**2. Transporter-Targeting Probes**

Most transporter-targeting probes are small-size molecules, carried into the intracellular space by transporters on the cell surface. Some transporter-associated probes may take part in cell metabolism [20,21]. Many transporter-based isotopes, including radioiodine, are routinely to image the recurrence and metastases of TC. Several alternatives to radioiodine can identify RR-DTC metastases lacking radioiodine uptake. Other transporter-based radiotracers like [201Tl]TlCl, [99mTc]Tc-sestamibi ([99mTc]Tc-MIBI), [99mTc]Tc-tetrofosmin, [ 99mTc]Tc-depreotide, [111In]In-diethylenetriaminepentaacetic acid-octreotide ([111In]In-DTPA-octreotide), and [18F]fluoro-D-glucose ([18F]FDG) have been synthesized, tested, and validated as beneficial for diagnosing TC [5,22]. In particular, [18F]FDG has been widely applied in the management of TC [5].
