Table 1.
CT acquisition parameters of the 41 subjects analysed divided into Group 1 and Group 2.
Table 2.
Detailed information of ESP phantom scans with different configurations.
Fig 1.
Definition of VOIcut from CT scan slices.
(a) RP definition based on the Femur Head Centre and Knee Centre. (b) VOI definition based on RP and OP by removing the portion extending 5cm posteriorly from the RP. (c) VOIcut selection. The visualization of the CT scan was obtained from the data collected during the study, which is available at [42].
Fig 2.
Example of fitted distribution of the HU in the VOIcut, with the extracted peaks of air, adipose and muscle tissues.
The "pdf value" on the y-axis represents the probability density function value.
Fig 3.
Graphical overview of the study.
Upper panel: the calibration phantom was employed to calibrate the CT scans for Group 1 subjects so that reference density values for air, adipose, and muscle tissues could be computed. These reference density values were later employed to calibrate through a phantomless calibration procedure the CT images of Group 2 subjects. Phantom scans were also available to calibrate Group 2 subjects, so that the outcomes of the phantomless and phantom-based calibration methodologies could be compared. Lower panel: phantom-based calibrations of Group 2 subjects were also employed to compute reference values for air, adipose, and muscle tissues to assess potential effects of different CT acquisition parameters on the reference density values. In the figure, ρHA stands for the density of the phantom, f stands for the distribution of the HU in the VOIcut (pdf value), HUphantom and HUsubject stand for HU values extracted from the CT scan of the phantom and subject, respectively.
Table 3.
Reference equivalent mineral density values (in mg/cm3) of air, adipose and muscle tissues obtained for the Group 1 and for all 41 subjects.
Fig 4.
Distribution of element-wise relative differences in Young’s modulus between both calibration methods.
Violin plots showing the distributions of element-wise relative differences in Young’s modulus values between phantom-based and phantomless calibration for Group 2 subjects. The solid black line represents the mean value, while the blue solid line represents the median. Outliers, identified using the inter-quartile range method, have been excluded.
Fig 5.
Spatial distribution of relative differences between Young’s modulus values coming from phantom-based and phantomless calibrations.
Frontal plane is the mean frontal section from the anterior view of the femur.
Fig 6.
Distribution of point-to-point relative differences in superficial principal strains coming from both calibration methods.
Violin plots showing the distributions of the point-to-point relative differences computed on superficial tensile (a) and compressive (b) principal strain values between phantom-based and phantomless calibrations, considering all 28 simulated femur impact poses for each the 17 subjects in Group 2. The solid black line represents the mean, the blue solid line represents the median. Outliers, identified using the inter-quartile range, have been excluded.
Fig 7.
Linear regressions plots between phantom-based and phantomless calibrations-derived highest tensile and lowest compressive strains.
The highest superficial tensile (a) and the lowest superficial compressive (b) principal strains for each of the 28 simulated impact poses for each of 17 subjects contained in Group 2 (R2 > 0.99).