Warm air system

Animals were anesthetized using isoflurane (4% for sleep induction and ~2% for sleep maintenance) in a 3:7 mixture of oxygen and air, before being positioned prone in the MR-compatible animal holder. Respiration was monitored during scanning (SA-instruments, Stony Brook, NY, USA). Core body temperature was maintained at 37 °C during scanning using a warm air system (SA-Instruments, Stony Brook, NY, USA). Magnetic resonance imaging images (n = 5–7 per group) were collected using a 9.4 T horizontal bore magnet (Varian, Yarnton, UK) equipped with a 40 mm millipede coil, as detailed^{5 (link)}. Fiji software (http://fiji.sc) was used to compute the volume of fat in different regions of interest in the body. Visceral fat was calculated as the difference between the total fat and the subcutaneous fat signal in the abdominal region. Total subcutaneous fat was calculated as the differences between total fat and visceral fat. Experiment was performed on the same mouse (F1) at the age of 3 months (MID) and 6 months (END).

Animals were anesthetized using isoflurane (4% for sleep induction and ~2% for sleep maintenance) in a 3:7 mixture of oxygen and air, before being positioned prone in the MR-compatible animal holder. Respiration was monitored during scanning (SA-instruments, Stony Brook, NY, USA). Core body temperature was maintained at 37 °C during scanning using a warm air system (SA-instruments, Stony Brook, NY, USA).
The MRI experiments (n = 6–7 per group) were conducted using a 9.4 T horizontal bore magnet (Varian, Yarnton, UK) equipped with a 40-mm millipede coil, as previously detailed^{45 (link)}. All images were collected on the matrix size 256 × 96 and a field-of-view of 51.2 × 51.2 mm². Fiji software (http://fiji.sc) was used to compute the volume of total fat (TF), visceral fat (VAT), and total subcutaneous fat (SAT). VAT was calculated as the difference between the TF signal and SAT signal in the abdominal region. MRI experiments were performed on the same mouse (F1) at P80 (MID) and P150 (END).

In vivo imaging was performed using a 7T preclinical MRI system (20‐cm bore, Varian Direct Drive scanner, Agilent, Palo Alta, California) equipped with a 39‐mm i.d. quadrature birdcage RF coil (Rapid Biomedical GmbH, Germany) for excitation and detection of the water and PARASHIFT agent signals. Mice were mounted in a dedicated bed, which included a pneumatic pillow system to measure the gate acquisition to animal respiration and a fiber‐optic thermometry system for temperature monitoring and control using a warm air system (SA Instruments, Stony Brook, New York). Mice were anaesthetized using isoflurane, and an intravenous line was inserted into a tail vein to allow injection of contrast agent from outside of the magnet. No other surgical preparation was used. To confirm positioning and visualize regional anatomy, conventional spin‐echo MRI scans were collected on the water resonance (pulse repetition time (TR)/echo time (TE) = 2200 (gated)/10.93 ms, 45 × 1 mm thick slices, field of view (FOV) 35 × 35mm, matrix 256 × 256). All animal experiments were performed in compliance with the UK Government Home Office under the Animals (Scientific Procedure) Act 1986.