Guidelines for QSM phantom production and evaluation ofcandidate phantom materials

PurposeTo measure magnetic susceptibility ({chi}) with Quantitative Susceptibility Mapping (QSM) and evaluate its repeatability using four phantom doping materials relevant to QSM applications. MethodsA cylindrical phantom was constructed containing vials of agarose gel doped with two paramagnetic materials (ferritin, USPIO) and two diamagnetic materials (CaCl2, CaCO3) at five concentrations each. Single orientation QSM measurements (MEDI+0) were carried out on the phantom at 3T and 7T. We measured molar susceptibility ({chi}mol) from QSM and evaluated the test-retest repeatability of {chi} using the standard error of the measurement (SEM). We evaluated material lifespan by conducting a t-test of {chi}mol at various timepoints. Results{chi}mol (ppm{middle dot}L{middle dot}mmol-1) were measured as 1.67 {+/-} 0.24 and 0.74 {+/-} 0.09 (USPIO: 3T and 7T, respectively), 10-2x(8.13 {+/-} 1.35; 8.13 {+/-} 1.19) (Ferritin: 3T; 7T), 10-4x(-2.68 {+/-} 0.24; -2.71 {+/-} 0.37) (CaCl2: 3T; 7T), and 10-5x(-9.52 {+/-} 1.44; -9.53 {+/-} 1.18) (CaCO3: 3T; 7T). The USPIO SEM (1.5 {+/-} 2.0; 5.1 {+/-} 2.0 ppb at 3T; 7T) was greater than the ferritin SEM (1.2 {+/-} 1.0; 2.2 {+/-} 1.3 ppb at 3T; 7T). The CaCl2 SEM (7.5 {+/-} 5.5; 1.2 {+/-} 0.6 ppb at 3T; 7T) was greater than the CaCO3 SEM (1.2 {+/-} 0.6; 0.9 {+/-} 0.7 ppb at 3T; 7T). We observed no significant changes in molar susceptibility for ferritin and CaCO3 over the measured timeframes (24 months and 15 months, respectively). ConclusionWe recommend using ferritin and CaCO3 in the construction of susceptibility phantoms, removing later echo times for CaCO3 QSM reconstructions.