Biodistribution of Radiopharmaceuticals in Nuclear Medicine

Flashcards about Biodistribution of Radiopharmaceuticals in Nuclear Medicine

What is the definition of Biodistribution?

The distribution of a radiopharmaceutical within the body over time

What is the radiopharmaceutical form of Sodium Pertechnetate?

⁹⁹ᵐTcO₄⁻

What is the approximate effective dose of ⁹⁹ᵐTcO₄⁻ per MBq?

~0.007 mSv/MBq

What is considered the major critical organ when using ⁹⁹ᵐTcO₄⁻?

Stomach

One method to minimize radiation dose from ⁹⁹ᵐTcO₄⁻ is:

Performing imaging shortly after injection

Which strategy helps reduce radiation exposure after ⁹⁹ᵐTcO₄⁻ administration?

Encouraging hydration and frequent voiding

How is ⁹⁹ᵐTc Sodium Pertechnetate produced?

From a ⁹⁹Mo/⁹⁹ᵐTc generator

What ions does ⁹⁹ᵐTcO₄⁻ mimic in the body?

Halide ions like iodide

What type of emission does ⁹⁹ᵐTc produce that makes it ideal for imaging?

Gamma rays at 140 keV

What factors influence biodistribution?

Molecular structure, route of administration, organ perfusion, transport mechanisms, metabolism and excretion

How is ⁹⁹ᵐTc Pertechnetate administered?

Intravenous injection

What describes the absorption of ⁹⁹ᵐTc Pertechnetate?

Immediate into bloodstream

How is ⁹⁹ᵐTc Pertechnetate distributed after administration?

Rapidly to several organs via blood

What is true about the metabolism of ⁹⁹ᵐTc Pertechnetate?

Minimal — it remains largely unchanged

What are the primary and minor routes of excretion for ⁹⁹ᵐTc Pertechnetate?

Renal (major), GI tract (minor)

What type of uptake does the thyroid show for ⁹⁹ᵐTcO₄⁻?

High uptake via active transport

How do the salivary glands interact with ⁹⁹ᵐTcO₄⁻?

Moderate uptake via active transport

What kind of uptake occurs in the gastric mucosa for ⁹⁹ᵐTcO₄⁻?

Moderate uptake via active transport

Which describes the biodistribution of ⁹⁹ᵐTcO₄⁻ in the choroid plexus?

Low uptake via passive diffusion

What is the uptake characteristic of ⁹⁹ᵐTcO₄⁻ in the kidneys and bladder?

High uptake due to excretion

How is ⁹⁹ᵐTcO₄⁻ handled in the colon?

Low uptake due to delayed excretion

What is ⁹⁹ᵐTcO₄⁻ used to detect in thyroid imaging?

Nodules, hyper/hypothyroidism

What is the purpose of using ⁹⁹ᵐTcO₄⁻ in Meckel’s Diverticulum imaging?

Detect ectopic gastric mucosa

What can ⁹⁹ᵐTcO₄⁻ imaging reveal in the salivary glands?

Obstruction or inflammation

Historically, ⁹⁹ᵐTcO₄⁻ was used in brain imaging for what now-obsolete purpose?

Tumor detection

What is the role of a target organ in nuclear medicine imaging?

It’s the organ intended for imaging

What defines a critical organ in radiopharmaceutical biodistribution?

It’s the organ that receives the highest radiation dose

In a thyroid scan using ⁹⁹ᵐTcO₄⁻, what is the target organ?

Thyroid

In a thyroid scan using ⁹⁹ᵐTcO₄⁻, what is the critical organ?

Stomach

What is the target organ for a Meckel’s scan using ⁹⁹ᵐTcO₄⁻?

Ectopic gastric mucosa

What is the critical organ for a Meckel’s scan using ⁹⁹ᵐTcO₄⁻?

Stomach

What is the target organ for a Salivary Gland scan using ⁹⁹ᵐTcO₄⁻?

