There are multiple definitions:

1. infinite impulse response(English)

   • FIR, LTI
   • Signal analysis

2. image intensity ratio(English)

   • used to quantify LA-LGE
   • AF, LA, LGE, T2P, CMR, TPS
   • Medical imaging, Cardiology, Ratio-based metric
   • https://doi.org…35/abc.20190064