How can I find a tile by coordinates?

CesiumJS
1

I need to get a reference on a quadtreeTile that is under my current camera position. First I do is:

const { position } = viewer.scene.camera;
const cartographic = Cesium.Cartographic.fromCartesian(position);
const tile = new Cesium.GeographicTilingScheme().positionToTileXY(cartographic, level);

This way, I get position (x, y) of my desired tile.
How can I use this data to get a reference on a quadtreeTile from a viewer?