Quantitative rotational tomography with ²⁰¹Tl and ^99mTc 2-methoxy-isobutyl-isonitrile: A direct comparison in normal individuals and patients with coronary artery disease

We tested the hypothesis that ^99mTc 2-methoxy-isobutyl-isonitrile (^99mTc MIBI), a new radiopharmaceutical for myocardial perfusion imaging, provides accurate noninvasive detection of coronary artery disease (CAD). Imaging in patients after exercise and at rest with ^99mTc MIBI was compared with imaging after exercise and redistribution with ²⁰¹Tl in 12 normal subjects and 38 patients with angiographic documentation of CAD (≥ 50% diameter stenosis). We used single-photon emission computed tomography (SPECT) and computer quantitation of regional tracer distribution. The quality of reconstructed images with ^99mTc MIBI judged visually was superior to that of ²⁰¹Tl in 88% of all studies performed and was comparable in the others. With the limits of normal as 2.5 SD below the mean of gender-matched normal volunteers, ²⁰¹Tl SPECT identified 32 and ^99mTc MIBI identified 36 patients with CAD (p = 0.2). ²⁰¹Tl SPECT identified 45 of 75 (60%) and ^99mTc MIBI identified 59 of 75 (79%) stenosed coronary arteries (p < 0.05). The quantitative severity of perfusion defects was similar for the two tracers. ²⁰¹Tl SPECT identified 104 reversibly ischemic myocardial segments compared with 134 with ^99mTc MIBI (p < 0.05). Thus, SPECT myocardial perfusion imaging with ^99mTc MIBI and computer quantitation provides an accurate method for the noninvasive detection of significant coronary artery disease. Furthermore, image quality is generally superior to ²⁰¹Tl, and reversibly ischemic myocardial segments may be better identified with ^99mTc MIBI.