Optimisation of the air fraction correction for lung PET/CT: addressing resolution mismatch.

BACKGROUND: Increased pulmonary [Formula: see text]F-FDG metabolism in patients with idiopathic pulmonary fibrosis, and other forms of diffuse parenchymal lung disease, can predict measurements of health and lung physiology. To improve PET quantification, voxel-wise air fractions (AF) determined from CT can be used to correct for variable air content in lung PET/CT. However, resolution mismatches between PET and CT can cause artefacts in the AF-corrected image. METHODS: Three methodologies for determining the optimal kernel to smooth the CT are compared with noiseless simulations and non-TOF MLEM reconstructions of a patient-realistic digital phantom: (i) the point source insertion-and-subtraction method, [Formula: see text]; (ii) AF-correcting with varyingly smoothed CT to achieve the lowest RMSE with respect to the ground truth (GT) AF-corrected volume of interest (VOI), [Formula: see text]; iii) smoothing the GT image to match the reconstruction within the VOI, [Formula: see text]. The methods were evaluated both using VOI-specific kernels, and a single global kernel optimised for the six VOIs combined. Furthermore, [Formula: see text] was implemented on thorax phantom data measured on two clinical PET/CT scanners with various reconstruction protocols. RESULTS: The simulations demonstrated that at [Formula: see text] iterations (200 i), the kernel width was dependent on iteration number and VOI position in the lung. The [Formula: see text] method estimated a lower, more uniform, kernel width in all parts of the lung investigated. However, all three methods resulted in approximately equivalent AF-corrected VOI RMSEs (<10%) at [Formula: see text]200i. The insensitivity of AF-corrected quantification to kernel width suggests that a single global kernel could be used. For all three methodologies, the computed global kernel resulted in an AF-corrected lung RMSE <10%  at [Formula: see text]200i, while larger lung RMSEs were observed for the VOI-specific kernels. The global kernel approach was then employed with the [Formula: see text] method on measured data. The optimally smoothed GT emission matched the reconstructed image well, both within the VOI and the lung background. VOI RMSE was <10%, pre-AFC, for all reconstructions investigated. CONCLUSIONS: Simulations for non-TOF PET indicated that around 200i were needed to approach image resolution stability in the lung. In addition, at this iteration number, a single global kernel, determined from several VOIs, for AFC, performed well over the whole lung. The [Formula: see text] method has the potential to be used to determine the kernel for AFC from scans of phantoms on clinical scanners.

Hybrid energy and angle dispersive X-ray diffraction computed tomography.

Pixelated energy resolving detectors enable acquisition of X-ray diffraction (XRD) signals using a hybrid energy- and angle- dispersive technique, potentially paving the way for the development of novel benchtop XRD imaging or computed tomography (XRDCT) systems, utilising readily available polychromatic X-ray sources. In this work, a commercially available pixelated cadmium telluride (CdTe) detector, HEXITEC (High Energy X-ray Imaging Technology), was used to demonstrate such an XRDCT system. Specifically, a novel fly-scan technique was developed and compared to the established step-scan technique, reducing the total scan time by 42% while improving the spatial resolution, material contrast and therefore the material classification.

A multi-method assessment of 3D printed micromorphological osteological features.

The evaluation of 3D printed osteological materials has highlighted the difficulties associated with accurately representing fine surface details on printed bones. Moreover, there is an increasing need for reconstructions to be demonstrably accurate and reliable for use in the criminal justice system. The aim of this study was to assess the surface quality of 3D prints (n = 9) that presented with micromorphological alterations from trauma, taphonomy and pathology processes. The archaeological bones were imaged using micro-CT scanning and 3D printed with selective laser sintering (SLS) printing. A multi-method experimental approach subsequently identified: (1) the 3D printed bones to be metrically accurate to within 1.0 mm; (2) good representation of micromorphological surface features overall, albeit with some loss of intricate details, depths, and fine textures that can be important for visual processing; (3) five of the nine 3D printed bones were quantitatively scored as accurate using the visual comparison method; and, (4) low mesh comparison distances (± 0.2 mm) between the original models and the digitised 3D print models. The findings offer empirical data that can be used to underpin 3D printed reconstructions of exhibits for use in courts of law. In addition, an adaptable pathway was presented that can be used to assess 3D print accuracy in future reconstructions.

Correlation of X-ray diffraction signatures of breast tissue and their histopathological classification.

This pilot study examines the correlation of X-ray diffraction (XRD) measurements with the histopathological analysis of breast tissue. Eight breast cancer samples were investigated. Each sample contained a mixture of normal and cancerous tissues. In total, 522 separate XRD measurements were made at different locations across the samples (8 in total). The resulting XRD spectra were subjected to principal component analysis (PCA) in order to determine if there were any distinguishing features that could be used to identify different tissue components. 99.0% of the variation between the spectra were described by the first two principal components (PC). Comparing the location of points in PC space with the classification determined by histopathology indicated correlation between the shape/magnitude of the XRD spectra and the tissue type. These results are encouraging and suggest that XRD could be used for the intraoperative or postoperative classification of bulk tissue samples.

Structural characterization of titanium-doped Bioglass using isotopic substitution neutron diffraction.

Melt quenched silicate glasses containing calcium, phosphorus and alkali metals have the ability to promote bone regeneration and to fuse to living bone. Of these glasses 45S5 Bioglass® is the most widely used being sold in over 35 countries as a bone graft product for medical and dental applications; particulate 45S5 is also incorporated into toothpastes to help remineralize the surface of teeth. Recently it has been suggested that adding titanium dioxide can increase the bioactivity of these materials. This work investigates the structural consequences of incorporating 4 mol% TiO(2) into Bioglass® using isotopic substitution (of the Ti) applied to neutron diffraction and X-ray Absorption Near Edge Structure (XANES). We present the first isotopic substitution data applied to melt quench derived Bioglass or its derivatives. Results show that titanium is on average surrounded by 5.2(1) nearest neighbor oxygen atoms. This implies an upper limit of 40% four-fold coordinated titanium and shows that the network connectivity is reduced from 2.11 to 1.97 for small quantities of titanium. Titanium XANES micro-fluorescence confirms the titanium environment is homogenous on the micron length scale within these glasses. Solid state magic angle spinning (MAS) NMR confirms the network connectivity model proposed. Furthermore, the results show the intermediate range order containing Na-O, Ca-O, O-P-O and O-Si-O correlations are unaffected by the addition of small quantities of TiO(2) into these systems.

Ti K-edge XANES study of the local environment of titanium in bioresorbable TiO2-CaO-Na2O-P2O5 glasses.

Ti K-edge XANES (X-ray absorption near edge structure) spectroscopy has been used to study the local coordination of titanium in biocompatible and bioresorbable TiO2-CaO-Na2O-P2O5 glasses. Both conventional melt-quenched glasses of composition (TiO2)x(CaO)0.30(Na2O)0.20-x(P2O5)0.50, where x = 0.01, 0.03 and 0.05, and sol-gel derived (TiO2)0.25(CaO)0.25(P2O5)0.50 glass have been studied. The results show that in all the materials studied, titanium is surrounded by an octahedron of oxygen atoms. Further analysis reveals that the TiO6 site in the amorphous samples is not heavily distorted relative to that in rutile, anatase or CaSiTiO5. The spectra from the (TiO2)0.25(CaO)0.25(P2O5)0.50 sol-gel samples reveal greater distortion in the TiO6 site in the dried gel compared to the heat-treated sol-gel glass. The XANES spectra from melt-quenched glass samples soaked in distilled water for various times do not shown any evidence of degradation of the titanium site over periods of up to 14 days.