There are multiple definitions:

1. point spread function(English)

   • used in ultrasound imaging
   • Ultrasound, Imaging, Hemodynamics
   • https://www.ncb…les/PMC3337770/
   • https://doi.org…fc.2022.3188803

2. pyriform sinus fistula(English)

   • causes acute suppurative thyroiditis
   • AST
   • ENT, Infection
   • https://doi.org…003489420966348

3. posterior [instrumented] spinal fusion(English)

   • ALIF, ASA, CCI, CO, EBL, LIF, LL, ODI, PI, PT, SVA, TK, TLIF, VAS
   • Spine (or spinal cord), Surgery
   • https://doi.org…6.8.SPINE151543

4. probe scaling factor(English)

   • can be used to obtain a common THI scale between different optical probe spacings or optical path lengths
   • THI
   • Scoring systems/scales, Erythrocyte, Oxygen, Critical Care
   • https://doi.org/10.1186/cc8000