MR-based Attenuation Correction for PET/MR - Correction Techniques in Emission Tomography - page 229

FIGURE 11.8: Simultaneous reconstruction of activity and attenuation dis-
tribution [35]: A study with patient data from PET/CT shows convergence of
the estimated attenuation (upper rows) and activity (lower rows). Overall
there is a good match between segmented (by simple region growing) esti-
mated attenuation map and the CT-derived attenuation map.
Early results (Figure 11.8) show that in principle this allows to predict bone
in the attenuation map. For clinical application no quantitative evaluation of
this approach has yet been presented.
11.4 Discussion
Various approaches for predicting the attenuation maps from MR im-
ages on PET/MR examinations of patients have been reviewed. While
segmentation-based approaches work well for brain applications, torso imag-
ing with PET/MR may require more sophisticated methodologies, such as
atlas-based image transformations from MR to pseudo-CT images. In gen-
eral, MR-AC needs to address more than adequate transformation of MR
pixel value information to appropriate PET attenuation values. In order for
MR-AC to be viable in clinical routine it needs to account for additional chal-
lenges in torso and whole-body imaging. These challenges include the accurate
representation of bone (typically not seen on MR), potential truncation effects
from patients extending beyond the transverse field-of-view of the MR and the
presence of MR surface coils typically not seen on MR.