Generator kinetics

Question 1

The quantity of 99m-Tc eluted from the generator depends on:

Answer 1

• Generator efficiency
• quantity of 99-Mo on the column
• Length of time between elutioins

Question 2

Describe generator yield

Answer 2

• The yield varies between generators; typically ranges between 85-95% of the theoretical value
• only 86% of 99-Mo decays to 99m-Tc

Question 3

Decribe how a column defect gives low yield

Answer 3

Air pockets within the column cause saline to not properly be dispersed, lowering yield

Question 4

Describe how radiolysis causes low yield

Answer 4

• The abundance of radioactivity creates ion pairs in H2O, resulting in the formation of H2O2 and HOO
• oxidants change the oxidation stae of 99m-Tc and cause it to bind more formly to the Al2O3 on the column
• Most often to occur if the generator has not been eluted in a few days
• May need to discar the first elution to remove these contaminants and re-milk generator

Question 5

Describe fractional elution

Answer 5

• Easiest way to prevent low generator yield is to elute the generator in 1 ml aliquots
• In the first 1 ml aliquot, there will not be much activity,but will contain production of radiolysis (can be discarded)
• The second and fourth 1 ml aliquots will have the most activity

Question 6

Describe 99-Tc content in 99m-Tc eluate

Answer 6

• Bothe 99-Mo (14%) and 99m-Tc decay to 99-Tc, therefore, eluate contains both 99m-Tc and 99-Tc
• After elution, as 99m-Tc decays, the fraction of99-Tc increases over time
• Important to consider if generator has notbeen eluted in a fe days

Question 7

Describe the result of 99-Tc content in eluate

Answer 7

• When prepping RPs, 99-Tc will compete with the 99m-Tc for chemical binding, resulting in a decreased tagging efficiency
• Some RPs specifiy that only ‘fresh’ eluate be used to prepare the kit
• IC. HMPAO eluate <2hours old and from a generator that has been eluted once in the past 24 hours

Question 8

Describe elution or generator efficiency

Answer 8

• Provides estimate of the amount of 99m-Tc that can be obtained from a generator
• Ratio of the average amount of activity that can be eluted vs. the amount of activity on the column
• If the elution efficiency of a generator is known, then one can calculate the ‘predicted yield’ of a 99m-Tc elution, for either before orafter equilibrium is reached
• The actual yield becomes the predicted yield

Question 9

Elution efficiency Formula

Answer 9

• Elution efficiency= (actual yield/theoretical yield) x 100

Question 10

Predicted yield formula

Answer 10

• Predicted yield= (theoretical yield)x(elution efficiency as a decimal)