ohif-viewer/Packages/viewerbase/client/components/studyBrowser/thumbnails/thumbnails.js

Template.thumbnails.helpers({
    thumbnails: function() {
        var study = this;
        var stacks = createStacks(study);
        
        var array = [];
        stacks.forEach(function(stack, index) {
            array.push({
                thumbnailIndex: index,
                stack: stack
            });
        });
        return array;
    }
});