CAPINTEC, INC. CAPTUS
®
4000e
5-10 QUALITY ASSURANCE August 17
17. Select the Exit button or press Alt+E to exit and return to Figure 5-1 Quality Assurance
Main Screen.
To print current results for record keeping, click the Print button or press Alt+P on the
Auto Calibration or Constancy Test screen after calibration is completed.
To view or print results for all the Quality Assurance tests performed to date, click the
Print / View History button or press Alt+V (Refer to the VIEWING AND PRINTING
HISTORY section on page 5-24).
About Auto Calibration
Calibration is done using Cs137 and Eu152 isotopes. First, calibration is performed with
Cs137 where the procedure makes use of its 662 keV and 32 keV peaks to automatically
adjust the high voltage, gain, and zero offset (as required by the CAP-MCA) to provide a
calibration of approximately 2.0 keV per channel in the MCA. Next, Eu152 provides multiple
gammas over an energy range of 41 keV to 1,408 keV. The CAPTUS
®
4000e software
provides a point-by-point energy calibration using these gammas. This function corrects for
any non-linearity in response of the NaI detector and provides accurate identification of the
energy of the peaks. It is important to complete the calibration of your system using Eu152.
The ROI’s in the Thyroid Uptake and Lab Tests are based on the energy ranges defined by
the Eu152 calibration. In addition, the automatic peak identification program, which is
accessed in the Wipe Test and MCA modules, requires the Eu152 energy calibration in order
to work properly.
Unless an error message is displayed, the software will have succeeded in finding a set of
adjustments, which places the 662 keV gamma peak to within ±2 channels of the theoretical
value for a calibration of 2.00 keV per channel. The software has preset limits that prohibit
operation outside of appropriate voltage, gain, and zero adjust values.
The Auto Calibration Test also calculates detector resolution by determining the FWHM (full
width-half maximum) area of the peak, and dividing by the peak centroid location. For peaks
such as the 662 keV peak of Cs137 whose shape is symmetrical or appears to follow a
Gaussian distribution, the FWHM is generally close to 2.35 . For flat-faced detectors the
resolution should be <9.5 percent measured at the Cs137 662 keV peak. For Well detectors
the resolution should be <10.0 percent. Detectors do age with use and this will result in a
very slight increase (1% to 3%) in resolution over a period of several years. A rapid increase
in percent resolution may indicate a problem with the detector assembly.
Note: Monitoring the stability of the resolution over time is one of the best indications of the
overall system performance.
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