Feasibility of simultaneous dual-isotope myocardial perfusion acquisition using a lower dose of sestamibi

The feasibility of simultaneous dual-isotope myocardial perfusion imaging was assessed using a ca. 12 mCi dose of technetium-99m sestamibi (MIBI) and ca. 3 mCi thallium-201. Planar and single-photon emission tomographic (SPET) data from 40 patients (41 studies) imaged with both a single- and a dual-isotope protocol were analyzed. Rest injected 201T1 (pure-T1) images were acquired using 20% windows at 70 and 166 keV about 15 min after the 201T1 injection. Patients were then stressed, and at peak stress 99mTc-sestamibi was injected. About 30 min later 99mTc data were recorded with a 20% window center at 140 keV, and simultaneous 201T1 (dual-T1) data were recorded with a single 20% window centered at 80 keV. Total myocardial counts based on SPET data in the dual-T1 images were increased by 18.61% +/- 2.91% (SEM) (range: -12.8% to 84.1%) compared to pure-T1 images. Region of interest analysis revealed the greater increase in counts in the apical region and the least in the lateral wall. Pure T1 and dual-T1 images were visually evaluated for image quality (IQ) on a five-point scale (0 = unacceptable to 4 = excellent). Dual-T1 IQ was lower than that of pure-T1 in 61% of cases, and similar in 37% (12% of the pure-T1 and 41% of the dual-T1 images fell into the 0 and 1 categories). Thallium perfusion abnormalities were of similar extent in 70% of segments, less severe in 18%, and more severe in 12%. There was an inverse correlation with patient weight, such that patients weighing more than 180 lbs had substantially worse images than those below this cutoff value. While dual-tracer images are of lower quality, they are interpretable if the patient is not severely overweight.