biodex ATOMLAB 950 - Page 27

notice a dotted line around <Abort>. This means that by pressing the space bar it will automatically stop
and you do not need to move the pointer to that pointer. The <Abort> button stops the system from
counting and also will not retain the information that has been counted during this function.
When the system finishes counting in the upper right you will see what looks like a MCA box sending
information to the computer pictorially. This means that a final download of information is being sent.
After the information is sent, a screen is displayed listing the full width half max (FWHM), the energy in
the peak channel. If this is acceptable click on <Accept> in the pop-up window. If you do not want to
accept it, press <Cancel>.
Both daily calibration and Chi-Square tests are performed using a 10 µCi Cs-137 button source. Once
calibration is underway, the system's unique differential spectrometer automatically measures the peak
height and subtracts the base line - which makes zero adjustment obsolete. It does this for 100,000 pulses
and then plots a spectrum in internal memory. The peak channel is located and equated to 662 keV,
which is the Cs-137 gamma entered. This gives the spectrometer the keV per channel which is used to
calibrate all of the other isotope gains. Each clinical isotope has a ROI defined with lower and upper
energy limits. These energy limits are then converted to channels in the MCA when a particular isotope is
counted. Corrections are made for sodium iodide NaI non-linearity. There is no need to view the
spectrum of calibration or any other isotope, although this is available on the display and in hard copy by
selecting the spectrum icon.
The multi-channel analyzer in the Atomlab 950 has several fixed precision gains and a regulated high
voltage supply. The pulse shapes are digitized and then processed by a high speed digital signal
processor. This processing results in a possible 1024 pulse heights which has zero offset. A spectrum
results when a histogram of these pulse heights (channels) is plotted. Calibration of the spectrometer is
defined as knowing the energy equivalence of each channel. This is accomplished by determining the Cs-
137 spectrum and then calculating the ratio of the 662 keV/peak channel. After calibration, the report
should always print a peak value very close to 662 keV (some precision round-off may occur), and the
change in calibration will be reflected in the keV/channel slope value. The fine gain can be thought of as
a floating point numerical gain. The HV adjust will ultimately determine the maximum energy one can
measure on the gain selected. It can be calculated by multiplying the keV/channel times 1024.
To Perform a Daily Calibration
1. After the system has been turned ON for at least one hour, select <Calibration> from the Operation
screen. The Calibration menu is now displayed on the screen. Select well or probe in the detector
window.
2. Position the 10 µCi Cesium-137 source approximately six inches in front of the appropriate detector.
3. Click on <Start> daily calibration.
4. The display will tell you that probe calibration is in progress. If calibration is successful, click on
<Accept>. Click on <Ignore> to discard the calibration without saving.
5. After accepting the calibration, you can print a report by clicking on the <Report> icon in the
primary tool bar at the left of the screen.
6. In the Report window you can enter the technologist's name and any comments required for these
reports. To review the report, click on <Preview>. To print the report, click on <Print>.
7. The printer page will now be displayed. If the correct printer is indicated, you can select multiple
copies or, for some reports, the number of the page you want to print.
NOTE: If you just click <Print> the calibration pages for both the well and probe will be printed. If you only performed the
calibration on one detector and only want to print that detector, you must indicate that on the print page. This is done by
adjusting the print range from All to Pages (from XX to XX). You can print at anytime the latest calibration screens for each
detector.
1. INTRODUCTION
ADMINISTRATION 3-2