3 Molecular Imaging
Image-based detection platforms are used extensively in medicine to detect, localize,
and characterize pathologies. Also, imaging has become an indispensable tool in
research, clinical trials, and diverse disciplines. Imaging can reveal complex structures and dynamic interactive processes located deep in the sample that are otherwise
difficult to decipher [54].
While conventional images provide anatomical and physiological information by
an external radiation field applied to the patient, new imaging strategies are used as
diagnostic tools.
Molecular imaging involves in vivo characterization and measurement of biologic
processes at the cellular and molecular level [55]. Through noninvasive methodologies, molecular imaging is being increasingly used for in vivo diagnosis as it
provides additional information to the conventional imaging strategies. Among
them, in vivo gene expression, antigen presence, metabolic alterations, cell pathways,
and molecular localization can be identified.
Generally the methodology consists in probe administration to the patient, and
after biodistribution, the probe accumulates on the target as a result of the probe
transport, binding to receptors and antigens, enzymatic reactions, biochemical or
mechanism trapping, phagocytosis, or combinations of these [56]. Finally, the signal
of the probe must be transferred throughout the tissue to be detected and to create the
image.
In fact, molecular imaging provides an alternative or complementary diagnostic
tool. Obtaining molecular information from a temporary context and in the environment of interest is the goal of this methodology. Real-time measurements make it
possible to detect changes produced by stimuli and in a wide range of unique studies.
Additionally, molecular imaging has the potential to play a leading role in the routine
use of therapeutics, particularly in oncology, where drug resistance develops over
time and targeted therapies can be extremely expensive [54].
For successful in vivo imaging, localization of the target, reasonable distribution
time, signal depth penetration, and energy and detection equipment are also features
to be considered to the design of the methodology. However, the molecular imaging
probe is most crucial, as it has both a targeting and an imaging component, and is
able to be introduced into the patient. However, the ratio between pathologic and
normal tissue must be high, and probe should not reside long in blood or in the
organs of metabolism [57].
Aptamers as targeting components are biomolecules with strong potential for the
development of molecular imaging agents. The small size and polyanionic nature of
aptamers may lead to rapid blood clearance and tissue uptake and may minimize the
residence time in the liver and kidneys, providing potentially useful features for
imaging [57]. Each imaging modality has advantages and disadvantages, and there
are increasing numbers of hybrid instruments that offer the possibility of combining
them [58]. Furthermore, the aptamer’s ability to bind a wide range of targets allows
extraordinary applications of aptamer-imaging probes [52, 53].
150
V. Calzada
Image-based detection platforms are used extensively in medicine to detect, localize,
and characterize pathologies. Also, imaging has become an indispensable tool in
research, clinical trials, and diverse disciplines. Imaging can reveal complex structures and dynamic interactive processes located deep in the sample that are otherwise
difficult to decipher [54].
While conventional images provide anatomical and physiological information by
an external radiation field applied to the patient, new imaging strategies are used as
diagnostic tools.
Molecular imaging involves in vivo characterization and measurement of biologic
processes at the cellular and molecular level [55]. Through noninvasive methodologies, molecular imaging is being increasingly used for in vivo diagnosis as it
provides additional information to the conventional imaging strategies. Among
them, in vivo gene expression, antigen presence, metabolic alterations, cell pathways,
and molecular localization can be identified.
Generally the methodology consists in probe administration to the patient, and
after biodistribution, the probe accumulates on the target as a result of the probe
transport, binding to receptors and antigens, enzymatic reactions, biochemical or
mechanism trapping, phagocytosis, or combinations of these [56]. Finally, the signal
of the probe must be transferred throughout the tissue to be detected and to create the
image.
In fact, molecular imaging provides an alternative or complementary diagnostic
tool. Obtaining molecular information from a temporary context and in the environment of interest is the goal of this methodology. Real-time measurements make it
possible to detect changes produced by stimuli and in a wide range of unique studies.
Additionally, molecular imaging has the potential to play a leading role in the routine
use of therapeutics, particularly in oncology, where drug resistance develops over
time and targeted therapies can be extremely expensive [54].
For successful in vivo imaging, localization of the target, reasonable distribution
time, signal depth penetration, and energy and detection equipment are also features
to be considered to the design of the methodology. However, the molecular imaging
probe is most crucial, as it has both a targeting and an imaging component, and is
able to be introduced into the patient. However, the ratio between pathologic and
normal tissue must be high, and probe should not reside long in blood or in the
organs of metabolism [57].
Aptamers as targeting components are biomolecules with strong potential for the
development of molecular imaging agents. The small size and polyanionic nature of
aptamers may lead to rapid blood clearance and tissue uptake and may minimize the
residence time in the liver and kidneys, providing potentially useful features for
imaging [57]. Each imaging modality has advantages and disadvantages, and there
are increasing numbers of hybrid instruments that offer the possibility of combining
them [58]. Furthermore, the aptamer’s ability to bind a wide range of targets allows
extraordinary applications of aptamer-imaging probes [52, 53].
150
V. Calzada