Biomedical Engineering Reference
In-Depth Information
FIGURE 5.12: Contrast agent-induced artifact. The contrast-enhanced CT
image (left) shows very high X-ray density in the vena cava (arrow) due to
bolus passage of a contrast agent during CT leading to an apparent focal FDG
uptake in the attenuation-corrected PET image (arrow). Using a native non-
enhanced CT image (middle) for attenuation correction results in no abnormal
FDG uptake in this region. The non-attenuation-corrected PET image (right)
also demonstrates no abnormal uptake.
steps on the CT image to delineate bones from contrast agent-contaminated
tissues. After segmentation, contrast-enhanced regions are properly scaled to
PET energies to account for the deviant properties of the contrast agent. The
main diculty here is to find a proper segmentation; investigated techniques
comprise segmentation on simple geometrical shapes [17] or manually defined
regions [68] as well as more complex ones that apply region-growing algorithms
[18] or combined region-boundary-based techniques [2].
Still other methods consider the use of negative oral contrast agents, i.e.,
substances with a lower CT density than human soft tissue. One such exam-
ple is water which, when given together with some additives that positively
influence its intestinal absorption, was shown to be an effective contrast agent
in bowel CT scans [28]. A well-suited agent of this category that has been
successfully used in PET/CT is a solution containing locust bean gum and
mannitol [5].
Yet another solution would be the use of dual energy CT data for attenu-
ation correction. In this approach, CT data at two different effective energies
are acquired. The specific attenuation behavior of contrast agent between the
two energies can be used to delineate contrast-enhanced regions from bone
material. This was shown to reduce contrast agent-induced image artifacts
when compared to single energy-based attenuation correction [78].
Similar problems arise in PET/CT and SPECT/CT scans if metallic im-
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