Modeling Lung Architecture in the XCAT Series of Phantoms: Physiologically Based Airways, Arteries and Veins

Abstract

The purpose of this paper was to extend the extended cardiac-torso (XCAT) series of computational phantoms to include a detailed lung architecture including airways and pulmonary vasculature. Eleven XCAT phantoms of varying anatomy were used in this paper. The lung lobes and initial branches of the airways, pulmonary arteries, and veins were previously defined in each XCAT model. These models were extended from the initial branches of the airways and vessels to the level of terminal branches using an anatomically-based volume-filling branching algorithm. This algorithm grew the airway and vasculature branches separately and iteratively without intersecting each other using cylindrical models with diameters estimated by order-based anatomical measurements. Geometrical features of the extended branches were compared with the literature anatomy values to quantitatively evaluate the models. These features include branching angle, length to diameter ratio, daughter to parent diameter ratio, asymmetrical branching pattern, diameter, and length ratios. The XCAT phantoms were then used to simulate CT images to qualitatively compare them with the original phantom images. The proposed growth model produced 46369 ± 12521 airways, 44737 ± 11773 arteries, and 39819 ± 9988 veins to the XCAT phantoms. Furthermore, the growth model was shown to produce asymmetrical airway, artery, and vein networks with geometrical attributes close to morphometry and model based studies. The simulated CT images of the phantoms were judged to be more realistic, including more airways and pulmonary vessels compared with the original phantoms. Future work will seek to add a heterogeneous parenchymal background into the XCAT lungs to make the phantoms even more representative of human anatomy, paving the way towards the use of XCAT models as a tool to virtually evaluate the current and emerging medical imaging technologies.

Accuracy of registration algorithms in subtraction CT of the lungs: A digital phantom study

“…These were generated using the improved 4D extended cardiac‐torso (XCAT) anthropomorphic digital phantom (Duke University, Durham, NC, USA) at different inspiration levels and cardiac phases, in addition to other varying conditions like whole body displacement, different intravenous iodine concentration, presence or absence of beam hardening artifacts simulated by adding titanium pins in the spine, addition of nodules in the lungs, wedge‐shaped perfusion defects in the pulmonary parenchyma of the contrast‐enhanced image, and different noise level. This digital phantom provides a virtual model of patient anatomy and physiology including pulmonary vasculature and bronchopulmonary structures up to the terminal branches, without collision of structures . The phantom, based on ICRP Publication 89 data, is commonly used in imaging research due to the flexibility of its nonuniform rational basis spline (NURBS)‐based surface primitives, variation in anatomy, motion, and variable spatial resolution, that can be simulated.…”

“…The patient motion was modeled using 4D‐tagged magnetic resonance imaging data (cardiac motion) and 4D high‐resolution respiratory‐gated CT data (respiratory motion) . These advantages also make it ideal for evaluation of registration algorithms …”

“…This digital phantom provides a virtual model of patient anatomy and physiology including pulmonary vasculature and bronchopulmonary structures up to the terminal branches, without collision of structures. 12,13 The phantom, based on ICRP Publication 89 data, is commonly used in imaging research due to the flexibility of its nonuniform rational basis spline (NURBS)-based surface primitives, variation in anatomy, motion, and variable spatial resolution, that can be simulated. The patient motion was modeled using 4D-tagged magnetic resonance imaging data (cardiac motion) and 4D high-resolution respiratory-gated CT data (respiratory motion).…”

“…12 These advantages also make it ideal for evaluation of registration algorithms. 13 The XCAT phantom allows for the specification of more than 200 parameters, including contrast administration comparable to clinical practice, patient and scan characteristics, and respiratory and cardiac phase. This allows manipulation of the voxel values representing different tissues with enhanced attenuation due to the presence of intravenous-iodinated contrast agent.…”

Considerations for Using the Vasculature as a Coordinate System to Map All the Cells in the Human Body

“…The vascular system adapts to individual body size and shape, accounting for inter-individual variations [Paruchuri 2015, Abadi 2018]. It defines the shape of functional units in different organs, such as liver lobules, kidney glomeruli, and lung alveoli.…”