Technetium radiopharmaceuticals

Technetium radiopharmaceuticals
• The chemical form of 99m Tc available from the Moly generator is
sodium pertechnetate ( 99m Tc-NaTcO 4 ). The pertechnetate ion, 99m TcO 4 ,
having the oxidation state +7 for 99m Tc.
• Chemically, 99m TcO 4 is a rather non reactive species and does not label
4
any compound by direct addition. In 99mTc-labeling of many
compounds, prior reduction of 99mTc from the 7 state to a lower
oxidation state is required.
• In 99m Tc-labeling of many compounds, prior reduction of 99m Tc from the
+7 state to a lower oxidation state is required.

• Various reducing agents that have been used are stannous chloride
(SnCl 2 H 2O 2 2), stannous citrate, stannous tartrate, concentrated HCl,
sodium borohydride (NaBH 4 ), dithionite, and ferrous sulfate.
• stannous chloride is the most commonly used reducing agent in
most preparations of 99mTc-labeled compounds

What Are Cold Kits?
o Non-radioactive components required to produce the
radiopharmaceutical after addition of the radionuclide.
o
o
Change the chemical and biodistribution is also altered.
The kits have a long shelf life and can be purchased and stored well
ahead of daily preparation
o 99m Tc-labeling can be accomplished simply by adding 99m TcO 4 to
most kits

Cold Kit Components
• Chelating/Complexing agent
• Reducing agent – usually stannous chloride
• Inert atmosphere (vacuum, nitrogen)
◦ Why?
• Stabiliser if required (ascorbic acid for MDP)
• Usually in a lyophilised state (freeze dried) for stability

• The chelating agent usually donates lone pairs of electrons to form
coordinate covalent bonds with reduced d 99mTc. Chemical groups
such as —COO,—OH,—NH2, and—SH are the electron donors in
compounds such as DTPA, gluceptate, and various proteins

• in a preparation of a 99m Tc-labeled compound, three 99m Tc species
may be present:
1. ‘‘Free’’ 99m Tc as 99m TcO 4 that has not been reduced by Sn 2+ .
2. ‘‘Hydrolyzed’’ 99m Tc, such as 99m TcO 2 that did not react with the
chelating agent; this includes reduced 99mTc bound to hydrolyzed
Sn 2+ (Sn(OH) 2 ).
3. ‘‘Bound’’ 99mTc-chelate, which is the desired compound formed by
binding of reduced 99m Tc to the chelating agent

Technetium radiopharmaceuticals

Clinical uses

preparation

Clinical uses

Preparation

uses

Preparation

Clinical uses

Tc-99m Labeled WBCs
•Used for localizing infection and
abscesses
•Principle of labeling
◦Tc-99m HMPAO is lipophilic and crosses lipid
bilayer of cell membranes
◦Inside the cell the HMPAO complex is broken
down and the resulting charged Tc-99m
species is trapped in the cell
◦All cells present are labeled so prior leukocyte
separation is necessary

Tc-99m WBC Labeling Procedure
• Obtain 30-50 mL whole blood
from patient t with anticoagulant
t
• add Hetastarch as a
sedimentation aid
• Hang syringe in an inverted
position
• Allow 30-60 min for RBC to
sediment

Tc-99m WBC Labeling Procedure
• Centrifuge. Remove platelet-rich
supernatant.
t
• Centrifuge. Use platelet-poor
plasma (PPP) to resuspend WBC
• Add 30 mCi freshly yprepared p Tc-
99m HMPAO: labeling 10 - 80 %.
Do NOT use Methylene Blue.
• Centrifuge. Remove supernatant.

Tc-99m WBC Labeling Procedure
• Resuspend labeled WBC in platelet
poor plasma
• Draw up dose for patient
• Inject patient. If patient has been on
dialysis, wait until procedure is
complete

Three Ways to Prepare Tc-99m
RBCs
•In vivo labeling
•Modified in vivo labeling
•In vitro labeling li (UltraTag)

In-Vitro Method
•Blood is drawn from patient and RBC’s are
separated by centrifugation and washing
•The cells are then incubated with
appropriate amount of Sn and then
washed to remove excess tin
•The appropriate amount of pertechnetate
is then added and allowed to incubate
•Labeling efficiency is >97%

In-Vivo Method
•A kit of Sn-PYP is reconstituted with
isotonic saline
•The proper dose (10-20 microgram/kg) is
injected into patient
•Wait 20 to 30 minutes and inject 20-30
mCi of pertechnetate to tag the RBC’s
immediately
•Labeling efficiency is 80-90%

Modified In-Vivo Method
•20-30 mCi pertechnetate
•Heparinized saline
•20 minutes post injection of Sn-PYP draw
3 ml of blood into Tc99m syringe and
incubate 10 minutes (shake gently)
•Inject labeled cells back into patient and
flush with saline
•Labeling yield >95%

Radioiodine( 131 I, 123 I, 125 I)
•Radionuclide R properties
◦Mod of decay
◦Energy
•Radionuclide production
• 124 Xe (n,γ)→ 125m Xe(57s)→ 125 I (60 d) → 125 Te
• 124 Xe (p,2n)→ 123 Cs(5.9 min)→ 123 I (13 d)→ 123 Te
• 235 U (n,f) → 131 Te (30h)→ 131 I (8 d) → 130 Xe
• 130 Te (n,γ)→ 131 Te (30h)→ 131 I (8 d) → 130 Xe

Iodine chemistry
•Chemical i l properties
•Labeling g with radioiodine
◦Electrophyllic substitution
◦Nucleophillic substitution
◦Isotope exchange

Protein labeling
• Monochloride iodine
• Chloramine T
•Solid phase
• Iodogen
• Iodobeads
• Bultone hunter

Iodine radiopharmaceutical
•Radioiodides
•Iobenguan(MIBG)
• 125 I-Albumin
• 123 I- or 131 I-Sodium Orthoiodohippurate

• 125 I-Sodium Iothalamate

Gallium
•Gallium radionuclides
•Radionuclide production
• 68 Zn (p,2n)→ 67 Ga(3.26 d)→ 67 Zn
•Gallium citrate

Indium
•ProductionP d • 111 Cd (p,n)→ 111 In(2.8 d)→ 111 Cd
•Radiopharmaceutical
◦Indium chloride
◦Indium oxime
◦In DTPA
◦In-Ab
◦In- penteriotide
◦In-WBC

In- WBC

Other radionuclides
• Thallium 201
• Xenon 133
• Chromium 51
• Cobalt 57
• Phosphorus 32
• Strontium 89
• Yttrium 90
• Samarium153