Calibration of Mosaic System

Preamp and Sumamp Offsets Time required: 15-30 minutes
Preamp offset calibration adjusts each PMT's preamp offset to get a specific baseline value. The sumamp offset calibration adjusts each trigger channel's sumamp offset to maximize the counts out of the trigger channel. Preamp & Sumamp Offset calibration can be performed independently of all other calibrations.

Automated Gain (preliminary) Time required: 4 hours
This procedure is normally performed at the factory only.

CFD Threshold Time required: 15-60 minutes
Constant Fraction Discriminator (CFD) Threshold calibration sets the threshold at the minimum energy required to trigger an event. Threshold calibration ensures that the CFDs gate out events at the proper point relative to the photopeak. Before running CFD threshold calibration a Preamp and Sumamp Offset calibration must be run.

Automated Gain (Final) Time required: 4-15 hours
Gain calibration adjusts the gain for each PMT, such that the output is approximately the same for all PMTs. Before running gain calibration, the following calibrations must be run: Preamp and Sumamp Offset, CFD Threshold, and Coincidence Timing. If this is not a new scanner or installation, after Gain calibration, the system linearity must be checked. If the system linearity does not pass, a Distortion removal (gdr) calibration must be run. If this is a new scanner or installation, Distortion removal (gdr) calibration must be run after the
Gain calibration. After running Gain calibration, the following calibrations must be run: Energy Correction, EC mock scans, Blank scans and Normalization.

Coincidence Timing Time required: 30-90 minutes
Coincidence Timing calibration adjusts the timestamp Least Significant Bit (LSB) and then all of the trigger channel timing delays to align all pulses. Before running Coincidence Timing calibration, the following calibrations must be run: Preamp and Sumamp Offset and CFD Threshold.

Distortion Removal (gdr) Time required: 28 hours - Data Collection 10 hours - Calculation 2 hours - Creve Process 16 hours
The GSO distortion removal (gdr) calibration is a spatial calibration that converts measured event positions to real, physical positions on the face of the detector. Before running distortion removal calibration, the following calibrations must be run: Preamp and Sumamp Offset, CFD Threshold, Coincidence Timing, and Automated Gain (final). After running distortion removal, the following calibrations must be run: Energy Correction, EC mock scans, Blank scans, and Normalization.

Energy Correction Time required: 15-30 minutes
Energy Correction allows the Global and Local Energy curves to be centered at a specified energy and curve shape to be made narrow about this center. Before running Energy Correction, the following calibrations must be run: Preamp and Sumamp Offset and CFD Threshold and Distortion removal (gdr). If the autoQC Energy Test gives warnings or fails, an Energy Correction will automatically be run.

Blank Scans Time required: 2 hours (2 scans)
Blank scans are transmission sinograms collected with nothing in the scanner field of view (the transmission source must be in the source holder). As part of the blank scan calibration, blank EC (emission contamination) sinograms are also collected. These blank EC sinograms are called leakage sinograms.

Time required: 8 hour collection (+1-2 hours to process and test)
Normalization is essentially independent of timing adjustments, as it is performed at a low enough rate to preclude randoms.

Gain changes affect normalization in two ways:
Spatial - Mispositioning of events moves counts from one part of the detector to another.
Sensitivity - As the gain of a PMT changes, the energy of events near that PMT also changes.

This can move counts out of the energy windows, leading to a local change in sensitivity. Energy correction should compensate for the sensitivity component of PMT gain changes.