Labelling Tc-99m Kits

Question 1

RPs need to change their oxidation state in order to label a pharmaceutical component. t/f

Answer 1

true

Question 2

what is oxidation?

Answer 2

the loss of electron(s)

Question 3

what is reduction?

Answer 3

the gain of electron(s)

Question 4

what are oxidizing agents?

Answer 4

substances that causes oxidation, therefore is reduced

Question 5

what are reducing agents?

Answer 5

substances that causes reduction, therefore is oxidized

Question 6

which RPs have the oxidation state of +7?

Answer 6

sodium pertechnetate and sulphur colloid

Question 7

in order for Tc-99m to react with the pharm. as a foreign label, it must be ______ (reduced/oxidized). why?

Answer 7

reduced
- it’ll bring it to a more reactive state

Question 8

what is the chemical behaviour “IN VIVO” of Tc-99m?

Answer 8

pertechnetate mimics I- (charge+size)
useful thyroid imaging agent

Question 9

what is the chemical behaviour “IN VITRO” of Tc-99m?

Answer 9

when Tc-99m is in its more reactive state, it can label compounds by forming covalent, ionic, or coordinate covalent bones

Question 9

what are the examples of technetium TAGGED compounds? (what does tagged compound mean?)

Answer 9

tagged = function is not dependent on Tc
examples: MDP, SC, MAA

Question 10

what are the examples of technetium ESSENTIAL compounds? (what does essential compound mean?)

Answer 10

essential = Tc needed in the structure for RP to work
examples: HMPAO, MAG3, ECD, MIBI

Question 11

what does lyophilized mean?

Answer 11

removal of all water

Question 12

what are found in RP kits?

Answer 12

reducing (Sn - tin) + complexing agents

Question 13

what may be contained in RP kits?

Answer 13

stabilizers, buffers, anti-oxidants, transfer ligands, inert atmospheres

Question 14

what is the goal of the reducing agent in terms of Tc-99m?

Answer 14

to oxidize Tc-99m to get from oxidation state of +7 to something lower.

Question 15

what is the most common reducing agent?

Answer 15

stannous chloride dihydrate
stannous = Sn2+

Question 16

what is the amount of Tc added to kits?

Answer 16

~10^-9M

Question 17

what is the amount of stannous Sn needed? what does it do?

Answer 17

0.1-1mg
needed to reduce the Tc

Question 18

what is the ratio of tin to Tc-99m?

Answer 18

Sn:Tc-99m
10^6-9:1

Question 19

why is the ratio between Sn to Tc-99m the way it is?

Answer 19

• ensure rapid reduction of Tc-99m
• inhibit the effects of radiolysis due to free radicals tending to act as oxidizing agents

Question 20

what is the complexing agent?

Answer 20

the pharmaceutical

Question 21

what are the common types of complexing agents?

Answer 21

a coordination/principle ligands, a chelating agent, or particles, proteins or antibodies

Question 22

what are coordinate covalent bonds?

Answer 22

bonds that has one atom donating a lone pair of electrons to the bond

Question 23

what is a ligand? what is it also known as?

Answer 23

the molecule that donates electron pair(s); pharm portion
aka chelating agent aka complexing agent

Question 24

what are coordination numbers?

Answer 24

number of bonds between the ligand and the metal ion

Question 25

what is the coordination numbers for technetium?

Answer 25

~4 to 9

Question 26

what is a monodentate ligand?

Answer 26

molecule forming ONE coordinate covalent bond with the metal ion

Question 27

what is a polydentate ligand? what is it also called?

Answer 27

molecule forming SEVERAL bonds with the metal ion aka chelating agent

Question 28

what is a chelate?

Answer 28

structure that involves a metal ion and a polydentate ligand/chelating agent

Question 29

what are the 2 reasons for excess complexing agents?

Answer 29

1. ensure the reduced tech. atoms are complexed with the pharm (ex. high efficiency) 2. complexes the access tin in the kit

Question 30

what happens to the reduced Tc that doesn't complexed with the pharm?

Answer 30

- oxidizes back to 7+ state or - react with water to hydrolyzed reduced tech (impurity)

Question 31

list these in the order of smallest to largest quantities. reducing agent, complexing agent, Tc-99m

Answer 31

99m-Tc < reducing agent < complexing agent

Question 32

what are transfer ligands?

