Gold Nanoparticles for X-ray Microtomography of Neurons.

Commonly used methods to visualize the biological structure of brain tissues at subcellular resolution are confocal microscopy and two-photon microscopy. Both require slicing the sample into sections of a few tens of micrometers. The recent developments in X-ray microtomography enable three-dimensional imaging at sub-micrometer and isotropic resolution with larger biological samples. In this work, we developed and compared original microtomography methods and staining protocols to improve the contrast for in vitro mouse neuron imaging. Using Golgi's method to stain neurons randomly, we imaged the whole set of mouse brain structures. For specific and nonrandom neuron labeling, we conjugated 20 nm gold nanoparticles to antibodies used in the immunohistochemistry (IHC) method, using anti-NeuN to label specifically neuronal nuclei. We applied an original subtraction dual-energy method for microtomography in the vicinity of the Au L-III absorption edge and compared image reconstructions to confocal microscopy images acquired on the same samples. The results show the possibility to characterize the 3D entire brain structure of mice. They demonstrated a high contrast and neuron detection improvement by applying the dual-energy method coupled to IHC staining.

Detective quantum efficiency for photon-counting hybrid pixel detectors in the tender X-ray domain: application to Medipix3RX.

Synchrotron-radiation-based X-ray imaging techniques using tender X-rays are facing a growing demand, in particular to probe the K absorption edges of low-Z elements. Here, a mathematical model has been developed for estimating the detective quantum efficiency (DQE) at zero spatial frequency in the tender X-ray energy range for photon-counting detectors by taking into account the influence of electronic noise. The experiments were carried out with a Medipix3RX ASIC bump-bonded to a 300 µm silicon sensor at the Soft X-ray Spectroscopy beamline (D04A-SXS) of the Brazilian Synchrotron Light Laboratory (LNLS, Campinas, Brazil). The results show that Medipix3RX can be used to develop new imaging modalities in the tender X-ray range for energies down to 2 keV. The efficiency and optimal DQE depend on the energy and flux of the photons. The optimal DQE values were found in the 7.9-8.6 keV photon energy range. The DQE deterioration for higher energies due to the lower absorption efficiency of the sensor and for lower energies due to the electronic noise has been quantified. The DQE for 3 keV photons and 1 × 10(4) photons pixel(-1) s(-1) is similar to that obtained with 19 keV photons. Based on our model, the use of Medipix3RX could be extended down to 2 keV which is crucial for coming applications in imaging techniques at modern synchrotron sources.

Computed tomographic metal artifact reduction for the detection and quantitation of small features near large metallic implants: a comparison of published methods.

Computed tomographic imaging of tissue surrounding metallic implants is often limited by metal artifacts. This paper compares 3 existing metal artifact reduction techniques that are based on segmentation of metal-affected regions in native images, followed by reprojection of segmented areas into original Radon space, removal of metal trace(s), and renewed reconstruction: Detector row-wise linear interpolation, 2-dimensional interpolation, and combination of row-wise linear interpolation and adaptive filtering. For each method, improvements of CT number accuracy and signal-noise as well as contrast-noise ratios near the prosthesis and in the image periphery over the values found for native images were evaluated in a phantom experiment simulating osteolytic bone lesions of different size and density around a Chrome-Cobalt hip prosthesis stem. Improvement in diagnostic usability was evaluated as lesion detectability by size. Quantitative and qualitative results showed that the linear interpolation and the combination method removed the artifacts most effectively. The mean accuracy error over different regions of interest placed in the direct vicinity of the metal and in the periphery of the object decreased 10-fold with linear interpolation. These methods increased contrast-noise ratio up to 68% of that measured on artifact-free images for the least dense lesion. Qualitatively, the linear interpolation and the combination method improved the lesion detectability and enabled differentiation of different lesion densities. However, in proximity to the stem, some artifacts remained for all methods. We conclude that published algorithms for metal artifact reduction substantially improve image quality for CT imaging of a metallic object and may be adequate for quantitative measurements except for the direct vicinity of the metallic object.