Radiopharmaceuticals

Radiopharmaceutical selection depends on the clinical question, imaging system, tracer availability, protocol, and patient characteristics.

SPECT Perfusion Tracers¶

Tc-99m Sestamibi and Tetrofosmin¶

These tracers enter viable myocytes in proportion to blood flow and localize primarily within mitochondria.

Advantages:

• Favorable 140-keV photon energy
• Better image quality than Tl-201
• Suitable for gated SPECT
• Relatively short half-life

Because redistribution is minimal, separate injections are required for rest and stress imaging.

Hepatobiliary activity may interfere with evaluation of the inferior wall. Delayed imaging, hydration, food, or repeat acquisition may help.

Thallium-201¶

Tl-201 behaves similarly to potassium and is taken up by viable myocytes through the sodium-potassium ATPase system.

Initial uptake reflects perfusion; delayed redistribution reflects membrane viability.

Disadvantages include:

• Lower photon energy
• Greater attenuation
• Lower count density
• Longer half-life
• Higher radiation exposure

It is now used less frequently for routine perfusion imaging.

PET Perfusion Tracers¶

Rubidium-82¶

Rb-82 is a potassium analog delivered from a strontium-82/rubidium-82 generator.

Advantages:

• No on-site cyclotron required
• Very short imaging protocol
• Reliable attenuation correction
• Quantitative myocardial blood flow

Limitations include reduced extraction at high flow, generator expense, and mandatory generator quality control.

N-13 Ammonia¶

N-13 ammonia provides high myocardial extraction and excellent image quality. Its short half-life generally requires an on-site or nearby cyclotron.

F-18 Flurpiridaz¶

Flurpiridaz F-18 is a mitochondrial complex-1 inhibitor with high myocardial extraction. Its longer half-life permits regional distribution and both exercise and pharmacologic PET imaging.

The FDA approved it in 2024 for PET myocardial perfusion imaging in adults with known or suspected coronary artery disease.

Metabolism and Inflammation¶

F-18 FDG¶

FDG is a glucose analog used to assess:

• Myocardial viability
• Cardiac sarcoidosis
• Prosthetic-valve or device infection
• Cardiac tumors
• Other inflammatory processes

Preparation depends on the indication:

• Viability: promote myocardial glucose uptake
• Inflammation: suppress normal myocardial glucose uptake with dietary preparation and fasting

Failed physiologic suppression may make an inflammatory study nondiagnostic.

Cardiac Amyloidosis¶

Bone-avid tracers include:

• Tc-99m pyrophosphate
• Tc-99m DPD
• Tc-99m HMDP

In the appropriate clinical setting, grade 2 or 3 myocardial uptake with no evidence of a monoclonal protein supports ATTR cardiac amyloidosis without biopsy.

SPECT or SPECT/CT is required to confirm true myocardial uptake and distinguish it from blood-pool activity.

Ventricular Function¶

Tc-99m-labeled red blood cells are used for equilibrium radionuclide ventriculography, commonly called MUGA.

Advantages include reproducible LVEF measurement. Limitations include radiation exposure and limited structural information.

Key Points¶

• Tc-99m agents are standard SPECT perfusion tracers.
• Tl-201 redistribution can assess viability but carries greater radiation burden.
• Rb-82 and N-13 ammonia permit quantitative PET perfusion imaging.
• F-18 flurpiridaz permits exercise or pharmacologic PET MPI.
• FDG preparation must match the clinical indication.
• Bone-avid tracer uptake alone does not exclude AL amyloidosis.

References¶

1. ASNC SPECT Protocols and Tracers Guidelines
2. ASNC/SNMMI PET Myocardial Perfusion and Metabolism Guidelines
3. FDA Approval of Flurpiridaz F-18
4. ASNC Cardiac Amyloidosis Resources