7.3 PET Radiopharmaceuticals
Key Takeaways
- F-18 (t½ ≈ 110 min, 511 keV annihilation photons) labels FDG, NaF, amyloid agents, fluciclovine, PSMA ligands, and other PET tracers; patient glucose control is critical for FDG
- F-18 FDG is a glucose analog trapped after hexokinase phosphorylation—oncology, infection/inflammation, and myocardial viability are core indications
- Somatostatin-receptor PET uses Ga-68 DOTATATE (Netspot®)/DOTATOC (t½ Ga-68 ≈ 68 min) or Cu-64 DOTATATE; PSMA PET uses F-18 piflufolastat (Pylarify®) or Ga-68 PSMA products (Illuccix®/Locametz®)
- Cardiac PET perfusion commonly uses generator-produced Rb-82 (t½ ≈ 76 s) or cyclotron N-13 ammonia (t½ ≈ 10 min)
- Prep traps: non-fasting/hyperglycemia for FDG, confusing amyloid vs tau agents, and mixing diagnostic PSMA/fluciclovine indications with wrong cancer pathways
7.3 PET Radiopharmaceuticals
Quick Answer: F-18 FDG (110 min) → glucose analog for oncology / infection / viability (NPO + glucose control). F-18 NaF → bone PET. Amyloid F-18 agents → brain plaques. Axumin® / PSMA agents → prostate pathways. Ga-68/Cu-64 DOTA-peptides → NETs. Rb-82 / N-13 ammonia → cardiac PET perfusion. All PET coincidence imaging uses 511 keV annihilation photons.
PET radiopharmaceuticals pair a positron emitter with a targeting molecule. After positron annihilation, detectors record 511 keV photon pairs. Entry-level CNMT focus: which tracer for which biology, half-life logistics, and prep traps—not full neurology research catalogs.
F-18 Family Physics Anchor
| Nuclide | Approx. half-life | Production note |
|---|---|---|
| F-18 | ~110 minutes | Cyclotron |
| Ga-68 | ~68 minutes | Usually Ge-68/Ga-68 generator |
| Cu-64 | ~12.7 hours | Cyclotron |
| Rb-82 | ~76 seconds | Sr-82/Rb-82 generator at bedside |
| N-13 | ~10 minutes | On-site cyclotron (ammonia) |
| C-11 | ~20 minutes | On-site cyclotron (less common in many clinics) |
F-18 FDG (Fluorodeoxyglucose)
Mechanism
FDG is a glucose analog. It enters cells via GLUT transporters and is phosphorylated by hexokinase to FDG-6-phosphate, which is not significantly metabolized further along glycolysis—so it is metabolically trapped. Tissues with high glucose use (many malignancies, brain, heart under some conditions, activated inflammatory cells) accumulate FDG.
Indications
| Domain | Examples |
|---|---|
| Oncology | Staging, restaging, treatment response for numerous FDG-avid cancers; unknown primary; solitary pulmonary nodule characterization (context-dependent) |
| Infection / inflammation | FUO, selected osteomyelitis/spine infection, sarcoid, device infection workups (protocol-driven) |
| Cardiology | Myocardial viability (often with glucose-loading protocols distinct from oncology fasting) |
| Neurology | Selected epilepsy and dementia metabolic patterns |
Patient Prep (Oncology-Style Teaching)
| Prep element | Why |
|---|---|
| NPO ~4–6 hours (water OK per protocol) | Lowers insulin and competitive glucose |
| Serum glucose check before injection | Hyperglycemia reduces tumor contrast; many labs reschedule if glucose too high (thresholds protocol-specific, often roughly >150–200 mg/dL concern zone) |
| Avoid strenuous exercise 24 h | Prevents muscle uptake |
| Warm, quiet uptake (~60 min) | Reduces brown fat and muscle artifact |
| Controlled diabetes management | Coordinate insulin timing with the authorized user/protocol |
| Pregnancy screening / breastfeeding policies | Standard PET radiation counseling |
Typical adult activity: often ~10–20 mCi (370–740 MBq) IV, weight-based in many labs. Image roughly 60 minutes after injection (protocols vary).
Traps: eating before FDG; insulin given immediately before injection driving muscle uptake; brown fat in cold patients; interpreting infection vs tumor without history; using oncology fasting rules unchanged for viability protocols.
