Laser speckle imaging technique was used to characterize the spatiotemporal changes in cerebral blood flow (CBF) in rat
cortex induced by the local ultraprofound hypothermia(0°C) with the duration time of 1 min, 2 min, 5 min, 7 min and
10 min. The experimental results showed significant difference of the spatiotemporal characteristics of changes in CBF
between short term and long term of ultraprofound hypothermia. For the short duration of ultraprofound hypothermia (1
min, 2 min and 5 min), the hypothermia cause the CBF decrease firstly, and then the CBF increase rapidly when the
temperature is recovered to 37°C, exceeding the baseline level and lasting 10±3 min, finally return to the baseline. This
trend of changes in CBF is similar in the regions of artery, vein and parenchyma, but with different amplitude. For the
duration time of 7 min, the changes in CBF also exhibit the similar decrease induced by ultraprofound hypothermia and
the rapid increase induced by the temperature recovering, however the increase does not show the overshoot, but only
reach around 75% of the baseline level. For the duration of 10 min of ultraprofound hypothermia, the CBF does not
increase rapidly when the temperature is recovered to 37°C, but remains at the low level of CBF for 12±2 min, and then
increases gradually at artery sites, or increases rapidly and then decrease slightly later at the vein and parenchyma sites.
Similar as the case in the duration time of 7 min, the final CBF only recovers to about 75% of the baseline level. The
experimental results suggest that the CBF can not recover to the baseline after a long duration of ultraprofound
hypothermia longer than 7 min.