Effect of isotope specific uniformity correction on SPECT image quality

Objectives To determine if an In-111, rather than vendor recommended Tc-99m, uniformity correction improves In-111 SPECT image quality.

Methods 100M count In-111 & Tc-99m uniformity corrections were acquired for a dual detector camera per vendor guidelines. A Jaszczak SPECT phantom was filled with 200 μCi In-111 in 80 mL water in 8, 12, 16 & 25 mL cylindrical inserts. To simulate increasing amounts of potentially de-tuning counts, 1-8 mCi Tc-99m was placed in the 5,600 mL surrounding water bath in 5 separate experiments. SPECT was acquired at 128 projections for 1, 5 & 10 sec/projection, using Tc-99m, then In-111, flood corrections. The 3 axial slices passing through the inserts were de-identified & shown side by side with In-111 & Tc-99m corrected images randomly displayed. Maximum intensity projection (MIP) cines for paired phantom tomograms were displayed side by side in random order. One experienced individual reviewed 44 paired axial images & 15 paired MIP cines, indicating which, if either, image was of higher quality.

Results For axial image pairs, the reader preferred In-111 corrected image 13 times, & Tc-99m corrected image 14 times and had no preference 17 times. There was no tendency to chose 1 energy map over the other (p = NS). The reader indicated no preference between In-111 and Tc-99m in 14/15 MIP cines.

Conclusions Data suggest that a Tc-99m correction flood can be used for In-111 SPECT studies, with no adverse impact on image quality. A separate In-111 correction flood is not necessary.