382
N. Ashwin Kumar et al.
could be exploited to generate thermal energy and used as a contrast agent for PAI.
In this regard, Maji et al. [321] developed NaYF4 (doped with Yb
3+ or Er
3+ ) UPCN
stabilized with oleic acid with α-cyclodextrin inclusion complexes to improve the
quenching process and photoacoustic signal. After 35 min, the images (f–j) presented
a localized enhancement of the contrast on the kidney was perceived. This enhancement, in contrast, was attributed to the luminescence quenching due to the effects of
solvent-induced non-radiative relaxation and thermal conductivity of UNCP.
Recently, a theranostic based on image-guided phototherapy, which integrates
diagnostics and therapy, could be a prospective modality for tumor treatment. In this
regard, MoO 3−x QDs have been developed to perform photothermal-/photodynamictherapy for treating tumors using guided photoacoustic imaging [322]. The QDs
used in this study have maximum absorption in the NIR region and can convert the
absorbed light into hyperthermia. This results in the formation of cytotoxic reactive
oxygen species surrounding the tumor cells resulting in phototherapy. Additionally,
this QD can be used for exogenous photoacoustic contrast agents for imaging of the
tumors, which are confirmed from in vivo studies on a mouse model.
9.2 Positron Emission Tomography (PET) and Single Photon
Emission Computed Tomography (SPECT)
Positron emission tomography (PET) and Single-photon emission computed tomography SPECT) are nuclear imaging modalities that can provide functional information by measuring the uptake and turnover quantity of radiotracers in a specific
tissue site. PET is based on specific decay properties of radioactive nuclides that
decay by positron emission [323]. This technique involves the injection of radioactive tracers into the subject, usually administered using an intravenous injection. A
tracer is usually a biological molecule of interest tagged with a radioactive isotope.
2-18F-fluoro-deoxy-D-glucose (
18 F-FDG) is widely used to tracer evaluate therapeutic response in oncology [324]. Some of the most commonly used radioactive
isotopes used in PET to label tracers include
15 O,
13 N,
11 C, and
18 F [325]. The tracer
molecules interact with specific proteins sugars or DNA elements. When the radioactive atom on a molecule decays, a positron is ejected from the nucleus by interacting
with the surrounding electrons, which results in the complete annihilation of both the
particles, positron, and the electron. This interaction results in generation of two high
energy photons travelling in the opposite direction. The detectors usually scintillator
crystals coupled to photomultipliers measure these photons to create an image in the
PET scanner.
Similar to PET, SPECT is another imaging modality that uses radioactive imaging
probes labeled with a single photon emitter. In the case of a SPECT, the imaging
device is a gamma camera which captures the radiation emitted from the body. The
most widely used radioisotopes in SPECT include technetium 99 m (
99m Tc), iodine
123 (
123 I), and thallium 201 (
201 Tl). However,
18 F-FDG is the most widely accepted
N. Ashwin Kumar et al.
could be exploited to generate thermal energy and used as a contrast agent for PAI.
In this regard, Maji et al. [321] developed NaYF4 (doped with Yb
3+ or Er
3+ ) UPCN
stabilized with oleic acid with α-cyclodextrin inclusion complexes to improve the
quenching process and photoacoustic signal. After 35 min, the images (f–j) presented
a localized enhancement of the contrast on the kidney was perceived. This enhancement, in contrast, was attributed to the luminescence quenching due to the effects of
solvent-induced non-radiative relaxation and thermal conductivity of UNCP.
Recently, a theranostic based on image-guided phototherapy, which integrates
diagnostics and therapy, could be a prospective modality for tumor treatment. In this
regard, MoO 3−x QDs have been developed to perform photothermal-/photodynamictherapy for treating tumors using guided photoacoustic imaging [322]. The QDs
used in this study have maximum absorption in the NIR region and can convert the
absorbed light into hyperthermia. This results in the formation of cytotoxic reactive
oxygen species surrounding the tumor cells resulting in phototherapy. Additionally,
this QD can be used for exogenous photoacoustic contrast agents for imaging of the
tumors, which are confirmed from in vivo studies on a mouse model.
9.2 Positron Emission Tomography (PET) and Single Photon
Emission Computed Tomography (SPECT)
Positron emission tomography (PET) and Single-photon emission computed tomography SPECT) are nuclear imaging modalities that can provide functional information by measuring the uptake and turnover quantity of radiotracers in a specific
tissue site. PET is based on specific decay properties of radioactive nuclides that
decay by positron emission [323]. This technique involves the injection of radioactive tracers into the subject, usually administered using an intravenous injection. A
tracer is usually a biological molecule of interest tagged with a radioactive isotope.
2-18F-fluoro-deoxy-D-glucose (
18 F-FDG) is widely used to tracer evaluate therapeutic response in oncology [324]. Some of the most commonly used radioactive
isotopes used in PET to label tracers include
15 O,
13 N,
11 C, and
18 F [325]. The tracer
molecules interact with specific proteins sugars or DNA elements. When the radioactive atom on a molecule decays, a positron is ejected from the nucleus by interacting
with the surrounding electrons, which results in the complete annihilation of both the
particles, positron, and the electron. This interaction results in generation of two high
energy photons travelling in the opposite direction. The detectors usually scintillator
crystals coupled to photomultipliers measure these photons to create an image in the
PET scanner.
Similar to PET, SPECT is another imaging modality that uses radioactive imaging
probes labeled with a single photon emitter. In the case of a SPECT, the imaging
device is a gamma camera which captures the radiation emitted from the body. The
most widely used radioisotopes in SPECT include technetium 99 m (
99m Tc), iodine
123 (
123 I), and thallium 201 (
201 Tl). However,
18 F-FDG is the most widely accepted