Detector Calibration
4-8
CardioMD Service Manual
1MAN0158-H11 04-2005 CSIP Level 1
4.2.3
High Voltage (HV) and PMT Calibration (PMT)
4.2.3.1
Description
A basic alignment of the PMT’s is necessary as a first step.
The PMT calibration program may start by loading previous tuning values. In that case, the cali-
bration is referred to as an update tune.
However, if a detector is being tuned for the first time, a basic calibration must be performed and
default values will be loaded. Subsequently, the high voltage is adjusted to a relatively low value
and then moves upwards in steps. For each HV step, 10 seconds are allowed for the autotune to
lock in on those tubes that have reached their lower working limit. Also for each HV step, the
working point for each PMT is monitored. The HV continues to step upwards until all PMT work-
ing points are in their dynamic range. From that step, the HV is increased by another 50 V to en-
sure all PMT’s are in sufficient gain range. The HV value is then stored in the tuning file.
Following the basic alignment of the PMT’s, a series of iterative flood images are acquired as dual
energy acquisitions with two energy windows around the specified isotope energy. The images are
spatially subdivided into regions, each representing the outline of a PMT. For each iteration, the
count rate for all PMT regions in both the low and the high energy window are compared indi-
vidually and, if they are not equal, that tube gain is adjusted accordingly.
When equilibrium has been reached for all tubes, the PMT tuning file is stored with the final tun-
ing values.
4.2.3.2
High Voltage Calibration Procedure
To be performed:
At installation and when the EDC board, PMT tube or crys-
tal is replaced.
Detector:
Both detectors at the same time, with or without collimators.
Source: None.
Total calibration time:
Approximately 3 minutes.
Calibration file created:
C:/Cardiocam/calibrations/hvcal.dat
.
WARNING
The high voltage is common to both detectors. Changing the high voltage set-
ting may affect all other calibrations of
both
detectors entailing a need for a
complete re-calibration of the other detector.
After performing a high voltage calibration, as a minimum perform a PMT
update and a QC check of the other detector.
If GeoCal is required on one detector following high voltage calibration, per-
form a GeoCal on the other detector, as well.
Note
. If the CardioMD system is equipped with the AC Option, the transmission scanners must be
removed before high voltage calibration can be performed. See Chapter 12
CardioMD AC Option
for instructions.
Summary of Contents for CARDIOMD
Page 1: ...CARDIOMD SERVICE MANUAL 1MAN0158 H11 04 2005 CSIP Level 1 ...
Page 10: ...Introduction x CardioMD Service Manual 1MAN0158 H11 04 2005 CSIP Level 1 ...
Page 16: ...Safe Operating Practices 1 6 CardioMD Service Manual 1MAN0158 H11 04 2005 CSIP Level 1 ...
Page 164: ...Detector Calibration Files 5 60 CardioMD Service Manual 1MAN0158 H11 04 2005 CSIP Level 1 ...
Page 328: ...Installation Procedures 9 38 CardioMD Service Manual 1MAN0158 H11 04 2005 CSIP Level 1 ...
Page 348: ...Planned Maintenance Procedures 11 6 CardioMD Service Manual 1MAN0158 H11 04 2005 CSIP Level 1 ...
Page 465: ......
