Nondestructive Microstructural Analysis of Porous Bioceramics by Microfocus X-ray Computed Tomography (μCT): A Proposed Protocol for Standardized Evaluation of Porosity and Interconnectivity Between Macro-pores

Microfocus X-ray computed tomography (μCT) has now become widely available for the nondestructive evaluation of porous bioceramics suitable for use as a bone substitute in orthopedic surgery. As part of an official Japanese working committee, we recently participated in the preparation of a proposed standard protocol for the quantitative μCT analysis of porous bioceramics sent to the International Organization for Standardization (ISO). In this protocol, the recommended basic conditions for analysis were [field of view (XY plane): 3.0 mm, spatial resolution: 6 μm/pixel (or the closest minimal values available for both parameters on a particular μCT system), matrix size: 512 pixels], and we have now further determined the optimal values for more detailed parameters (e.g., threshold determination). To validate the utility of the complete protocol, three different types of ceramic sample [a ceramic of β-tricalcium phosphate (β-TCP) and two types of hydroxyapatite (HAp) with different porosities] were evaluated with three different types of cone-beam μCT scanner (the Shimadzu SMX-100CT, Shimadzu inspeXio-90CT, and Skyscan-1174 scanners). Acquired images were quantified using 3D-reconstruction software, VGStudio MAX (version 1.2). After comparing data obtained from these three μCT scanners, we have found that determinations of both porosity and pore-interconnectivity were very similar from one system to the other although the total number of measured pores did vary between scanners. The present data indicate that our protocol for μCT analysis is reliable enough to quantify the porosity and interconnectivity of porous bioceramics and would therefore facilitate both large-scale screening and quality control of porous bioceramic samples.