Avance 3 nmr system

All magnetic resonance imaging experiments were performed on an Avance III NMR system (Bruker, Rheinstetten, Germany), controlled by the ParaVision^® 5.1 imaging software (Bruker). The NMR scanner was operated at the proton Larmor frequency of 500.13 MHz in combination with a Micro 5 micro-imaging probe base and a Micro 5 gradient system, driven at 40 A, which results in a maximum gradient strength of 2 Tm⁻¹.
Throughout the experiments, the attenuation (ATT) was varied from 70 dB to 50 dB (0.025W ≤ P ≤ 2.5W) in steps of 0.5 dB. The relationship between ATT and P is given by
$\begin{array}{c}\hfill P={10}^{\frac{{\text{ATT}}_0-\text{ATT}}{10\text{dB}}}{P}_0,\end{array}$
where P₀ = 1 W and ATT₀ = 54 dB. Acquisition parameters were set to: repetition time TR = 500 ms, echo time TE = 5.3 ms, flip angle α = 90°, effective slice thickness SI = 100 μm, field of view FOV = (1.92mm)², matrix MTX = 64 × 64 and hence 30 × 30μm⁻² in-plane resolution, number of averages NEX = 4 and an acquisition time (TA) per scan of 2 min 8 s.
Obtained MR reference images without any Lenz lens present are given in S3 Fig, while the acquired image sequences for LL1-LL4 are depicted in S4–S7 Figs. The effect of varying pulse power is clearly visible in these four images, from which the optimal power can be derived by inspection.

Mice were anesthetized using 5% isoflurane in O₂/N₂O and maintained at 2% isoflurane in O₂/N₂O with a nose cone. Respiration and external body temperature were monitored during imaging using an MR-compatible small animal monitoring and gating system (SA Instruments, Stony Brook, NY, USA). External body temperature was maintained at 37°C with a heating circulator bath (Thermo Scientific Haake, Karlsruhe, Germany). Mouse heads were held in place with a tooth bar inside a custom-built 24 mm diameter, 300 MHz inductively coupled quadrature RF volume coil (NRC Institute for Biodiagnostics, Winnipeg, MB, Canada). The entire apparatus was placed inside a Bruker BGA12-S actively shielded gradient system with integrated shim coils (Bruker BioSpin, Milton, ON, Canada). All MR experiments were performed on a 7 T 21 cm Bruker Avance III NMR system with Paravision 5.0 (Bruker BioSpin). The mouse brain was imaged in prone position rostral to caudal using 12 slices with a slice thickness of 0.75mm and an interslice distance of 1.0mm.