T₁ estimation for aqueous iron oxide nanoparticle suspensions using a variable flip angle SWIFT sequence.

Area of Science:

• Magnetic Resonance Imaging
• Nanoparticle Contrast Agents
• Quantitative MRI

Background:

• T1 quantification of super-paramagnetic iron oxide nanoparticles (SPIONs) is crucial for in vivo MRI applications.
• Accurate T1 measurements are challenging, especially at higher SPION concentrations.

Purpose of the Study:

• To propose and evaluate a sweep imaging with Fourier transformation using variable flip angles (VFAs-SWIFT) method for T1 quantification of SPION suspensions.
• To compare VFA-SWIFT with conventional methods for T1 measurement of SPIONs.

Main Methods:

• T1 values of aqueous SPION suspensions (1-7 mM) were measured using VFA-SWIFT and 3D spoiled gradient-recalled echo with VFAs (VFA-SPGR) sequences at 7 T.
• Spectroscopic inversion-recovery sequence on a 7 T spectrometer was used for validation.

Main Results:

• VFA-SWIFT accurately quantified T1 for SPION suspensions up to 7 mM.
• VFA-SPGR failed at higher concentrations, while VFA-SWIFT showed its advantage.
• Both methods yielded linear relaxivity relationships (1.006 and 1.051 s⁻¹ mM⁻¹ at 7 T) in agreement with spectroscopic measurements (1.019 s⁻¹ mM⁻¹).

Conclusions:

• VFA-SWIFT enables accurate T1 quantification of aqueous SPION suspensions up to 7 mM.
• The VFA-SWIFT method offers a reliable approach for characterizing SPIONs in MRI.