T1-T2 Dual-Modal Magnetic Resonance Imaging: From Molecular Basis to Contrast Agents

Abstract

Multimodal imaging strategies integrating manifold images have improved our ability to diagnose, to guide therapy, and to predict outcomes. Magnetic resonance imaging (MRI) is among the most widely used imaging technique in the clinic and can enable multiparameter anatomical demonstration of diagnosis. Due to the inherent black-and-white production of MR images, however, MRI detection is largely hampered by the occurrence of false-positive diagnoses. In this Perspective, we introduce the paradigm of manipulating the multiparameter MRI, T₁-T₂ dual-modal MRI, along with enhancement by specific contrast agents. We hope this discussion will promote emerging research interest in T₁-T₂ dual-modal MRI and provoke the rational design of contrast agents for sophisticated MRI applications.

Figure 1:

(a) The phenomenon of T₂ relaxation correlates to the dephasing of the magnetization at xy plane (M_xy). The M_{xy, max} is the M_xy immediately after the nuclear magnetic resonance upon a 90° radiofrequency (RF) pulse. (b) The phenomenon of T₁ relaxation describes the recovery of magnetization at z direction (M_z) from zero to the M_{z, max} along with nuclear spin. A second 90° RF is required to flip over the magnetization from z direction to xy plane in order to measure the M_z, so that strong T₂ dephasing effect would attenuate T₁ due to this inherent process. (c) The direct coordination with and the diffusion around a magnetic nanoparticle are related to the T₁ and T₂ relaxation enhancement of water protons, respectively. The effective T₁ and T₂ relaxation enhancement result in brighter contrast in T₁ and darker contrast in T₂ imaging. (d) The logic of T₁-T₂ dual-modal imaging can be described as OFF-ON (0-1), ON-OFF (1-0), ON-ON (1-1), OFF-OFF (0-0) states, featuring the multiple-parameter demonstration of MRI.