Corrections for Physical Factors - Correction Techniques in Emission Tomography - page 86

FIGURE 5.14: FDG PET/CT scan showing typical curvilinear cold arti-
fact at the lung base (black arrow) due to respiration-induced misalignment
between PET and CT (white arrows).
sometimes severe impact of this problem in oncology PET/CT scans [9] [73],
especially when using CT data acquired during inspiration (see Figure 5.15).
Although first studies in cardiac PET/CT demonstrated accurate attenuation
maps generated by CT [49], several other studies have shown that misregistra-
tion artifacts in both cardiac PET/CT [36] [52] [63] and SPECT/CT [35] are
also quite common, often resulting in false-positive findings especially in the
antero-lateral region as demonstrated in Figure 5.16. In stand-alone emssion
tomography, this type of artifact is usually not as severe as in hybrid sys-
tems, as both emission and transmission scans require several minutes, thus
effectively canceling out differences in respiration between them.
FIGURE 5.15: PET/CT images of a liver tumor close to the diaphragm.
While the tumor (arrow) is clearly visible in the non-corrected (right) and
the corrected PET image (left) using CT data in end-expiration, it is almost
invisible when using end-inspiration CT data for attenuation correction (left).