Phantom Laboratory Catphan 503 - Bead Point Source for Slice Sensitivity Profile (SSP)

19
Bead point source for slice sensitivity prole
The bead in this module can be used to calculate the slice sensitivity prole (SSP).
The above image illustrates how the bead will produce an ovoid object in a 3 dimensional
reconstruction. The length of the object at the Full Width at Half Maximum signal
indicates the SSP. This measurement can be easily obtained on some systems, by
making a sagittal or coronal reconstruction through the bead. The bead image in these
reconstructions will appear as a small line. By setting the FWHM (use the same
technique described in the Scan slice geometry section) measuring the z axis length of
the bead image to obtain the SSP.
If the scanner does not have the ability to measure z axis lengths in the sagittal or
coronal planes, a SSP can be made by incrementing or spiraling the slice through the
bead and reconstructing images in positive and negative table directions from the bead
(using the smallest available increments) and plotting the peak CT number of the bead
image in each slice. The FWHM measurement can then be made from the plotted CT
values of the bead as a function of z axis table position.