180 degree versus 360 degree Myocardial studies using simultaneous emission transmission tomography

Full text: Attenuation artefacts are a common cause of defects demonstrated in myocardial perfusion imaging. Our objective was to assess whether non-uniform attenuation correction (AC), based on simultaneous emission transmission tomography (SETT), was better for 180 degree or 360 degree acquisition. Compartments of a thorax phantom representing myocardium, lungs and liver were filled with thallium-201, in similar concentrations to that seen in clinical studies. SETT images were acquired suing 180 degree and 360 degree rotation. Attenuation maps were reconstructed using filtered back-projections. Emission projections were reconstructed using filtered back-projection (FBP) without attenuation correction, and also maximum likelihood (ML) reconstruction (32 iterations) incorporating the measured attenuation map. Reconstructions were compared in terms of contrast between the myocardium and ventricle (Cv) and the uniformity of activity around the myocardium, measured as mean inter-regional contrast (Cm). Noise was determined as the normalised standard deviation (NSD) for a uniform cardiac region using separately acquired studies. Uniformity of activity around the myocardium was best for 360 degree attenuation corrected studies. However myocardial to ventricle contrast was best for non-corrected 180 degree data. Noise was not significantly different for 180 degree v 360 degree studies. Results suggest that 360 degree may be preferable despite the relatively poor Cv, which is most likely attributed to scatter