Nuclear medicine tracers using 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 and . Thus, attenuation correction for is challenging because it emits two photons (171 and ) 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 , 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 and an effective photon energy based on the emission probabilities and linear attenuation coefficients of the photons. This approach allows us to treat the emissions from as a single photon with an effective energy of . We obtained emission projection data from a tank filled with a uniform solution of . 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 (the derived ). The reconstructed tomographic images demonstrate that the use of no attenuation correction, or correction assuming photon energies of 171 or introduces inaccuracies into the reconstructedradioactivity 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 . Although these results are specific to , the foundation could easily be extended to other multiple-energy isotopes.
Components of the SPECT/CT system used in this research were provided by an equipment grant from GE Healthcare. Funding support for this research project was provided through the UCSF Radiology Research and Education Fund, a National Institutes of Health grant (NIH 5R21-CA86893 “Improved Prostate Staging with Dual-Mode Imaging”), a UC Discovery Grant (bio02-10296) from the University of California with corporate sponsorship from GE Healthcare, and an unrestricted gift from Cytogen Corporation.
II. THEORY OF DUAL-ENERGY ATTENUATION CORRECTION
III. METHODS AND MATERIALS
III.A. The Discovery VH SPECT/CT system
III.B. Experimental SPECT/CT imaging of the uniform tank
III.C. Collimator blurring and scatter effects
IV.A. Experimental SPECT/CT imaging of the uniform tank
IV.B. Collimator blurring and scatter effects
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