Inhomogeneity of gated and ungated SPECT technetium-99m-sestamibi bull's-eyes in normal dogs: comparison with thallium-201.

By computer simulation, we have previously hypothesized, independent of the isotope imaged, that differences in view-to-view resolution and attenuation patterns predictably cause count density distortions in SPECT images. We tested the simulation predictions for both ECG-gated and ungated SPECT 99mTc-sestamibi and SPECT 201Tl myocardial perfusion images in normal dogs. In agreement with the predictions of the computer model, distortions in SPECT 99mTc-sestamibi myocardial perfusion images are virtually equivalent to SPECT 201Tl, dependent on the exact SPECT acquisition orbit and markedly different for a posterior 180 degrees acquisition arc compared to an anterior 180 degrees acquisition arc. Furthermore, ungated and gated SPECT 99mTc-sestamibi images show similar count inhomogeneities. These results suggest that little is to be gained from a 360 degrees acquisition with SPECT 99mTc-sestamibi, and that image distortions from gated or ungated SPECT 99mTc images with 180 degrees orbits will be similar to those in SPECT 201Tl images.