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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.