B

Fig. 13. Zero filled interpolation and spatial resolution. In these phantom images, images with true 2.0 mm section thickness and no zero filling (left, 32 sections of 2.0 mm without zero filling) appear sharper than those acquired using 4.0 mm section thickness zero filled to an apparent 2.0 mm section thickness (right, 16 sections of 4.0 mm with zero filled interpolated to yield 32 sections of an interpolated 2.0 mm interpolated thickness). Both acquisitions yielded 32 sections with seemingly equal "2.0 mm" thickness, but only the left image was acquired with 2.0 mm spatial resolution and only A offers true 2.0 mm spatial resolution [Images courtesy of Thomas K.F. Foo, Ph.D]

Fig. 13. Zero filled interpolation and spatial resolution. In these phantom images, images with true 2.0 mm section thickness and no zero filling (left, 32 sections of 2.0 mm without zero filling) appear sharper than those acquired using 4.0 mm section thickness zero filled to an apparent 2.0 mm section thickness (right, 16 sections of 4.0 mm with zero filled interpolated to yield 32 sections of an interpolated 2.0 mm interpolated thickness). Both acquisitions yielded 32 sections with seemingly equal "2.0 mm" thickness, but only the left image was acquired with 2.0 mm spatial resolution and only A offers true 2.0 mm spatial resolution [Images courtesy of Thomas K.F. Foo, Ph.D]

Fig. 14. Zero filled interpolation. Using phantoms, the relative benefits of zero filling are apparent when comparing an image from an acquisition without zero filling (left, 16 sections of 2.0 mm thickness) to a similar acquisition with zero filling (right, 16 sections of 2.0 mm thickness "zero filled" to yield 32 sections of 1.0 mm interpolated thickness). Note the smoother margins noted in the right side phantom images [Images courtesy of Thomas K.F. Foo, Ph.D]

which k-space data is zero "padded" or "filled" in the periphery prior to its fast Fourier transform [55,56]. This results in the reconstruction of image data in smaller spatial steps than that of the acquired resolution, and the generation of smaller voxel sizes for the reconstructed data. It is important to note that zero filling does not actually improve the true spatial resolution (Fig. 13) of the data set, since this is determined by the acquired resolution. However, it does result in "higher resolution" interpolated image sets (Fig. 14) that will improve post-processing of the 3D data, especially for multi-planar reformation, MIP and VR oblique projections.

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