Return Physical Material Usage

Does anyone know of a method to determine if a PhysicalMaterial is used in the current part?

I have
Dim LocalMaterials()As PhysicalMaterial = displaypart.MaterialManager.PhysicalMaterials.GetUsedMaterials

but this return materials that are used in components as well as displayPart. The Manage Materials windows differentiates between used, un-used, and used in components. I just can't seem to locate a method to get this information.