@article{378c8ad4a90948938cfbf9c89efc8af5,
title = "An investigation of the filtering of TEW scatter estimates used to compensate for scatter with ordered subset reconstructions",
abstract = "With the Triple Energy Window (TEW) scatter correction method, scatter is estimated by interpolation between narrow energy windows placed on either side (or from a single window just below) the photopeak window. The use of narrow windows results in a noisy estimate which requires filtering to prevent significant amplification of noise in the corrected images. Using Monte Carlo simulated projections of a digital model of the anatomy of the torso, we investigated two-dimensional pre-reconstruction filtering of the scatter estimate by the Wiener low-pass filter, and Butterworth lowpass filters with various cutoff frequencies. The scatter estimate was either subtracted from the photopeak window projection or used directly in ordered-subset maximumlikelihood (OS-ML) reconstruction. Using the normalized mean square error (NMSE) between the estimated and true slices as the criterion, it was observed that; 1) low-pass filtering of the TEW scatter estimate dramatically decreases the NMSE compared to that of no filtering of this estimate; 2) the cutoff frequency of the Butterworth filter used to filter the scatter estimate is lower than that typically used for photopeak window images; 3) the cutoff frequency of the Butterworth filter has a broad range of values over which the NMSE is near its minimum value; 4) the cutoff frequency at which the Butterworth reaches its minimum value depends on the number of counts in the TEW window(s), and source distribution; 5) the Wiener low-pass filter adapts to produce a low, but not necessarily the minimum, NMSE; and 6) the inclusion of the scatter estimate directly into OS-ML reconstruction results in a lower NMSE than subtraction of the scatter estimate from the photopeak window prior to reconstruction.",
author = "King, {M. A.} and Devries, {D. J.} and Pan, {T. S.} and Pretorias, {P. H.} and Case, {J. A.}",
note = "Funding Information: Scatter correction is essential for accurate attenuation compensation, and to restore contrast [I]. A number of scatter compensation strategies have been proposed and investigated 12-12]. One of the energy-spectrum based methods which {\textquoteleft}This publication was made possible by grant number HL 50349 from the National Heart, Lung, and Blood. It{\textquoteright}s contents are solely the responsibility of the authors and do not necessarily represent the official views of the National Heart, Lung, and Blood Institute has been observed to be both clinically feasible and relatively accurate is the Triple Energy Window (TEW) scatter correction method of Ogawa, et al. [7]. With this method scatter is estimated by interpolation between narrow energy windows placed on either side the photopeak window for multi-energy photon emitting radionuclides, or when there are multiple radionuclides present. Interpolation is between the counts per keV in a single window below the photopeak, and zero counts per keV (no window above the photopeak) for single-energy photon emitters such as Tc-99m [lo]. The use of narrow (or even moderate) windows results in a noisy scatter estimate which requires filtering to prevent significant amplification of noise in the corrected images. Excessive filtering can bias the scatter estimate; whereas, too little filtering can elevate noise levels in the reconstnrcted slices. Funding Information: E 0.015 - m This publication was made possible by grant number HL 50349 ;L from the National Heart, Lung, and Blood Institute. It{\textquoteright}s contents are 0 .010 - solely the responsibility of the authors and do not necessarily represent the official views of the National Heart, Lung, and Blood Institute. The authors would like to thank James Bowsher, PhD, for O0 o0o050 ; helpful suggestions regarding the history, convergence rate, and 000 005 0 10 0 15 020 025 030 035 comparison criteria for the method of direct use of the scatter Spatia I Frequency (C ycle slC m ) estimate in iterative reconstruction.",
year = "1997",
doi = "10.1109/23.596978",
language = "English (US)",
volume = "44",
pages = "1140--1145",
journal = "IEEE Transactions on Nuclear Science",
issn = "0018-9499",
publisher = "Institute of Electrical and Electronics Engineers Inc.",
number = "3 PART 2",
}