Objective:To evaluate the feasibility of using a T

1

fl2 d to monitor a high-intensity focused ultrasound（HIFU） ablation procedure in ex vivo/in vivo experiments. Methods:HIFU ablations in cow’s liver（ex vivo） and rabbit leg muscle（in vivo） were monitored with a T

1

weighted fast low-angle shot two-dimensional（T

1

fl2d） sequence. The ex vivo experiment aimed to demonstrate the relationship between changes in signal magnitude and necrosis. During sonication

the changes in the signal magnitude was calculated and divided into five ranges:

>

15%

>

20%

>

25%

>

30%

and

>

35%. The area corresponding to these five ranges and the actual area of coagulative necrosis were compared to find signal variation rate. Then

the feasibility of using T

1

fl2d-based monitoring in vivo was studied during HIFU ablations in rabbit leg muscle. The area corresponding to the signal variation rate and the area of nonperfusion on the contrast-enhanced MR image were compared to observe the application of T

1

fl2d-based monitoring in vivo. Results:For the ex vivo HIFU experiment

28 sonicated sites were obtained;only when the signal variation rate was greater than 25%

there was no significant difference between the corresponding area of（79.17±21.80） mm2 and the actual area of coagulative necrosis of（81.45 ±15.45） mm2（t =0.758

P =0.455）. As expected

15 sonicated sites were obtained in vivo rabbit leg muscle experiments

the area of nonperfusion on the enhanced image was（72.21±18.51） mm2

and the area with a signal variation rate greater than 25% was（74.25±24.45） mm2

without significant differences between the two areas（t=0.664

P=0.517）. Conclusion:The use of a T

1

fl2 d to monitor HIFU ablation procedures in ex vivo/in vivo experiments is feasible

and this approach may have potential applications in clinical treatment.