Figure 2. Influence of Undersampling on Modified Shepp-Logan Phantoms.

Axial slices of modified Shepp-Logan phantom lung with simulated TE = 0.08 ms are shown at progressively decreasing levels of sampling (left to right) and increasing matrix size (top to bottom). Windowing and leveling were identical for all images. (a-d) 64³ phantom. Apparent ${\mathrm{T}}_2\mathrm{*}$ ($\text{a}{\mathrm{T}}_2\mathrm{*}$) maps of the 64³ matrix phantom show increased $\text{a}{\mathrm{T}}_2\mathrm{*}$ in the phantom parenchyma volume compared to the input ${\mathrm{T}}_2\mathrm{*}$ of 0.4 ms. Increased $\text{a}{\mathrm{T}}_2\mathrm{*}$ mean and standard deviation are observed with spurious “hot spots” of long $\text{a}{\mathrm{T}}_2\mathrm{*}$ voxels near the simulated vasculature regions. (e-h) 96³ matrix phantom. Increased $\text{a}{\mathrm{T}}_2\mathrm{*}$ deviation persists (±0.20 ms) but is reduced relative to the 100% sampled image. (i-l) 128³ matrix phantom. The $\text{a}{\mathrm{T}}_2\mathrm{*}$ maps display mean $\text{a}{\mathrm{T}}_2\mathrm{*}=0.4\text{ms}$ with increased homogeneity away from vessels, even when image is sampled only 10%.