Investigation of microenvironmental factors influencing the longitudinal relaxation times of drugs and other compounds

Eight-channel transceiver RF coil array tailored for ¹H/¹⁹F MR of the human knee and fluorinated drugs at 7.0 T

The purpose of this study was to evaluate the feasibility of an eight-channel dual-tuned transceiver surface RF coil array for combined (1)H/(19)F MR of the human knee at 7.0 T following application of (19)F-containing drugs. The (1)H/(19)F RF coil array includes a posterior module with two (1)H loop elements and two anterior modules, each consisting of one (1)H and two (19)F elements. The decoupling of neighbor elements is achieved by a shared capacitor. Electromagnetic field simulations were performed to afford uniform transmission fields and to be in accordance with RF safety guidelines. Localized (19)F MRS was conducted with 47 and 101 mmol/L of flufenamic acid (FA) – a (19)F-containing non-steroidal anti-inflammatory drug – to determine T1 and T2 and to study the (19)F signal-to-dose relationship. The suitability of the proposed approach for (1)H/(19)F MR was examined in healthy subjects. Reflection coefficients of each channel were less than -17 dB and coupling between channels was less than -11 dB. Q(L)/Q(U) was less than 0.5 for all elements. MRS results demonstrated signal stability with 1% variation. T1 and T2 relaxation times changed with concentration of FA: T1 /T2 = 673/31 ms at 101 mmol/L and T1 /T2 = 616/26 ms at 47 mmol/L. A uniform signal and contrast across the patella could be observed in proton imaging. The sensitivity of the RF coil enabled localization of FA ointment administrated to the knee with an in-plane spatial resolution of (1.5 × 1.5) mm(2) achieved in a total scan time of approximately three minutes, which is well suited for translational human studies. This study shows the feasibility of combined (1)H/(19)F MRI of the knee at 7.0 T and proposes T1 and T2 mapping methods for quantifying fluorinated drugs in vivo. Further technological developments are necessary to promote real-time bioavailability studies and quantification of (19)F-containing medicinal compounds in vivo.

Trifluoromethoxy-benzylated ligands improve amyloid detection in the brain using (19)F magnetic resonance imaging

The chemical properties of probes that improve amyloid detection by non-invasive (19)F magnetic resonance imaging (MRI) are of interest. We synthesized benzoxazole compounds with trifluoromethoxy groups, and found that these compounds displayed sharp (19)F nuclear magnetic resonance (NMR) signals in an assay buffer. However, the intensities of the (19)F NMR signals were dramatically reduced in mouse brain lysates. Our results indicate that the inhibitory effect of brain tissue on the (19)F NMR signals from these probes can be attributed to the hydrophobicity of the tissue. These results highlight the importance of using hydrophilic (19)F-MRI agents to avoid the inhibitory effects of brain tissues on (19)F NMR signals.

Gd-enhanced MR images of substrates other than water

This communication reports the dramatic relaxation enhancements that can be obtained upon the interaction of substrates like lactate, trifluorolactate and inorganic phosphate with the paramagnetic GdDO3A agent. This occurs thanks to the formation of kinetically labile ternary complexes in which the substrate nuclei are in close proximity to the paramagnetic center. It is demonstrated that heteronuclear (13)C, (19)F and (31)P-MR images can be obtained from phantoms containing the substrate in the millimolar concentration range.