Assessment of acute myocardial ischemia with unenhanced T1 mapping MR imaging

Methods 8 rats had an inflatable balloon coronary occluder surgically inserted via thoracotomy. They were allowed to recover for 10-14 days. MRI was performed to obtain baseline measurement of ventricular function. T1 mapping was performed using the Small-Animal LookLocker Inversion Recovery (SALLI) technique. Without removing the animals from the scanner, the left coronary artery was occluded for 30 minutes. Myocardial function and T1 were measured during ischemia. MRI was performed on a whole-body 3.0-T MR unit with a 70 mm solenoid coil for rats. After generation of survey images and of a long-axis set of cine images, a stack of LV short-axis cine images was acquired to assess global function. Short axis SALLI MR imaging was performed using the same short axis orientation in the mid ventricle, distal to the occluder. Typical SALLI parameters were as follows: 64 x 64 mm field of view, 0.60 x 0.60 mm pixel size, 3.0 mm-thick sections, 5.2/2.2, 10° flip angle, 4000 ms AD, 4000 ms RD, 12 phases (i.e., temporal resolution of 16.7 ms at 300 beats per minute), temporal undersampling factor of two, three signals acquired, and acquisition time of 8 minutes 30 seconds per slice. SALLI imaging was repeated throughout the duration of ischemia. Images were transferred to a dedicated software package and T1 values were obtained for the left ventricle at baseline, and then for both the ischemic region of interest identified by myocardial hypokinesis and a remote zone unaffected by the coronary occlusion.