An open-source CT texture phantom for radiomic imaging studies: Design, manufacture, and initial evaluation

The lack of standardized, reproducible, and publicly available reference objects limits the interpretability and reproducibility of radiomic imaging studies across institutions. Current handcrafted phantoms lack the precision, reproducibility, and accessibility required for large-scale, multi-center validation studies.

This work presents the design, manufacture, and initial evaluation of an open-source modular CT texture phantom intended as a reproducible, accessible platform for quantitative imaging research.

A modular phantom system was designed comprising an epoxy-filled cylindrical body and eight cavities for interchangeable 3D-printed texture inserts. The inserts utilized mathematically defined geometric primitives (e.g., periodic rod lattices, and random shape distributions) to provide standardized and reproducible printable objects. The design files for the phantom body and inserts were released in the public domain. Initial evaluation of the phantom body and inserts was done by manufacturing three copies of the phantom body and four sets of the inserts and then performing four assessments: (a) phantom body uniformity quantified through intra- and inter-phantom HU evaluations; (b) texture insert reproducibility based on an evaluation of the intraclass correlation coefficient (ICC) and coefficient of variation (CV) of radiomic feature values across insert replicates; (c) evaluating that the set of inserts provide non-redundant texture stimuli by performing a principal component analysis (PCA) on radiomic features extracted from each insert; and (d) evaluating the sensitivity of inserts to CT imaging protocol variation across two dose levels and three reconstruction kernels.

The manufacturing pipeline demonstrated high intra- and inter-phantom uniformity across all four phantom bodies (<5 HU). The texture inserts demonstrated exceptional reproducibility of radiomic features across independent manufacturing runs with a ICC > 0.999 both across insert set prints and between slices. The PCA demonstrated that the set of inserts provided distinct texture stimuli. The protocol variation investigation demonstrated that the inserts showed anticipated variation in texture-based features across CT dose levels and reconstruction kernels.

We present an open-source phantom design and manufacturing approach capable of producing high-fidelity, reproducible reference objects for radiomic imaging studies using consumer-grade equipment and low-cost materials. The public domain release of design files removes licensing barriers and enables any research group to replicate, extend, and share phantom designs, supporting standardized phantom-based investigation of radiomic feature behavior across institutions.