F-18 Sodium Fluoride (NaF)
Mechanism: Bone mineral incorporation (fluoride ion exchanges onto hydroxyapatite)—high sensitivity PET bone imaging for osteoblastic metastases and selected bone viability questions.
| Item | Teaching point |
|---|---|
| vs Tc-99m MDP | Higher sensitivity/resolution PET; different logistics/cost |
| Admin | IV; image often ~30–60+ min after injection |
| Prep | Hydrate; void; less “glucose drama” than FDG |
F-18 Amyloid Imaging Agents
These bind β-amyloid plaques in brain for Alzheimer disease workup support (positive/negative amyloid status)—not a stand-alone clinical diagnosis.
| Agent (brand) | Notes |
|---|---|
| Florbetapir (Amyvid®) | F-18 amyloid PET |
| Florbetaben (Neuraceq®) | F-18 amyloid PET |
| Flutemetamol (Vizamyl®) | F-18 amyloid PET; often color-scale display teaching |
Prep: minimize head motion; follow product-specific uptake times (often ~30–90 min class). Trap: amyloid-positive ≠ automatic Alzheimer diagnosis; correlation with neurology is mandatory. Distinguish from tau imaging (flortaucipir, Tauvid®)—different target (neurofibrillary tau pathology overview-level only).
Prostate-Pathway PET: Fluciclovine and PSMA
| Agent | Mechanism (exam level) | Flagship use |
|---|---|---|
| F-18 fluciclovine (Axumin®) | Synthetic amino acid analog transported into prostate cancer cells | Biochemically recurrent prostate cancer localization |
| F-18 piflufolastat (Pylarify®) | PSMA-targeted ligand | PSMA-positive prostate cancer imaging (staging/recurrence per labeling) |
| Ga-68 PSMA-11 (Illuccix®, Locametz®) | PSMA binder (Ga-68) | Similar PSMA PET indications; generator logistics |
Axumin prep traps: short uptake time (often image ~3–5 min after injection begins for early frames—follow insert); avoid exercise; bladder activity management. PSMA traps: salivary/lacrimal/kidney/bladder physiologic uptake; recent ADT effects are interpretation nuances—know physiologic hot spots so you do not call them all metastases.
Somatostatin-Receptor PET
| Agent | Nuclide half-life | Role |
|---|---|---|
| Ga-68 DOTATATE (Netspot®) | Ga-68 ~68 min | SSTR PET for NETs—successor mindset to Octreoscan |
| Ga-68 DOTATOC | Same Ga-68 | Related SSTR peptide (availability varies) |
| Cu-64 DOTATATE | Cu-64 ~12.7 h | SSTR PET with longer half-life logistics |
Mechanism: peptides bind somatostatin receptors (especially subtype 2) on many neuroendocrine tumors. Hold/timing of cold somatostatin analog therapy matters (short-acting vs long-acting depot schedules). Compared with In-111 pentetreotide SPECT, PET offers higher resolution and quantitative SUVs.
Cardiac PET Perfusion Agents
| Agent | Half-life | Source | Teaching use |
|---|---|---|---|
| Rb-82 chloride | ~76 seconds | Sr-82/Rb-82 generator | Rest/stress MPI PET; potassium-analog extraction |
| N-13 ammonia | ~10 minutes | Cyclotron | MPI PET; high extraction fraction |
Ultra-short half-lives demand on-site production/infusion systems, precise timing, and generator QC (Rb-82 breakthrough limits for Sr-82/Sr-85). Pharmacologic stress is common. These are not FDG viability protocols—different biology and prep.
Other F-18 Agents (Overview)
| Agent | Target idea | Clinical niche |
|---|---|---|
| F-18 fluoroestradiol (FES, Cerianna®) | Estrogen receptor | ER-positive breast cancer characterization |
| F-18 flortaucipir (Tauvid®) | Tau protein | Tau PET in cognitive impairment workups (overview) |
Know they exist and what they target; deep scoring criteria are specialist-level.
Master Selection Table
| Clinical goal | Prefer |
|---|---|
| Most oncology metabolic staging | F-18 FDG |
| Bone mets with PET sensitivity | F-18 NaF |
| Brain amyloid status | Florbetapir / florbetaben / flutemetamol |
| Prostate biochemical recurrence (amino acid) | F-18 fluciclovine |
| PSMA-avid prostate disease | F-18 or Ga-68 PSMA agents |
| SSTR-positive NETs | Ga-68 DOTATATE/DOTATOC or Cu-64 DOTATATE |
| Cardiac PET perfusion | Rb-82 or N-13 ammonia |
| Cardiac viability metabolism | F-18 FDG (viability prep) |
FDG + cookies before injection → ruined scan. Ga-68 DOTATATE → NETs, not PSMA. 76-second Rb-82 → generator at the scanner, not a 2-hour shipping isotope.
What is the primary mechanism of F-18 FDG localization in viable tumor cells?
Which pair correctly matches a PET agent to its primary clinical target?
A patient arrives for oncology F-18 FDG PET/CT after eating a full breakfast and has a markedly elevated fingerstick glucose. What is the most appropriate technologist concern?