biodex ATOMLAB 500, Operation And Service Manual, Page: 203 / 212

Linearity
Linearity is defined as the proportionality of the measurement result to the activity measured as
determined over the intended range of use for the dose calibrator.
This test is performed using a vial or syringe of Tc-99m whose activity is at least as large as the
maximum activity normally assayed in a prepared radio pharmaceutical kit, in a unit dosage
syringe, or in a radio pharmaceutical therapy, whichever is the largest.
There are several acceptable methods for preparing linearity testing. The difference in these
methods is the reading used for decay correction of the activities. The following methods are all
acceptable for determining the normalized value:
1. Decay correct the test sample from the first reading and compare each reading to the decay
corrected reading.
2. For Tc-99, select 30 hours as the normalized reading and decay correct the reading to
calculate the expected activities at the times the readings were taken. Compare the
readings to the calculated activities. The time can be changed from 30 hours to another and
the normalized calculation can be performed from that time point.
Note: The Atomlab 500 automated linearity test uses 30 hours as the default normalized
reading.
3. The following decay method (described in detail) corrects each reading, averages the
calculated activities, and divides the average by the time-corrected reading to determine a
correction factor. If the correction factor is between certain values, the calibrator is linear.
Decay Method:
1. Zero the background by touching <Zero Background>.
2. Assay the Tc-99m syringe or vial in the dose calibrator to obtain the activity. The first assay
should be performed in the morning at a convenient time (e.g., 8:00 am).
3. Repeat steps 1 and 2 several times per day until the displayed activity is 10 microcuries or
below the lowest activity assayed in accordance with applicable State/NRC regulation or the
condition of the license. Two to four readings should be collected every day. Additional
readings are acceptable depending on the isotope used.
If the display indicated less than 50 µCi (1.85 MBq), wait 30 seconds before recording the
reading. To get a faster reading, adjust the transition threshold on the Atomlab controller.
Record the date, the time to the nearest minute, and the activity for each reading.
Note: Some state regulations allow linearity tests to end at activities greater than 10 µCi.
Where permitted by state regulations or license, the linearity can be ended at the stated
activity.
Note: Use of a spreadsheet (such as Microsoft Excel) in steps 4 and 5 will simplify
calculations.
4. Convert the time and date recorded date and time information to hours ( t ) elapsed since the
first assay. Decay-correct each displayed activity measurement ( M ) using the equation:
𝑀
!
= 𝑀 × 2
!
!
!
!
Where:
𝑇
!
!
= 6.007 h.