Post reconstruction method to correct partial volume effect in SPECT imaging

The partial volume effect (PVE) is the most important factor of loss of quantification in Nuclear Medicine, in particular for evaluation in regions of interest (ROIs) smaller than the full-width at half-maximum (FWHM) of the point spread function (PSF) of the imaging system. The study focused on the application of a post reconstruction correction algorithm of PVE at regional level in SPECT imaging. After a quantitative evaluation of the sigma of the PSF of the SPECT imaging system, several experimental situations have been studied using the standard NEMA IEC Body phantom, which contains six spherical inserts that mimic lesions with diameters of 10, 13, 17, 22, 28, and 37 mm. A signal-to-background activity concentration ratio of 10:1 was adopted. The post-reconstruction algorithm based on the mathematical theory implemented in MATLAB was used to correct the PVE in SPECT images studied. The experimental measurements were performed with two activity concentrations of ^99mTc: 4.6 and 12.19 mCi/L. The PVE correction approach has been employed in this article to correct PVE on spherical VOIs of different sizes and to evaluate the recovery of quantitative data. Images were reconstructed using Ordered-Subset Expectation Maximization (OSEM) algorithm, applying scatter and attenuation corrections, both with and without the application of Butterworth filter. The rate of the mean difference between the corrected and raw image, when we consider the size of the sphere of 13, 17, and 22 mm, gives a percent improvement rate of PVE correction for images with Butterworth is approximately 52.66% at 4.6 mCi/L versus 31.7% at 12.19 mCi/L respectively and for images without Butterworth is approximately 69.7% at 4.6 mCi/L versus 32.87% at 12.19 mCi/L, respectively. This work shows that the application of the PVE correction method allows the recovery of the loss of dosimetric quantification. (author)