Imaging Performance Analysis of Green Mussel Shell-Derived Hydroxyapatite as a Sustainable Material for Bone Phantom Fabrication

Abstract

Bone phantom is a testing tool in radiology used to mimic the radiological properties of human bone tissue, with hydroxyapatite (HA) as one of its key mineral components. In this study, HA was synthesized from green mussel shells (Perna viridis) through two different shell preparation methods, namely HA 1 produced by calcining the shells in whole (uncrushed) form and HA 2 produced by calcining the shells after they had been crushed into powder. The mussel shell powder was first characterized using an Atomic Absorption Spectrophotometer (AAS) to determine its Calcium Oxide (CaO) content, followed by X-Ray Diffraction (XRD) after the HA synthesis process to confirm the formation of the HA material. Each HA powder was mixed with rice bran at ratios of 1:1, 1:2, and 2:1 to fabricate bone phantom prototypes, which were subsequently evaluated through X-Ray Radiography and CT-Scan imaging. Radiographic images were analyzed to obtain the mean gray value, hereafter reported as Optical Density (OD), while CT images were analyzed to obtain Hounsfield Unit (HU) values; both were compared against the reference radiodensity range of human bone. AAS analysis showed that the CaO content of the green mussel shells was 30.89%, and XRD confirmed the presence of HA diffraction peaks in a semi-crystalline phase for both HA 1 and HA 2. The highest OD value, 142.76, was obtained from HA 1 (whole-shell calcination) at a 1:1 ratio and 40 kVp, while the highest HU value, 2180.67 HU, was obtained from HA 2 (crushed-shell calcination) at a 1:1 ratio and 80 kV, a value that falls within the Hounsfield range of cortical bone (+700 to +3000 HU). These results indicate that the 1:1 ratio produced the most bone-equivalent radiodensity for each respective HA type, supporting the potential of green mussel shell-derived hydroxyapatite as a low-cost, sustainable material for bone phantom fabrication. This study contributes a reproducible, low-cost protocol for converting an underutilized marine waste stream into a bone-equivalent phantom material, together with quantitative OD and HU benchmarks across HA-type, composition-ratio, and exposure-voltage combinations, providing an empirical basis for the wider adoption of biogenic hydroxyapatite phantoms in radiological quality assurance and medical physics education.