[Double injection of Tc99m-methoxy isobutyl isonitrile in the same session: diagnostic accuracy in tomography compared with that of thallium-201 chloride]. / Doppia iniezione di tecnezio 99m metossi isobutil isonitrile nella stessa seduta: accuratezza diagnostica dell'indagine tomografica rispetto a quella con tallio-201 cloruro.

Radionuclide imaging with thallium-201 is widely accepted for identifying the presence and the severity of coronary artery disease, but this radiotracer is hampered by some limitations (low-energy photons and long physical half-life) and by delivering difficulties. Therefore, various technetium 99m-labelled compounds have been proposed as myocardial perfusion agents. In particular, technetium 99m methoxy isobutyl isonitrile (Tc99m-MIBI) showed the most favourable characteristics for clinical applications. Recently a study protocol involving a split dose of the radiocompound injected in the same day has been proposed. The aim of this work has been to evaluate the diagnostic accuracy of this procedure coupled with tomographic study (SPECT-MIBI) in a group of patients with documented coronary artery disease and to compare the results with those obtained by means of Tl-201 tomographic studies (SPECT-Tl) in the same patient group. Twenty-four patients, 21 males and 3 females, entered the study: the mean age was 57 +/- 6 years (44-71). For the rest study the patients were given 250 MBq of Tc99m-MIBI. Then, after 2-3 hours, they were reinjected with a second dose of 750 MBq when exercise endpoints were reached. The studies with Tl-201 were carried out the week before or subsequent the Tc99m-MIBI studies. Sensitivity was 88% with SPECT-Tl and 78% with SPECT-MIBI for the anterior descending artery (LAD), 86% and 64% respectively for right coronary artery disease (RCA) and 69% with both procedures for the left circumflex artery (LCX). Specificity was 88% with SPECT-Tl and 78% with SPECT-MIBI LAD, 60% with both procedures for RCA and 55% and 81% respectively for LCX. Coronary artery disease, involving 2 or more vessels, was correctly identified in 93% of patients by Tl-201 studies and only in 60% of patients by Tc99m-MIBI. In several cases the high count rate obtained by Tc99m-MIBI did not allow the identification of hypoperfused segments. In conclusion, a rest-stress double injection of Tc99m-MIBI in a same-day protocol has shown a lower sensitivity for detecting coronary lesions than Tl-201. Moreover, radiation exposure for medical and technical staff is greater with Tc99m-MIBI than with Tl-201.