Biomedical Engineering Reference
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FIGURE 4.2: PET acquisition of a homogenously filled cylindrical phantom
with 20 cm diameter. Top image: reconstructed using attenuation and scatter
correction; middle image: reconstructed with attenuation correction but with-
out scatter correction; bottom image: reconstructed without corrections. The
shown profiles are measured along a vertical line (one pixel wide) through the
center of the phantom at the slide that is shown on the right side.
image structures with pathological tracer uptake in a central localization in the
body may not be detected due to photon attenuation; an example can be found
in Figure 4.3. The influence of photon attenuation for SPECT acquisitions is
shown in Figure 4.4 (top and bottom). Also in SPECT the line profile of the
image not corrected for photon attenuation shows the same characteristics as
for PET; however, the activity in the center of the phantom is underestimated
only by a factor of 3. This minor effect is due to the fact that in PET photon
attenuation occurs along the whole line of response, whereas in SPECT it
occurs only from the center of the phantom to the detector.
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