Lifelike and Deformable Lung Phantoms for 4DCT Imaging: A Three-Dimensional Printing Approach.

Respiratory motion phantoms can be used for evaluation of CT imaging technologies such as motion artifact reduction algorithms and deformable image registration. However, current respiratory motion phantoms do not exhibit detailed lung tissue structures and thus do not provide a realistic testing environment. This paper presents PixelPrint^4D, a method for 3D-printing deformable lung phantoms featuring highly realistic internal structures, suitable for a broad range of CT evaluations, optimizations, and research. The phantom in this study was designed with a patient 4DCT as a reference and 3D-printed using an extended version of the PixelPrint method for developing patient-specific CT phantoms. A flexible thermoplastic polyurethane (TPU) 3D-printing material was used, which produced regions with attenuation between -840 and -48 Hounsfield units (HU). A linear compression device was then designed and used to compress the phantom in the superior-inferior (SI) direction, and the phantom was scanned at different compression levels matched to the diaphragm displacements measured on the reference patient 4DCT. Deformable image registration (DIR) was performed, and motion vector fields were obtained for both patient and phantom images. SI displacements of selected features in the lung had mean errors of 0.5 mm difference from the patient, or less than the reconstructed slice thickness. In conclusion, the deformable lung phantom developed in this study exhibits realistic lung structures and deformation characteristics under compression, indicating potential for advancing more lifelike respiratory motion phantoms.