Radio-labeled Nanoparticles for Biomedical Imaging - Nanotechnology for Biomedical Imaging and Diagnostics - page 190

dendrimers and amphiphilic nanoparticles [23, 24]; and (3) lipid nanoparticles that
include liposomes and solid lipid nanoparticles [25-29]. These nanoconstructs,
owing to their high surface area-to-volume ratio, can be further modified to have
multivalency and multifunctionality, thus altering the drug delivery capacity, cellular
response, and sensitivity for molecular imaging. furthermore, one can manipulate the
particles for multimodality imaging, providing both functional and anatomic infor-
mation for synergistic applications [30-34]. Among various molecular imaging modal-
ities, radionuclide-based positron emission tomography (peT) and single-photon
emission computed tomography (SpeCT) are commonly used for nanoparticle-based
diagnostic applications. Straightforward radiochemistry, high imaging sensitivity, and
translational potential make radiolabeled nanoparticles an invaluable tool [35]. To date,
a great number of nanoconstructs have been radiolabeled with a variety of radioiso-
topes, resulting in significant contributions to drug discovery, oncology, cardiovascular
imaging, neurology, lung-related diseases, and clinical diagnostics [30, 31, 33, 36, 37].
7.2 Radiolabeled NaNopaRticles foR biomedical
imagiNg
Nanoparticles are currently one of the most widely investigated constructs for deliv-
ering radioactive doses for imaging and therapeutic studies in preclinical and clinical
settings. The capacity of radiolabeled nanoparticles to improve the detection limits and
resolution of imaging applications is constantly being improved upon. Radiolabeling
of nanoparticles can be accomplished by labeling the surface of the nanoparticle,
labeling the core of the nanoparticle, or radiolabeling a payload encapsulated within
the nanoparticle [38]. multivalency of nanoparticles is important in achieving high
specific activity labeling, thus allowing administration of trace amounts of compound
for diagnosis [35]. Additionally, the binding kinetics must fall into ranges suitable for
the desired biological application, especially when a stable bond is required between
the probe and target [39]. for clinical applications, care must be taken in choosing
radioisotopes with a translational capability [40].
7.3 Radiolabeled NaNopaRticle foR spect imagiNg
7.3.1 γ-Ray-emitting Radionuclides
SpeCT is a powerful nuclear imaging technique that utilizes gamma-emitting
radioisotopes to visualize both physiological and functional information at a
molecular level. Radioisotopes with energies ranging between 30 and 370 keV, and
optimally between 100 and 200 keV [28], are commonly employed. Among them,
technetium-99m ( 99m Tc), produced from a 99 mo/ 99m Tc generator, is the most widely
used isotope for nuclear imaging. Currently, about 85% of diagnostic imaging is
carried out using 99m Tc. Other commonly used SpeCT radionuclides are summa-
rized in Table 7.1.