11.7 t vertical bore scanner

MRI experiments were performed on a Bruker 11.7-T vertical bore scanner using a 25-mm transmit/receive volume coil. CEST images were acquired using continuous-wave RF saturation pulse of 3 s followed by a RARE imaging sequence. CEST data were acquired using six different saturation power (B₁) from 1 to 6 μΤ for optimization. Seventy-one CEST offsets between ±7 ppm with 0.2-ppm difference were acquired to produce saturation images and Z-spectra plus 1 at +20,000 Hz as M₀. Other sequence parameters include the following: centric encoding; acquisition matrix size, 64 × 48; slice thickness, 1-mm slice; and repetition time (TR)/echo time (TE), 5000/3.39 ms. For pixel-by-pixel B₀ inhomogeneity calculation, water saturation shift referencing (WASSR) images were calculated using B₁ = 0.5 μΤ with 42 offsets from −1.5 to +1.5 ppm.

The specimens were transferred to PBS for five days before MRI, and placed in 20-mm diameter tubes that were filled with Fomblin (Solvay Inc., Princeton, NJ, USA), a proton-free perfluoropolyether, to prevent dehydration and for susceptibility matching at the tissue-air interface. MRI experiments were performed on an 11.7 T vertical-bore scanner (Bruker Biospin, Billerica, MA, USA) equipped with an actively-shielded Micro2.5 gradient system with a maximum gradient strength of 1500 mT/m. A 20-mm-diameter birdcage volume coil was used as the radiofrequency transceiver. The mouse brains were scanned with the dorsal-ventral axis of the skull oriented along the main magnetic field direction. A 3D multi-echo gradient echo (MGE) sequence with fast flyback for monopolar readout gradients was used for image acquisition. The imaging parameters were as follows: flip angle = 30°, pulse repetition time (TR) = 100 ms, first echo time (TE₁) = 4 ms, 8 echoes with inter-echo spacing = 3.8 ms, 4 signal averages, and receiver bandwidth = 70 kHz. The 3D multi-echo data were acquired at an isotropic spatial resolution of 70 μm with a scan time of 3 h 45 min. The imaging field-of-view and acquisition matrix size were 12 mm × 9.2 mm × 17.6 mm and 170 × 132 × 252, respectively.