Introduction - Motion Correction in Thoracic Positron Emission Tomography - page 10

Fig. 1.7 4 dual gating of patient data. The images show coronal slices of the left

ventricle. The rows vary in the cardiac and the columns in the respiratory phases. The respiratory
and cardiac gating signal was determined as described in connection with Figs. 1.4 and 1.6

Example of a 4 ×

1.4.1 PVE: Tissue Fraction

One component of the PVE, called tissue fraction , results from the discretization of
the measured data on a finite voxel grid. The intensity value of a voxel is given by
an averaging of all measured data inside the volume defined by the voxel.
Figure 1.8 illustrates tissue fraction at the borderline of two neighboring “tissues”
in a 1D example. The signal with tissue fraction shows mixed intensities at the
border of neighboring structures (in this case of the zero background and the
foreground peak). These averaged intensities, however, do not appear in the original
signal.

1.4.2 PVE: Spill-Over

During the process of PET data acquisition, several factors lead to image degrada-
tion. Suppose a point source is measured, the reconstructed image would show a
smeared-out version of the original signal. The signal of the point source is spilled