Quantification of partial volume effects in planar imaging

The limited resolution of the imaging system causes partial volume effects (PVEs). These results in spreading of image counts to the neighboring pixels. This phenomenon is called spill-out effect. This study aimed at quantifying PVEs using ImageJ.
Technetium-99m solution of concentration of 74 kBq/ml was filled into spheres A, B and C of diameters: 26 mm, 20 mm and 16 mm respectively. The spheres were imaged mounted inside a Jaszczak phantom filled with activity free water using a Siemens E-Cam dual head gamma camera. Images were quantified using ImageJ following a two-step method. Step 1: Drawing of region of interest 1 (ROI 1) closely on the boundary of the planar image to extract images counts before PVEs correction. Step 2: Drawing region of interest 2 (ROI 2) to extract true sphere image counts. ROI 2 extends from the boundary of ROI 1 by the FWHM of the imaging system.
The studyrevealed that PVEs are aggravated by decrease in sphere size. Underestimation of image counts on the 64 × 64 pixels matrix was found to be: 9.7%; 15% and 26% in the order of decreasing sphere size. However, an improvement in the spatial resolution decreased PVEs (128 × 128 pixels: 6.7%; 12.0% and 22.5%; 256 × 256 pixels: 6.5% ; 9% and 19.3%; 256 × 256 pixels: 6.1%; 8.0% and 18.7% in the order of decreasing sphere size).
ImageJ successfully quantified PVEs attributed to the spill-out effect in planar imaging.