Salivary Gland

What is the critical organ for a Salivary Gland scan using ⁹⁹ᵐTcO₄⁻?

Thyroid

During salivary gland imaging, what organ receives the highest dose of radiation?

Thyroid (critical organ)

What is Pharmacokinetics (PK)?

What the body does to the drug, includes absorption, distribution, metabolism, excretion (ADME)

What is Pharmacodynamics (PD)?

What the drug does to the body, includes receptor interactions, localization, biological effects

What is the radiopharmaceutical for Technetium Sodium Pertechnetate?

⁹⁹ᵐTcO₄⁻

What is the chemical behavior of Technetium Pertechnetate?

Mimics halide ions (especially iodide)

What is the physical half-life of Technetium Pertechnetate?

~6 hours

What is the excretion route of Technetium Pertechnetate?

Renal (major), GI tract (minor)

Where does Technetium Pertechnetate accumulate?

Thyroid, salivary glands, gastric mucosa, choroid plexus

What are the organs with normal biodistribution of Technetium Pertechnetate?

Thyroid, Salivary glands, Gastric mucosa, Choroid plexus, Kidneys/bladder, Colon

What are the thyroid imaging applications of Technetium Pertechnetate?

Nodules, hyper/hypothyroidism

What is Meckel’s Diverticulum imaging application of Technetium Pertechnetate?

Detect ectopic gastric mucosa

What is Salivary Gland imaging application of Technetium Pertechnetate?

Obstruction or inflammation

What is Brain imaging application of Technetium Pertechnetate?

Tumor detection (obsolete)

What factors affect the biodistribution of Technetium Pertechnetate?

Patient hydration status, Renal function, Medications, Pathological changes

What is the major critical organ for Technetium Pertechnetate?

Stomach

What is ⁹⁹ᵐTc Macroaggregated Albumin (MAA)?

⁹⁹ᵐTc-labeled human serum albumin particles

What is ⁹⁹ᵐTc-MAA used for?

Lung perfusion imaging

What is the particle size of ⁹⁹ᵐTc-MAA?

10–90 µm (capillary-level embolization)

What is the distribution of ⁹⁹ᵐTc-MAA?

Entrapped in pulmonary capillaries

What is the primary localization of ⁹⁹ᵐTc-MAA?

Lungs

What are the imaging applications of ⁹⁹ᵐTc-MAA?

Evaluate pulmonary embolism (PE), Preoperative lung function evaluation, Assess right-to-left shunts

What is the target organ of ⁹⁹ᵐTc-MAA?

Lungs

What is the critical organ of ⁹⁹ᵐTc-MAA?

Lungs

What factors affect the biodistribution of ⁹⁹ᵐTc-MAA?

Particle size and number, Cardiac output and pulmonary perfusion, Right-to-left shunt, Injection technique

What are the precautions of ⁹⁹ᵐTc-MAA?

Contraindicated in severe pulmonary hypertension

How is ⁹⁹ᵐTc-MAA administered?

Intravenous injection

Where does ⁹⁹ᵐTc-MAA get trapped after administration?

Pulmonary capillaries

How is ⁹⁹ᵐTc-MAA metabolized in the body?

Gradually broken down by the reticuloendothelial system

What are the excretion pathways for ⁹⁹ᵐTc-MAA over time?

Renal and hepatobiliary

What happens to ⁹⁹ᵐTc-MAA particles after injection?

They embolize in the pulmonary arterioles

What does ⁹⁹ᵐTc-MAA imaging reflect?

Regional blood flow in the lungs

⁹⁹ᵐTc-MAA is used with ventilation agents to assess what?

V/Q mismatch

Does ⁹⁹ᵐTc-MAA involve active transport or receptor binding?

No, neither is involved

Where does the majority of ⁹⁹ᵐTc-MAA localize after injection?

Lungs (≥ 90% of dose)

Minor uptake of ⁹⁹ᵐTc-MAA in the liver or spleen is usually due to:

Particle shunting or aggregation

What describes kidney and bladder involvement with ⁹⁹ᵐTc-MAA?

