Assessment of myocardial perfusion defect size after early and delayed SPECT imaging with technetium-99m-hexakis 2-methoxyisobutyl isonitrile after stress

It is thought that the distribution of ^99mTc-sestamibi undergoes minimal change during the first 4 hr after injection. Thus [^99mTc] sestamibi unlike ²⁰¹Tl should not demonstrate significant redistribution in ischemic myocardium. We tested this assumption by quantifying perfusion defect size in early and delayed clinical SPECT images obtained after exercise stress or after dipyridamole infusion using an automated algorithm. Twenty patients with coronary artery disease aged 55 ± 10 yr (13 male and 7 female) underwent stress imaging. Technetium-99m-sestamibi was injected at peak exercise stress in 12 patients and after an intravenous infusion of dipyridamole in 8 patients; SPECT images were obtained 1 and 4 hr later. All patients underwent rest imaging with a second dose of ^99mTc-sestamibi 1-3 days after the stress studies. Total left ventricular mass and left ventricular defect mass were quantified with an automated algorithm previously validated in animal and patient studies. Estimates of total left ventricular mass from studies obtained 1 hr after stress (341 ± 90 g) were comparable to values obtained after 4 hr (336 ± 89 g), with a correlation of r = 0.97; p < 0.0001. The left ventricular defect size 1 hr after exercise or dipyridamole infusion (149 ± 74 g) was similar to that observed after 4 hr (151 ± 73 g). The two measurements of hypoperfusion with stress were highly correlated (r = 0.91; p < 0.0001) and were significantly larger than the defect size at rest (121 ± 70 g). These observations support the conclusion that ^99mTc-sestamibi does not redistribute significantly in ischemic myocardium between 1 and 4 hr after injection.