Estimating Amounts of Iron Oxide from Gradient Echo Images

W Thomas Dixon¹, Daniel J. Blezek², Lisa A. Lowery¹, Dan E. Meyer¹, Amit M. Kulkarni¹, Brian C. Bales¹, Danielle L. Petko¹, Thomas K. Foo¹

Rat legs directly injected with SPIO provided a test of iron measurements based on dual gradient-echo images. We fitted three ways to a point dipole field model, fitting the amount of iron to the volume blackened by intravoxel phase difference, fitting to the phase pattern of either echo, and fitting to the difference in phase between the 1st and 2nd echoes. Following a 3 microgram injection, the latter method gave 2.480.26 microgram std following 18 independent measurements. Iron free control regions gave -90 and -140 nanogram estimates. The other methods were much less accurate and were artifactually orientation dependent.