Comparison of Performances of Standard Low Energy Collimators and a Medium Energy Collimator Specially Designed for Imaging with (p,2n) I-123

摘要

The use of iodine 123 produced via the Te-124 (p,2n) I-123 reaction is readily available and less expensive than (p,5n) I-123. The use of standard collimators with (p,2n) I-123 results in poor image quality due to a high percentage of photons with energies greater than 159 keV resulting from I-124 contamination. A High Resolution Medium Energy (HR-ME) collimator has been developed to improve image quality and evaluated. LSF were measured at a depth of 20,60 and 100 mm using a source inside a plexiglas phantom, 200 mm high, placed at 100 mm from the collimator and compared to results of Low Energy High Resolution (LE-HR) and a Low Energy General Purpose (LE-GP) collimators. Sources consisted of p,5n and p,2n I-123. The latter used at 10 and 24 h EOB. Septal penetration was estimated by recording the spectrum at 80% window. The results show that FWHM and FWTM of the LE collimators are always smaller than the ME collimator with all sources. The FWHM and FWTM for each collimator increased with (p,5n) I-123 and (p,2n) I-123 10 h and 24 h after EOB, respectively. The ME collimator reduces septal penetration and minimizes the difference between spectra. It gives better results than the LE-HR collimator up to frequency 0.28 cycles/cm for p,5n and up to 0.39 cycles/cm for p,2n I-123. The MTF of the ME collimator are equal to or better than those of the LE-GP collimator at all frequencies. Although the results of the (p,2n) 10h EOB are better than the (p,2n) 24 h EOB the differences are not significant. In conclusion, the ME collimator improves the quality of (p,2n) I-123 for both static and tomographic imaging and it could be used for In-111 imaging. (ERA citation 10:021785)