Nanoscale Contrast Agents for Magnetic Resonance Imaging: A Review

Abstract

Today, magnetic resonance imaging (MRI) is one of the most widely applied noninvasive clinical imaging modalities with excellent applicability in bio- and nanomedicine, particularly in specific detecting and high-quality three-dimensional imaging of tumors/cancers. In this context, the design of efficient nanoscale contrast agents (NCAs) for MRI with high magnetic relaxivity and specificity/selectivity has garnered immense interest deploying a variety of innovatively designed nanostructures. Some important characteristics of NCAs such as biocompatibility, improved relaxivity, high dispersibility, specific targeting, and low toxicity make them ideal candidates for imaging/biosensing applications. The hybridization and surface functionalization/modification of these materials by applying suitable functional groups/agents can help to improve their properties and multifunctionality. However, there is still a long way to go in the clinical applications of these nanoagents to serve as a substitute for Gd-based contrast agents or other commercial materials. Importantly, nanotoxicological and biosafety issues of these NCAs need to be systematically addressed both at pre- and clinical stages; construction of smart multifunctional NCAs with clinical diagnostic and imaging potentials is thus warranted. Herein, recent advancements related to the diagnostic and imaging applications of MRI NCAs are deliberated, focusing on important challenges and future directions.

A Review of Advanced Multifunctional Magnetic Nanostructures for Cancer Diagnosis and Therapy Integrated into an Artificial Intelligence Approach

“…Clarification and interpretation of MRI images can be improved with contrast agents. MNPs are commonly used as contrast agents for T2, whereas paramagnetic complexes are used for T1 [ 122 ]. In general mechanism, a radio frequency pulse is applied to the human body in a static magnetic field in order to cause magnetic resonance (MR) by excitation of hydrogen protons in the body.…”

Structure–Property–Activity Relationships in Carbon Dots

“…Magnetic resonance imaging (MRI) is a nonintrusive medical imaging technique which applies strong magnetic fields and radio waves to the atomic nuclei in the body that absorb radio frequency energy resulting in spin polarization and inducing radio frequency signals . Contrast agents are substances that can improve the signals of MRI by shortening the longitudinal ( T 1 ) and transverse ( T 2 ) relaxation times . Two major types of contrast agents include paramagnetic lanthanide ion complexes and transition metal manganese that can shorten T 1 and the superparamagnetic materials that are able to shorten T 2 by reducing the signals from the negative contrast agents .…”

“…141 Contrast agents are substances that can improve the signals of MRI by shortening the longitudinal (T 1 ) and transverse (T 2 ) relaxation times. 142 Two major types of contrast agents include paramagnetic lanthanide ion complexes and transition metal manganese that can shorten T 1 and the superparamagnetic materials that are able to shorten T 2 by reducing the signals from the negative contrast agents. 143 Paramagnetic ion complexes incorporating CDs have been reported as good nanoscale contrast agents for MRI.…”

Mn(ii) complex impregnated porous silica nanoparticles as Zn(ii)-responsive “Smart” MRI contrast agent for pancreas imaging

“…Although several Gd(III)-based small molecules have been clinically approved as MRI contrast agents, the prolonged retention of the Gd(III) ions in the central nervous system and ion-aggravated nephrogenic systemic fibrosis (NSF) in patients with renal impairment have switched attention to Mn(II) complexes. [12][13][14][15][16][17] Furthermore, the Gd(III)-based contrast agents are primarily nonspecific and the observed signal is solely due to the distribution of the contrast agent across the body. [18][19][20] Hence, developing non-gadolinium-based, organ-specific and bioresponsive contrast agents through pH, enzyme action, temperature, and ion reflux has drawn paramount attention for better diagnosis of lesions and for non-invasive pathology.…”