Low uptake and delayed excretion

Abnormal biodistribution of ⁹⁹ᵐTc-MAA to the brain or body suggests what?

Right-to-left shunt

What is the primary imaging application of ⁹⁹ᵐTc-MAA?

Lung perfusion scintigraphy

⁹⁹ᵐTc-MAA can help evaluate which serious condition?

Pulmonary embolism (PE)

Why is ⁹⁹ᵐTc-MAA used before lung surgery?

To evaluate lung function preoperatively (e.g., before lobectomy)

What vascular abnormality can be assessed with ⁹⁹ᵐTc-MAA?

Right-to-left shunts

What is the primary target organ for ⁹⁹ᵐTc-MAA in perfusion assessment?

Lungs

Which organ receives the highest radiation dose during normal biodistribution of ⁹⁹ᵐTc-MAA?

Lungs

Under conditions of shunting or abnormal distribution, which organs may become critical with ⁹⁹ᵐTc-MAA?

Liver and spleen

What particle factors influence ⁹⁹ᵐTc-MAA biodistribution the most?

Particle size and number

Which physiological factor plays a major role in biodistribution of ⁹⁹ᵐTc-MAA?

Cardiac output and pulmonary perfusion

What abnormality can significantly alter biodistribution of ⁹⁹ᵐTc-MAA?

Right-to-left shunt (e.g., PFO, AVM)

Why should a bolus injection be avoided in patients with shunting?

It may bypass the lungs, altering biodistribution

What are the common agents for ⁹⁹ᵐTc Phosphonate/Phosphate Radiopharmaceuticals?

⁹⁹ᵐTc-MDP, ⁹⁹ᵐTc-HDP, ⁹⁹ᵐTc -PYP

What is the chemical structure of ⁹⁹ᵐTc Phosphonate/Phosphate Radiopharmaceuticals?

phosphate or phosphonate backbone

What is the pharmacodynamics of ⁹⁹ᵐTc Phosphonates?

Localizes in areas of osteoblastic activity

What is the high uptake of ⁹⁹ᵐTc Phosphonates?

Skeletal system

What are the imaging applications of ⁹⁹ᵐTc Phosphonates?

Metastatic disease, Fracture detection, Osteomyelitis, Arthritis and degenerative bone disease, Bone viability in orthopedic procedures

What is the target organ of ⁹⁹ᵐTc Phosphonates?

Bone (skeleton)

What is the critical organ of ⁹⁹ᵐTc Phosphonates?

Bladder wall

What factors influence the biodistribution of ⁹⁹ᵐTc Phosphonates?

Bone turnover rate, Renal function and hydration, Injection technique and timing, Medications

What is the approximate effective dose of ⁹⁹ᵐTc-MAA?

~0.011 mSv/MBq

Which organ is considered the critical organ for ⁹⁹ᵐTc-MAA dosimetry?

Lungs

⁹⁹ᵐTc-MAA is contraindicated in which condition?

Severe pulmonary hypertension

What special consideration is recommended for infants or patients with poor pulmonary circulation?

Use a reduced dose

How does ⁹⁹ᵐTc-MAA localize in the lungs?

Mechanical trapping in pulmonary capillaries

What does ⁹⁹ᵐTc-MAA enable in terms of imaging?

Functional imaging of lung perfusion

What is the critical organ for ⁹⁹ᵐTc-MAA and why?

Lungs, due to receiving the most radiation

What role do V/Q scans play when using ⁹⁹ᵐTc-MAA?

They remain key in pulmonary embolism (PE) evaluation

How are ⁹⁹ᵐTc phosphonates administered?

Intravenous injection

Where do ⁹⁹ᵐTc phosphonates distribute most rapidly after injection?

Bone and renal system

When does peak skeletal uptake of ⁹⁹ᵐTc phosphonates typically occur?

1–4 hours post-injection