Table 1.
Literature summary of the soft tissue artefact of different body locations.
Figure 1.
Acrylic glass plate with five MRI visible markers (paintballs: M1, M2, M3, M4, MC, with distances of M1–M2 = 180 mm, M2–M3 = 70 mm) and two lamb vertebrae, shown in the forward tilted position (45°).
Figure 2.
Measurement set-up including (a) the “IfB-marker-set” of the trunk and the pelvis (for explanation of abbreviations and for segmental allocation, see Table 2) and (b) the three analysed seating positions with an example of a corresponding MR image including a local coordinate system of a vertebral body.
Upright seating position: lower spine had partial contact with the backrest, and the whole upper body was in an upright position. Flexed seating position: upper body was tilted about 30° forward and supported on a bar, while the arms were rested on their lap. Extended seating position: the subject's bottom was pushed approximately 20 cm forward and the head was supported by the backrest. (from left to right).
Table 2.
Marker placement, segment allocation and abbreviations.
Table 3.
Direction-related (rx, ry, rz) mean marker artefact (mean) and the absolute values (|r|) with their standard deviations (SD) of the lumbar and thoracic skin markers in the flexed and extended positions.
Figure 3.
Scatter diagram of the lumbar (a) and thoracic curvature angle (b) in the upright (circle), flexed (triangle) and extended positions (star).
The x-axis represents the values calculated from the markers, and the y-axis from the vertebral bodies. The crosses show the open MRI's measurement uncertainty of the curvature angles calculated from the markers (x-axis) and calculated from the vertebral bodies (y-axis).
Figure 4.
Range of lumbar (a/b) and thoracic (c/d) curvature angle of the subjects, calculated using the vertebral bodies (black) and the skin markers (hatched).
The range was defined from the upright to the flexed (a/c) and to the extended positions (c/d).
Table 4.
Mean (SD) lumbar (αlumbar) and thoracic curvature angle (αthoracic) in the upright, flexed and extended sitting positions calculated with the vertebral bodies and the skin marker, as well as the mean differences (SD; RMSE) between the values from the skin marker and the vertebral bodies.