The Tomophan™ phantom uses the well-established Phantom Laboratory technique of trigonometric projection of z-axis depth onto the x-y plane. The phantom includes to two sets of two angled bead ramps (left and right of center). Each set has two ramps, with the top bead of the lower ramp centered .25mm below the bottom bead in the upper ramp (see illustrations below). The diameter of each bead is 0.18mm, and beads are spaced vertically at 0.25mm. The angled bead ramps in the above illustration are shown in blue. The illustration below shows a side view of a reversing bead ramp set which rise 10mm in the z direction. The ramps on the right side of the phantom run opposite to the ramps on the left side of the phantom. 15 To evaluate the slice width or slice sensitivity profile (SSP), measure the full width at half-maximum (FWHM) of the bead’s intensity profile. Subtract the background value from the maximum value and add half that value to the backgound to calculate the half-maximum. Count the number of beads with a maximum intensity over the halfmaximum and multiply by 0.25mm the z-axis spacing. Note a profile needs to be made through both ramps in the set to make sure all the beads over the half maximum are seen. In the above example the maximum value is 1300 and the minimum value is 40 so the half maximum is 670. There are 10 beads with a maximum signal greater than 670 so the slice width would be measured as 10 x .25mm = 2.5mm. Note that as the slice thickness increases the maximum value for the beads decreases due to volume averaging. Presuming the slice thicknesses are accurate, the peak signal over background in a 1mm slice should be double that of the peak signal over the background in a 2mm slice. This rule, due to the effects of tomographic reconstruction only loosely applies.