Capintec CAPTUS 2000, Owner'S Manual

Page: 161 / 206

CAPINTEC, INC CAPTUS
®
2000
To exit the screen without saving any setup data, select the CANCEL button. To save data
input into the Setup screen, exit by selecting the DONE button.
To input a value, use the
Tab key or trackball indicator to move to the desired text box, and
type in the desired value.
I 131 and I 123 generate counts which also appear in the I 125 ROI. This is generally
referred to as “spillover or cross contamination.” This spillover ratio has been measured for
CAPTUS
®
2000 systems, and the nominal values entered into the software. Counts for I 125
will automatically be corrected for spillover. You may re-measure these ratios on your
individual unit and edit the default values as desired. To determine a spillover ratio, count
the I 131 standard in the MCA mode, and set an ROI for both I 131 and I 125. Measure the
counts in each ROI. Repeat the calculation using I 123.
ROI) cpm(I131
ROI) cpm(I125
R
=
R ROI) cpm(I131 - cpm(I125) Cor
× =
where R = spillover ratio
Cor = correction factor for I 125 counts
Enter the counting time in units of seconds. Insure that counting time is sufficiently long for
adequate counting statistics. A bioassay measurement counting time of at least 300
seconds is recommended when using the standard ANSI Thyroid Uptake Collimator, or a
counting time of at least 120 seconds when using the Bioassay Collimator.
EFFICIENCY MEASUREMENTS
To measure the efficiency for any one of the iodides, first obtain a standard source with a
known activity and enter the source calibration date and activity into the appropriate text box.
The CAPTUS
®
2000 software will automatically decay correct the calibration activity to the
current date and time. Note that all efficiency measurements must be made using a
geometry which simulates the bioassay measurement. A standard iodine capsule or solution
of known activity in a thyroid uptake neck phantom placed flush against the edge of the
collimator is an ideal geometry for measuring bioassay efficiencies. Once the source
calibration information has been entered, select the
MEASURE EFFICIENCY button from the
bottom of the Setup screen. Figure 9-3, the staff bioassay efficiency data acquisition screen
will appear.
To exit the Data Acquisition screen at any time, choose the
EXIT button. To begin counting,
choose the START PROCEDURE button. Note the Go To MCA command located at the top
of the Data Acquisition screen. This features provides a direct link to the complete MCA
program without exiting from the Bioassay module. Use this feature to check the isotope
identification of a source, verify a region of interest or any other MCA use.
A sequence of screens will appear and prompt you through the correct measurement
process. As the measurement process begins and counts are acquired, the live spectra will
be displayed on the screen. The ROI selected will be highlighted in red to easily verify that it
is correct. The live time remaining will appear in the upper right hand corner of the screen,
July 00 BIOASSAY 9-3