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

Figure 3

Dependence of ¹⁹F relaxation rates ρ₁ =  and ρ₂ =  on the biosensor concentration [Rx]. Measurements taken at 9.4 Tesla and 293 K using the MMP-2/-9 specific biosensor diluted in 9 : 1 v/v H₂O/acetonitrile mixture. (a) ¹⁹F relaxivity ρ₁/[Rx] measurement of the intact biosensor revealed no detectable concentration dependence of ¹⁹F longitudinal relaxation with an approximate average value of ρ₁ = 93 s⁻¹·ms (red dashed line). (b) The transverse relaxation rate of the intact biosensor also exhibited little dependence on [Rx] with an average of ρ₂ = 298 s⁻¹·ms (red dashed line). (c, d) After MMP-2 responsive biosensor cleavage, a strongly reduced and concentration [Rx]-dependent longitudinal and transverse relaxation rates (ρ₁ and ρ₂, (c) and (d), respectively) was observed. The solid blue lines in (c) and (d) show data fitting for relaxivity ρ/[Rx] defined by a concentration [Rx]-dependent part ρ^[Rx] and a concentration independent offset ρ⁰ (Table 3 for determined values).