P27 Calibrating d-PFG Filtered MRI Using a Novel Anisotropic Diffusion Phantom

Diffusion Phantom Michal Komlosh 1, Evren Ozarslan 1, Martin Lizak 1, Ferenc Horkay 1, Peter Basser 1 1 National Institute of Health Introduction: Diffusion MRI methods can provide valuable microstructural in­ formation about tissues and porous media within an imaging volume [1-3], how­ ever, calibrating them is problematic owing to the lack of suitable anisotropic diffusion MRI phantoms. Here we constructed an anisotropic diffusion MRI phantom to calibrate diffusion MRI sequences and validate models that relate the diffusion MRI signal to the MRI pulse sequences and material microstruc­ ture. We then use this phantom to calibrate a d-PFG filtered MRI experiment to measure and map mean pore size [4]. Materials and Methods: This new phantom consists of four 2 mm thick waterfilled glass capillary arrays (GCA) (Photonis USA). The nominal pore diameter of two wafers is 10 μm; that of the other two is 25 μm. D-PFG filtered NMR sequences were acquired by applying two wave vectors sequentially, and by vary­ ing the angle between them from 0◦ to 360◦. A 7 T vertical-bore Bruker DRX microimager was used with PFG NMR parameters: δ = 3.15ms, Δ = 75ms, and G between 0 and 221 mT/m; and MRI parameters: TR/TE = 7000/12 ms, FOV = 30 mm and slice thickness = 2 mm. An operator-based modeling frame­ work [5-7], which predicts the MRI signal attenuation due to restricted diffusion within packs of impermeable cylinders as well as a free water compartment for each d-PFG filtered MRI sequence, was used to estimate the pore diameter map. ROI analysis was used to measure the average pore diameter and pixel-by-pixel analysis was applied to create a mean pore diameter map. Results and Discussion: ROI analysis of the d-PFG filtered MRI data yields a pore diameter of 27.7 ± 0.1 and 27.75 ± 0.04 μm for the 25 microns ID wafers