Investigation on the resolution of a micro cone beam CT scanner scintillating detector using Monte Carlo methods

The impact of several physical quantities on the spatial resolution of an X-ray scintillating pixel detector for a micro cone beam CT (µCBCT) is investigated and discussed. The XtremeCT from SCANCO Medical AG was simulated using the EGSnrc/EGS++ Monte Carlo (MC) framework and extensively benchmarked in a previous work. The resolution of the detector was determined by simulating a titanium knife-edge to obtain the edge spread function (ESF) and the modulation transfer function (MTF). Propagation of the scintillation light through the scintillator and its coupling into the fiber optics system was taken into account. The contribution of particles scattered in the main scanner components to the detector signal is very low and does not affect the spatial resolution of the detector. The resolution obtained from the energy deposition in the scintillator without any blurring due to the propagation of the scintillation light into the fiber optics array was 31 µm. By assuming isotropic light propagation in the scintillator, the resolution degraded to 360 µm. A simple light propagation model taking into account the impact of the scintillator's columnar microstructures was developed and compared with the MANTIS Monte Carlo simulation package. By reducing the width of the model's light propagation kernel by a factor of 2 compared to the isotropic case, the detector resolution can be improved to 83 µm, which corresponds well to the measured resolution of 86 µm. The resolution of the detector is limited mainly by the propagation of the scintillation light through the scintillator layer. It offers the greatest potential to improve the resolution of the µCBCT imaging system.

Muscle and Myotendinous Tissue Properties at the Distal Tibia as Assessed by High-Resolution Peripheral Quantitative Computed Tomography

High-resolution peripheral quantitative computed tomography (HR-pQCT) quantifies bone microstructure and density at the distal tibia where there is also a sizable amount of myotendinous (muscle and tendon) tissue (M_T); however, there is no method for the quantification of M_T. This study aimed (1) to assess the feasibility of using HR-pQCT distal tibia scans to estimate M_T properties using a custom algorithm, and (2) to determine the relationship between M_T properties at the distal tibia and mid-leg muscle density (MD) obtained from pQCT. Postmenopausal women from the Hamilton cohort of the Canadian Multicenter Osteoporosis Study had a single-slice (2.3 ± 0.5 mm) 66% site pQCT scan measuring muscle cross-sectional area (MCSA) and MD. A standard HR-pQCT scan was acquired at the distal tibia. HR-pQCT-derived M_T cross-sectional area (M_TCSA) and M_T density (M_TD) were calculated using a custom algorithm in which thresholds (34.22-194.32 mg HA/cm³) identified muscle seed volumes and were iteratively expanded. Pearson and Bland-Altman plots were used to assess correlations and systematic differences between pQCT- and HR-pQCT-derived muscle properties. Among 45 women (mean age: 74.6 ± 8.5 years, body mass index: 25.9 ± 4.3 kg/m²), M_TD was moderately correlated with mid-leg MD across the 2 modalities (r = 0.69-0.70, p < 0.01). Bland-Altman analyses revealed no evidence of directional bias for M_TD-MD. HR-pQCT and pQCT measures of M_TCSA and MCSA were moderately correlated (r = 0.44, p < 0.01). Bland-Altman plots for M_TCSA revealed that larger MCSAs related to larger discrepancy between the distal and the mid-leg locations. This is the first study to assess the ability of HR-pQCT to measure M_T size, density, and morphometry. HR-pQCT-derived M_TD was moderately correlated with mid-leg MD from pQCT. This relationship suggests that distal M_T may share common properties with muscle throughout the length of the leg. Future studies will assess the value of HR-pQCT-derived M_T properties in the context of falls, mobility, and balance.