Investigating acquisition protocols for gated, dynamic myocardial imaging in PET and SPECT

Typical myocardial SPECT imaging using Tc99m labelled sestamibi or PET imaging using N-13 labelled ammonia assumes that the amount of tracer uptake within the myocardium correlates directly with myocardial blood flow. However, this assumption has been seen to only be accurate over a limited range of blood flow rates. The uptake of alternative ligands such as Tc99m labelled Tebororime or O-15 labelled H₂O have been seen to better correlate with actual blood flow rates. Difficulties arise however in imaging these pharmaceuticals due to the relatively fast washout of tracer from the myocardium, thereby making simultaneous measurements of perfusion and wall motion difficult. An alternative image reconstruction strategy is presented in which both myocardial blood flow and myocardial wall motion can be determined in a single study from very low count projection data. The proposed method uses the dynamic expectation maximization (dEM) algorithm in combination with temporal filtering across cardiac gates in order to improve reconstructed image quality. Data acquisition can be performed from any tomographic acquisition type ranging from a single head, slow rotation SPECT acquisition, to a fixed ring, PET geometry. A computer simulation has been performed in order to evaluate the image quality produced when using this imaging approach with a variety of SPECT acquisition parameters.