Warm air heating system

Mice were anesthetized through a nose cone with 1–2% isoflurane and O₂; they were then positioned on an animal bed with the abdomen secured to reduce motion artifacts and placed in the scanner. Respiration rate was monitored, and body temperature was maintained using a warm air heating system (SA Instruments, New York, NY, USA). MRI was performed on a 7T/30-cm AVIII spectrometer (Bruker Biospin, Billerica, MA) equipped with a 12-cm gradient set and using a 40-mm quadrature RF volume coil and Paravision 6.0.1. A T₂-weighted RARE sequence was used to visualize the liver tumors, with the following parameters: repetition time (TR)/echo time (TE) = 5000/24 ms, field of view (FOV) of 35 mm², acquisition matrix=256×256, 30–47 slices (depending on liver tumor size) with a slice thickness of 0.7 mm, 8 averages, and a RARE factor=8. The tumor volume was calculated based on the aggregates of tumor nodule volumes using the DSI studio volume calculation function.

For magnetic resonance studies, at or near 10, 25, and 42 days of age, rabbits were transported to the Pittsburgh NMR Center for Biomedical Research at Carnegie Mellon University. Rabbits were preanesthetized with an intramuscular injection of ketamine (100mg/ml) and xylazine (20 mg/ml) in a 9:1 solution at a dose of 0.6 mg/kg. All rabbits underwent tracheotomy and were ventilated (Harvard Apparatus, Holliston, MA) via an endotracheal tube with 1–1.5% isoflurane in a N₂O:O₂ (1:2) gas mixture. The rabbits were placed in dorsal recumbency and an indwelling catheter was inserted into the femoral artery. Arterial blood gases were collected immediately before and after MRI. Arterial CO₂ tension (P_aCO₂) was maintained between 20 and 46 mmHg for the duration of the study. This has been reported as the normal P_aCO₂ for rabbits [27 (link)]. During MRI assessment animals were maintained at 36±0.5°C via a warm air heating system (SA Instruments, Stony Brook, NY).