A Comprehensive Introduction to Magnetic Resonance Imaging Relaxometry and Contrast Agents

Abstract

The development of imaging technologies allowing noninvasive observation through solid bodies has represented a breakthrough in medical diagnosis, facilitating the comprehension of biomolecular events underlying disease and the development of more efficient therapeutic approaches. Some of the traditional limitations of these techniques are nowadays fading away thanks to the combination of imaging with nanotechnology, allowing the development of novel functional biomaterials that increase the sensitivity of detection, enable sensitivity to specific targets, and facilitate the combination of therapeutic and diagnostic functions (theragnosis) with molecular platforms functioning simultaneously as imaging probes and drug delivery carriers. The design of such functional biomaterials requires a comprehensive understanding of the principles that govern the generation of signal and modulation of contrast for a given imaging modality to exploit its capabilities to the maximal level. In this sense, magnetic resonance imaging (MRI) is a technique that presents a complex relationship between the detected signal and the physical−chemical properties of its sourcing matter, allowing the generation of multiple image contrasts. Thus, while magnetic resonance imaging is a highly versatile imaging modality, it requires specific knowledge of its physical principles to take advantage of all of its possibilities. This work reviews the origin of the image signal and contrast in MRI and the concepts of relaxometry and MRI contrast agents.

Advancements and Challenges in the Application of Metal-Organic Framework (MOF) Nanocomposites for Tumor Diagnosis and Treatment

“…MRI analyzes the data by accepting the signal of relaxation and reveals a picture of the impact. 84 Due to the inherently low resolution of MRI, better imaging clarity often requires a large dose of developer Optimal MRI contrast agents typically embody paramagnetic or superparamagnetic properties, furnished by elements such as gadolinium (Gd), iron (Fe), and manganese (Mn). For enhancing T1-weighted images, paramagnetic metals like Gd and Mn are preferred, whereas superparamagnetic Fe is sought for T2-weighted enhancements.…”

Label-Free Chemically and Molecularly Selective Magnetic Resonance Imaging

“…Unlike solution NMR which is used in most chemical and biochemical experiments, not all biomolecules in organs, intact tissue, and cells can be detected by MRS in vivo. Usually, only those with millimolar concentrations and above, and proper T 1 or T 2 relaxation times within the limits of the MR hardware can be detected due to the sensitivity and dynamic range of MRS, for example, extracellular low molecular weight metabolites. Many macromolecules that are compartmentalized and restricted in the tissue with very short T 2 or long T 1 may not be detectable by MRS. , While these “tissue-specific” properties can be a disadvantage in terms of sensitivity under certain data acquisition conditions, resulting in spectra that represent an incomplete picture of molecules present, these properties are also used by MRI physicists and engineers.…”

Kilogram scale facile synthesis and systematic characterization of a Gd-macrochelate as T1-weighted magnetic resonance imaging contrast agent

“…Magnetic resonance imaging (MRI) has become a well-known clinical diagnosis apparatus with the advantages of safety, non-invasiveness, multi-parameters, and high-quality three-dimensional images of soft tissue [ 1 – 3 ]. Millions of MRI exams are performed annually all throughout the world and 40–50% of them have used contrast agents (CAs) to improve diagnostic accuracy [ 4 – 6 ]. According to their contrast generating mechanisms, MRI CAs are mainly classified into two categories: T 1 -weighted CAs ( i.e ., paramagnetic and positive contrast agents) and T 2 -weighted CAs ( i.e ., super-paramagnetic and negative contrast agents).…”