P099] Comparative assessment of three scatter correction techniques in 99M-TC and 131-I planar imaging

Abstract

Purpose The purpose of this study is to evaluate and compare single (SEW), dual (DEW) and triple energy window (TEW) scatter correction techniques, on 99mTc and 131I planar images, based on signal-to-noise ratio (SNR) criterion. Methods Four reference sources filled with known activities of 99mTc and 131I were prepared. Voxel size for 256x256 matrix during planar acquisition was defined. Serial planar acquisitions of the reference sources were performed on a SOPHA DST-Xli, dual head γ -camera and single head γ -camera. Furthermore, planar images of patient’s sample that have been administered with 99mTc and 131I were analyzed. During acquisition of 99mTc images, to perform TEW scatter correction, main window was centered 140 keV, whereas the windows used to estimate the scatter contribution were placed at 93 keV (67Ga) and 173 keV (111In) with a width of 20%. In the case of 131I images DEW scatter correction was performed after setting the main window centered 364 keV, whereas adjacent window was placed at 280 keV (75Se). TEW and DEW scatter correction and background subtraction was applied to all planar images and this energy-window removal processing was performed through ImageJ software. Moreover, a study about SNR was performed to achieve quantification of the obtained images. For this processing counts for a specific irradiated volume of interest and background were obtained, both for each window image. Results Planar images for both radioisotopes were acquired to enhance the comparison of energy windows. The analysis of 99mTc images for a specific activity indicated the SNR for SEW was equal 35,55, while for DEW 39,25 and for TEW 43,40. In the case of 131I image the SNR of SEW corresponded to 39,15 while for DEW 54,30. The increase of SNR was proportional to the growth of energy windows indicating that as the number of energy-windows increases, the more noise is reduced. Conclusions The analysis indicates that TEW method was more precise than DEW one for both radioisotopes. This method produces significant improvement of scatter correction leading to development nuclear medicine images with high quality.