In the diagnosis of acute cerebral infarction, information on the extent of ischemic lesion obtained by CT and MRI is important to determine its therapeutic strategy, particularly in the case of thrombolytic therapy in the clinical scenario, a simple and quick method is required for this purpose.

It is known that the incidence of hemorrhagic complications increases drastically when early ischemic signs are present in more than one third of the middle cerebral artery (MCA) territory on initial CT. Hence, the 1/3 MCA rule has been adopted in several large-scale randomized trials for thrombolytic therapies such as ATLANTIS^*, STARS^*, and ASPECTS^*. Although each protocol has its own merits, most of them are too complicated and/or not applicable to MRI in general, and it appears that there is no optimal criterion for the clinical use in an acute stroke setting.
^*ATLANTIS = Acute Noninterventional Therapy in Ischemic Stroke; ^*STARS = Standard Treatment with Alteplase to Reverse Stroke; ^*ASPECTS = Alberta Stroke Programme Early Computed Tomography Score

ASIST-Japan, following the reassessment of multiple criteria from a practical viewpoint, proposes a new criterion. It is based on the ASPECTS rule; however, a white matter region(W) has been added and in total, there are 11 regions for evaluation. The number of regions showing the ischemic sign is deducted from a total of 11 points, and the affected MCA area is considered to be more than one-third of the MCA territory when the score is 8 or less.

A comparative experiment is currently in progress, and the results will be reported in near future.

The new scoring system proposed by ASIST-Japan. It is based on the ASPECTS rule, but a white matter region (W) has been added, and in total there are 11 regions for evaluation. The number of regions showing ischemic sign is deducted from a total of 11 points, and the affected MCA area is considered to be more than one-third of the MCA territory when the score is 8 or less.