private double _getMaxRadius(byte[][] array, Point center)
    {
      // Calculate the boundary points. In order to calculate North point (the 
      // point on the north edge of brain ), a group of pixels will be 
      // identified first, then the center of the group will be computed and 
      // used as the North point.
      int MIN_GROUP_NUM = 1;
      Point north = _getNorth(array,MIN_GROUP_NUM );
      Point south = _getSouth(array,MIN_GROUP_NUM );
      Point west = _getWest(array, MIN_GROUP_NUM);
      Point east = _getEast(array, MIN_GROUP_NUM);  
      double dist_N = center.getY() - north.getY();
      double dist_S = south.getY() - center.getY();
      double dist_W = center.getX() - west.getX();
      double dist_E = east.getX() - center.getX();
      double r = 0;

      if(dist_N>dist_S && dist_N>dist_W && dist_N>dist_E) r = dist_N;
      else if (dist_S>dist_N && dist_S>dist_W && dist_S>dist_E) r = dist_S;
      else if (dist_W>dist_N && dist_W>dist_S && dist_W>dist_E) r = dist_W;
      else r = dist_E;
      return r;
    }