1. I have read that it is OK to do the CT Perfusion study either before or after the CTA (AJNR Am J Neuroradiol 2008 29: e23-e30). I have always done the CTA first, but I would like to know what other people are doing, and what the relevant considerations are.
2. Is 80 the optimal kVp for the perfusion study?
Thanks
CT perfusion for stroke: 2 questions
Excellent questions. Number 2 first:
2. Yes – absolutely, 80 kV is the only choice. It’s closer to the k-edge of iodine than 120 or 140 kV, so that iodine conspicuity is increased at a lower radiation dose. mAs should be 100-200, with a minimum 60 second acquisition and total CTDI radiation dose no greater than 500 mGy (0.5 Gy).
1. As you have read, either CTA or CTP can be done first, both theoretically and empirically. Because all CTP post-processing software looks at the passage of contrast through the brain capillaries relative to the baseline at the start of scanning, as long as there is sufficient increase in attenuation, perfusion maps can be calculated. Dillon and Wintermark verified this in patients a couple of years ago.
Having stated this, the greater the baseline-to-peak attenuation difference, the less noisy the time-density-curves, and hence, the less noisy the resulting calculated perfusion parameter maps. Any potential advantage here, however, is trumped by the clinical requirement for rapid assessment of vessel occlusions by CTA for management decisions regarding endovascular treatment in acute stroke patients. Our stroke neurologists insist on doing the CTA first, not only for greater speed, but also as “insurance” in case the IV blows, or the patient moves, or the exam can’t be completed for any reason.
Hope this helps!
PS – one of the residents at Winthrop hospital was a research fellow for over 2 years at the MGH neurovascular lab; I’m sure he’d be delighted to share our stroke imaging protocols and his expertise with you …
Thank you for your valuable detailed response. Shamir is doing well and says hello.