Angular JS: JSON data is not getting displayed in ng-Grid

I have created MVC 4.0 app using Web API which returns data in JSON format (I am serializing object to json using NewtonSoft.Json) and trying to bind data in ng-Grid. I am receiving data in following format:

"[{\"Name\":\"FIRST_NAME\",\"Value\":\"FIRST_NAME\"},{\"Name\":\"CURRENT_DATE_TIME\",\"Value\":\"CURRENT_DATE_TIME\"},{\"Name\":\"CLIENTID\",\"Value\":\"CLIENTID\"},{\"Name\":\"CALLMODE\",\"Value\":\"CALLMODE\"}, {\"Name\":\"new 321\",\"Value\":null}]"

When i tried to assign same to data: of ng-Grid, each char populated on different row. following is the javascript i have written:

var guidesRespApp = angular.module('guidesRespApp', ['ngGrid']);

//Get Data from restful API.
guidesRespApp.controller('MyCtrl', function ($scope, $http) {
    $http.get('/api/datadictionary').success(function (thisdata) {
            $scope.myData  =  thisdata;
    });

     $scope.filterOptions = {
        filterText: '',
        useExternalFilter: true,
    };


    //Setting grid options
    $scope.gridOptions = {
      data: 'myData',
      multiSelect: true,
      filterOptions: { filterText: '', useExternalFilter: false },
      enableRowReordering: false,
      showGroupPanel: false,
      maintainColumnRatios: false,
      groups: [],
      showSelectionCheckbox: true,
      showFooter: true,
      enableColumnResize: true,
      enableColumnReordering: true
    };


//    $scope.totalFilteredItemsLength = function() {
//        //return self.filteredRows.length;
//        };

});

If manually assigned like below, data is getting displayed in grid:

$scope.myData = [{"Name":"FIRST_NAME","Value":"FIRST_NAME"},{"Name":"CURRENT_DATE_TIME","Value":"CURRENT_DATE_TIME"},{"Name":"CLIENTID","Value":"CLIENTID"},{"Name":"CALLMODE","Value":"CALLMODE"}];

can anyone please help me to understand how to fix it? Also i wanted to display count of filtered items when i key in values in filte