Journal Article Zernike phase contrast full-field X-ray microscopy nanotomography 1HG84L3525 FFPE lung tissue Formaldehyde Sensor3D model U-Net model X-ray nanotomography air artifact suppression computer-aided image segmentation conditional GANs deep learning denoising human chest phantom image quality in situ experiments lacuna-canalicular network machine learning near-field holography near-field ptychography phase contrast phase contrast micro-CT propagation based imaging rapid phase contrast CT single-photon-counting detector time resolution virtual histology