Dual-isotope brain SPECT imaging with technetium and iodine-123: Validation by phantom studies

Phantom studies were employed to determine whether the enhanced energy resolution (9.7% FWHM) of a new high-resolution, three-headed single-photon emission computed tomograph might permit the simultaneous acquisition of ^99mTc and ¹²³I. Various window widths (15% and 10%) and positions (centered and asymmetric to the photopeak) were used to examine cross- contamination between these two isotopes. Brain phantom experiments using a 15% centered ^99mTc window in conjunction with a 10% asymmetric ¹²³I window (upper half of the ¹²³I photopeak) demonstrated that approximately 95% of observed counts were derived from the isotope of interest. Shifting the ¹²³I window from asymmetric to centered resulted in a significant increase in contamination of the ¹²³I window. Shifting the ^99mTc window from centered to asymmetric did not significantly alter image quality for ^99mTc. Separate experiments employing vials with varying isotope concentrations demonstrated that quantitative recovery from mixed ^99mTc and ¹²³I sources was equivalent to that from matched single-isotope sources (r² ≥ 0.90).