Abstract
BackgroundDevelopments in single photon emission tomography instrumentation and reconstruction methods present a potential for decreasing acquisition times. One of such recent options for myocardial perfusion imaging (MPI) is IQ-SPECT. This study was motivated by the inconsistency in the reported ejection fraction (EF) and left ventricular (LV) volume results between IQ-SPECT and more conventional low-energy high-resolution (LEHR) collimation protocols. IQ-SPECT and LEHR quantitative results were compared while the equivalent number of iterations (EI) was varied. The end-diastolic (EDV) and end-systolic volumes (ESV) and the derived EF values were investigated.A dynamic heart phantom was used to produce repeatable ESVs, EDVs and EFs. Phantom performance was verified by comparing the set EF values to those measured from a gated multi-slice X-ray computed tomography (CT) scan (EFTrue). The phantom with an EF setting of 45, 55, 65 and 70% was imaged with both IQ-SPECT and LEHR protocols. The data were reconstructed with different EI, and two commonly used clinical myocardium delineation software were used to evaluate the LV volumes.ResultsThe CT verification showed that the phantom EF settings were repeatable and accurate with the EFTrue being within 1% point from the manufacture’s nominal value. Depending on EI both MPI protocols can be made to produce correct EF estimates, but IQ-SPECT protocol produced on average 41 and 42% smaller EDV and ESV when compared to the phantom’s volumes, while LEHR protocol underestimated volumes by 24 and 21%, respectively. The volume results were largely similar between the delineation methods used.ConclusionsThe reconstruction parameters can greatly affect the volume estimates obtained from perfusion studies. IQ-SPECT produces systematically smaller LV volumes than the conventional LEHR MPI protocol. The volume estimates are also software dependent.
Highlights
Developments in single photon emission tomography instrumentation and reconstruction methods present a potential for decreasing acquisition times
Horiguchi et al have shown that the number of projections in an IQ-single photon emission computed tomography (SPECT) study has a significant effect on thallium-201 myocardial perfusion imaging (MPI) results [14]
The end-systolic volumes (ESV) was verified with non-gated computed tomography (CT) scan and with manual measurements, and the ESVTrue was found to be 34.0 and 32.9 ml, respectively
Summary
Developments in single photon emission tomography instrumentation and reconstruction methods present a potential for decreasing acquisition times One of such recent options for myocardial perfusion imaging (MPI) is IQ-SPECT. The three main components of IQ-SPECT are variable-focus collimators (SmartZoom), a cardiocentric acquisition orbit and an iterative reconstruction algorithm incorporating collimator-detector response compensation for the SmartZoom collimators [9] It has been shown using static cardiac phantoms that IQ-SPECT preserves both image quality and the results of quantitative measurements with a quarter of the acquisition time or a quarter of administered activity used in conventional MPI [8, 10]. Havel et al have shown how IQ-SPECT produces significantly higher summed stress, rest and difference scores, lower EF values and higher left ventricular (LV) volumes than the conventional LEHR imaging protocol with filtered back projection reconstruction [13]. As the published results remain inconsistent, it is difficult to have a clear conclusion on the reliability of IQ-SPECT
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