Abstract #0497

Protocol Optimization of the Double Pulsed Field Gradient (D-PFG) Based Filter-Exchange Imaging (FEXI) Sequence Enables Comparative Studies of the Diffusional Apparent Exchange Rate (AXR) at Reduced Scan Times and Smaller Group Sizes.

Bjrn Lampinen¹, Filip Szczepankiewicz¹, Danielle van Westen², Pia Sundgren², Freddy Sthlberg¹,², Jimmy Ltt³, Markus Nilsson⁴

¹Department of Medical Radiation Physics, Lund University, Lund, Sweden; ²Department of Diagnostic Radiology, Lund University, Lund, Sweden; ³Center for Medical Imaging and Physiology, Lund University Hospital, Lund, Sweden; ⁴Lund University Bioimaging Center, Lund University, Lund, Sweden

Filter-exchange imaging (FEXI) is based on a double pulsed field gradient (d-PFG) sequence, and provides a fast, non-invasive method for mapping water exchange expressed in its parameter apparent exchange rate (AXR). We used an analytical technique based on the Cramer-Rao Lower Bound to optimize the acquisition protocol. A new protocol is presented which reduces the coefficient of variance (CV) by 30% for measured AXR. With this optimized protocol, comparative studies searching for alterations in the AXR of magnitude three times larger than the inter-subject standard deviation can be performed using as few as four individuals per group with scan time below 15 minutes. This will enable future investigations of AXR as a biomarker for disease and treatment effects.