Advances in multimodal imaging techniques in nanomedicine: enhancing drug delivery precision

Abstract

Nanosystems that deliver drugs have revolutionized modern therapy via the accurate targeting and controlled release of drugs. The importance of real-time monitoring of these systems lies in the evaluation of their pharmacokinetics and biodistribution, as well as preventative treatment efficacy. Imaging methods thus gave birth to real-time monitoring, allowing visualization of nanoparticles (NPs) inside biological systems. This review introduces current imaging techniques such as optical imaging, computed tomography (CT), magnetic resonance imaging (MRI), nuclear imaging, ultrasound, and finally, hybrid techniques that are on the verge of being used. The principles, merits, demerits, and applications of each modality in tracking nanodrug delivery are summarized. Special importance is given to multimodal imaging based on the fact that it can help to overcome the limitations of any individual imaging modality, thereby offering better insight into drug delivery. Advances in imaging probes and imaging-guided drug delivery systems are illustrated to show this transformation of imaging in nanomedicine.

Fig. 1. Multimodal multifunctional nanoparticles allow the in vivo imaging of anatomy, physiology, and molecular events at various spatiotemporal scales. Reproduced from ref. . Shown here are representative images of a mouse subjected to surgical ligation of the right femoral artery to induce hindlimb ischemia followed by the inflammatory response, which is assessed with a receptor for an advanced glycation end product (RAGE)-targeted nanoparticle-based multimodal agent labeled with both fluorophore (rhodamine) and radioisotope (⁶⁴Cu). The anatomy was assessed with X-ray computed tomography (CT) imaging (A). In contrast, molecular proinflammatory events were quantitatively assessed in vivo with positron emission tomographic (PET) imaging (B), whole-body fluorescence (C).

Fig. 2. Sensitivity and spatial resolution ranges of different imaging modalities. Reproduced from ref. .

Fig. 3. Physical principles of diffusion-weighted imaging (DWI). Reproduced from ref. .

Fig. 4. Radiolabelled nanomaterials for biomedical applications. Reproduced from ref. .

Fig. 5. Schematic representation of the mechanism of action of contrast-enhanced ultrasound using an intravenously administered contrast agent. Reproduced from ref. .

Fig. 6. Diagram of a microbubble constructed for drug delivery. Reproduced from ref. . With permission from the BMJ.

Fig. 7. Schematic representation of the mechanism of action of photoacoustic imaging. Reproduced from ref. .