The importance of a correct positioning of the heart using IQ-SPECT system with multifocal collimators in myocardial perfusion imaging: A phantom study

We have recently validated a quarter-time protocol in Myocardial Perfusion Imaging named IQ-SPECT, whose basic principle is to implement a multifocal collimator; However, in clinical practice, it may sometimes be difficult to center the heart in the region of highest magnification of the multifocal collimators (the so-called sweet spot). We therefore aimed to evaluate whether a heart mispositioning may affect results in MPI. We simulated a rest study with an anthropomorphic phantom with an in vivo distribution of 400 MBq [99mTc]tetrofosmin, with and without a transmural defect (TD). For each set of images, we performed 5 acquisitions, one with a correct centering and with other 4 degrees of mispositioning. Raw data and reconstructed images were evaluated qualitatively and quantitatively, including no corrections, correction for attenuation, for scatter or for both. We assessed polar plot uniformity, LV wall thickness, and TD and cavity contrast. Images obtained either with a correct heart centering or with mild misposition showed no differences, both qualitatively and quantitatively. Those obtained with major mispositioning differed in uniformity and TD contrast depending on correction parameters. This is the first study investigating how a heart mispositioning can affect diagnostic accuracy with IQ-SPECT system. Mild-to-moderate mispositioning (≤2.5 cm) is unlikely to significantly affect results.