Answer 32

a weak ligand that is added to temporarily bind reduced tech during slow labelling reactions

Question 33

what are ancillary chelating agents?

Answer 33

takes over for complexing agents that don't have affinity for Sn.

Question 34

what are adjuvants?

Answer 34

additional ingredients found in the kits

Question 35

what do stabilizers do for the kits?

Answer 35

maintains the integrity of the RP - keeps the RP in its intended state

Question 36

what are some examples of stabilizers?

Answer 36

- bactericidal agents (benzyl alcohol, parabéns) - anti-oxidants (ascorbic acid, gentisic acid)

Question 37

what are anti-oxidants for in the kits?

Answer 37

to limit the effect of free radicals because they are more easily oxidized than other kit components

Question 38

what is radiochemical purity referring to?

Answer 38

% bound to the pharmaceutical

Question 39

what are the three chemical forms of Tc-99m found in the kits?

Answer 39

1. bound tc-complex 2. free pertechnetate 3. hydrolyzed reduced

Question 40

describe bound tc-complex.

Answer 40

Tc is in its desired form and bound to the pharm.

Question 41

describe free pertechnetate. (TcO4-)

Answer 41

Tc that is NOT REDUCED or bound to the pharm.

Question 42

describe hydrolyzed reduced. (TcO2)

Answer 42

Reduced Tc but not bound to pharm.

Question 43

what are the notable exceptions for chelates?

Answer 43

MAA, SC, MIBI

Question 44

_____ (lower/higher) amount of bound Tc = better image quality.

Answer 44

higher

Question 45

%bound is also known as? which describes what?

Answer 45

%tag - describes the measure of radiochemical purity

Question 46

metal ions are soluble in ___ (high/low) pH and if ___ (bound/unbound) to a ligand.

Answer 46

low - acidic bound to ligands

Question 47

TcO4- (free pert) tends to undergo hydrolysis. t/f

Answer 47

false only Sn2+ and reduced Tc are concerns for hydrolysis

Question 48

describe free radicals.

Answer 48

- result of indirect radiolysis - free radicals will break bones between radionuclides and complexing agents then act as oxidizing agents

Question 49

free radical formation is exaggerated in the presence of O2. t/f

Answer 49

true

Question 50

the number of free radicals increases with time. therefore making the older eluate having the higher amount of free radicals. t/f

Answer 50

true

Question 51

radiolysis is more common with ____ (high/low) activity and with ____ (high/low) energy radionuclides.

Answer 51

high activity and high energy radionuclides

Question 52

how are insoluble colloid particles formed?

Answer 52

when metal reacts with water (hydrolysis)

Question 53

why is carrier 99Tc bad?

Answer 53

if there is a high amount of carrier, it can use up too much of the other kit's ingredients

Question 54

what are some characteristics of 99Tc?

Answer 54

- amount of carrier increases with time - it builds up in the generator between elutions as well as in the vial after elution

Question 55

what kit component(s) is/are at risk of undergoing oxidation? a) pertechnetate (TcO4-) b) reduced Tc-99m c) pertechnetate (TcO4-) and Sn2+ d) reduced Tc-99m and Sn2+

Answer 55

d) reduced Tc-99m and Sn2+

Question 56

what kit component(s) is/are at risk of undergoing hydrolysis? a) pertechnetate (TcO4-) b) reduced Tc-99m c) pertechnetate (TcO4-) and Sn2+ d) reduced Tc-99m and Sn2+

Answer 56

d) reduced Tc-99m and Sn2+

Question 57

why is free pertechnetate an issue?

Answer 57

it causes non-target uptake (usually in thyroid and stomach)

Question 58

what causes free pertechnetate (TcO4-)?

Answer 58

- oxidizing agents (O2 or free radicals) -- oxidization of Sn2+ or reduced Tc

Question 59

what are some solutions to help with free pertechnetate?

Answer 59

- use of excess stannous ions - avoid introducing o2 - backfilling with nitrogen and argon - use of anti-oxidants - avoid using old eluate

Question 60

what forms when reduced 99mTc undergoes hydrolysis?

Answer 60

formation of insoluble colloid particles occur

Question 61

what occurs when Sn2+ undergoes hydrolysis?

Answer 61

formation of colloid that binds with reduced tech