Quantitative planar imaging with technetium-99m methoxyisobutyl isonitrile: comparison of uptake patterns with thallium-201.

To compare the myocardial uptake pattern of 99mTc-labeled methoxyisobutyl isonitrile [( 99mTc] MIBI) and 201TI, planar scintigraphy were performed in both patients with documented coronary artery disease and subjects with a low likelihood of disease. Quantitative analysis was employed using a standard interpolative background subtraction algorithm and a new algorithm modified to better accommodate for the differences in extracardiac activity seen with [99mTc]MIBI rest images. Among patients with coronary artery disease, the standard algorithm yielded no significant difference in relative defect magnitude between [99mTc]MIBI and 201TI on stress scintigrams (p = 0.48), although the magnitude of [99mTc]MIBI defects was greater on resting images (p = 0.02). When the modified algorithm was employed, defect magnitude was similar for both stress (p = 0.91) and rest (p = 0.20) images. Normal segmental uptake ratios derived from a comparison of contralateral segments (e.g., septal:posterolateral) in the low likelihood patients were similar for both [99mTc]MIBI and 201TI. Thus, modification of the standard interpolative background subtraction algorithm is necessary for quantitative planar [99mTc]MIBI perfusion imaging. When appropriate background subtraction is employed, myocardial uptake and quantitative defect magnitude of [99mTc]MIBI and 201TI planar images are similar.