Fluke Biomedical 76-903 - Manual (Page 9)

Theory of Operation
Omni Directional Application
3
3-1
Section 3
Theory Of Operation
3.1 Omni Directional Application
Since MR images are obtained not only in axial but also sagittal and coronal orientation, the phantom is
designed to be placed in all three directions. The selection of inserts, their sizes and arrangements are
made to obtain the maximum amount of imaging information in any orientation in a single scan.
3.2 Concentric Conical Rings Section
The concentric conical rings are machined by cutting out a circular groove at an angle of 45°, as shown
(Figure 3-1).
Figure 3-1. Outside diameter, 9, Number of segments, 4
The conical section can provide the following information by simple visual inspection:
• Slice thickness uniformity
• Aspect ratio
• Magnetic field homogeneity
3.2.1 Slice Thickness Uniformity
The dark and light concentric rings in the image represent the slice thickness multiplied by the square root
of 2.0 due to the 45° grooves. The width of the rings (bands) should be the same throughout the image
for uniform slice thickness. More careful analysis can be carried out by measuring the brightness profiles
with region of interest computer routines.
3.2.2 Aspect Ratio
Visual inspection followed by a measurement of the diameter of the outermost ring can provide
information on the aspect ratio. The video display should be checked independently to avoid any
distortions in the display screen.