In the SPECT/CT imaging of HT-29 tumor xenografts, [99mTc]1 showed a higher NTSR1-specific tumor uptake than [99mTc]2 at all time points after tracer injection, with 12 ± 2.8 %ID/g for [99mTc]1 vs. 3.1 ± 1.1 %ID/g for [99mTc]2 at 4 h p.i. and adequate tumor-to-background ratios. The gene discussed is NTSR1; the disease is neoplasm.