Horizontal bore 4.7 t magnet

When the tumor volume reached 500-1,000 mm³, baseline MRI was performed using a horizontal bore 4.7-T magnet (Varian, Palo Alto, CA) with homebuilt 3.5 cm diameter single-turn solenoid volume coil [49 (link)]. Animals were anesthetized with isoflurane (1.5%) in air (1 L/min) and kept warm using a circulating warm water blanket. Animal body temperature and respiration were monitored with a small animal physiological monitoring system (Small Animal Instruments, Inc. Stony Brook, NY) throughout the experiment. A catheter was secured in the tail vein and kept in situ. T₁ maps (spin echo; TE= 20 ms, TR= 0.1, 0.2, 0.3, 0.5, 0.7, 0.9, 1.5, 2.5, 3.5 s) were acquired during initial air breathing and with oxygen challenge prior to DCE. Interleaved BOLD (multi-echo gradient echo; TR = 150 ms, ten echo times from 6 to 69 ms, flip angle = 20° with acquisition time 38 seconds per map) and TOLD (gradient echo; TR/TE = 30/5 ms, flip angle = 45° with total acquisition time 3 seconds per dynamic) MRI were acquired with the intervention of an oxygen challenge (from air to 100% O₂ after about 10 mins). With continued oxygen breathing, DCE (spin echo; TR/TE = 200/15 ms) was performed with IV injection of gadolinium contrast (0.1 mmol/kg body weight Gadovist, Schering, Berlin, Germany). MRI was performed on the day prior to, 24 hours and one week after the first SBRT treatment.