Fig 1.
Computed tomography (CT) image showing the reconstructed field of view (36 cm diameter).
Internal calibration regions of interest (ROIs) (air, muscle, adipose, bone, blood) were selected in the axial plane. The scan included various tissue samples, a custom sucrose water phantom, and two traditional bone phantoms (Bone Density Calibration Phantom BDC-6, QRM GmbH; Model 3 CT Calibration Phantom, Mindways Inc.). The (hydroxyapatite) HA bone phantom was used to validate the sucrose water phantom (S1 Fig). A) Axial slice including cortical bone, blood, one of the ten muscle samples, and the sucrose water phantom. B) Axial slice including adipose, air, and two of the ten muscle samples. Note that the ten muscle samples were all included in the scan, although they are not all visible in the slices shown.
Fig 2.
The muscle samples were scanned at five different positions within the scanner bore (70 cm diameter): left, right, top, bottom, and centre. The position of the samples was altered by adjusting the table positioning. Note that the scan setup was approximately 19 cm in height and could therefore be moved into different positions by adjusting table positioning.
Fig 3.
Bland-Altman plots comparing calibration methods.
Bland-Altman plots comparing the differences between internal derived muscle density values and reference sucrose water phantom derived muscle density values (n = 10 muscle samples). Different combinations of regions of interest (ROIs) for the internal calibration method are represented in different colours. The mean differences are shown as solid lines and 95% limits of agreement are shown as dashed lines. A) Bland-Altman plot with all tested internal calibration ROI combinations. B) Bland-Altman plot with two internal calibration ROI combinations (air, adipose; air, blood).
Fig 4.
Regression plot comparing calibration methods.
Regression plot comparing the muscle density values (n = 10 muscle samples) derived from the internal calibration method and the reference sucrose water phantom method. Solid line indicates regression line, dashed line indicates the line of unity.
Fig 5.
Boxplot comparing coefficient of variation (CV) values.
Coefficient of variation (CV) for muscle density (n = 10 muscle samples) values across different two scan protocols and five scan positions. The left boxplot represents native Hounsfield units (HU). Muscle density values were derived from the reference sucrose water phantom calibration method (middle boxplot) and the internal calibration method (right boxplot). Each box extends from the 25th percentile to the 75th percentile of the distribution of the respective values. The horizontal lines within each box denote median values and the vertical lines outside the box denote the minimum and maximum values.