title: Quantification of myocardium at risk in myocardial perfusion SPECT by co-registration and fusion with delayed contrast-enhanced magnetic resonance imaging--an experimental ex vivo study.
abstract: BACKGROUND
  Myocardial perfusion single-photon emission computed tomography (MPS) can be used to assess myocardium at risk in occlusive coronary ischaemia. The aim was to develop a method to quantify myocardium at risk as perfusion defect size on ex vivo MPS using co-registration and fusion with ex vivo magnetic resonance imaging (MRI).
  
  
  METHODS
  Pigs (n = 19) were injected 99mTc-tetrofosmin prior to concluding 40 min of coronary artery occlusion, followed by reperfusion and MRI contrast injection. The excised heart was imaged with T1-weighted MRI and MPS, and images were co-registered using freely available software (Segment v1.8, http://segment.heiberg.se). The left ventricle was semi-automatically delineated in MRI and copied to MPS. The threshold for a MPS perfusion defect was defined as the mean counts in the MPS image at the MRI-determined border between remote myocardium and air. The threshold was measured using count maxima set to the 100th-95th percentile of counts within the myocardium. The count maximum that gave the lowest threshold variability (SD) was considered the most robust.
  
  
  RESULTS
  A count maximum using the 100th percentile yielded a threshold of (mean ± SD) 55 ± 6·2%. This method showed the lowest SD compared to 99th-95th percentile count maxima (6·6-7·2%).
  
  
  CONCLUSIONS
  We describe a method for objective quantification of myocardium at risk as perfusion defect size on MPS using knowledge of the anatomy of the myocardium from co-registered MRI. This enables simultaneous quantification of myocardium at risk by MPS and infarct size by MRI for the evaluation of treatments for myocardial infarction.
authors.affiliation: Cardiac MR Group, Department of Clinical Physiology, Lund University and Skåne University Hospital, Lund, Sweden.
authors.forename: Martin
authors.initials: M
authors.lastname: Ugander
authors.forename: Helen
authors.initials: H
authors.lastname: Soneson
authors.forename: Henrik
authors.initials: H
authors.lastname: Engblom
authors.forename: Jesper
authors.initials: J
authors.lastname: van der Pals
authors.forename: David
authors.initials: D
authors.lastname: Erlinge
authors.forename: Einar
authors.initials: E
authors.lastname: Heiberg
authors.forename: Håkan
authors.initials: H
authors.lastname: Arheden
mesh_terms: D000818:Animals; D003287:Contrast Media; D003326:Coronary Circulation; D054059:Coronary Occlusion / Q000150:complications / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000473:pathology / Q000503:physiopathology; D004195:Disease Models, Animal; D005260:Female; D008279:Magnetic Resonance Imaging; D008297:Male; D009203:Myocardial Infarction / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000209:etiology / Q000473:pathology / Q000503:physiopathology; D009206:Myocardium / Q000473:pathology*; D009943:Organophosphorus Compounds; D015609:Organotechnetium Compounds; D011237:Predictive Value of Tests; D019275:Radiopharmaceuticals; D013552:Swine; D015899:Tomography, Emission-Computed, Single-Photon
chemical_list: D003287:Contrast Media; D009943:Organophosphorus Compounds; D015609:Organotechnetium Compounds; D019275:Radiopharmaceuticals; C078700:technetium tc-99m tetrofosmin