Nanotechnology in Diagnostic Imaging

Early and precise diagnosis is pivotal to prevent disease progression or spillover or to determine the suitable therapeutic regimen. Based upon the type of disease and its phenotypic manifestations, several diagnostic methods are employed, and in this context, diagnostic imaging techniques have found niche applications. Different popular diagnostic imaging modalities such as optical imaging, radiographic techniques, magnetic resonance imaging (MRI), computed tomography (CT), and ultrasonography and their nano-enhancements for improved diagnosis have constituted the core of the current discussion. For instance, gold nanoparticles (AuNPs) and silver nanoparticles (AgNPs) based dark-field microscopy, multiphoton plasmon resonance microscopy, optical coherence microscopy, hyper-Rayleigh scattering spectroscopy, and Raman spectroscopy have been evolved for biomedical imaging. In ultrasound imaging, mesoporous silica nanoparticles (MSNs), polystyrene particles, etc. are employed as contrasting agents. Using fluorescent mesoporous silica nanoparticles as a contrast agent, targeted endoscopic detection is performed in colorectal cancer. There are also two other imaging techniques, i.e., thermal imaging and nuclear imaging based on infrared radiation and ionizing electromagnet radiation, respectively. Iron oxide NPs or magnetic NPs (MNPs), Au core/hollow mesoporous silica shell nanoparticles, etc. are exploited in thermal imaging, whereas AuNPs are utilized as X-ray contrast agents in radiographic imaging to enhance the resolution of the images. Three-dimensional cross-sectional image with high spatial and temporal resolution is developed in computed tomography technique. AuNPs, iodine-based NPs are employed in this technique to obtain images with enhanced contrast and better resolution. Iodine-based NPs offer better tumor penetration ability in addition to their biodegradable and clearance properties, making them an appropriate contrast agent. In magnetic resonance imaging, superparamagnetic iron oxide nanoparticles (SPIONS), gadolinium-based dendrimers are efficiently being exploited as contrast agent. Positron emission tomography (PET) and single-photon emission computerized tomography (SPECT) are mostly used nuclear imaging modalities in the clinical diagnosis. In terms of sensitivity and resolution, PET is more gainful in comparison to SPECT. A variety of liposomes have been evolved in addition to other nanomaterials that act as a contrasting agent in PET imaging. Functionalized gold NPs aided SPECT is employed in lymphatic mapping and early-stage cervical cancer detection. On the basis of electrical properties like conductivity, permittivity, and impedance, electrical impedance tomography (EIT) technique has been evolved. It can provide images of a specific region in the human body based on the electrical conductivity of the tissues. So diagnostic imaging aided by nanotechnology has already proved to be efficient to gain ample attention and application imminently.