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Effects of zero-filled interpolation on cervical magnetic resonance angiographic measurement
Kirsten P Forbes1, James G Pipe, John P Karis
1Barrow Neurological Institute, Phoenix, AZ, USA.
Background And Purpose:
The aim of this study was to assess the effect of zero-filled interpolation (ZIP) on measurements of the cervical arteries because its benefits on the accuracy and precision of measurements in medium-sized arteries remains unknown.
Methods:
Three observers measured 36 computer-simulated vessels (2-6.8 mm) and 130 normal cervical vessels (assessed with two-dimensional time-of-flight MR angiography) from 512-, 256-, and 256-ZIP matrix source images. The accuracy and precision of measurement was assessed for each matrix by using the Student t test and F test of variance, respectively. The effect of vessel size and matrix placement on measurement error was determined by means of linear regression and the Student t test, respectively.
Results:
No significant difference was observed between simulated measurements obtained on the 512 matrix and their true value. The 256 matrix caused overestimation of vessel diameter compared with 512 matrix (mean bias, 0.3 mm for computer-simulated vessels and 0.1 mm for normal vessels). This effect was reduced with ZIP, by a mean of 0.1 mm for both groups (P <.03). Precision was not affected by the matrix size or ZIP, and vessel size and matrix placement did not alter the measurement error.
Conclusion:
Vessel diameter is overestimated on 256-matrix MR angiographic source images. ZIP reduces this overestimation; however, the effect is small and unlikely to be clinically important.