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Calculation and validation of the use of effective attenuation coefficient for attenuation correction in In‐111 SPECT
Author(s) -
Seo Youngho,
Wong Kenneth H.,
Hasegawa Bruce H.
Publication year - 2005
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 - 10.1118/1.2128084
Subject(s) - attenuation , correction for attenuation , collimator , attenuation coefficient , single photon emission computed tomography , photon , projection (relational algebra) , iterative reconstruction , physics , energy (signal processing) , optics , spect imaging , image quality , emission computed tomography , computational physics , nuclear medicine , computer science , positron emission tomography , algorithm , image (mathematics) , computer vision , medicine , quantum mechanics
Nuclear medicine tracers using In111 as a radiolabel are increasing in their use, especially in the domain of oncologic imaging. In these applications, it often is critical to have the capability of quantifying radionuclide uptake and being able to relate it to the biological properties of the tumor. However, images from single photon emission computed tomography (SPECT) can be degraded by photon attenuation, photon scattering, and collimator blurring; without compensation for these effects, image quality can be degraded, and accurate and precise quantification is impossible. Although attenuation correction for SPECT is becoming more common, most implementations can only model single energy radionuclides such as Tc99 mand I123 . Thus, attenuation correction for In111 is challenging because it emits two photons (171 and 245 keV ) at nearly equal rates (90.2% and 94% emission probabilities). In this paper, we present a method of calculating a single “effective” attenuation coefficient for the dual‐energy emissions of In111 , and that can be used to correct for photon attenuation in radionuclide images acquired with this radionuclide. Using this methodology, we can derive an effective linear attenuation coefficient μ eff and an effective photon energy E eff based on the emission probabilities and linear attenuation coefficients of the In111 photons. This approach allows us to treat the emissions from In111 as a single photon with an effective energy of 210 keV . We obtained emission projection data from a tank filled with a uniform solution of In111 . The projection data were reconstructed using an iterative maximum‐likelihood algorithm with no attenuation correction, and with attenuation correction assuming photon energies of 171, 245, and 210 keV (the derived E eff ). The reconstructed tomographic images demonstrate that the use of no attenuation correction, or correction assuming photon energies of 171 or 245 keV introduces inaccuracies into the reconstructed radioactivity distribution when compared against the effective energy method. In summary, this work provides both a theoretical framework and experimental methodology of attenuation correction for the dual‐energy emissions from In111 . Although these results are specific to In111 , the foundation could easily be extended to other multiple‐energy isotopes.