In March 2000 I came to England to start a PhD, and pet went from meaning a small animal you kept at home to meaning Positron Emission Tomography. There were months where my timetable was set by the half-life of iodine-124 (4.16 h), and my mind was occupied by the relative merits and problems with direct and indirect labelling of annexin V.

It has therefore pleased me to be able to commission a few protocols for radiolabeling molecules that could be used for PET or SPECT imaging.

The very first one that we published was:

Preparation of N-succinimidyl 3-[*I]iodobenzoate: an agent for the indirect radioiodination of proteins

http://www.nature.com/nprot/journal/v1/n2/full/nprot.2006.99.html

And now, in our most recent batch, we have published a group of three protocols for radiolabelling peptides and proteins with fluorine-18 using the silicon fluoride acceptor (SiFA) approach. Common to both the iodine and the fluorine radiolabelling is that a lot of effort is expended making a precursor with a labile group that will rapidly be exchanged for the radioactive ion. You want the radiolabelling reaction to go quickly and cleanly so that both the reaction and the purification can be performed in the shortest time possible maximising the amount of the radiotracer that can be used for your experiments.

The SiFA approach is almost miraculous, because it relies on the fact that for this extraordinary moiety fluorine-18 will replace the stable isotope, fluorine-19. Shown below is the reaction scheme for labelling peptides.

The three SiFA protocols are:

One-step ¹⁸F-labeling of peptides for positron emission tomography imaging using the SiFA methodology
http://www.nature.com/nprot/journal/v7/n11/full/nprot.2012.109.html

Synthesis of [¹⁸F]SiFB: a prosthetic group for direct protein radiolabeling for application in positron emission tomography
http://www.nature.com/nprot/journal/v7/n11/full/nprot.2012.110.html

Protein labeling with the labeling precursor [¹⁸F]SiFA-SH for positron emission tomography
http://www.nature.com/nprot/journal/v7/n11/full/nprot.2012.111.html

Here is a complete list of Nature Protocols that involve radiolabelling with isotopes suitable for PET or SPECT imaging:

Carbon-11, PET

Labeling of aliphatic carboxylic acids using [¹¹C]carbon monoxide
http://www.nature.com/nprot/journal/v1/n2/full/nprot.2006.112.html

Tagging recombinant proteins with a Sel-tag for purification, labeling with electrophilic compounds or radiolabeling with ¹¹C
http://www.nature.com/nprot/journal/v1/n2/full/nprot.2006.87.html

Fluorine-18, PET

One-step ¹⁸F-labeling of peptides for positron emission tomography imaging using the SiFA methodology
http://www.nature.com/nprot/journal/v7/n11/full/nprot.2012.109.html

Synthesis of [¹⁸F]SiFB: a prosthetic group for direct protein radiolabeling for application in positron emission tomography
http://www.nature.com/nprot/journal/v7/n11/full/nprot.2012.110.html

Protein labeling with the labeling precursor [¹⁸F]SiFA-SH for positron emission tomography
http://www.nature.com/nprot/journal/v7/n11/full/nprot.2012.111.html

Synthesis of N-succinimidyl 4-[¹⁸F]fluorobenzoate, an agent for labeling proteins and peptides with 18F
http://www.nature.com/nprot/journal/v1/n4/full/nprot.2006.264.html

Preparation of ¹⁸F-labeled peptides using the copper(I)-catalyzed azide-alkyne 1,3-dipolar cycloaddition
http://www.nature.com/nprot/journal/v6/n11/full/nprot.2011.390.html

PET imaging of herpes simplex virus type 1 thymidine kinase (HSV1-tk) or mutant HSV1-sr39tk reporter gene expression in mice and humans using [¹⁸F]FHBG
http://www.nature.com/nprot/journal/v1/n6/full/nprot.2006.459.html

Molecular PET imaging of HSV1-tk reporter gene expression using [¹⁸F]FEAU
http://www.nature.com/nprot/journal/v2/n2/full/nprot.2007.49.html

Copper-64, PET

Preparation of carbon nanotube bioconjugates for biomedical applications
http://www.nature.com/nprot/journal/v4/n9/full/nprot.2009.146.html

Radiolabeling of TETA- and CB-TE2A-conjugated peptides with copper-64
http://www.nature.com/nprot/journal/v1/n6/full/nprot.2006.431.html

Gallium-68, PET

Facile radiolabeling of monoclonal antibodies and other proteins with zirconium-89 or gallium-68 for PET imaging using p-isothiocyanatobenzyl-desferrioxamine
http://www.nature.com/protocolexchange/protocols/412

Conjugation of DOTA-like chelating agents to peptides and radiolabeling with trivalent metallic isotopes
http://www.nature.com/nprot/journal/v1/n2/full/nprot.2006.175.html

Yttrium-86, PET

Conjugation of DOTA-like chelating agents to peptides and radiolabeling with trivalent metallic isotopes
http://www.nature.com/nprot/journal/v1/n2/full/nprot.2006.175.html

Zirconium-89, PET

Conjugation and radiolabeling of monoclonal antibodies with zirconium-89 for PET imaging using the bifunctional chelate p-isothiocyanatobenzyl-desferrioxamine
http://www.nature.com/nprot/journal/v5/n4/full/nprot.2010.13.html

Technetium-99m, SPECT

Radiolabeling of HYNIC–annexin V with technetium-99m for in vivo imaging of apoptosis
http://www.nature.com/nprot/journal/v1/n1/full/nprot.2006.17.html

Methods for MAG3 conjugation and ^99mTc radiolabeling of biomolecules
http://www.nature.com/nprot/journal/v1/n3/full/nprot.2006.262.html

An improved synthesis of NHS-MAG3 for conjugation and radiolabeling of biomolecules with ^99mTc at room temperature
http://www.nature.com/nprot/journal/v2/n4/full/nprot.2007.144.html

Indium-111, SPECT

Conjugation of DOTA-like chelating agents to peptides and radiolabeling with trivalent metallic isotopes
http://www.nature.com/nprot/journal/v1/n2/full/nprot.2006.175.html

Iodone-124 / Iodine-125, PET / SPECT

Preparation of N-succinimidyl 3-[*I]iodobenzoate: an agent for the indirect radioiodination of proteins
http://www.nature.com/nprot/journal/v1/n2/full/nprot.2006.99.html