title: Optimisation of reconstruction--reprojection-based motion correction for cardiac SPECT.
abstract: OBJECTIVE
  Cardiac motion is a challenging cause of image artefacts in myocardial perfusion SPECT. A wide range of motion correction methods have been developed over the years, and so far automatic algorithms based on the reconstruction--reprojection principle have proved to be the most effective. However, these methods have not been fully optimised in terms of their free parameters and implementational details.
  
  
  METHODS
  Two slightly different implementations of reconstruction--reprojection-based motion correction techniques were optimised for effective, good-quality motion correction and then compared with each other. The first of these methods (Method 1) was the traditional reconstruction-reprojection motion correction algorithm, where the motion correction is done in projection space, whereas the second algorithm (Method 2) performed motion correction in reconstruction space. The parameters that were optimised include the type of cost function (squared difference, normalised cross-correlation and mutual information) that was used to compare measured and reprojected projections, and the number of iterations needed. The methods were tested with motion-corrupt projection datasets, which were generated by adding three different types of motion (lateral shift, vertical shift and vertical creep) to motion-free cardiac perfusion SPECT studies.
  
  
  RESULTS
  Method 2 performed slightly better overall than Method 1, but the difference between the two implementations was small. The execution time for Method 2 was much longer than for Method 1, which limits its clinical usefulness. The mutual information cost function gave clearly the best results for all three motion sets for both correction methods. Three iterations were sufficient for a good quality correction using Method 1.
  
  
  CONCLUSIONS
  The traditional reconstruction--reprojection-based method with three update iterations and mutual information cost function is a good option for motion correction in clinical myocardial perfusion SPECT.
authors.affiliation: Department of Radiation Therapy, Vaasa Central Hospital, Hietalahdenkatu 2-4, 65130, Vaasa, Finland, tuija.kangasmaa@vshp.fi.
authors.forename: Tuija S
authors.initials: TS
authors.lastname: Kangasmaa
authors.forename: Antti O
authors.initials: AO
authors.lastname: Sohlberg
mesh_terms: D000465:Algorithms; D016477:Artifacts; D003198:Computer Simulation; D005260:Female; D006321:Heart / Q000000981:diagnostic imaging*; D006801:Humans; D007257:Information Theory; D008297:Male; D008954:Models, Biological; D009038:Motion; D009943:Organophosphorus Compounds; D015609:Organotechnetium Compounds; D019275:Radiopharmaceuticals; D013997:Time Factors; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods*
chemical_list: D009943:Organophosphorus Compounds; D015609:Organotechnetium Compounds; D019275:Radiopharmaceuticals; C078700:technetium tc-99m tetrofosmin