In equine medicine, assisted bone regeneration, including use of biomaterial substitutes like hydroxyapatite (HAP), is crucial for addressing bone defects. To follow-up on the outcome of HAP-based bone defect treatment, the advancement in quantified diagnostic imaging protocols is needed. This study aimed to quantify and compare the radiological properties of the HAP graft and natural equine bone using Magnetic Resonance (MR) and Computed Tomography (CT), both Single (SECT) and Dual Energy (DECT). SECT and DECT, allow for the differentiation of three HAP grain sizes, by progressive increase in relative density (RD). SECT, DECT, and MR enable the differentiation between natural cortical bone and synthetic HAP graft by augmentation in Effective Z and material density (MD) in HAP/Water, Calcium/Water, and Water/Calcium reconstructions, alongside the reduction in T2 relaxation time. The proposed quantification provided valuable radiological insights into the composition of HAP grafts, which may be useful in follow-up bone defect treatment. In equine medicine, there is a need for advanced strategies for assisted bone regeneration, particularly for treating bone diseases like subchondral cystic lesions (SCLs). One strategy involves filling bone defects with biomaterial substitutes like hydroxyapatite (HAP). This study aimed to quantify and compare the radiological properties of HAP grafts and natural equine bone using Single Energy Computed Tomography (SECT), Dual Energy Computed Tomography (DECT), and Magnetic Resonance (MR). Three HAP types with different grain sizes were combined with equine blood or bone marrow and imaged in a two-stage experiment. The first stage investigated grain size-dependent changes, while the second stage tested the similarity to natural bone. SECT (A), DECT (B), and MR (C) images were then quantified. This protocol provided valuable insights into the composition of HAP grafts, which may be useful in follow-up bone defect treatment. Display omitted