Open AccessExperimental determination of the weighting factor for the energy window subtraction-based downscatter correction for I-123 in brain SPECT studies
Author(s) -
Robin de Nijs,
Sven Holm,
Gerda Thomsen,
Morten Ziebell,
Claus Svarer
Publication year - 2010
Publication title -
journal of medical physics/journal of medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.292
H-Index - 24
eISSN - 1998-3913
pISSN - 0971-6203
DOI - 10.4103/0971-6203.71765
Subject(s) - weighting , subtraction , iodine 123 , energy (signal processing) , nuclear medicine , contrast (vision) , physics , a weighting , image subtraction , background subtraction , mathematics , optics , computer science , image (mathematics) , statistics , artificial intelligence , medicine , image processing , binary image , arithmetic , acoustics , pixel
Correction for downscatter in I-123 SPECT can be performed by the subtraction of a secondary energy window from the main window, as in the triple-energy window method. This is potentially noise sensitive. For studies with limited amount of counts (e.g. dynamic studies), a broad subtraction window with identical width is preferred. This secondary window needs to be weighted with a factor higher than one, due to a broad backscatter peak from high-energy photons appearing at 172 keV. Spatial dependency and the numerical value of this weighting factor and the image contrast improvement of this correction were investigated in this study. Energy windows with a width of 32 keV were centered at 159 keV and 200 keV. The weighting factor was measured both with an I-123 point source and in a dopamine transporter brain SPECT study in 10 human subjects (5 healthy subjects and 5 patients) by minimizing the background outside the head. Weighting factors ranged from 1.11 to 1.13 for the point source and from 1.16 to 1.18 for human subjects. Point source measurements revealed no position dependence. After correction, the measured specific binding ratio (image contrast) increased significantly for healthy subjects, typically by more than 20%, while the background counts outside of all subjects were effectively removed. A weighting factor of 1.1-1.2 can be applied in clinical practice. This correction effectively removes downscatter and significantly improves image contrast inside the brain.