Abstract
PurposePartial-volume correction (PVC) using the Geometric Transfer Matrix (GTM) method is used in positron emission tomography (PET) to compensate for the effects of spatial resolution on quantitation. We evaluate the effect of misspecification of scanner point-spread function (PSF) on GTM results in amyloid imaging, including the effect on amyloid status classification (positive or negative).MethodsTwenty-nine subjects with Pittsburgh Compound B ([11C]PiB) PET and structural T1 MR imaging were analyzed. FreeSurfer 5.3 (FS) was used to parcellate MR images into regions-of-interest (ROIs) that were used to extract radioactivity concentration values from the PET images. GTM PVC was performed using our “standard” PSF parameterization [3D Gaussian, full-width at half-maximum (w) of approximately 5 mm]. Additional GTM PVC was performed with “incorrect” parameterizations, taken around the correct value. The result is a set of regional activity values for each of the GTM applications. For each case, activity values from various ROIs were combined and normalized to produce standardized uptake value ratios (SUVRs) for nine standard [11C]PiB quantitation ROIs and a global region. GTM operating-point characteristics were determined from the slope of apparent SUVR versus w curves.ResultsErrors in specification of w on the order of 1 mm (3D) mainly produce only modest errors of up to a few percent. An exception was the anterior ventral striatum in which fractional errors of up to 0.29 per millimeter (3D) of error in w were observed.ConclusionWhile this study does not address all the issues regarding the quantitative strengths and weakness of GTM PVC, we find that with reasonable caution, the unavoidable inaccuracies associated with PSF specification do not preclude its use in amyloid quantitation.
Highlights
Image-based partial volume correction is frequently used in positron emission tomography (PET) to compensate for the effects of imperfect spatial resolution on image quantitation
While this study does not address all the issues regarding the quantitative strengths and weakness of Geometric Transfer Matrix (GTM) Partial-volume correction (PVC), we find that with reasonable caution, the unavoidable inaccuracies associated with point-spread function (PSF) specification do not preclude its use in amyloid quantitation
Overall characterization of GTM as a function of PVC full-width at half-maximum The main results of this work are shown in Fig. 1 in which standardized uptake value ratios (SUVRs) is plotted for the global [11C]PiB region and constituent [11C]PiB ROIs as a function of w used in performing a GTM PVC
Summary
Image-based partial volume correction is frequently used in positron emission tomography (PET) to compensate for the effects of imperfect spatial resolution on image quantitation. The method assumes that the true distribution of activity is related to the measured distribution via an image-based convolution operation, and is usually implemented assuming a translationally invariant convolution kernel with a simple functional form. While both assumptions are important, this work examines the effects of convolution kernel misspecification. The convolution kernel is frequently taken to be Gaussian with a full-width at half-maximum (w) determined from point-source measurements. The true functional form of the scanner point-spread function (PSF) is not Gaussian and is not translationally invariant [3]. The mean positron range in water for 18F is 0.6 mm while this value is 1.2 mm for 11C and 3.0 mm 15O [4]
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