On the challenges of greyscale-based quantifications using X-ray computed microtomography

3D-imaging and quantitative assessment for size-related penetration of HfO2 nanoparticles in breast cancer tumor by synchrotron radiation microcomputed tomography

The development of quantitative analytical methods to assess the heterogeneous distribution and penetration of nanodrugs in solid tumors is of great importance for anticancer nanomedicine. Herein, Expectation-Maximization (EM) iterate algorithm and threshold segmentation methods were used to visualize and quantify the spatial distribution patterns, penetration depth and diffusion features of two-sized hafnium oxide nanoparticles (s-HfO₂ NPs in 2 nm and l-HfO₂ NPs in 50 nm sizes) in mouse models of breast cancer using synchrotron radiation micro-computed tomography (SR-μCT) imaging technique. The three-dimensional (3D) SR-μCT images were reconstructed based on the EM iterate algorithm thus clearly displayed the size-related penetration and distribution within the tumors after intra-tumoral injection of HfO₂ NPs and X-ray irradiation treatment. The obtained 3D animations clearly show that a considerable amount of s-HfO₂ and l-HfO₂ NPs diffused into tumor tissues at 2 h post-injection and displayed the obvious increase in the tumor penetration and distribution area within the tumors at day 7 after combination with low-dose X-ray irradiation treatment. A thresholding segmentation for 3D SR-μCT image was developed to assess the penetration depth and quantity of HfO₂ NPs along the injection sites in tumors. The developed 3D-imaging techniques revealed that the s-HfO₂ NPs presented more homogeneous distribution pattern, diffused more quickly and penetrated more deeply within tumor tissues than the l-HfO₂ NPs did. Whereas, the low-dose X-ray irradiation treatment greatly enhanced the wide distribution and deep penetration of both s-HfO₂ and l-HfO₂ NPs. This developed method may provide quantitative distribution and penetration information for the X-ray sensitive high-Z metal nanodrugs in the cancer imaging and therapy.

A high-resolution study of PM2.5 accumulation inside leaves in leaf stomata compared with non-stomatal areas using three-dimensional X-ray microscopy

Plant leaves retain atmospheric particulate matter (PM) on their surfaces, helping PM removal and risk reduction of respiratory tract infection. Several processes (deposition, resuspension, rainfall removal) can influence the PM accumulation on leaves and different leaf microstructures (e.g., trichomes, epicuticular waxes) can also be involved in retaining PM. However, the accumulation and distribution of PM on leaves, particularly at the stomata, are unclear, and the lack of characterization methods limits our understanding of this process. Thus, in this study, we aimed to explore the pathway through which PM_2.5 (aerodynamic diameter ≤ 2.5 μm) enters plant leaves, and the penetration depth of PM_2.5 along the entry route. Here, an indoor experiment using diamond powder as a tracer to simulate PM_2.5 deposition on leaves was carried out. Then, the treated and non-treated leaves were scanned by using three-dimensional (3D) X-ray microscopy. Next, the grayscale value of the scanned images was used to compare PM_2.5 accumulation in stomatal and non-stomatal areas of the treated and non-treated leaves, respectively. Finally, a total PM_2.5 volume from the abaxial epidermis was calculated. The results showed that, first, a large amount of PM_2.5 accumulates within leaf stomata, whereas PM_2.5 does not accumulate at non-stomatal areas. Then, the penetration depth of PM_2.5 in stomata of most tree species was 5-14 μm from the abaxial epidermis. For the first time, 3D X-ray microscope scanning was used to confirm that a pathway by which PM_2.5 enters the leaves is through the stomata, which is fundamental for further research on how PM_2.5 translocates and interacts with tissues and cells in leaves.