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?
Glucose-analog transport and hexokinase phosphorylation with metabolic trapping of FDG-6-phosphate
Chemiadsorption to hydroxyapatite identical to MDP bone scanning only
Mechanical trapping in pulmonary arterioles as 10–90 µm particles
Irreversible covalent binding to dopamine transporters in the striatum
Which pair correctly matches a PET agent to its primary clinical target?
Ga-68 DOTATATE — myocardial perfusion via Rb-generator kinetics
F-18 NaF — somatostatin receptors on neuroendocrine tumors
Rb-82 — β-amyloid plaque imaging in Alzheimer workups
F-18 piflufolastat (Pylarify®) — prostate-specific membrane antigen (PSMA) imaging
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?
Image quality will improve because insulin-driven muscle uptake always increases tumor contrast
Hyperglycemia and a non-fasting state can reduce tumor-to-background contrast and may require rescheduling per protocol
FDG requires no dietary preparation because it is excreted only as an inert gas
The study should proceed as a Xe-133 ventilation examination instead
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