We have developed a multiphase MR collateral perfusion imaging technique, named "the MR collateral map", along with an accompanying collateral perfusion grading method defined using the MAC score, ranging from 0 (very poor) to 5 (excellent). The MR collateral map was generated using the dynamic signals obtained from DCE MR angiography or DSC MR perfusion. Our previous studies have demonstrated a linear negative association between the MAC scores of the MR collateral map and the mRS scores at 90 days for patients with acute anterior circulation ischemic stroke (Radiology 2020;295:192-201), Additionally, we have explored the MR collateral map's predictive ability for the lesion growth and penumbra in a separate publication (European Radiology https://doi.org/10.1007/s00330-023-10084-6). In this conference, we will introduce a novel CT collateral perfusion imaging method, referred to as "the CT collateral map", which is derived from CT perfusion. We will also present the clinical significance and value of the CT collateral map.