Same day injections of Tc-99m methoxy isobutyl isonitrile (hexamibi) for myocardial tomographic imaging: Comparison between rest-stress and stress-rest injection sequences

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Abstract
It has been shown that both rest and stress 99mTc-hexamibi myocardial perfusion imaging can be performed on the same day using two different doses injected within few hours (the first one at rest followed by a second at stress). In order to evaluate and compare 2 sequences (rest-stress and stress-rest) of 99mTc-hexamibi injections performed the same day, 18 patients with either abnormal 201Tl myocardial scan or abnormal coronary angiography were studied with 2 99mTc-hexamibi injections protocols. The rest-stress study was performed as follows: 7 mCi 99mTc-hexamibi was injected at rest. Single photon emission computed tomography (SPECT) was performed 60 min later. Immediately after the rest study, patients were injected at peak stress with 25 mCi 99mTc-hexamibi. Tomographic imaging was repeated 1 h later. Patients were submitted to the stress-rest protocol within 3 days. Tomographic imaging was done 1 h after a 7 mCi injection at stress. This study was followed by an injection of 25 mCi 99mTc-hexamibi at rest, a tomographic study was performed 60 min later. Myocardial sections were reconstructed in horizontal long, vertical long, and short axes. Data analysis also included polar map representation. A total of 324 segments were interpreted blind by 3 observers, there was an agreement in 283/324 (87.3%) segments between the 2 protocols. However, 24 segments (7.4%) judged ischemic on rest-stress were called scars on stress-rest. In three patients, myocardial segments were judged normal on the rest image of the rest-stress protocol while they were found abnormal (false positive images) on the stress-rest sequence. Stress images from both protocols were judged similar in 17 patients. In conclusion, when using a short time interval (less than 2 h) between two 99mTc-hexamibi injections, it is preferable to do a rest-stress sequence since the rest image performed initially represents a true rest study, which is not necessarily the case with the stress-rest sequence.

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