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Quantitative Monte Carlo‐based holmium‐166 SPECT reconstruction
Author(s) -
Elschot Mattijs,
Smits Maarten L. J.,
Nijsen Johannes F. W.,
Lam Marnix G. E. H.,
Zonnenberg Bernard A.,
van den Bosch Maurice A. A. J.,
Viergever Max A.,
de Jong Hugo W. A. M.
Publication year - 2013
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 - 10.1118/1.4823788
Subject(s) - monte carlo method , spect imaging , collimator , physics , single photon emission computed tomography , imaging phantom , iterative reconstruction , dosimetry , nuclear medicine , computer science , optics , computer vision , mathematics , medicine , statistics
Purpose: Quantitative imaging of the radionuclide distribution is of increasing interest for microsphere radioembolization (RE) of liver malignancies, to aid treatment planning and dosimetry. For this purpose, holmium‐166 ( 166 Ho) microspheres have been developed, which can be visualized with a gamma camera. The objective of this work is to develop and evaluate a new reconstruction method for quantitative 166 Ho SPECT, including Monte Carlo‐based modeling of photon contributions from the full energy spectrum.Methods: A fast Monte Carlo (MC) simulator was developed for simulation of 166 Ho projection images and incorporated in a statistical reconstruction algorithm (SPECT‐fMC). Photon scatter and attenuation for all photons sampled from the full 166 Ho energy spectrum were modeled during reconstruction by Monte Carlo simulations. The energy‐ and distance‐dependent collimator‐detector response was modeled using precalculated convolution kernels. Phantom experiments were performed to quantitatively evaluate image contrast, image noise, count errors, and activity recovery coefficients (ARCs) of SPECT‐fMC in comparison with those of an energy window‐based method for correction of down‐scattered high‐energy photons (SPECT‐DSW) and a previously presented hybrid method that combines MC simulation of photopeak scatter with energy window‐based estimation of down‐scattered high‐energy contributions (SPECT‐ppMC+DSW). Additionally, the impact of SPECT‐fMC on whole‐body recovered activities (A est ) and estimated radiation absorbed doses was evaluated using clinical SPECT data of six 166 Ho RE patients.Results: At the same noise level, SPECT‐fMC images showed substantially higher contrast than SPECT‐DSW and SPECT‐ppMC+DSW in spheres ≥17 mm in diameter. The count error was reduced from 29% (SPECT‐DSW) and 25% (SPECT‐ppMC+DSW) to 12% (SPECT‐fMC). ARCs in five spherical volumes of 1.96–106.21 ml were improved from 32%–63% (SPECT‐DSW) and 50%–80% (SPECT‐ppMC+DSW) to 76%–103% (SPECT‐fMC). Furthermore, SPECT‐fMC recovered whole‐body activities were most accurate (A est = 1.06 × A − 5.90 MBq, R 2 = 0.97) and SPECT‐fMC tumor absorbed doses were significantly higher than with SPECT‐DSW (p = 0.031) and SPECT‐ppMC+DSW (p = 0.031).Conclusions: The quantitative accuracy of 166 Ho SPECT is improved by Monte Carlo‐based modeling of the image degrading factors. Consequently, the proposed reconstruction method enables accurate estimation of the radiation absorbed dose in clinical practice.