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TU‐FG‐209‐02: Effective Elimination of Aliased Signal Using An Apodized Aperture Pixel Design
Author(s) -
Shankar A,
Russ M,
Vijayan S,
Bednarek D,
Rudin S
Publication year - 2016
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4957572
Subject(s) - nyquist frequency , anti aliasing filter , aliasing , apodization , detector , optics , filter (signal processing) , nyquist rate , optical transfer function , pixel , aperture (computer memory) , noise (video) , nyquist–shannon sampling theorem , signal (programming language) , sinc function , image quality , physics , low pass filter , sampling (signal processing) , computer science , artificial intelligence , band stop filter , computer vision , acoustics , image (mathematics) , programming language
Purpose: Signal and noise aliasing are major issues with high resolution direct and indirect detectors for which the Apodized Aperture Pixel (AAP) design provides an alternative solution. Methods: High resolution detectors for neurovascular interventions have MTFs that remain significant even at the Nyquist frequency. Under‐sampling in such detectors, leads to aliasing of object frequencies and noise. Frequencies above the Nyquist wrap into the lower frequency range leading to aliasing. The conventional approach of convolving images with low‐pass filters such as pixel binning helps in noise reduction but still allows aliasing. The AAP design proposed by Cunningham et.al, uses super sampled images with subpixels from a high resolution detector, convolved with a sinc function to get an image of the desired pixel size while apodizing the MTF beyond the Nyquist. The performance of the AAP filter in eliminating signal aliasing with respect to a standard filter such as simple 2x pixel binning are compared. Results: Three detectors were considered for this study including two indirect detectors with varying thickness of CsI (350µm, HR) and 500µm, HL) and a direct detector (aSe ‐ 1000µm thickness – MTF after Rivetti et.al,). The presampled MTFs of respective detectors were convolved with a 2x pixel binning kernel and the AAP filter. The Fourier transform of an AAP filter, being the box function, the MTF remains high, up to Nyquist and then drops off drastically to zero. Detailed comparisons of resulting MTFs along with the original presampled MTF are shown. The AAP filter resulted in the least degradation of spatial resolution while eliminating aliasing thus outperforming 2x pixel binning Conclusion: In neurovascular imaging using high resolution detectors, the AAP design provides a viable option to effectively remove signal aliasing without compromising high spatial resolution. Partial support from NIH Grant R01‐EB002873 and Toshiba Medical Systems Corp.