Quadro t1000

A baseline CT scan (Philips Brilliance 64 CT scanner, Philips, Best, Netherlands) was used to obtain 3D data (slice thickness 0.67 mm, contiguous slices, reconstruction matrix 512 × 512).
The (2D) fluoroscopic images for registration were acquired with a mobile C-arm system (Philips Zenition 70, Philips, Best, Netherlands). The imaging settings were set to the spine protocol (variable kV, typical dose-level 0.408 mGy 20 cm PMMA) to achieve optimal image quality of the vertebrae, which was part of the regular software (version 5.1.7: IQ NA HC R5.1.7).
All imaging data files were transferred to a secured portable computer in Digital Imaging and Communications in Medicine (DICOM) format.
The non-invasive marker model consisted of a randomly applied pattern of prototype hybrid skin markers (radiopaque and optical), which were an update of previously used optical markers [14 (link)]. The update consisted of a radiopaque sphere added to the marker’s center to make them visible on fluoroscopy (Fig. 1).Fig. 1

Examples of the hybrid skin markers. a Fluoroscopic image capturing nine markers containing a radiopaque sphere, b nine markers applied to the skin

The 3D2D registration was performed offline by running image data through a prototype algorithm (Philips Healthcare, Best, the Netherlands) on a regular computer (Intel® Core™ i7-9750H processor, NVIDIA Quadro® T1000 graphics card).

The experiments were carried out on a laptop PC with Intel ${}^{\circledR }$ Core ${}^{™}$ i7-9750H CPU @ 2.60 GHz, 32 GB RAM, NVIDIA Quadro T1000 (4 GB) graphics card and Windows 10 Pro 64-bit operating system. The implementation was based on Python 3.8.6, with functions from dicom-parser 0.1.6 [47 ], NumPy 1.18.5 [48 (link)], Pandas 1.1.3 [49 ,50 (link)], pylidc 0.2.2 [51 (link),52 ], pynrrd 0.4.2 [53 ] and Py-Radiomics 3.0.1 [42 ,54 (link)]. For reproducible research purposes, all the code and settings are available on the following GitHub repository: https://github.com/bianconif/stability_radiomics_features_lung_ct, accessed on 3 July 2021.