In an embodiment, a method of non-destructively testing a polycrystalline diamond (“PCD”) element includes providing a PCD element including a plurality of bonded diamond grains defining a plurality of interstitial regions, at least a portion of the plurality of interstitial regions including one or more interstitial constituents disposed therein. The method further includes exposing the PCD element to neutron radiation from a neutron radiation source, receiving a portion of the neutron radiation that passes through the PCD element, and determining at least one characteristic of the PCD element at least partially based on the portion of the neutron radiation received. For example, the at least one characteristic may be the presence and distribution of metal-solvent catalyst, residual metal-solvent catalyst, an infiltrant, residual infiltrant, or other interstitial constituents within a PCD element.