Table 1.

Pros and cons of the use of Technetium-99m radionuclide vs. Gallium-68 and Indium-111 radionuclides.

99mTc (SPECT)	68Ga (PET)	111In (SPECT)
PROS. Optimal nuclear properties (t1/2 = 6.02 h; Eγ = 140 keV). t1/2 is sufficiently long, allowing completing RP synthesis in radiopharmacies, distribution to hospitals, dose preparation, administration, and collection of clinically useful images. The monochromatic 140 keV photons (90% abundance) are ideal for obtaining SPECT imaging with high spatial resolution using commercial gamma cameras. Low radiation exposure to patients and to personnel due to the absence of corpuscular radiation. 99mTc half-life nicely matched the PK of small and medium-size peptides. On-site availability from inexpensive portable 99Mo/99mTc generator system, which overcomes the problem of worldwide distribution. Rich and versatile coordination chemistry. 99mTc-RPs are efficiently prepared in situ through commercially available lyophilized instant kits. 99mTc-RPs produce lower radiation effective doses than 68Ga-RP. Wider distribution of SPECT technology over PET. CONS. SPECT has lower spatial resolution (7–8 mm) than PET. The sophisticated Tc chemistry might complicate the setting of instant cold kits.	PROS. Good nuclear properties (t1/2 = 67.71 min; Eβ+ = 1899 keV). t1/2 is sufficiently long to allow the synthesis, purification, dose preparation of RP, administration and collection of clinically useful images. 68Ga t1/2nicely matched the PK of peptides On-site availability from portable 68Ge/68Ga-generator system. The long t1/2 of 68Ge (270.8 days) allows the utilization of a single generator for a long period (1/2 y). 68Ga RPs can be produced through the use of kits that consent to a wide availability of the corresponding imaging agents. PET higher image resolution (4–5 mm) and relevant features over SPECT. CONS. The low t1/2 does not allow for widespread shipping of the isotope. The amount of 68Ga obtainable from generator in a single elution is sufficient to synthetize the tracer for only one or two patients, limiting the number of investigations for a single day. The higher energy of 68Ga positron with respect to 18F, can lead to lower spatial resolution and high radiation dose to the patients. The are fewer PET cameras installed worldwide with respect to SPECT ones. This limits the utility of this modality in daily clinical practice.	PROS. The long t1/2 (2.8 d) makes this radionuclide useful for SPECT imaging of biomolecules with slow kinetics, such as antibodies and their fragments. CONS. Suboptimal nuclear properties (t1/2 = 2.8 d; Eγ = 171 and 245 keV with 91% and 94% abundance, respectively). The high energy both γ rays produce low spatial resolution using commercial gamma cameras. Restrict availability of 111InCl3 due to the cyclotron production. High production costs.