Labelling Tc-99m Kits Flashcards
RPs need to change their oxidation state in order to label a pharmaceutical component. t/f
true
what is oxidation?
the loss of electron(s)
what is reduction?
the gain of electron(s)
what are oxidizing agents?
substances that causes oxidation, therefore is reduced
what are reducing agents?
substances that causes reduction, therefore is oxidized
which RPs have the oxidation state of +7?
sodium pertechnetate and sulphur colloid
in order for Tc-99m to react with the pharm. as a foreign label, it must be ______ (reduced/oxidized). why?
reduced
- it’ll bring it to a more reactive state
what is the chemical behaviour “IN VIVO” of Tc-99m?
pertechnetate mimics I- (charge+size)
useful thyroid imaging agent
what is the chemical behaviour “IN VITRO” of Tc-99m?
when Tc-99m is in its more reactive state, it can label compounds by forming covalent, ionic, or coordinate covalent bones
what are the examples of technetium TAGGED compounds? (what does tagged compound mean?)
tagged = function is not dependent on Tc
examples: MDP, SC, MAA
what are the examples of technetium ESSENTIAL compounds? (what does essential compound mean?)
essential = Tc needed in the structure for RP to work
examples: HMPAO, MAG3, ECD, MIBI
what does lyophilized mean?
removal of all water
what are found in RP kits?
reducing (Sn - tin) + complexing agents
what may be contained in RP kits?
stabilizers, buffers, anti-oxidants, transfer ligands, inert atmospheres
what is the goal of the reducing agent in terms of Tc-99m?
to oxidize Tc-99m to get from oxidation state of +7 to something lower.
what is the most common reducing agent?
stannous chloride dihydrate
stannous = Sn2+
what is the amount of Tc added to kits?
~10^-9M
what is the amount of stannous Sn needed? what does it do?
0.1-1mg
needed to reduce the Tc
what is the ratio of tin to Tc-99m?
Sn:Tc-99m
10^6-9:1
why is the ratio between Sn to Tc-99m the way it is?
- ensure rapid reduction of Tc-99m
- inhibit the effects of radiolysis due to free radicals tending to act as oxidizing agents
what is the complexing agent?
the pharmaceutical
what are the common types of complexing agents?
a coordination/principle ligands, a chelating agent, or particles, proteins or antibodies
what are coordinate covalent bonds?
bonds that has one atom donating a lone pair of electrons to the bond
what is a ligand? what is it also known as?
the molecule that donates electron pair(s); pharm portion
aka chelating agent aka complexing agent
what are coordination numbers?
number of bonds between the ligand and the metal ion
what is the coordination numbers for technetium?
~4 to 9
what is a monodentate ligand?
molecule forming ONE coordinate covalent bond with the metal ion
what is a polydentate ligand? what is it also called?
molecule forming SEVERAL bonds with the metal ion
aka chelating agent
what is a chelate?
structure that involves a metal ion and a polydentate ligand/chelating agent
what are the 2 reasons for excess complexing agents?
- ensure the reduced tech. atoms are complexed with the pharm (ex. high efficiency)
- complexes the access tin in the kit
what happens to the reduced Tc that doesn’t complexed with the pharm?
- oxidizes back to 7+ state
or - react with water to hydrolyzed reduced tech (impurity)
list these in the order of smallest to largest quantities.
reducing agent, complexing agent, Tc-99m
99m-Tc < reducing agent < complexing agent
what are transfer ligands?
a weak ligand that is added to temporarily bind reduced tech during slow labelling reactions
what are ancillary chelating agents?
takes over for complexing agents that don’t have affinity for Sn.
what are adjuvants?
additional ingredients found in the kits
what do stabilizers do for the kits?
maintains the integrity of the RP - keeps the RP in its intended state
what are some examples of stabilizers?
- bactericidal agents (benzyl alcohol, parabéns)
- anti-oxidants (ascorbic acid, gentisic acid)
what are anti-oxidants for in the kits?
to limit the effect of free radicals because they are more easily oxidized than other kit components
what is radiochemical purity referring to?
% bound to the pharmaceutical
what are the three chemical forms of Tc-99m found in the kits?
- bound tc-complex
- free pertechnetate
- hydrolyzed reduced
describe bound tc-complex.
Tc is in its desired form and bound to the pharm.
describe free pertechnetate. (TcO4-)
Tc that is NOT REDUCED or bound to the pharm.
describe hydrolyzed reduced. (TcO2)
Reduced Tc but not bound to pharm.
what are the notable exceptions for chelates?
MAA, SC, MIBI
_____ (lower/higher) amount of bound Tc = better image quality.
higher
%bound is also known as? which describes what?
%tag - describes the measure of radiochemical purity
metal ions are soluble in ___ (high/low) pH and if ___ (bound/unbound) to a ligand.
low - acidic
bound to ligands
TcO4- (free pert) tends to undergo hydrolysis. t/f
false
only Sn2+ and reduced Tc are concerns for hydrolysis
describe free radicals.
- result of indirect radiolysis
- free radicals will break bones between radionuclides and complexing agents then act as oxidizing agents
free radical formation is exaggerated in the presence of O2. t/f
true
the number of free radicals increases with time. therefore making the older eluate having the higher amount of free radicals. t/f
true
radiolysis is more common with ____ (high/low) activity and with ____ (high/low) energy radionuclides.
high activity and high energy radionuclides
how are insoluble colloid particles formed?
when metal reacts with water (hydrolysis)
why is carrier 99Tc bad?
if there is a high amount of carrier, it can use up too much of the other kit’s ingredients
what are some characteristics of 99Tc?
- amount of carrier increases with time
- it builds up in the generator between elutions as well as in the vial after elution
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+
d) reduced Tc-99m and Sn2+
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+
d) reduced Tc-99m and Sn2+
why is free pertechnetate an issue?
it causes non-target uptake (usually in thyroid and stomach)
what causes free pertechnetate (TcO4-)?
- oxidizing agents (O2 or free radicals) – oxidization of Sn2+ or reduced Tc
what are some solutions to help with free pertechnetate?
- use of excess stannous ions
- avoid introducing o2
- backfilling with nitrogen and argon
- use of anti-oxidants
- avoid using old eluate
what forms when reduced 99mTc undergoes hydrolysis?
formation of insoluble colloid particles occur
what occurs when Sn2+ undergoes hydrolysis?
formation of colloid that binds with reduced tech
