Biomedical Engineering Reference
In-Depth Information
a
b
Signal
Tissue fraction
Fig. 1.8
Tissue fraction for a 1D signal. Tics on x-axis denote sampling intervals. (
a
) Input signal.
(
b
) Due to tissue fraction the signal is an average of the intensities within each respective sampling
area. The input signal is plotted as a
dashed line
in (
b
) for orientation
over to the neighborhood which is why we speak of the
spill-over
effect. This effect
and the combination of spill-over and tissue fraction is illustrated in a 1D example
in Fig.
1.9
.
a
b
Spill-over
Spill-over and tissue fraction
Fig. 1.9
Partial volume effects for the 1D input signal given in Fig.
1.8
a. Tics on x-axis denote
sampling intervals. (
a
) Spill-over causes part of the signal intensity to appear outside of the peak
area. (
b
) Combined effect of tissue fraction and spill-over. The input signal is plotted as a
dashed
line
for orientation
The spill-over effect can be thought of as a convolution of the original signal
with a (locally adaptive) filter mask. The filter mask is called
Point Spread Function
(PSF) and is often approximated by a Gaussian kernel. The disruptive factors which
are responsible for the spill-over effect in PET are illustrated in Fig.
1.10
and will
be described in more detail in the following.
1.4.2.1
Positron Range
β
+
decay, the emitted positron travels a short path until it annihilates with
an electron. This distance is called the
positron range
and complicates the exact
In
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