Mechanical thrombectomy of acute ischemic stroke caused by major vessel occlusion of the anterior circulation has become an accepted procedure in the last decade. Recent IAT modalities have been classified as suction aspiration,stent retrieval and combination modality. The suction aspiration technique is limited by the possibility of breaking the entire thrombus during the IAT. In addition, the stent retrieval technique is also limited because of thrombus migration during stent removal from an acute-angled artery as in the case of a carotid siphon.

According to recent development of suction catheter, investigators expected that suction aspiration will prevent breaking the entire thrombus during the IAT. Investigators will evaluate the radiological and clinical outcome of suction aspiration technique in comparison with combination technique in the large artery occlusion feasible to both suction aspiration and combination technique prospectively in a randomized trial.

*Hospital code for the participant hospitals Bundang Cha Hospital (A) Inje University Haeundae Paik Hospital(I) Samsung Medical Center Sungkyunkwan University (B) Kosin University Gospel Hospital (C) Daegu Good morning Hospital (D) Yeungnam University Medical Center (E) Pohang S hospital(G) Inje University Ilsan Paik Hospital(H) SM christianity Pohang Hospital(L) Choongnam National University Hospital(N) Inha University Hospital(P) Catholic University of Korea Bucheon ST. Mary's Hospital (Q) Catholic University of Korea Uijeongbu ST. Mary's Hospital (R) Catholic University of Korea ST. Vincent's Hospital (S) Ulsan University Hospital (U)

Alphabetic number of each hospital is an each hospital code.

If the patient with acute cerebral infarction will be feasible to suction aspiration and combination technique, the investigator who can enroll the patient should check the order of random table in open chatting board and perform the ordered method after completion of consent for the COMPETE trials.

Each investigator in the hospitals participated in COMPETE trials will write the competetrials spread sheet on google web.

The image files of thrombectomy including pre-thrombectomy and post-thrombectomy will be converted to zip file and send to the independent neurointerventional radiologist on e-mail about 2 ~ 4 times a year. the independent examiner will re-send to the investigator after completion of modified TICI grade in the image files of thrombectomy.

This study should not enroll atherosclerotic tandem occlusion. Other etiologies such as cancer related stroke or dissection should not be enrolled in this study.

Cases of Atherosclerotic steno-occlusion will be included in this study. Rescue treatment such as primary stenting or conventional modality will be performed according to the favored modality of each investigator.

Inclusion Criteria:

• interventionist
• minimal experiences of thrombectomy ≥ 50 cases
• successful recanalization (TICI≥2b) of radiological outcome in all cases treated by thrombectomy > 70% Patient inclusion criteria
• age ≥ 18
• acute cerebral infarction with initial NIHSS ≥ 4
• patients with agreement for clinical trials
• detection of large artery occlusion based on CT or Magnetic resonance angiography
• definition of large artery occlusion: 1) anterior circulation internal carotid artery(ICA), M1, M2 segment A1, A2 segment 2)posterior circulation Vertebrobasilar occlusion including P1 segment
• Last normal time ≤ 24 hours
• Flow/volume mismatch ≥ 1/2 based on perfusion image

Exclusion Criteria:

• Previous disabled patients before mechanical thrombectomy(MT) (Karnofsky performance Status Scale(KPS) ≤ 80)
• Patient or patient's guardian refused to the clinical trial
• Small vessel disease of TOAST classification
• Other determined etiologies of TOAST classification
• Patients with Initial NIHSS ≤ 3
• Diffusion/perfusion matched lesion or flow/volume matched lesion