MAESTRO thorax phantom rib motion mechanism: (a) 3D CT study at exhale showing the shaped Perspex frame, denoted “P,” onto which the pivots are fixed; (b) CAD diagram of the thorax illustrating the motion for ribs 3-4 and 15-16. The ribs, attached to the base of the frame (small black discs), rotate about the pivots (large black discs) due to the linear motion applied in the SI direction (see c). The dashed lines represent the centre position and the plain lines represent the exhale position. (c) Bottom view of the phantom showing the Perspex frame moved by a stepper motor, denoted M in (d), through a belt and screw mechanism to convert rotational to translational motion. (d) Phantom with infrared markers tracked by the VICON Nexus system to characterize the ribs motion.
Phantom inserts: (a) 3D slide system attachment for lung inserts (1), ionization chamber insert (2), inserts for 5 cm diameter film (3,4); (b) wax blocks for TLDs (5–7) or ionization chamber (8).
2D repeatability of the slider motion for AP and SI using a sinusoidal waveform with period 6.3 s, SI amplitude 14 mm, and AP amplitude 12 mm over three successive cycles c1, c2, and c3.
Nonlinear relationship between the signal sent to the stepper motor to move the ribs and the main rib motion in SI: (Top) normalized input trajectory sent to the rib motor drive system; (bottom) resulting position measured by position sensor LISP P 103.
Rib cage motion linearity and repeatability for markers located in S15-16 (left column) and R15 (right column), see Fig. 1(a) . The correlation between SI and AP motion increases with the amplitude of motion and depends on the shape of the fixed plate supporting the pivots around which the ribs rotate. The location of the marker R15 near the pivot mechanism results in smaller amplitudes than observed for S15-16.
(a) Irregular signal of varying period, amplitude, and frequency generated by the phantom and measured (30 Hz sampling) at point S15-16 using the VICON system (http://www.vicon.com/) for three successive repetitions (c1-c3). (b)–(d) Extracts from the VERO 4D modelling module (preclinical version) showing (a) motion correlation between external (cyan/light grey) and internal markers (orange/dark grey). (b) External reflective markers located on the MAESTRO thorax phantom; (c) Fiducial marker located on ionization chamber insert monitored with kV-X-ray.
Effect of rib motion on the area enclosed within the skin of the phantom: “○” and “+” represent the areas of the polygons obtained by contouring each CT image. The area enclosed within the outline of the CT images at inhale (bottom right) and exhale (bottom left) correspond to the points indicated by “×” and “*” (top). The different densities used to manufacture cartilage, ribs, and spine are clearly identifiable together with the Perspex frame used to move the ribs.
Range of motion of the rib cage for sensor location indicated in Fig. 1(d) .
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