Revisiting gallium-67 imaging: investigation of the energy photopeaks

Background Ga-67 has multiple energy emissions of different abundances and the quality of images is affected by these inhomogeneous energy distributions Thus the purpose of this study was to investigate whether two or three energy peaks of Ga 67 would be the most appropriate setting in terms of gamma-camera performance and image quality measurements Materials and methods The physical performance of the gamma camera using Ga-67 has been tested, in particular, the effect of different gallium energy settings (two vs three energy photopeaks) on the extrinsic and intrinsic uniformity and resolution of the gamma-camera The multicontrastiresolution phantom (OPRAXMEDICAL model 74 345) has been used to compare the two energy settings The average contrast of the lesions and the contrast-to-noise ratio were measured and the significance of the result was determined using the paired Student's t-test To test the effects of size and contrast on the detectability of defects, contrast detail curves have been generated for both the acquisition energy settings For the optimization of the energy window, multiple static liver phantom images were acquired using the dual-energy photopeak acquisition method However, each image was taken at different symmetric energy window combinations and the window settings were (5, 10, 15, and 20%) for 92 and 184 keV, respectively Results For the two energy window acquisitions, the intrinsic uniformity calculated by the integral and differential equations for the useful field of view was 2 26 and 1 39%, respectively However, for the three energy windows, the values were 304 and 1 81%, respectively The integral and differential values for the dual energy flood images were 10 97 and 3 75%, respectively, whereas the integral and differential values for the triple energy flood images were 13 3 and 4 13%, respectively A slight improvement in the system's intrinsic spatial resolution was observed in the dual-window setting with a full width at half maximum of 924 mm compared with 10 42 mm for the triple-energy acquisition The full width at window acquisitions, but the full width at tenth maximum was found to be larger The two energy acquisitions yielded a significant improvement by 205 and 22% in the mean contrast of the planar images of the phantom filled with 2 and 5 mCi of Ga-67, respectively (P value <001) Single-photon emission computed tomography images acquired for the liver phantom showed an improvement in the mean contrast by 29 and 276% using two windows (P<0 001) for 2 and 5 mCi activity concentration, respectively Unlike planar imaging, single-photon emission computed tomography images yielded a 45% increase in the contrast-to-noise ratio using the two window acquisitions with a mean CNR of 5 24 +/- 3 47 and 2 9 +/- 2 23 for two and three windows respectively, P value less than 005 The contrast detail curves showed better detectibality for small-sized lesions and lower contrast when using dual energy settings The best contrast, on average, was achieved using 10% for 92 keV and 5, 10, 15, and 20% for 184 keV, respectively, and it was improved by 16, 24, and 35% compared with other settings Conclusion A significant improvement in image quality can be achieved by simply applying different window widths over the different photopeaks Our results indicated that two photopeaks with optimized window widths can significantly outperform three windows in terms of spatial and contrast resolution and lesion detectability with a relatively negligible reduction of count sensitivity Nucl Med Commun 31 1068-1074 (C) 2010 Wolters Kluwer Health vertical bar Lippincott Williams & Wilkins Nuclear Medicine Communications 2010 31 1068-1074