Clinical tracer selection: which radioisotope is routinely used to study thyroid gland uptake and function in diagnostic nuclear medicine?

Introduction / Context:
The thyroid actively takes up iodine to synthesize hormones (T3 and T4). Nuclear medicine leverages this physiology using radioiodine to image the gland, measure uptake, or ablate overactive tissue. Knowing the appropriate tracer is essential for clinical protocols and exam questions in radiological sciences.

Given Data / Assumptions:

• Diagnostic imaging or uptake measurement of the thyroid.
• Preference for isotopes with suitable half-life and gamma emissions (for imaging) or beta emissions (for therapy).
• Standard practice in clinical settings.

Concept / Approach:
Iodine isotopes are organ-specific tracers for the thyroid. I-123 is commonly used for diagnostic imaging due to favorable gamma emissions and lower radiation dose; I-131 is used for therapy and sometimes uptake tests, offering beta particles for ablation but with higher dose. The chemical form (e.g., radioiodide) is bioidentical to stable iodine, ensuring physiologic uptake through the sodium-iodide symporter.

Step-by-Step Solution:
1) Identify organ physiology: thyroid concentrates iodine.2) Select tracer aligned with physiology: radioiodine is ideal.3) Conclude that “iodine” is the correct choice among the listed isotopes.

Verification / Alternative check:
Diagnostic protocols list I-123 for imaging and I-131 for uptake/therapy; alternatives like technetium-99m pertechnetate can image thyroid due to similar transport but are not listed among the options.

Why Other Options Are Wrong:
Cobalt and iron target different clinical applications (e.g., Co-60 therapy sources, Fe tracers for hematology) and do not show selective thyroid uptake.Carbon radioisotopes (e.g., C-11) are used in PET tracers but not as thyroid-specific uptake agents.

Common Pitfalls:
Confusing organ-specific tracers; assuming any gamma emitter is appropriate regardless of biochemical pathway.

Final Answer:
Iodine