imag-ing (EPI) sequence, the activation pattern may suffer from thewell-known bias due to draining veins, especially close to thepial surface [4].Introduction•Assessment whether spin-echo (SE) EPI, less influ-enced by spurious vasculature effects [5], improvesthe definition of colour-selective stripes across cor-tical depth in V2 compared to GE-EPI.• Stripe width was determined to estimate signalspecificity across cortical depth.ObjectivesExperimental design•One volunteer was invited to 5 scanning sessions at differ-ent days: 1 x MP2RAGE [6] plus standard retinotopy [7],4 x colour-selective stripe measurement (2 x GE-EPI, 2 xSE-EPI), see fig. 1.MRI data acquisition• 7 T whole-body MR scanner (MAGNETOM 7T, SiemensHealthineers, Erlangen, Germany).• 32 channel phased array head coil (NOVA Medical Inc.,Wilmington MA, USA).• For fMRI, 2D slices were acquired with 1 mm3 isotropic voxelsize covering early visual areas.•GE-EPI (TR = 3 s; TE = 26 ms; FA = 78◦; GRAPPA = 4;number of slices = 56), SE-EPI (TR = 3 s; TE = 32 ms;GRAPPA = 4; number of slices = 42).Analysis•A multi-run fixed effects GLM was performed using SPM12(contrast of interest: chromatic > achromatic).•No smoothing was applied to the data.•Cortex was segmented using SPM12 (for brain mask gen-eration) and FreeSurfer with manual pial surface correctionbecause of incomplete dura removal.• For cortical depth-dependent analysis, the cortex was auto-matically contoured into four layers (deep layer, lower middlelayer, upper middle layer, superficial layer) using the equi-volume depth model [8] implemented in CBS tools.•Contrast estimates were sampled from single layers andmapped onto the central surface mesh of the cortical surfacereconstruction.Chromatic stimulus Achromatic stimulus(7 min/run)Experimental design Differential paradigm with 2 condi-tions (moving chromatic and achromatic gratings; 24 s/block).Details can be found in [1].1Methodst-score1.3 5.0(a) GE-EPI (Sess. 1) (b) GE-EPI (Sess. 2) (c) GE-EPI (average) (d) SE-EPI (average)V1V2 V1V2 V1V2 V1V2Colour selectivity Thresholded t-maps (no correction for multiple comparisons) on the in-flated cortex of the left hemisphere. t-scores averaged across depth are depicted. (a)-(b) showestimates in single GE-EPI sessions, which demonstrates scan-rescan reliability. (c)-(d) showthe average over GE- and SE-EPI sessions, respectively. The typical stripe-like structure can beidentified in each map.2(a) (b) (c)Contrast estimates in a.u.(Session 1)Contrastestimatesina.u.(Session2) = 0:73GE-EPI-6 -4 -2 0 2 4 6 8 10 12-8-6-4-20246810Contrast estimates in a.u.(Session 1)Contrastestimatesina.u.(Session2) = 0:64SE-EPI-6 -4 -2 0 2 4 6 8 10 12-6-4-20246Contrast estimates in a.u.(GE-EPI)Contrastestimatesina.u.(SE-EPI) = 0:56-6 -4 -2 0 2 4 6 8 10 12 14 16-4-202468Reliability measure Vertex-to-vertex correlations within V2 of both hemispheres. Estimateswere taken from the deep layer. (a)-(b) show scan-rescan reliability and (c) illustrates repro-ducibility between sequences. Because of the spatial non-independence of neighbouring vertices,analysis was restricted to randomly selected 10% of vertices, cf. [1]. All correlations were sta-tistically significant at the p = 0.0001 level.31.35.0t-score(a) Deep layer (b) Lower middle layer (c) Upper middle layer (d) Superficial layerV1 V2CSV1 V2CSV1 V2CSV1 V2CS4Colour selectivity across depth Thresholded t-maps (no correction for multiple comparisons)on the flattened patch cut through the calcarine sulcus (CS) of the right hemisphere. (a)-(d)show the average over GE-EPI sessions through cortical depth. White arrowheads point toputative colour-selective stripes in ventral and dorsal parts of V2. Green arrowhead indicatesthe colour-selective area VO/V8 [9,10].(a) (b) (c)Meancontrastestimatesina.u.Deep layerLower middlelayerUpper middlelayerSuperficial layerGE-EPISE-EPI01234StripewidthinmmDeep layerLower middlelayerUpper middlelayerSuperficial layerGE-EPISE-EPI0123456Lag in mmNormalisedautocorrelationGE-EPISuperficial layerUpper middle layerLower middle layerDeep layer-40 -30 -20 -10 0 10 20 30 40-0.4-0.200.20.40.60.81Sensitivity and specificity (a) Mean contrast estimates within stripes in V2. (b) Mean widthof colour-selective stripes in V2. First, contrast estimates were sampled from 10 lines parallelto the V1/V2 border on each hemisphere. Stripe width was then defined as the width of thenormalised autocorrelation main peak at height indicated as dashed line in (c). Error bars markstandard error of the mean.5Results•The study demonstrates the feasibility of mapping colour-selective columns at different cortical depths using GE- andSE-EPI.•GE-EPI shows generally higher t-scores and a stronger depen-dence on cortical depth than SE-EPI.• Stripe width estimations are similar between sequences withloss of reliability in the superficial layer indicated by widerstripe patterns in line with blurring due to draining veins.•However, at deeper cortical layers, width estimations are com-parable to [1].•Overall, SE-EPI shows reduced sensitivity to the BOLD sig-nal without improved specificity for measuring the topology ofcortical columns throughout the cortex exemplified by colour-selective stripes in human V2.• Future work will extent this study by increasing sample size andconsidering more sequences (3D GE-EPI,“inverse-keyhole”3DGE-EPI and 3D-VASO [11]).DiscussionOHBM,Singapore,2018,Posternumber:1758References[1] Nasr S et al. J Neurosci 2016; 36:1841.[2] Dumoulin SO et al. Sci Rep 2017; 7:733.[3] Tootell RB et al. J Neurosci 1989; 9:2620.[4] Polimeni JR et al. Neuroimage 2010; 52:1334.[5] Yacoub E et al. Magn Reson Med 2003; 49:655.[6] Marques JP et al. Neuroimage 2010; 49:1271.[7] Sereno MI et al. Cereb Cortex 2013; 23:2261.[8] Waehnert M et al. Neuroimage 2014; 93:210.[9] Hadjikhani N et al. Nat Neurosci 1998; 1:235.[10] Lafer-Sousa R et al. J Neurosci 2016; 36:1682.[11] L. Huber et al. Neuron 2017; 96:1.

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Mapping colour-selective columns in V2 across cortical depth using GE- and SE-EPI

Mapping colour-selective columns in V2 across cortical depth using GE- and SE-EPI

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