Fluke 76-908 - Manual (Page 15)

Operation
Tests with 3D Resolution and Slice (3DRAS) Phantom
2
2-5
direction) is measured and related to the slice position. For a 45° ramp, the distance from a centered
reference pin to the slice profile midpoint will be equal to the point of the ramps located at the isocenter.
All measurements should be made along the line made up of the magnet isocenter and the centers of the
imaging planes.
Comparison of external position marker should generally agree with the actual slice position within +2
mm. Slice separation disagreement should typically be less than 20% of the total slice separation or
whichever is greater.
2.3.6 Example Images
Figures 2-1 through 2-12 represent examples of images obtained using the phantom in a 1.5 T MR
system.
Figure 2-1 is an axial image with imaging parameters of TR=60 msec, TE=22 msec and slice thickness of
3 mm. This axial image from a body coil shows resolution holes of 2 mm, 1 mm, and 0.75 mm well
resolved. There are two sets of holes shown in vertical and horizontal directions. The resolution image
can be viewed in a zoom mode. Thin vertical lines from the resolution pin within two black blocks are
placed in other orientations and have no meaning in axial orientation.
Figure 2-1.
On the right and left-hand sides of the phantom image two sets of horizontal short lines are shown. They
represent the slice thickness image of hot ramps sandwiched between two cold ramps. The thinner set is
from the 1 mm ramp and the thicker set comes from the 2 mm ramp. A set of two crossed ramps are used
as shown in Figure 1-4.
It should also be noted that the gap between the slice thickness lines on the left side of the figure is larger
than that on the right, indicating that the phantoms were not placed properly in the MRI system. In a
proper setting the gaps should be identical on both sides.