Accelerated ¹⁹F·MRI Detection of Matrix Metalloproteinase-2/-9 through Responsive Deactivation of Paramagnetic Relaxation Enhancement

Figure 1

Sketch of MMP responsive line narrowing and PRE deactivation. (I) Gd^III PRE-activated ¹⁹F probe for sequence-specific MMP-9/12, (II) Gd^III PRE-activated ¹⁹F broad-range probe. Before cleavage, the Gd^III is in close proximity to the ¹⁹F causing short T₂ times that can be observed as ¹⁹F·NMR line broadening. However, a strong paramagnetic relaxation enhancement (PRE) effect is also present that enables rapid signal averaging due to short T₁ times. After cleavage (III), the distance r between the Gd^III and the ¹⁹F moieties substantially increases, leading to line narrowing but also to the deactivation of ¹⁹F·PRE due to the 1/r⁶ dependence of paramagnetic relaxation.