Biomedical Engineering Reference
In-Depth Information
1.4.3
Mass-Preservation
Tissue compression and PVE, as introduced in Sects.
1.4.1
and
1.4.2
, lead to inten-
sity modulations at corresponding points in different gated reconstructions [
91
].
Especially for relatively thin structures like the myocardium the true uptake values
are affected by the PVE. A patient example is given in Fig.
1.11
where a systolic
and diastolic slice (same respiratory phase) and corresponding line profiles of a
dual gated 3D data set are shown. Especially the maximum intensity values of the
two heart phases indicate that corresponding points can differ in intensity.
Fig. 1.11
Slices of the HLA (cf. Sect.
1.6
)ofthe(
a
) systole and (
b
) diastole and (
c
) corresponding
line profiles for patient data. The
solid line
belongs to the systole and the
dashed line
to the diastole.
It can be observed that the maximum peaks in these line profiles vary a lot due to the PVE
To deal with the challenges caused by intensity artifacts, we consider the mass-
preserving property of PET images. In gating, all gates are formed over the
same time interval, i.e., the whole acquisition time. Hence, the total amount of
radioactivity in each gate is approximately equal. In other words, in any respiratory
and/or cardiac gate no radioactivity can be lost or added apart from some minor
changes at the edges of the field of view. We refer to this property as
mass-
preservation
in the following.
To further illustrate the mass-preserving property we artificially construct two
2D structures with different width and height in Fig.
1.12
and simulate the PVE
as performed in connection with Fig.
1.9
b. The integral over the total intensity
(respectively mass) of the two signals is equal. The original signals are shown in
the top row of Fig.
1.12
. The same signals with simulated PVE are shown in the
mid row. Line profiles through the images, shown in the bottom row, illustrate the
varying intensities after simulating the PVE (solid lines) compared to the original
images with the same maximal intensity (dashed line).
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