Types/Applications of Photoacoustic Contrast Agents: A Review

Abstract

Ultrasound imaging, one of the common diagnosis techniques, is frequently used since it is safe, cost-efficient technique and real-time imaging can be conducted. However, various organs and tissues reflect ultrasonic waves, which leads to difficulty in imaging small biomolecules and to a low spatial resolution for deep-tissue images. As such, there have been significant advances in photonics and optical molecular probes in recent years, and photoacoustic (PA) tomography (PAT) has emerged as a promising modality that can overcome the limitations of ultrasound. PAT relies on the photoacoustic effect, which is the conversion of absorbed optical energy into acoustic energy. Since fewer biomolecules exhibit the photoacoustic effect compared to the scattering or reflection of ultrasound, PAT can be employed to generate high-resolution images. PAT also has a number of other advantages when compared to conventional biomedical imaging modalities such as optical tomography, ultrasound imaging, computed tomography, positron emission tomography and magnetic resonance imaging. This review provides a general overview of the contrast agents used for PAT, including organic, inorganic and hybrid contrast agents, and describes their application. This review also identifies limitations of current PAT contrast agents and suggests future research directions for their development.

Advances in the application of manganese dioxide and its composites for theranostics

“…184–186 Consequently, a variety of materials such as semiconductors, noble metals and polymers have been utilized as PA imaging agents. 187 In their study, Yan and colleagues 18 synthesized a polymer of gold nanorods (Au NRs) and manganese dioxide nanosheets (Au NR–MnO 2 ). Based on their findings, Au NR–MnO 2 exhibits a stronger absorption in the NIR region compared to Au NRs.…”

Copper Sulfide Small Nanoparticles as Efficient Contrast Agent for Photoacoustic Imaging

“…This means they should be efficiently concentrated in the region of a living organism that must be imaged, and they should be rapidly excreted from the organism after imaging. Both features can be optimized in PAI contrast agents by chemical modifications, often indicated as biological targeting [13,14]. This strategy requires that the agent displays suitable chemical reactivity [15,16].…”

Electronic Characterization of Vis–NIR Absorbing Noninnocent Ruthenium Oxyquinolate–merocyanine Complexes and their Photoacoustic Emission in Aqueous Micellar Solution†

“…There is also a rich history of using time-resolved photoacoustic spectroscopy to inform on exited-state thermodynamics and kinetics of molecular systems (6)(7)(8)(9), as well as the more niche modern applications of two-photon-induced photoacoustic imaging and photoacoustic microscopy (10)(11)(12)(13)(14)(15)(16)(17)(18)(19), which often rely on more intense laser fluences restricted to ex vivo studies unless ultrashort pulse durations are attainable. This increase in photoacoustic studies has also seen a parallel growth in the development of exogenous photoacoustic contrast agents varying across a wide spectrum of materials including molecular dyes, semiconducting polymers, carbon-based nanomaterials, plasmonic nanomaterials and hybrid nanocomposites (20)(21)(22)(23)(24)(25)(26)(27)(28). Furthermore, there is a growing trend in the development of bi-functional contrast agents, prime examples being for theranostic (photoacoustic imaging + photothermal therapy) and chemical signaling applications, such as targeted activatable photoacoustic contrast agents for biomarker recognition and binding (29)(30)(31)(32).…”