Fig. 7.

Axial-plane needle artifact position error for the 15 tested needle orientations. The plots show the axial plane difference between the center of the titanium needle void and the center of the glass needle void for all axial image slices physically intersecting the needles. The needle locations are physically identical, but the titanium needle image void is displaced with respect to the actual needle position that is given by the glass rod. The rows represent needle tilt angles of (from top to bottom) +18°, +28°, and +38°. The columns represent needle rotation angles of −30°, −15°, 0°, +15°, and +30°. ‘delta X’ and ‘delta Y’ represent R (right) and A (anterior) coordinate directions in scanner coordinates, respectively. ‘○’ represents the error value from manually located artifact center position, and ‘×’ represents that from fitted line as seen in Fig. 5.