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AJNR - American Journal of Neuroradiology

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Effects of Zero-Filled Interpolation on Cervical Magnetic Resonance Angiographic Measurement

Kirsten P. Forbes^a, James G. Pipe^a, John P. Karis^a and Joseph E. Heiserman^a

^a From the Barrow Neurological Institute, Phoenix, AZ

View larger version (64K): [in a new window]   FIG 1. Computer-simulated vessels. Image shows computer-simulated vessels of four diameters (2, 3.3, 5.1 and 6.8 mm) displayed in three matrices (512, 256, and 256 ZIP) and in three pixel locations. Vessels are displayed in random order.

View larger version (64K): [in a new window]   FIG 2. Typical 2D TOF MRA source image obtained in a healthy volunteer. Image shows a source image (512 x 512 matrix) used for vessel measurement.

View larger version (12K): [in a new window]   FIG 3. Computer-simulated vessels: comparison of different matrix measurements. Graph shows differences in mean vessel measurements between the 512 matrix and the 256 and 256 ZIP matrices, with results for each observer shown separately. Error bars indicate the standard deviation of the measurements. Compared with the 512 matrix, both the 256 and 256 ZIP matrices consistently led to overestimation of the size of the vessel. With ZIP, however, a small but significant reduction in luminal diameter was observed for observers 1 and 2.

View larger version (12K): [in a new window]   FIG 4. Normal vessels: comparison of different matrix measurements. Graph shows differences in mean vessel measurements between the 512 matrix and the 256 and 256 ZIP matrices; the results for each observer are shown separately. Error bars indicate the standard deviation of the measurements. Compared with the 512 matrix, the 256 matrix consistently led to overestimation of the size of the vessel. With ZIP, however, a small but significant reduction in luminal diameter was noted for all observers; these results were not significantly different from those of the 512 matrix.

View larger version (12K): [in a new window]   FIG 5. Signal-intensity profile of a computer-simulated vessel. Plot reveals that the 512, 256, and 256 ZIP matrices show the same vessel size at a signal intensity of approximately 50%. At signal intensities lower than this, the 256 matrix shows the largest vessel diameter, the 256 ZIP matrix a slightly smaller diameter, and 512 shows the smallest diameter.