Peter Hannon, MD

Lin L, Bivard A, Levi CR, and Parsons MW. Comparison of Computed Tomographic and Magnetic Resonance Perfusion Measurements in Acute Ischemic Stroke: Back-to-Back Quantitative Analysis. Stroke. 2014

While data has been mixed, perfusion imaging has been an enticing modality for some time now to help triage patients for treatment during acute ischemic strokes (AIS). CT perfusion (CTP) is often done in the acute setting due to time constraints, but in some institutions MR perfusion (MRP) may be done in follow-up imaging to minimize radiation exposure. In this study, authors Longting et al. compared CTP and MRP in AIS to assess for how interchangeable these modalities are.

This was a three-part study comparing CTP and MRP after AIS. In steps 1 and 2 (n=45 and 15 respectively), data was obtained from patients that had CTP and MRP within 2 hours of each other, both within 9 hrs of AIS, and was meant to derive the perfusion map with least difference between CTP and MRP. In step 3 (n=45), CTP was performed within 9 hrs of AIS with a follow-up MRP done 24-48 hrs later, and was meant to assess 3 months outcomes based on reperfusion rates. Authors found that among 8 perfusion maps (CBV, CBF, et) only time-to-peak (labeled Tmax) had a non-significant difference in delineating perfusion defects, with the best concordance at 6 seconds. Even between modalities, increased reperfusion predicted improved outcomes, with authors noting that with each 1% increase in reperfusion, the odds of good clinical outcome (mRS of 2 or less) increasing by 1.1 (p<0.05).

What to do with this data? This study could be helpful in research settings where MR Perfusion may be a more tenable follow-up to CTP if re-perfusion rates are being assessed. While CTP is still commonly used in our setting, it is with the knowledge that studies like MR RESCUE have managed to throw some doubt on the importance of a perfusion mismatch in triaging to intervention. As we continue to search for ideal patients for interventions, studies such as this one could help detect and fine-tune when, where and what role perfusion imaging has in acute stroke management.