Performance of a triple-detector, multiple-pinhole SPECT system with iodine and indium isotopes

• Main Authors: Zimmerman, R.E., Moore, S.C., Mahmood, A.
• Format: Conference Proceeding
• Language: English
• Subjects: Cameras; Collimators; Indium; Isotopes; Noise level; Optical imaging; Pollution measurement; Probes; Tungsten; X-rays
• ISSN: 1082-3654; 2577-0829
• DOI: 10.1109/NSSMIC.2004.1462746

SPECT imaging with isotopes other than /sup 99m/Tc is useful for developing new molecular probes for in-vivo imaging. We have recently modified a standard 3-head gamma camera system for /spl mu/SPECT with 6 pinhole tungsten collimators using a 3D-OSEM reconstruction algorithm. We have previously reported on the /sup 99m/Tc performance of this /spl mu/SPECT imager. We have recently measured the performance of the /spl mu/SPECT system for imaging with /sup 125/I, /sup 123/I, and /sup 111/In. The smallest of the interchangeable apertures (0.8-mm) was used for all tests. Point sources consisted of droplets or ion exchange beads with /sup 123/I and /sup 111/In. The imaging of /sup 125/I was simulated using the 30-keV X-rays from /sup 123/I. The volume source was a 30 cc syringe containing 25 ml. Point and volume projection data were acquired separately. The projection data sets of point and volumes were scaled and added before reconstruction. The pinhole-collimated /sup 123/I energy spectrum demonstrated 18% contribution from high-energy photons detected in the 159-keV, 20% wide window, whereas a low-energy parallel-hole collimator allowed 60% contamination. The point-source sensitivity at 159 keV was comparable to that measured previously for /sup 99m/Tc (18 cpm/kBq), and was 3.6 times higher than that measured in the X-ray region (30-keV, 50% window). Point sensitivity for /sup 111/In was 39 cpm/kBq. Volume sensitivities were 1.4 cpm/kBq at 30 keV, 4.3 cpm/kBq at 159 keV and 14 cpm/kBq for /sup 111/In. With 1 iteration, the average FWHM resolution at 30 keV was 1.05 mm, at a background noise level of 40%. Average resolution for /sup 123/I and /sup 111/In were both measured to be 1.2 mm at a 10% noise level with 1 iteration and decreased to 0.9 mm at 25% noise level and 3 iterations. The /spl mu/SPECT system performs comparably for /sup 99m/Tc, /sup 123/I and /sup 111/In and acceptably for /sup 125/I. New iodinated probes and mice containing /sup 111/In are now being imaged with the system.