5. To find the peak in the ROI, click on <Find Peak>. Click on <Save> to save this second region of
interest as ROI #2. To create additional regions of interest, click on <Show Cursors> and repeat steps
4 and 5.
6.
To
print
a
Spectrum
Analysis
Report,
click
on
<Print
Preview>
at
the
bottom
right
of
the
Cursor
Window
for
a
preview.
To
print
the
report,
click
on
<Print>.
7. To exit Spectrum Analysis, click on <Close> at the bottom center of the Spectrum Analysis screen.
How is ROI Determined?
The preset ROI energy window values do not change as the user switches between well or probe,
regardless of the mode selected (i.e., Uptake, Schilling, MCA, etc.). The ROI is defined in units of energy
(keV) and then converted to channel numbers with the keV/channel slope value that is measured during
calibration. The channel number for the ROI values can and will change from probe to well if the
calibration keV/channel is different between probe and well.
Example
Tc-99m has a peak energy of 140 keV according to the radionuclide decay scheme. The Atomlab 950 uses
a default of +/- 15% energy window around the peak energy. These values calculate to be 119 keV to 162
keV and are displayed on the Isotope Editing page. When either the probe or well is selected, the ROI
channels are calculated based upon the Cs-137 calibration results for that particular detector. If the
calculation of the probe results in a .3775 keV/channel on gain 8, the TC-99m default gain, the channel
ROI will be 119 keV/.3775 keV channel = channel 315 and 162/.3775 = channel 429. For the well detector,
we might have a calibration of .3325 keV/channel. In this case, the ROI channels will calculate channel
358 to 487. Even though the ROI channels are different, the energy windows are the same. This will
become apparent when the spectrum for each detector is printed.
NOTE: It is not necessary to fix a symmetrical percent around the peak. In fact, some isotopes are multi-peaked,
which can cause an asymmetric spectrum. Keep in mind that if a calibration is performed you must save the result
in order to have it used in ROI calculations.
If you select an isotope from the Isotope Editing page, the screen will display the isotope name, LLD,
ULD, and gain setting as demonstrated in the following chart.
Gain Max keV Half Scale
1 3000 1500
2 1500 750
4 750 375
8 375 187
12 250 125
48 64 32
A. Lower Level Discriminator (LLD) = 0.85 times the Min keV of interest.
B. Upper Level Discriminator (ULD) = 1.15 times the Max keV of interest.
1. INTRODUCTION
ADMINISTRATION 3-22
To Next Page
Loading...
