Biomedical Engineering Reference
In-Depth Information
t
1
0
V
T
V
A
Pulse
generator
Detector A
Gate-pulse
generator
A
Pulse overlap
=> coincidence
A
Logic unit
Coincidence
window = 2
τ
B
t
t
1
t
2
B
Region of
coincidence
detection
Gate-pulse
generator
Detector B
Pulse
generator
t
2
0
VV
V
B
= Positron annihilation
= Accepted by coincidence detection
= Rejected by coincidence detection
Figure 2.2:
Annihilation coincidence detection. The two gamma-ray detectors
are placed at the opposite ends of the object to detect the photons that originate
from the positron annihilation site. The event is registered if the annihilation
occurs within the region of coincidence detection of the detector pairs. If the
gamma rays originate outside the region of coincidence detection of the two
detectors but only one of the photons is detected, the event is not registered as
the detection of a single photon violates the condition of coincidence.
coincidence detection
[21], which is unique to PET imaging. It should be noted,
however, that the condition of
coincidence
(or simultaneity) is not achievable in
practice, and a
coincidence resolving time
(or a
coincidence timing window
)
of less than 15 ns is often used to account for differences in arrival times of the
